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, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae). Growers in the north 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 concentrations of adults at the field edge. Frequency of fields with significantly 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 distance from the previous potato field and later planting date. The effects of both physical and chemical barriers to movement into potato fields from the field edges were studied in small plot trials and at the edges of commercial potato fields. In small plot trials, physical barriers had a greater impact than chemical barriers on adult beetle movement from a potato trap crop to the protected potatoes beyond the barrier. Barrier treatments reduced beetle numbers in and just beyond the barrier in commercial fields, but the effects were localized and no significant reduction of beetles was observed further into the field. Beetle flight was hypothesized to be responsible for the localized effects of barrier treatments and the lack of edge concentrations in later planted and more distantly rotated fields. In field studies, larger potato plants attracted more colonizing potato beetles than smaller plants. Attracting Colorado potato beetles to trap crops containing potato plants that were larger than those in the remainder of the field, however, provided no significant reduction of beetles in the remainder of the field. We found little opportunity to reduce beetle populations with trap crops at the edges of potato fields without controlling the adults in the trap crop itself. Growers can exploit naturally occurring concentrations of adults at the edges of early and adjacent potato plantings if they are prepared to monitor and regularly treat the field edges.