Increasing the effectiveness of spring trap crops for Leptinotarsa decemlineata

Insecticide resistance problems have increased interest in trap crops as a cultural control strategy for overwintered Colorado potato beetle adults, L eptinotarsa decemlineata Say (Coleoptera: Chrysomelidae). Growers in the no rth central United States have noticed and treated concentrations of adults at the edge of some of their potato fields each spring. Based on sampling in commercial potato fields over a 2-year period, early planted fields that are adjacent to the previous year's potato crop are most likely to have co ncentrations of adults at the field edge. Frequency of fields with signific antly more adults at the edges than in the center sections as well as adult population density in the center sections of fields declined with both dis tance from the previous potato field and later planting date. The effects o f both physical and chemical barriers to movement into potato fields from t he field edges were studied in small plot trials and at the edges of commer cial potato fields. In small plot trials, physical barriers had a greater i mpact than chemical barriers on adult beetle movement from a potato trap cr op to the protected potatoes beyond the barrier. Barrier treatments reduced beetle numbers in and just beyond the barrier in commercial fields, but th e effects were localized and no significant reduction of beetles was observ ed further into the field. Beetle flight was hypothesized to be responsible for the localized effects of barrier treatments and the lack of edge conce ntrations in later planted and more distantly rotated fields. In field stud ies, larger potato plants attracted more colonizing potato beetles than sma ller plants. Attracting Colorado potato beetles to trap crops containing po tato plants that were larger than those in the remainder of the field, howe ver, provided no significant reduction of beetles in the remainder of the f ield. We found little opportunity to reduce beetle populations with trap cr ops at the edges of potato fields without controlling the adults in the tra p crop itself. Growers can exploit naturally occurring concentrations of ad ults at the edges of early and adjacent potato plantings if they are prepar ed to monitor and regularly treat the field edges.