Eight weevils can be controlled with steinernema carpocapsae nematodes- Bugs For Growers
What are weevils?
Like other beetles, weevils belong to an insect order Coleoptera but unlike other beetles, they have a distinct narrow beak or rostrum extending in front of their heads with chewing mouthparts are located at the tip of rostrum. Several species of weevils that have been described so far are considered as the most serious pests of many plant species including field and fruit crops, ornamentals, forest trees and turf grasses. The common names that are assigned to different species of weevils are usually associated with the common names of their host plants (see below). Also, the sizes and colors of both grubs also called as larvae (Photo 1) and adults (Photo 2) generally differ with their species. Following eight species of weevils can be controlled with beneficial entomopathogenic nematode, Steinernema carpocapsae nematodes.
Alfalfa weevil, Hypera postica
Adult weevils are light brown in color with a broad darker stripe extending down their midline. Young larvae of alfalfa weevils are tiny and yellowish green with black heads whereas their older larvae are greenish in color with black heads and a distinct white line down the center of their backs and white lines along each side of body. Although both adults and larvae of alfalfa weevils cause damage to alfalfa leaves, the damage caused by larvae is more severe than the damage caused by adults. In case of sever infestation, larvae can completely defoliate the plants and reduce the yields. Although all the stages including eggs, larvae, pupae and adults of alfalfa weevil are completed on the plants, sometime their mature larvae can pupate in the leaves that are fallen to the ground. So these mature larvae and pupae that are fallen to the ground can be targeted with beneficial entomopathogenic Steinernema carpocapsae nematodes.
Annual bluegrass weevil, Listronotus maculicollis
The annual bluegrass weevil prefers to feed mainly on annual bluegrass (Poa annua) compared to any other grass species and therefore they are named as annual bluegrass weevils. The larvae of blue grass weevil are creamy white and legless whereas adults are black colored with small hairs and gold scales on their forewings (elytra). Although both adults and larvae (grubs) of annual bluegrass weevil cause damage to turf grass, their larvae cause the most severe damage to annual bluegrass. Overwintering adults become active early in the spring and start feeding on the grass leaves and mate. The eggs laid by female weevils hatch early in the May into young larvae that start feeding by tunneling into grass stems. The symptoms of damage caused by bluegrass weevil include yellowing of grass leaves and subsequently dying of grass. Matured grubs generally move out of the tunnels and begin feeding externally on the surface of stems, crowns and roots of grass. In case of severe infestation, they can cut off stems from roots causing complete drying and loss of turf grass. Then mature larvae move in the soil for pupation. Both mature larvae and pupae can be easily targeted with Steinernema carpocapsae nematodes.
Billbugs, Sphenophorous parvulus, S. cicastriatus
The billbugs are weevils but they are commonly called as snout beetles. Although billbugs prefer Kentucky bluegrass, they also feed on perennial ryegrass, tall fescue, corn, rye and wheat. Adult weevils are blackish or greyish in color with elbowed antennae and distinct grooves running longitudinally down their forewings. Billbug grubs are legless, cream in color with brown head capsules and slightly curved body. Overwintering billbug adults emerge out from their hiding places in April and start feeding on the grass leaves. Female billbugs then lay eggs inside a hole chewed by them in the stem near the base of the turf plant. After hatching from eggs, young larvae generally move towards crown and roots by burrowing through the grass stem. These grubs will then feed voraciously and completely damage the crowns and eventually kill the entire grass plant. Damage by billbugs generally starts appearing as irregular mottling or thinning patches of the turf in mid-June through August. As both larval and pupal stages of billbugs found in the soil, they can be easily killed with Steinernema carpocapsae nematodes.
Black vine weevil, Otiorhynchus sulcatus
The black vine weevils are considered as one of the most damaging insect pests of many nursery and landscape plants. Adult weevils are black or gray in color with elbowed antennae and a prominent short snout. Fully-grown grubs are C-shaped, legless and whitish in color with brown head capsules. Although both adults and larvae of black vine weevil cause direct damage to host plants, adults mostly feed on foliage and flowers whereas larvae (grubs) feed on the roots. Feeding damage caused by adults can be easily recognized because of a typical notched appearance of damaged leaves or flowers. Adult weevils also feed on the developing young buds and shoots. Larvae of black vine weevils cause a serious damage to roots of different host plants. Heavy infestation of black vine weevil can kill the entire plant. Since all the larval stages and pupae live in the soil, they can be easily found and killed by entomopathogenic nematodes like Steinernema carpocapsae nematodes.
Red palm weevil, Rhynchophorus ferrugineus
The red palm weevil is considered as one of the major pest of palms in the Mediterranean Basin but they can be considered as a serious threat to date production in California. Adult weevils are reddish brown in color with a long curved rostrum (snout) and dark spots on the upper side of the middle part of the body whereas their larvae are white in color with a brown head capsule. Damage to palms is mainly caused by the larvae and only becomes visible long after infestation. By the time the first symptoms of the pest infestation are noticed, the palm plants are already so seriously damaged that they cannot survive. As mature larvae of red palm weevil move in the leaf litter at the base of tree trunk for pupation, both larvae and pupae can be targeted and killed with Steinernema carpocapsae nematodes.
Strawberry root weevils, Otiorhynchus ovatus
The strawberry root weevils are one of the most serious insect pests of strawberry crop. Adult weevils are reddish brown to black in color whereas their larvae are creamy white in color, C-shaped, legless with tanned heads. Adults of strawberry root weevil feed on the edges of strawberry leaves (notching of leaves) whereas all of their larval stages cause feeding damage by tunneling in the roots and crowns. The main symptoms of damage caused by larvae of strawberry weevils include pruning of roots, weakening, stunting of plant growth and eventually killing of entire plants. As both larvae and pupae of Strawberry root weevils, Otiorhynchus ovatus live in the soil; they are easy target for entomopathogenic nematodes.
Citrus root weevil, Diaprepes abbreviates
The citrus root weevil is one of the major insect pests of citrus and many ornamental plants in California and Florida. Adults of citrus root weevil are black in color with small white, red, orange or yellow colored scales on the forewings (elytra). The larvae (grubs) are white and legless with light head capsule. Adults cause leaf notching by feeding on the margins/ edges of leaves. The larvae of citrus weevil mainly feed on the roots of their hosts. In the severe cases they can girdle main roots that can result into death of citrus trees. As all the larval stages and pupae of the citrus root weevil live in the soil, they can be easily controlled with the application of entomopathogenic nematodes like Steinernema carpocapsae.
Pecan weevil, Curculio caryae
The pecan weevil is considered as one of the most devastating pest of pecans. The adults of pecan weevils are brown to grey in color with a characteristic snout, as its length is equal to the length of weevil’s body. Larvae of the pecan weevil are creamy white in color with reddish head capsule. The adults of the pecan weevil will emerge from pupae in the soil, then they will move out of the soil into the tree canopy either by crawling on the tree trunk or directly flying in August through September. Once in the canopy, adult weevils begin feeding by puncturing young developing nuts that will fall off the trees prematurely within 2-3 days. While feeding adult weevils mate. The mated females then lay eggs inside the nuts by chewing a hole into its hardened shell. After hatching from eggs inside the nut, larvae start feeding immediately on a developing kernel and mature within 2-3 weeks. When the damaged nuts fall to the ground, the mature larvae exit the nuts by cutting a small circular hole in the shell and then burrow into the soil and pupate. Three weeks after pupation, adult weevils emerge in August. It takes about 2-3 years for pecan weevils to complete their life cycle. Since all the mature larval, pupal and adult stages of pecan weevil live in the soil under pecan tree, they can be easily targeted by pre-emergence applications of beneficial entomopathogenic nematodes in early May, June and in late June or in early July.
