While visiting my dad for Father’s Day, he mentioned he saw some Colorado potato beetles (Coleoptera: Chrysomelidae: Leptinotarsa decemlineata) feeding on his cultivated potato plants (Solanum tuberosum, Solanaceae). We headed out to look for some and found quite a few larvae.
The plants had been sprayed with an insecticide some time earlier, but Colorado potato beetles are notorious for evolving resistance to chemicals (Bessin 2003). When an insecticide is applied most of the insects die. Genetic variation among individuals, however, almost guarantees there will be at least a few with genes that convey resistance to the chemical. Resistant insects survive and breed, and in turn their offspring receive their chemical-resistant genes. This selection for resistant individuals amplifies their resistance over time. Eventually entire populations become highly resistant, making the insecticide in question nearly worthless.
The creation of insecticide-resistant populations can be avoided by rotating insecticides from different classes and using alternate control methods (Bessin 2003). The bacterium Bacillius thuringiensis var tenebrionis (Bt) is effective against young larvae (Bessin 2003). Parasitic flies and predatory stink bugs can be helpful in controlling potato beetles, if these beneficials aren’t killed by insecticide applications (Bessin 2003). Since there weren’t too many plants in my dad’s plot, we proceeded to simply squash the larvae by hand.
Colorado potato beetles are the most serious insect pest of potato plants (Bessin 2003). They will also feed on other members of the family Solanaceae, and can also be a serious pest of tomatoes, eggplants, peppers, and tobacco (Jacques and Fasulo 2000, Bessin 2003). Even in the absence of these crops, the beetles can feed on a wide variety of wild members of the family Solanaceae, including common nightshade, belladonna, ground cherry, and buffalo-bur (Jacques and Fasulo 2000). Ever adaptable, these beetles are capable of surviving off of whatever members of this plant family are locally abundant.
Bessin, R. 2003. ENTFAC-312: Colorado Potato Beetle Management. Cooperative Extension Service, University of Kentucky College of Agriculture.
Jacques, R.L. Jr. and Fasulo, T.R. 2000. Featured Creatures: Potato beetles. University of Florida Institute of Food and Agricultural Sciences/Florida Department of Agriculture and Consumer Services.