Beneficial nematodes for Grapholita molesta control
What is an oriental fruit moth?
The Oriental fruit moth Grapholita molesta is an one of the most devastating Lepidopterous insect pests of many fruit crops including apples, apricots, nectarines and peaches. The life cycle of oriental fruit moth consists of four developmental stages including eggs, larvae, pupae and adults. Of these four developmental stages, only larval stage is harmful to growing parts of fruit trees and their fruits.
Adults are gray colored moths that do not cause any damage to trees or fruits. Females of oriental moth generally lay their eggs on the succulent twigs and underside of the leaves near growing points. Eggs are round to oval in shape and translucent white in color. Eggs hatch into young larvae that develop through four to five instars. All the young larval instars are whitish in color with brown heads but the mature larvae are pinkish to red in color. The Mature larvae possess three pairs of true legs, four pairs of pro-legs and anal comb on their last abdominal segment. The mature larvae overwinters in cocoons generally in the soil or in crevices under bark and then pupate early in the spring. The pupae are yellowish- brown to blackish in color. The first generation adult moths generally emerge from pupae early in the spring.
All the four larval instars of oriental fruit moth are damaging to young twigs and fruits of their host plants. Immediately after hatching from eggs, first generation young larvae bore into tips of growing shoots or twigs and start feeding on internal tissues by making tunnels downwards. When they reach to the hard tissue, they exit the twigs, then look for new succulent twigs/shoots and bore into them again. All these infested shoots then wilt and die. The second or third generation larvae generally cause damage to small fruits by burrowing into them through stems or directly through the holes bored by them into the fruits. When inside the fruit, these larvae will feed on fruit tissue by making irregular tunnels in a confined area. The mature larvae then exit the damaged fruit and will overwinter in the cocoons especially in the soil. Early in the spring, mature larvae pupates, then emerge as adults and life cycle continues.
The overlapping generations of oriental fruit moth during growing season of fruits makes it difficult to reduce their damage to many fruits. Also, this insect has developed a resistance many insecticides. Therefore, many fruit growers are looking for an alternative to control oriental fruit moths.
Nematodes that are parasitic to many insect pests are called as beneficial entomopathogenic nematodes that mainly belong to two main genera including Steinernema and Heterorhabditis that have many characteristics of classical biological control agents. Therefore, these nematodes have been used for controlling many soil-dwelling insect pests (Grewal et al., 2005) including oriental fruit moth (Lacey et al., 2005). The infective juveniles of Steinernema and Heterorhabditis carry symbiotic bacteria in the genera Xenorhabdus and Photorhabdus, respectively and use them as a weapon to kill their insect hosts like oriental fruit moths. These beneficial nematodes can be used to target mature larvae that have been moved in the soil for overwintering and pupation.
In 2006, Riga and other researchers have reported that the beneficial entomopathogenic nematodes including Steinernema carpocapsae, Steinernema feltiae, Steinernema riobrave and Heterorhabditis marelatus can cause over 63% mortality of oriental fruit moth under laboratory and fruit bin conditions. Recently, Negrisoli et al (2013), also tested several strains of beneficial entomopathogenic nematodes under laboratory and field conditions and demonstrated that the application of two nematode species including Steinernema rarum strain RS69 and Heterorhabditis bacteriophora Strain RS33 on the peach trunk can kill over 94% of oriental fruit moths. This research suggests that the beneficial nematodes have a great potential to use as the biological control agent to suppress the population of the oriental fruit moth.
Three beneficial entomopathogenic nematodes
Of these six most effective species of beneficial entomopathogenic nematodes that can kill oriental fruit moth, only Heterorhabditis bacteriophora, Steinernema carpocapsae and S. feltiae are commercially available. These three nematodes can be applied using traditional sprayers at the rate of 1 billion nematodes per acre to manage populations of the oriental fruit moths infesting different fruit crops.
- Steinernema carpocapsae: Steinernema carpocapsae nematodes generally use ambush type of foraging strategy in which the infective juveniles of this nematode “sit and wait” for larvae of insect host to come by and they attack and kill them.
- Steinernema feltiae: Steinernema feltiae nematode is a cold tolerant nematode and uses intermediate type of foraging strategy that is between ambush and cruise type to find and kill their insect pests including oriental fruit moth.
- Heterorhabditis bacteriophora: Heterorhabditis bacteriophora nematodes cruising type of foraging strategy in which the infective juveniles of this nematode constantly move in the soil to find their insect hosts such as oriental fruit moth larvae or pupae.
Read following papers for more information on the interaction between beneficial entomopathogenic nematodes and the oriental fruit moths.
- Grewal P.S., Ehlers, R-U, Shapiro-Ilan D.I. 2005. Nematodes as Biocontrol Agents. CABI, New York, NY.
- Lacey, L.A., Neven, L.G., Headrick, H.L. and Fritts, R., Jr. 2005. Factors affecting entomopathogenic nematodes (Steinernematidae) for the control of overwintering codling moth (Lepidoptera: Tortricidae) in fruit bins. Journal of Economic Entomology 98:1863–1869.
- Negrisoli, C.R.D.B., Negrisoli, A.S., Garcia, M.S., Dolinski, C. and Bernardi, D. 2013. Control of Grapholita molesta (Busck, 1916) (Lepidoptera: Tortricidae) with entomopathogenic nematodes (Rhabditida: Heterorhabditidae, Steinernematidae) in peach orchards. Experimental Parasitology 135: 466-470.
- Riga, E., Lacey, L.A. and Headrick, H.L 2006. Control of the oriental fruit moth, Grapholita molesta, using entomopathogenic nematodes in laboratory and fruit bin assays. Journal of Nematology 38:168-171.