Biological control of weevils with Steinernema carpocapsae nematodes
Because of cryptic habitats of weevils, their management with chemical insecticides is difficult. During completion of entire life cycle at least one stage (either adult, larva or pupa) of almost all the above stated species of weevils lives in the soil and this soil dwelling stage can be easily targeted and killed with the inundative application of beneficial entomopathogenic nematodes. Entomopathogenic nematodes including Steinernema carpocapsae have been proved to be the best biological control agents to manage weevils that infesting different crops. It has been demonstrated that S. carpocapsae nematodes when applied at the rate of 23000 nematodes per square foot or 1billion nematodes per acre, they can cause between 50 and 100% mortality of many weevil species including alfalfa weevils, annual bluegrass weevils, black vine weevils, citrus root weevils, large pine weevils, pecan weevils, red palm weevils and strawberry root weevils (Abbas, et al., 2001; Ansari and Butt, 2011; Dembilio et al., 2010; Duncan et al., 1996; Lacer et al., 2009; McGraw et al., 2010; Shah et al., 2011; Schroeder, 1992, Simser and Roberts, 1994).
How does Steinernema carpocapsae Nematode Kill Weevils?
Beneficial Steinernema carpocapsae nematodes are parasites of insects and most effective against soil-dwelling stages of many insect pests including weevils at temperatures ranging from 22 to 28°C (72 – 82°F). Infective juveniles of Steinernema carpocapsae nematode use an “ambush” foraging strategy to find their insect hosts. In this strategy, the infective juveniles of this nematode (Photo 3) “sit-and-wait” to attack passing by and highly mobile larvae/ grubs of insects including weevils. Also, infective juveniles of this nematode can move in the soil and insect host larvae. These nematodes always carry symbiotic bacteria called Xenorhabdus nematophila in their gut and use them as a weapon to kill their insect hosts and as food for their development and reproduction inside the host cadavers. When the infective juveniles S. carpocapsae are applied either to the surface of the soil in the field, thatch layer on golf courses or plant growing medium in the pots, they begin searching for their hosts including weevil grubs and their pupae. Once they locate a grub and/or pupa, the infective juveniles will penetrate into the body cavity of grubs or pupae via natural openings like mouth, anus and spiracles. Once in the body cavity, infective juveniles will release symbiotic bacteria, Xenorhabdus nematophila from their gut in the blood of grubs or pupae. Multiplying nematode-bacterium complex in the blood causes septicemia and kills the grub usually within 48 h after infection. Nematodes feed on multiplying bacteria, mature into adults, reproduce and then emerge as infective juveniles from the cadaver to seek new grubs or pupae in the potting medium/soil.
Photo 3. Infective Juveniles of Steinernema carpocapsae nematodes
- Abbas, M.S.T., Saleh, M.M.E. and Akil, A.M. 2001. Laboratory and field evaluation of the pathogenicity of entomopathogenic nematodes to the red palm weevil, Rhynchophorus ferrugineus (Oliv.) (Col.: Curculionidae). Anzeiger Fur Schadlingskunde-Journal of Pest Science. 74: 167-168.
- Bullock, R.C., Pelosi, R.R. and Killer, E.E. 1999. Management of citrus root weevils (Coleoptera : Curculionidae) on Florida citrus with soil-applied entomopathogenic nematodes (Nematoda : Rhabditida). Florida Entomologist. 82: 1-7.
- Dembilio, O., Karamaouna, F., Kontodimas, D. C., Nomikou, M. and Jacas, J. A. 2011. Short communication. Susceptibility of Phoenix theophrasti (Palmae: Coryphoideae) to Rhynchophorus ferrugineus (Coleoptera: Curculionidae) and its control using Steinernema carpocapsae in a chitosan formulation. Spanish Journal of Agricultural Research 9: 623-626.
- Dembilio, O., Llacer, E., de Altube, M.D.M. and Jacas, J.A. 2010. Field efficacy of imidacloprid and Steinernema carpocapsae in a chitosan formulation against the red palm weevil Rhynchophorus ferrugineus (Coleoptera: Curculionidae) in Phoenix. Pest Management Science 66: 365-370.
- Dembilio, O., Llacer, E., de Altube, M.D.M. and Jacas, J.A. 2010. Field efficacy of imidacloprid and Steinernema carpocapsae in a chitosan formulation against the red palm weevil Rhynchophorus ferrugineus (Coleoptera: Curculionidae) in Phoenix canariensis. Pest Management Science. 66: 365-370.
- Duncan, L.W and McCoy, C.W. 1996 Vertical distribution in soil, persistence, and efficacy against citrus root weevil (Coleoptera: Curculionidae) of two species of entomogenous nematodes (Rhabditida: Steinernematidae; Heterorhabditidae). Environmental Entomology. 25: 174-178.
- Duncan, L.W. McCoy, C.W. and Terranova, A.C. 1996. Estimating sample size and persistence of entomogenous nematodes in sandy soils and their efficacy against the larvae of Diaprepes abbreviatus in Florida. Journal of Nematology. 28: 56-67.
- Llacer, E., de Altube, M.M.M. and Jacas, J.A. 2009. Evaluation of the efficacy of Steinernema carpocapsae in a chitosan formulation against the red palm weevil, Rhynchophorus ferrugineus, in Phoenix canariensis. Biocontrol. 54: 559-565.
- McGraw, B.A., Vittumb, P.J. Cowlesc, R.S.and Koppenhoumlfera, A.M. 2010. Field evaluation of entomopathogenic nematodes for the biological control of the annual bluegrass weevil, Listronotus maculicollis (Coleoptera: Curculionidae), in golf course turfgrass. Journal Biocontrol Science and Technology. 20: 149 – 163.
- Schroeder, W.J. 1992. Entomopathogenic nematodes for control of root weevils of citrus. Florida Entomologist 75: 563-567.
- Shah, N.K., Azmi, M.I. and Tyagi, P.K. 2011. Pathogenicity of Rhabditid nematodes (Nematoda: Heterorhabditidae and Steinernematidae) to the grubs of alfalfa weevil, Hypera postica (Coleoptera: Curculionidae). Range Management and Agroforestry 32: 64-67.
- Shapiro-Ilan, D. and Gardner, W.A. 2012. Improved control of Curculio caryae (Coleoptera: Curculionidae) through multi-stage pre-emergence applications of Steinernema carpocapsae. Journal of Entomological Science 47: 27-34.
- Shapiro-Ilan, D. and Hall, M.J. 2012. Susceptibility of adult nut Curculio, Curculio hicoriae (Coleoptera: Curculionidae) to entomopathogenic nematodes under laboratory conditions. Journal of Entomological Science 47: 375-378.
