Beneficial nematodes for control of pecan weevils
Pecan weevils are scientifically called as Curculio caryae. Both the adult and larval stages of pecan weevil cause a serious damage to pecan nuts.
Adults of pecan weevil generally emerge from soil in late July to August and move in the tree canopy by either crawling on the trunk or directly flying. Once in the canopy, adults start puncturing and feeding on the young nuts. These damaged nuts fall off the tree within 2-3 days.
While feeding on young nuts, adults mate and females lay eggs by chewing a hole into developing nuts. Eggs hatch inside the nut and hatched larvae immediately starts feeding on a developing kernel and matures (fourth stages) within 2-3 weeks. When the damaged nuts fall to the ground, the mature larvae will cut a small circular hole in the nut shells and exit the nuts, then burrow 4 to 8 cm deep into the soil and remain there for about 1-2 years. Then larvae pupate in the soil. Three week 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, all these soil dwelling stages can be targeted by three consecutive pre-emergence applications of beneficial entomopathogenic nematodes in early May, June and in late June or in early July. The applied nematodes will find, infect and kill the larval, pupal and adult stages of pecan weevils, which in turn will reduce the emerging populations of pecan weevil adults in late July to August.
The main advantage of three consecutive beneficial nematode applications is that all the weevil stages that survived after the first nematode application will be infected and killed by each subsequent application of beneficial nematodes.
As we know beneficial entomopathogenic nematodes are very effective against soil dwelling stages many insect pests, Shapiro-Ilan, and Gardner, (2012) also observed 49 to 81% control of pecan weevils when entomopathogenic Steinernema carpocapsae nematode applied in the field at the rate of 1 billion nematodes per acre at three time intervals (i. e. early in May and June, and in late June) before the emergence of pecan weevil adults.
Literature:
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.