Cover crops: Controlling pests at multiple trophic levels
Eggplant, Solanum melongena L., is a favored food for Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), which commonly invades fields causing intense defoliation leading to extreme yield loss. In our region eggplant is often grown on small farms where long distance crop rotation isn’t feasible. Previous work has shown that increasing the diversity of the field habitat with straw or winter cover crops can slow CPB invasion, reduce their numbers, and increase predator density. We are currently conducting research to refine the use of winter cover crop residues and conservation tillage techniques to increase economic benefits for eggplant growers. Taking full advantage of the field ecosystem requires understanding two common predatory stink bugs, Perillus bioculatus (Fabricius) and Podisus maculiventris (Say), which feed on CPB. While these bugs are voracious predators their numbers are greatly suppressed by wasps which parasitize stink bug eggs. These wasps use a variety of chemical and environmental cues to locate eggs, which may be disrupted by cover crop residue.
In 2014 57% and 26% of the egg masses located in eggplant fields were P. bioculatus and P. maculiventris, respectively. Numbers of eggs were not different among treatments for either species. Of the eggs for which fate could be determined 65% of P. bioculatus, and 82% of P. maculiventris were killed by parasitoid wasps. The distribution of parasitized eggs was not significantly different among treatments for P. bioculatus, but P. maculiventris eggs were significantly more parasitized in the fallow treatment than in the treatments with either cover crops residue. Parasitoids use a variety of cues to locate and hosts, and habitat diversification sometimes interferes with these cues preventing parasitoids from finding their host. It’s likely that diversifying the environment in eggplant fields may prevent parasitoids from finding beneficial stink bug eggs, adding another benefit to a promising system.