- Shapiro, D.I. and McCoy, C.W. 2000a. Susceptibility of Diaprepes abbreviatus (Coleoptera : Curculionidae) larvae to different rates of entomopathogenic nematodes in the greenhouse. Florida Entomologist. 83: 1-9.
- Shapiro, D.I. and McCoy, C.W. 2000b. Effects of culture method and formulation on the virulence of Steinernema riobrave (Rhabditida: Steinernematidae) to Diaprepes abbreviatus (Coleoptera: Curculionidae). Journal of Nematology 32: 281-288.
- Shapiro, D.I., Cate, J. R., Pena, J., Hunsberger, A. and McCoy, C.W. 1999. Effects of temperature and host age on suppression of Diaprepes abbreviatus (Coleoptera : Curculionidae) by entomopathogenic nematodes. Journal of Economic Entomology. 92: 1086-1092.
- Simser, D. and Roberts, S. 1994. Suppression of strawberry root weevil, Otiorhynchus-ovatus, in cranberries by entomopathogenic nematodes (Nematoda, Steinernematidae and Heterorhabditidae. Nematologica 40: 456-462.
Damage caused by Mealybugs
Mealybugs are one of the most damaging insect pests of many fruits, field and greenhouse crops. While feeding, all the stages of mealybugs attach to plant parts and secrete a white powdery wax layer that gives them their common name and cover their entire bodies for protection (Photo 1). Like other hemipterous insects, mealybugs cause serious damage to plants by sucking cell sap from all the plant parts including leaves, twigs, stems, flowers, fruits and roots. Symptoms of direct damage caused by mealybugs include irregular and stunted plant growth, yellowing and immature drop off leaves. Indirect damage caused by mealybugs includes secretion of sticky honeydew on the leaves and stems that helps to develop black sooty mold on the leaves. This black sooty mold generally covers whole leaf area and badly affects the photosynthesis, a process used by plants to convert light energy from sun to chemical energy for the synthesis of their own food including carbohydrates and proteins. This black sooty mold also reduces the quality of the produce and aesthetic value of many ornamental plants. In addition, mealybugs are known to transmit different types of viruses from plant to plant.
Photo 1. Mealybugs that are covered with white powedery wax layer feeding on okra plants
Biological control of Mealybugs
As the use of chemical pesticides is avoided due to their detrimental effects on humans, animals and environment, the control of mealybugs with beneficial insects is essential to reduce the crop losses caused by them in organic productions. Among the several natural enemies, green lacewings (Chrysopa carnea or Chrysoperla rufilabris) considered as one of the most aggressive predators of many soft- bodied insects like whitefly larvae, scale insects including mealybugs. Green lacewing generally feed on nectar, pollen and honeydews whereas their larvae feed on all the stages of mealybugs. Although green lacewings are commercially sold in three developmental stages including eggs, larvae and adults, only larval stages are predatory in nature (Photo 2). Place eggs of green lacewings directly in the garden but make sure that egg hatching coincides with the outbreak of mealybugs so that the hatched larvae can immediately start feeding on the different stages of mealybugs. For quick control of mealybugs, larvae of the green lacewings should be released on the heavily infested plants. Adults of green lacewings should be released for their continuous recycling and mealybug control.
Photo 2. Green lacewing larva holding mealybug nymph
- Duelli P. 1980. Preovipository migration flights in the green lacewing, Chrysopa carnea (Planipennia, Chrysopidae). Behav. Ecol. Sociobiol. 7:239–246
- Goolsby, J.A., Rose, M., Morrison, R.K., Woolley, J.B. 2000. Augmentative biological control of longtailed mealybug by Chrysoperla rufilabris(Burmeister) in the interior plantscape. Southwest Entomol 25:15–19.
- Messelink, G.J., Vijverberg, R., Leman, A. J. 2016. Biological control of mealybugs with lacewing larvae is affected by the presence and type of supplemental prey. BioControl 61: 555- 565.
Aphid killer wasp, Aphelinus abdominalis
1. Aphid killer wasps, Aphelinus abdominalis are commercially available.
- Aphid parasitic Aphelinus abdominalis wasps are excellent biological control agents that occur naturally in the gardens or fields but their numbers are not always enough to suppress the population of aphids at the considerable level and prevent the damage caused by aphids.
- Therefore, Aphelinus abdominalis wasps are now commercially produced on a large scale and sold to growers as adults or “aphid mummies (from which adult wasps emerge)” to supplement the low populations of naturally occurring wasps for the effective management of various species of aphids responsible for causing an economic damage to many economically important crops grown in the greenhouses, fields, organic vegetable gardens and orchards.
2. Aphid killer wasps, Aphelinus abdominalis have a wide host range.
Aphelinus abdominalis wasps feed on a wide range of host species of aphids that cause a serious damage to different crops.
Following are the few examples of aphid hosts of Aphelinus abdominalis wasps.
- Alfalfa aphid, Acyrthosiphon pisum
- Bird cherry-oat aphid, Rhopalosiphum padi
- California Laurel aphid, Euthoracaphis umbellulariae
- Cereal aphid, Sitobion avenae
- Cotton aphid, Aphis gossypii
- Green peach aphid, Myzus persicae
- Melon aphid, Aphis gossypii
- Potato aphid, Macrosiphum euphorbiae
3. Aphid killer wasps, Aphelinus abdominalis are easy to handle and release in aphid infested greenhouses or fields.
- Aphelinus abdominalis are shipped as mummies in small vials. Mummies are parasitized dead aphids that are filled with wasp pupae. Adults of parasitic wasp generally emerge from these pupae inside the mummies and then they emerge from mummies by cutting an exit hole.
- Upon arrival, the packages of wasps can be stored in a dark and cool place until you are ready to release wasps in the garden, field or greenhouse.
- Wasps should be released in the garden, field or greenhouse within 15-20 hours of their arrival.
- Avoid direct exposure of mummies to sunlight that can kill them.
- If ants are present on aphid-infested plants, control them first before releasing Aphelinus abdominalis wasps, as ants will defend aphids from these parasites to protect their honeydew food. If ants are not controlled, effectiveness of wasps as a parasite will be reduced.
- As a preventive measure, release 4-5 adult wasps per 100 square ft. weekly by opening vials and walking slowly in the garden or greenhouse. Adult wasps should escape themselves from the vials. Then randomly place the un-hatched mammies in shaded areas in the garden, field or greenhouse so that adult wasps will emerge in the as soon as they mature.
- As a curative measure, release 25 -30 mummies or hatched wasp adults per 100 square ft. weekly in the colonies of aphids or in the heavily aphid infested areas in the vegetable gardens, greenhouses or fields.
4. Aphid killer wasps (Aphelinus abdominalis) are quick to find aphid colonies.
- Adults of Aphelinus abdominalis generally use alarm signals produced by aphid infested plants and smell of honeydews secreted by aphids on the infested plants to find aphid colonies (Photo 1).
- Once in the aphid colony, they also use their antennae to select a suitable size aphid for laying eggs in aphid body.
- Aphelinus abdominalis wasps perform better against aphids when temperatures are between70 and 77°F and relative humidity between 60 and 80%.
