TIMING OF INFESTATION BY THE COLORADO POTATO BEETLE (COLEOPTERA, CHRYSOMELIDAE) ON THE SUPPRESSIVE EFFECT OF FIELD RELEASED STINKBUGS (HEMIPTERA, PENTATOMIDAE) IN WASHINGTON

Delaying infestation of potatoes by overwintering Colorado potato beetles Leptinotarsa decemlineata (Say) by either 10 or 20 d following plant emergence increased damage to the potatoes. The egg deposition period was reduced from 5 to 3 wk; both increased rates of egg deposition and feeding occurred over a shorter period of time. Potatoes infested at plant emergence by Colorado potato beetle had fourth instars feeding during a 4-wk period of time while infestation 20 d after plant emergence reduced this feeding period to 2 wk and resulted in significantly greater defoliation than those infested at plant emergence. Delayed infestation by either 10 or 20 d had a negative effect on predation by Perillus bioculatus (Fabr.). Potato plants infested by Colorado potato beetles at plant emergence with releases of P. bioculatus 4 d later had the greatest percentage reduction in fourth instars and provided significantly greater foliage protection than plants infested at 10 or 20 d after plant emergence. Based on population levels of fourth instar Colorado potato beetles, multiple releases of P. bioculatus and P. maculiventris were not significantly more effective than a single release based on population comparisons of beetles. However, three releases (three predators per plant each release) of both species of predators provided greater potato foliage protection than a single release (three predators per plant).