Protracted emergence of the Colorado potato beetle (Leptinotarsa decemlineata) and the relationship to neonicotinoid resistance

The Colorado potato beetle, Leptinotarsa decemlineata (Say), has been a significant pest of potato in Wisconsin since 1866. Historically, Colorado potato beetle (CPB) has had an exceptional ability to develop resistance to conventional chemical control tactics. Development of localized resistance to the neonicotinoid class insecticides (IRAC MoA 4A) has created new challenges for management of this pest. Moreover, observed temporal shifts in post-diapause crop colonization by CPB are hypothesized to be related to this protracted adult emergence pattern. Extended or delayed emergence increases the likelihood of low dose, chronic exposure to in-plant, systemic neonicotinoid insecticides in potato. During the fall of 2009 and spring of 2010, the overwintering phenology and post-diapause fecundity of four CPB populations was measured. Specifically, a common garden overwintering experiment was constructed to examine the relationships between insecticide resistance, emergence phenology, environmental factors, and gender. Four collected populations with documented resistance ratios were released into replicated 6’ x 6’ screen cages at the Hancock Agricultural Research Station, Hancock WI. Emerging adults were collected, sexed, weighed and measured every other day between April 21 and June 30, 2010 then weekly between July 1 and July 31, 2010 to assess spring emergence patterns. Additionally, extracted soil cores were used to assess the relative number of surviving insects remaining in diapause. Cumulative spring emergence of caged CPB was fit with logistic regression. Fecundity and overwintering survivorship varied among test populations related to neonicotinoid resistance estimates.