5. Aphid killer wasps, Aphelinus abdominalis have an ability to recycle.
- When adults of Aphelinus abdominalis are released in the aphid infested areas, they will follow alarm signals produced by aphid infested plants and smell of honeydews secreted by aphids on the infested plants to find aphid colonies.
- Once in the aphid colony, females of Aphelinus abdominalis will use their antennae to select a right size aphid for laying eggs. Females will insert tip of their ovipositor into the ventral side of aphid abdomen and lay eggs in the body of aphids.
- Within the aphid body wasp eggs will hatch into young larvae that feed on the body content of aphid and complete their development within the aphid body.
- While wasp larvae are feeding on the body content, parasitized aphids will be still alive, reproduce and feed on plant tissue for a while but they will die as soon as the larvae of Aphelinus abdominalis wasp become mature and pupate.
- These dead aphids will then turn into “mummies” (which are commercially sold to use as biological control of aphids).
- After 14- 15 days, adult wasps will start emerging from mummies again and life cycle continues.
6. Aphid killer wasps, Aphelinus abdominalis are not harmful.
- Aphelinus wasps are safe to animals, humans and the environment.
- They do not cause damage to plants.
- They are not harmful to the personnel involved in their production and application.
- Wasp treated food products are safe to handle and eat.
What are Bio-pesticides?
Bio-pesticides are certain types of chemical products with pesticide properties derived from animals, microorganisms, plants and some kind of minerals. Bio-pesticides are known for their effectiveness against several insect pests and less toxicity to humans and the environment as compared to the traditional chemical pesticides.
Organic zucchini (Photo 1) is grown as a high-value crop in large commercial farms as well as in small organic gardens but several insect pests like aphids, squash bug and whiteflies (Bemisia tabaci) cause a serious damage to zucchini (Cucurbita pepo) plants. The zucchini whiteflies, also known as silverleaf or sweetpotato whiteflies are the most devastating pests of many crops. Whiteflies (Photo 2) cause damage to plants by sucking cell sap with their beak-like mouthparts from leaf and stem tissues. The main symptoms of whitefly damage include yellowing, and drying and falling off leaves from plants prematurely. While feeding whiteflies also excrete sticky honeydew on the leaves. This sticky honeydew encourages growth of black sooty mold on the leaves and is generally known to affect the process of photosynthesis in which plants use sunlight as a source of energy to make their own food. Sweet honeydew also attracts ants that generally interferes the activity of beneficial insects that may be useful in the natural control of whiteflies and other soft-bodied insects. Whiteflies are also known for transmitting many viruses including bean yellow disorder virus, cucumber bean yellowing virus, cucurbit yellow stunting disorder virus, sweetpotato chlorotic stunt virus, tomato chlorosis virus and tomato yellow leaf curl virus.
Photo 1. Healthy zucchini plant
Photo 2. An adult of whitefly species
Biological Control of Whiteflies
Control of whiteflies is difficult but there are several natural enemies including predatory insects (lacewings, bigeyed bugs, minute pirate bugs and whitefly predatory beetle, Delphastus pusills), predatory mites (Amblyseius swirskii) and parasitic wasps (Eretmocerus eremicus and Encarsia formosa) and beneficial nematodes (Steinernema carpocapsae and Steinernema feltiae) have been used as biological control agents to manage whiteflies. In addition to live biological control agents, plant based compounds including Azadirachtin (found in leaves and kernels of neem tree) and Pyrethrin (found in chrysanthemum flowers) and microbial based products such as Spinosad (found in bacteria, Saccharopolyspora spinose; Mertz and Yao, 1990) have been used as bio-pesticides to control insect pests of different crops. Recently, Razze et al. (2016) demonstrated that pyrethrin and insecticidal soap have a potential to be used as safe bio-pesticides to control whiteflies infesting different crops including zucchini in the organic gardens.
For more information on the biological control of whiteflies read my blog entitled “Control whiteflies with predatory mite Amblyseius swirskii”
- Mertz, F. P. and Yao, R. C. 1990. “Saccharopolyspora spinosa sp. nov. Isolated from Soil Collected in a Sugar Mill Rum Still”. International Journal of Systematic Bacteriology. 40: 34–39.
- Razze, J.M., Liburd, O.E., Nuessly, G.S. and Samuel-Foo, M. 2016. Evaluation of bioinsecticides for management of Bemisia tabaci (Hemiptera: Aleyrodidae) and the effect on the whitefly predator Delphastus catalinae (Coleoptera: Coccinellidae) in organic squash. Journal of Economic Entomology 109: 1766-1771.
What are Whiteflies?
Whiteflies are about 2-3 mm long tiny insects with yellowish bodies, white colored wings and piercing and sucking types of mouthparts. Adult whiteflies generally gather on the underside of the leaves where they mate. After mating, females lay over 200 eggs on the lower surface of leaves. Eggs hatch within 7 days into pale to translucent colored and wingless nymphs. These nymphs develop through four developmental stages (instars). The first stage individuals are called ‘crawlers’ because they have well-developed legs for crawling on plant surfaces and antenna for locating permanent feeding sites on the underside of leaves. After finding a suitable feeding site, crawlers enter into the second stage nymphs, flatten and become legless. These nymphs then become immobile by attaching themselves to the selected feeding site by inserting their mouthparts into leaf tissue where they continuously feed for about 3-4 weeks. While feeding, nymphs molt twice into the third and fourth stages (instars) and then form pupae. After 7-10 days, adult whiteflies emerge from pupae and the life cycle continues. Although adult whiteflies live only for a month, they can complete several generations during the growing season of host crops.
Whiteflies are known to cause both direct and indirect damage to their host plants which include various types of vegetables, ornamental plants, fruits and field crops.
In the case of direct damage, both adult and nymphal stages use their piercing and sucking types of mouthparts to suck cell sap from the underside of leaves of their host plants. Heavy feeding by whiteflies generally causes yellowing of leaves that eventually dry and fall off prematurely from the plant. Also, plants, which are heavily infested with whiteflies generally look unhealthy and eventually die off prematurely.
In the case of indirect damage, whiteflies, while feeding, secrete honeydew that stimulates the growth of black sooty mold on the surface of leaves. This black sooty mold covers the whole leaf and badly affects photosynthesis, a process used by plants to convert light energy from sun to chemical energy for the synthesis of their own food. This black sooty mold also reduces the quality of the produce and aesthetic value of many ornamental plants. In addition, whiteflies are known to transmit different types of diseases causing plant viruses, which are responsible for tremendous economic loss to the agricultural, horticultural and greenhouse industries.
Biological control of whiteflies
Several chemical insecticides have been recommended for the effective control of whiteflies. However, their use in the greenhouses and organic gardens is restricted due to their detrimental effects on the human health and environment. Therefore, there is a need to find alternatives to chemical insecticides to manage whitefly problems. Biological control agents like predatory mites, Amblyseius swirskii have shown a potential to manage whiteflies without compromising human health and the environment.
What is the predatory mite, Amblyseius swirskii?
