Effects of Cyromazine on Larval Survival, Pupation, and Adult Emergence of Colorado Potato Beetle (Coleoptera: Chrysomelidae)

Abstract

Results of laboratory and field experiments to test the effects of the insect growth regulator cyromazine on Colorado potato beetle, Leptinotarsa decemlineata (Say), are reported. We describe symptoms of cyromazine poisoning of larvae. When second instars were fed cyromazine-treated potato foliage in laboratory bioassays, all larvae died within 10 d. Second instars of the insecticide-resistant Long Island strain survived longer than those of the susceptible Vestaburg strain when fed a low concentration, but survival between strains fed at a higher concentration did not differ. Survival to pupation of fourth instars fed cyromazine-treated foliage was 12-16% lower than that of controls, but the differences were not significant. Treated larvae pupated later and were less likely to develop into adults than untreated larvae. In the field, cyromazine sprays reduced the number of first and second instars and affected third and fourth instars by inhibiting feeding and lowering rates of pupation. Cyromazine treatment reduced adult emergence 53-fold and increased yield of size-A potatoes 2- to 4.5-fold compared with results from untreated plots. The effectiveness of cyromazine at low rates and on all stages of insect development makes it a valuable addition to integrated pest management programs for Colorado potato beetle.