Adults of the predatory mite, Amblyseius swirskii are pear-shaped, about 0.5 mm long with four pairs of legs. Female mites lay oval-shaped, 0.15 mm long and pale-whitish colored eggs on the lower surface of the leaves. After hatching from eggs, larvae start feeding on the thrips and develop through three developmental stages and then become adults. Since the optimum temperature required for the normal reproduction and development of Amblyseius swirskii is between 20°C (68°F) and 29°C (84.2°F), they are considered to be ideal biological control agents for controlling thrips in US greenhouses where temperatures often exceed 25°C during summer.
Amblyseius swirskii mites are commercially available as mixed populations of adults and larvae and are currently used as a biological control agent for controlling tiny pests, which cause serious damage to many economically important crops. Both larvae and adults of Amblyseius swirskii are predatory in nature and can be easily released in greenhouses. Since these predatory mites are very active, they can disperse quickly after their application in the greenhouses where they will locate and start munching on whiteflies. Many researchers have demonstrated that each adult predatory mite can consume 15 larvae of whiteflies or 10 eggs of whiteflies per day. It is also well know that under favorable environmental conditions these mites can recycle continuously in the greenhouses as long as there is enough food around, and help to keep the whitefly population under the economic threshold level. For the effective control of whiteflies it is recommended to release over 5000 predatory mites per acre 2-3 times on a bi-weekly basis. Predatory mites can be released as a preventive measure before the occurrence of pests or as a curative measure after the incidence of pest mites. These warm adapted predatory mites perform better when they are released at optimum temperature mentioned above. The activity of Amblyseius swirskii mites will be reduced if they are released under cooler conditions. Also, these mites will not survive under really cold and frosty temperatures.
Amblyseius swirskii mites feed on following species of whiteflies
- Ash whitefly, Siphoninus phillyreae
- Banded wing whiteﬂy, Trialeurodes abutiloneus
- Citrus whiteﬂy, Dialeurodes citri
- Cloudy-winged whiteﬂy, Dialeurodes citrifolii
- Crown whitefly, Aleuroplatus coronate
- Giant whiteﬂy, Aleurodicus dugesii
- Greenhouse whiteﬂy, Trialeurodes vaporariorum
- Iris whitefly, Aleyrodes spiraeoides
- Mulberry whitefly, Tetraleurodes mori
- Rhododendron whitefly, Massilieurodes chittendeni
- Silver leaf whitefly, Bemisia argentifolii
- Sweet potato whitefly, Bemisia tabaci
- Woolly whitefly, Aleurothrixus floccosus
Hoogerbrugge, H., Calvo, J., Houten, Y. and Bolckmans, K., 2005. Biological control of the tobacco whitefly Bemisia tabaci with the predatory mite Amblyseius swirskiia in sweet pepper crops. Bulletin OILB/SROP 28, 119–122.
Xiao, Y.F., Avery, P., Chen, J.J., McKenzie, C. and Osborne, L. 2012. Ornamental pepper as banker plants for establishment of Amblyseius swirskii (Acari: Phytoseiidae) for biological control of multiple pests in greenhouse vegetable production. Biological Control 63: 279-286.
The fungus gnat
Fungus gnats (Bradysia spp) are serious pests of many household plants and ornamentals grown in greenhouses and nurseries. These ornamentals include African violets, carnations, chrysanthemums, cyclamen, lilies, geraniums, impatiens and poinsettias.
Adults of fungus gnats are tiny brown or black winged insects that are always roaming in greenhouses or even in houses. Adult gnats are a nuisance to people and are known to disseminate spores of disease causing fungal pathogens from plant to plant when they migrate in through the house or greenhouse.
Fungus gnat maggots are colorless, translucent and always live in the soil. Only maggots of fungus gnats can cause direct damage to plant roots and stems by chewing/stripping and tunneling through them. While feeding on the plant roots, maggotscan also transmit disease causing fungal pathogens including Fusarium, Phoma, Pythium and Verticillium. Severely damaged plants appear unhealthy, discolored and eventually dry out.
Overlapping generations of fungus gnats in the greenhouse makes it difficult to reduce their populations to below their damaging threshold level. Relying on chemical insecticides to manage fungus gnats in greenhouses is not a safe option because they can be detrimental to both the environment and human health. Therefore, environmentally safer and effective alternatives are required for the management of fungus gnats in greenhouses.
The predatory mite
The predatory mite Stratiolaelaps scimitus previously known as Hypoaspis miles has been widely used as an effective biological control agent to control soil-dwelling stages of dark-winged fungus gnats. Predatory mites are good for controlling fungus gnats because they are adapted to survive and reproduce quickly in the same potting media/mix and the environment where fungus gnat maggots thrive best. This predatory mite generally feeds on the soil-dwelling stages of fungus gnats.
Adults, nymphs & eggs of predatory mites.
Adults of Stratiolaelaps scimitus are clear brown to tan colored tiny mites that are about 0.8- 1.0 mm in size. Females of Stratiolaelaps scimitus generally lay oval shaped eggs in the soil or potting mix. These eggs hatch into tiny brown to black colored maggots. The newly hatched maggots then develop through two successive developmental stages known as protonymphal and deutonymphal stages. Both these immature nymphal stages resemble to their parents and they are known to feed on the eggs and maggots of fungus gnats that are present in the soil. The optimum temperature required for the reproduction and development of this predatory mite is between 15-25°C (59-77°F). At this temperature range these mites generally complete their egg-to-egg life cycle within 13-15 days. This means these mites will recycle themselves in the potting mix and continue feeding on fungus gnats.
For more information on the rate and timing of application of Stratiolaelaps scimitus against fungus gnats visit www.bugsforgrowers.com.
Importance of Japanese beetles
We are all familiar with Japanese beetles (Popillia japonica) and the damage caused by them to our turf grass, beautiful ornamentals and crops. Being native to Japan, Japanese beetles were accidentally introduced to the U.S. in 1916 and have become a major turf pest since.
Japanese beetle adults are easy to identify due to their oval shape and attractive shiny metallic-green color with a row of white spots around the abdomen (Photo 1). They can be easily spotted when feeding on leaves, flowers and fruits from June through July. Japanese beetle grubs are C-shaped (when disturbed), whitish in color with a yellowish-brown colored head capsule and three pairs of thoracic legs (Photo 2).
Photo 1. Japanese beetle adults
Photo 2. Japanese beetle grubs
Japanese beetle adults mate while feeding (Photo 3). After mating, females lay eggs in the soil near the grass root zone. Eggs hatch within a week into tiny grubs, which immediately start feeding on grass roots and organic matter. Grubs pass through three developmental stages from August through October. During this time they continuously feed on grass roots, However, when the temperature starts cooling down at the end of September these grubs start moving deep into the soil for overwintering. Throughout the winter they live in earthen cocoons deep in the soil and as soon as temperatures start warming up in the April, they move back into the turf root zone and start feeding on the roots again and then enter into the fourth stage. These matured grubs then pupate in the soil in early June. Japanese beetle adults will emerge from the pupae within 1-2 weeks and the life cycle continues.
Photo 3. Mating of Japanese beetle adults
Damage caused by Japanese beetles
Adults of Japanese beetles cause severe damage to leaves (Photo 4), flowers and ripening fruits whereas their grubs cause damage to roots (Photo 5). In the case of severe infestation, adult Japanese beetles completely skeletonize all the leaves that easily fall off the plants and eventually defoliate the whole plants. Severe damage caused by grubs to turf grass is easily recognized as the localized patches of dead turf grass are noticed throughout the lawn (Photo 6). These patches of dead grass are always confused with symptoms of water stress. As the feeding activity of grubs increases, the small patches of dead turf join together to form the large areas of dead turf. This dead turf is generally loose and can be easily picked up like a piece of carpet. The most significant sign of the presence of Japanese beetle grubs in the lawn is that the infested area is destroyed by diggings animals such as raccoons, skunks or birds that are looking for grubs to feast on them.
Photo 4. Japanese beetle adults are feeding on rose leaves
Photo 5. Japanese beetle grubs cause damage to turfgrass roots
Photo 6. Patches of dead grass caused by grubs of Japanese beetles
To reduce future outbreaks of Japanese beetles and the damage caused by them to ornamentals and turf next summer, it is essential to kill the overwintering grub population now. Beneficial entomopathogenic Heterorhabditis bacteriophora nematodes (Photo 7) also called insect-parasitic nematodes have been used as biological control agents to kill both grubs and pupae of Japanese beetles. Heterorhabditis bacteriophora nematodes can be applied three times a year. The first application within the first 2 weeks of October (early fall) will target grubs before they move deep in the soil for overwintering. The second application in the April targets the grubs that survived the first nematode application and moved back from their overwintering sites into the turf root-zone, and the third application in August targets newly hatched grubs.
Photo 7. An infective juveniles of beneficial entomopathogenic Heterorhabditis bacteriophora nematode can kill Japanese beetle grubs
How do beneficial entomopathogenic nematode kill grubs?
Beneficial Heterorhabditis bacteriophora nematodes are commercially available and can be easily applied at the rate 23,000 nematodes per square foot of area by simplly using water cans (Photo 8) or knapsack sprayers. These nematodes always carry several cells of symbiotic bacteria called Photorhabdus luminescens in their gut and use them as weapons to kill their insect hosts. When the entomopathogenic nematodes are applied to the soil surface or thatch layer, they move into the soil and look for Japanese beetle grubs. Once the nematodes find a grub, they enter the grub’s body cavity via natural openings such as the mouth, anus or spiracles and release the symbiotic bacteria from their gut into the grub’s blood. In the grub’s blood, the multiplying nematode-bacterium complex causes septicemia and usually kills the grubs within 48 hours after infection. Nematodes generally feed on multiplying bacteria, mature into adults, reproduce and then emerge as infective juveniles from the cadaver to seek new Japanese beetle grubs or other insect hosts that present are in the soil.
Photo 8. Use watering can for the application of beneficial nematodes (Courtesy of www.nematodeinformation.com)
Grewal, P.S., Koppenhofer, A.M., and Choo, H.Y., 2005. Lawn, turfgrass and Pasture applications. In: Nematodes As Biocontrol Agents. Grewal, P.S. Ehlers, R.-U., Shapiro-Ilan, D. (eds.). CAB publishing, CAB International, Oxon. Pp 147-166.
Koppenhofer, A.M., Fuzy, E.M., Crocker, R.L., Gelernter, W.D. and Polavarapu, S. 2004. Pathogenicity of Heterorhabditis bacteriophora, Steinernema glaseri, and S. scarabaei (Rhabditida : Heterorhabditidae, Steinernematidae) against 12 white grub species (Coleoptera : Scarabaeidae). Biocontrol Science and Technology 14: 87-92.
Maneesakorn, P., An, R., Grewal, P.S.and Chandrapatya, A. 2010. Virulence of our new strains of entomopathogenic nematodes from Thailand against second instar larva of the Japanese beetle, Popillia japonica (Coleoptera: Scarabaeidae). Thai Journal of Agricultural Science 43: 61-66.
Mannion, C.M., McLane, W., Klein, M.G., Moyseenko, J., Oliver, J.B. and Cowan D. 2001. Management of early-instar Japanese beetle (Coleoptera : Scarabaeidae) in field-grown nursery crops. Journal of Economic Entomology 94: 1151-1161.
Power, K.T., An, R. and Grewal, PS. 2009. Effectiveness of Heterohabditis bacteriophora strain GPS11 applications targeted against different instars of the Japanese beetle Popillia japonica. Biological Control 48: 232-236.
Two predatory insects, green lacewing and two spotted lady beetle are currently used for the control of cotton aphids
There are several types of natural enemies including predatory and endoparasitic insects that are feed on different species of aphids and help to keep aphid population under control. Of the several naturally occurring parasites and predators, green lacewing (Chrysopa carnea) and two spotted lady beetle (Adalia bipunctata) have shown a potential to control cotton aphids, (Aphis gossypii), which are known to transmit cucumber mosaic virus (CMV) to many of their host plants.
What are cotton aphids?
Cotton aphids are scientifically called as Aphis gossypii. They are tiny about 1 to 10 mm long, pear-shaped and soft- bodied insects that cause a serious damage to many agricultural and horticultural crops, and ornamental plants. Aphids tend to live in colonies. Each such colony of aphids consists of a mixture of baby aphids called nymphs, winged and wingless adults. The wingless forms have ovoid body shape and green shades whereas winged forms have black colored head and thorax, greenish colored abdomen and fusiform body. In addition to cotton crop, this aphid can cause damage to several different economically important host crops including cantaloupe, citrus, cucumber (Fig. 1.), eggplants (Fig. 2.), green pepper (Fig. 3.), okra (Fig. 4.), pumpkin (Fig. 5.), squash and watermelon. Both the adults and nymphs have piercing and sucking type of mouthparts that they use for sucking cell sap (juice) from all the tender plant parts including buds, stems and leaves. Heavy feeding by both adults and nymphs can cause yellowing of leaves that eventually dry and fall off prematurely from the plant. Aphids also transmit different types of disease causing viruses like cucumber mosaic virus (CMV) to many plant species that causes a tremendous economic loss to all the agricultural, horticultural and greenhouse industries.
Fig. 1. Cucumbers are one of the susceptible hosts of Aphis gossypii aphids
Fig. 2. Eggplants are one of the susceptible hosts of Aphis gossypii aphids
Fig. 3. Green peppers are one of the susceptible hosts of Aphis gossypii aphids
Fig. 4. Okra plants are one of the susceptible hosts of Aphis gossypii aphids
Fig. 5. Pumpkin plants are one of the susceptible hosts of Aphis gossypii aphids
What is a cucumber mosaic virus?
This virus is called cucumber mosaic virus because it was first discovered on cucumber. In addition to cucumber, CMV infects several plant species including bean, celery, lettuce, pepper, spinach, squash and tomato. Although the CMV symptoms differ among plant species, major symptoms generally includes chlorosis and mosaic of young leaves, development of ringspot patterns on fruits and leaves, wrinkling of leaves, stunted and bushy growth, and inward rolling of leaves.
Biological control of aphids
Use of chemical pesticides is not allowed in organic productions due to their detrimental effects on human and animal health, and the environment. Therefore, it is essential to use beneficial insect like green lacewing (Chrysopa carnea) and two spotted lady beetle (Adalia bipunctata) as a safe biological alternative to chemical pesticides to control aphids and reduce the crop losses caused by them in the organic productions.
What are green lacewing, Chrysopa carnea?
Green lacewing, Chrysopa carnea is considered as predatory insect because its larvae directly munch on all the stages of aphids and other soft-bodied insects. Larvae of green lacewing look like tiny alligators. These larvae have a pair of long piercing type of mandibles that they use for catching aphids and injecting digestive enzymes into aphid’s body. These enzymes liquify internal organs of aphids. Lacewing larvae then feed on the liquified body content. Each larva of lacewing can feed over 50 aphids per day. Adults of green lacewing are bright green in color with long antennae and glossy eyes (Fig. 6.). Adults are not predatory in nature meaning they do not feed any other insects or organisms but they survive by feeding on pollen and nectar.
Green lacewings Chrysopa carnea are commercially supplied as larvae, which should be released in the field or garden immediately upon their arrival. They are generally released by tapping out of container on the aphid infested plants or they can be transferred as an individual larva with a fine brush on aphid infested plant leaves or twigs.
Depending on the intensity of aphid infestation green lacewings Chrysopa carnea can be released at the following rates for best control of aphids.
- Low aphid incidence: Release 5-6 larvae of green lacewing per 10 square feet bi-weekly for 2-3 times
- Medium aphid incidence: Release 8-10 larvae of green lacewing per 10 square feet bi-weekly for 2-3 times
- Heavy aphid incidence: Release 12-15 larvae of green lacewing per 10 square feet bi-weekly for 2-3 times
Fig. 6. An adult of green lacewing
What are two spotted lady beetle, Adalia bipunctata?
Two spotted lady beetles, Adalia bipunctata are one of the best known predators that feed on different species of aphids. Both the adults and larvae of lady beetle feed on adults as well as nymphs of aphids. Adult lady beetles can be red or black in color. As name implies, adults have two spots, one on the center of each of two fore wings. The black colored lady beetles have two red spots whereas red colored beetles have two black spots. Female beetles generally lay a cluster of 25-50 yellow to orange colored and ovoid-shaped eggs per day on the leaves nearby a aphid colony. Eggs hatch within a week into small larvae that start feeding on aphids and develop through four developmental stages. Larvae of two spotted lady beetle also look like tiny alligators with six legs, greyish black color, and a few yellow and white spots on the body. Matured larvae pupate on the leaves or on any hard surface. After 5-6 days, adult beetles start emerging from pupae.
Two spotted lady beetles, Adalia bipunctata are commercially supplied as larvae (Fig. 7.), which should be released in the field or garden immediately upon their arrival. They are generally released near to aphid colonies on the aphid infested plants or they can be transferred as an individual larva with a fine brush on aphid infested plant leaves or twigs. If they are supplied in jute bugs, hang those bags on the twigs of the plants that are heavily infested with aphids. Generally ants are present in aphid colonies because they like to feed on honeydew excreted by aphids. Since these ants can attack and kill lady beetle to protect aphid colonies, they should be eliminated before releasing lady beetle larvae on the plants.
Depending on intensity of aphid infestation larvae of two spotted lady beetle, Adalia bipunctata should be released at the following rates for best control of aphids
- Low aphid incidence: Release 5-10 larvae of two spotted lady beetle per plant bi-weekly for 1- 2 times
- Medium aphid incidence: Release 10-15 larvae of two spotted lady beetle per plant bi-weekly for 2-3 times
- Heavy aphid incidence: Release 15-25 larvae of two spotted lady beetle per plant bi-weekly for 2-3 times
Fig. 7. Larvae of lady beetle
- Aqueel, M.A., Collins, C.M., Raza, A.M., Ahmad, S., Tariq, M. and Leather, S.R. 2014 Effect of plant nutrition on aphid size, prey consumption, and life history characteristics of green lacewing. Insect Science 21: 74-82.
- Enkegaard, A., Sigsgaard, L. and Kristensen, K. 2013. Shallot aphids, Myzus ascalonicus, in strawberry: Biocontrol potential of three predators and three parasitoids. Journal of Insect Science (Tucson) 13:1-16.
- Garzon, A., Budia, F., Medina, P., Morales, I., Fereres, A. and Vinuela, E. 2015. The effect of Chrysoperla carnea (Neuroptera: Chrysopidae) and Adalia bipunctata (Coleoptera: Coccinellidae) on the spread of cucumber mosaic virus (CMV) by Aphis gossypii (Hemiptera: Aphididae). Bulletin of Entomological Research 105: 13-22.
- Jalali, M.A. and Michaud, J.P. 2012. Aphid-plant interactions affect the suitability of Myzus spp. as prey for the two spot ladybird, Adalia bipunctata (Coleoptera: Coccinellidae). European Journal of Entomology 109: 345-352.
- Lommen, S.T.E., Holness, T.C., van Kuik, A.J., de Jong, P.W. and Brakefield, P.M. 2013. Releases of a natural flightless strain of the ladybird beetle Adalia bipunctata reduce aphid-born honeydew beneath urban lime trees. Biocontrol 58: 195-204.
- Mehrnejad, M.R., Vahabzadeh, N. and Hodgson, C.J. 2015. Relative suitability of the common pistachio psyllid, Agonoscena pistaciae (Hemiptera: Aphalaridae), as prey for the two-spotted ladybird, Adalia bipunctata (Coleoptera: Coccinellidae). Biological Control 80: 128-132.
- Nadeem, S., Hamed, M., Ishfaq, M., Nadeem, M. K., Hasnain, M. and Saeed, N. A. 2014. Effect
of storage duration and low temperatures on the developmental stages of Chrysoperla carnea (stephens) (Neuroptera: Chrysopidae). Journal of Animal and Plant Sciences 24: 1569-1572.
- Sarwar, M. 2014. The propensity of different larval stages of lacewing Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) to control aphid Myzus persicae (Sulzer) (Homoptera: Aphididae) evaluated on Canola Brassica napus L. Songklanakarin Journal of Science and Technology 36:143-148.
- Shrestha, G. and Enkegaard, A. 2013. The green lacewing, Chrysoperla carnea: Preference between lettuce aphids, Nasonovia ribisnigri, and western flower thrips, Frankliniella occidentalis. Journal of Insect Science (Tucson) 13:1-10.
Two entomopathogenic bacteria, Xenorhabdus bovienii and Photorhabdus luminescens
The bacteria that are symbiotically associated with the beneficial entomopathogenic nematodes are called as entomopathogenic bacteria. In this mutualistic relationship, both bacteria and nematodes depend on each other for their reproduction, development and survival. As entompathogenic bacteria do not live freely in the nature, they have to depend on the nematodes for their survival in the nematode’s gut and, also, for carrying them inside the insect host body and releasing in the insect blood (also called haemolymph) where bacteria can develop and multiply. Entomopathogenic nematodes on the other hand depend on these bacteria for killing their insect hosts as well as food.
Briefly, the infective juveniles of beneficial entomopathogenic nematodes (Photo 1) that live in the soil always carry a few entomopathogenic bacterial cells in their guts or in special pouches. In the soil, infective juveniles of different species of beneficial nematodes use different foraging strategies including “ambush” (sit-and-wait), “cruise” (moving throughout soil profile) and “intermediate (both ambush and cruise strategies) for searching their insect hosts. When infective juvenile nematodes find their insect host, they generally enter into host body through natural openings like anus, mouth and spiracles. Once inside the insect body, infective juveniles release bacterial cells through their anus in the insect blood where bacteria multiply, cause septicemia and kill insect hosts within 48 hours.
Photo 1. An infective juvenile of entomopathogenic nematode
Inside the dead insects (cadavers), 3rd stage infective juvenile (also called daure juvenile) nematodes recover by shedding off their second stage cuticle and begin feeding on multiplying bacteria. While feeding on bacteria, nematodes develop, reproduce and complete 2-3 generations. Then after depletion of food (when bacteria stop multiplying), nematodes exit cadavers as infective juveniles in the soil. These exiting infective juveniles make sure that they are carrying a few bacterial cells in their guts to use them as weapon to kill the new host. Inside the insect cadaver, multiplying bacteria also produce several different kinds of metabolites/antibiotics with bactericidal, fungicidal and nematicidal properties to preserve cadavers from decomposition (Webster et al., 2001).
Entomopathogenic bacteria belong to two major genera such as Xenorhabdus and Photorhabdus in the family Enterobacteriocae. Most of the species of Xenorhabdus and Photorhabdus are generally associated with Steinernematid and Heterorhabditid nematodes, respectively. Each of the species of these two genera is generally symbiotically associated with a specific species of entomopathogenic nematodes. For example, Xenorhabdus bovienii, Xenorhabdus nematophilus and Photorhabdus luminescens bacteria are associated with a beneficial entomopthogenic nematode species called Steinernema feltiae, Steinernema carpocapsae and Heterorhabditis bacteriophora, respectively.
It is a well-known fact that this entomopathogenic nematode-bacteria complex can kill a wide variety of their insect hosts within 48 hours after infection. However, entomopathogenic nematodes without their bacterial partner are less effective in killing their host insects and bacteria even cannot kill their insect hosts unless they are introduced into insect body through injections or infective juveniles. Further more, nematodes with or without entomopathogenic bacteria cannot kill disease causing plant pathogens but different kinds of metabolites produced by laboratory cultured entomopathogenic bacteria in broth can kill a wide range of disease causing plant pathogens. For example, recent studies conducted by Shapiro-Ilan et al (2014) showed that broth containing different kinds of metabolites collected from two entomopathogenic bacteria, Xenorhabdus bovienii and Photorhabdus luminescens suppressed the intensity of pecan diseases caused by Fusicladium effusum and Phytophthora cactorum and peach disease caused by Armillaria luminescens.
For detail information on the interaction between entomopathogenic bacteria and plant pathogens, please read following research papers.
- Shapiro-Ilan, D.I., Bock, C.H. and Hotchkiss, M.W. 2014. Suppression of pecan and peach pathogens on different substrates using Xenorhabdus bovienii and Photorhabdus luminescens. Biological Control 77: 1-6.
- Webster, J.M., Chen, G., Hu, K and Li, J. 2001. Bacterial metabolites. In: Entomopathogenic Nematodes. (ed. Gaugler, R.). CABI Publishing, NY. pp 99-113.
Beneficial nematodes and dog flea, Ctenocephalides canis control
Fleas are small wingless insects that cannot fly but can easily jump on their hosts including cats, dogs, humans and rats (Glazer et al., 2005). Fleas have piercing and sucking type of mouthparts that they use for sucking of blood from their hosts. While feeding on the host blood, fleas can also transmit disease causing organisms to their host and make them sick. Fleas develop through four different developmental stages including eggs, larva, pupa and adult. Fleas lay eggs on host’s body. These eggs then fall off on the ground where their host usually rests or sleeps during day or night time. Eggs hatch within 1-2 weeks and the hatched larvae begin feeding on only organic matter. These larvae cannot feed on host blood or cause any direct damage to their hosts. Only adult fleas are capable of feeding on the host blood, transmitting diseases and causing direct damage to their hosts. While feeding on the organic matter, larvae develop through three larval stages. The matured larvae then pupate inside the silken cocoons in soil. Adult fleas generally use cues like carbon dioxide, heat and vibration from their hosts to emerge from cocoons. The emerged adult fleas then hop on the host body whenever their hosts are visiting their resting/ sleeping place. Once on the host body, fleas feed on the host blood, mate and lay eggs. Eggs fall off of host on the ground and life cycle continues.Fleas complete several generations during summer through the fall season and then overwinter as larvae and pupae in the soil mostly at the resting place of their host animals especially dogs. Generally, declining temperatures during fall season provide an important cue for fleas to get ready for winter weather. Therefore, during fall as temperature begins cooling down most of the larval and pupal population of fleas will remain in the soil throughout the winter and then they will emerge as adults from pupae during spring. Since adult fleas are always hopping on and off their host bodies, they are very difficult to control with either insecticides or biological control agents. In contrast, both larval and pupal stages of fleas are always live in the soil and therefore, they can be easily targeted and killed by using either chemical pesticides or the biological control agents like beneficial entomopathogenic nematodes.
Biological control of dog fleas, Ctenocephalides canis
Chemical pesticides can be effective in killing both the larval and pupal stages of fleas but their use in back yards and around houses is restricted due their detrimental effects on humans, pet animals (cats and dogs) and the environment. Biological control agents such as beneficial entomopathogenic Steinernema carpocapsae nematodes are the best alternatives to chemical pesticides in reducing population of fleas because they are not harmful to humans, pets, wild animals and the environment. Since fleas generally overwinter as larval and pupal stages in the soil, they are easily targeted and killed by applying beneficial entomopathogenic Steinernema carpocapsae nematodes. Late fall is the best time to apply beneficial entomopathogenic Steinernema carpocapsae nematodes against fleas in the soil because during this time of the year temperatures definitely decline and therefore, a large number of larval and pupal stages of fleas prefer to avoid cold winter by remaining 1-2 inch deep in the soil at resting places of animals especially dogs (Photo 1). The spot application of Steinernema carpocapsae at these resting places of dogs during fall can reduce the existing populations both larvae and pupae in the soil, which in turn will reduce future outbreaks of fleas in the spring. For complete elimination of this noxious pest, you can apply beneficial nematodes monthly again in the spring through summer to target overlapping larval and pupal populations of fleas.
Photo 1. Fleas feed on dogs
Recommended rates of beneficial entomopathogenic Steinernema carpocapsae nematodes for different sizes of area.
Area in sq. ft. = Number of nematodes required
43,560 (1 Acre)………….1,000,000,000
- Glazer, I, Samish, M. and del Pino, F.G. 2005. Applications for the Control of Pests of Humans and Animals. In: Nematodes as biological control agents (ed. Grewal, P.S., Ehlers, R.-U. and Shapiro-Ilan, D.I.) CABI Publishing, pp 295-315.
- Henderson, G., Manweiler, S.A., Lawrence, W.J., Templeman, R.J. and Foil, L.D. 1995. The effects of Steinernema carpocapsae (Weiser) application to different life stages on adult emergence of the cat flea Ctenocephalides felis (Bouche). Vet. Dermatol. 6:159-163.