Flight Activity and Susceptibility to Insecticides of Variegated Cutworm, Peridorma saucia (Hubner) Attacking Field Tomatoes in Southwestern Ontario
The variegated cutworm, Peridroma saucia (Hübner), is a polyphagous pest that sporadically damages processing field tomatoes in southwestern Ontario. Recent anecdotal reports have suggested that it has developed resistance to pyrethroid insecticides used to control them. The objectives of this study were to acquire information on variegated cutworm flight activity in southwestern Ontario tomato fields and to assess the toxicity of currently registered and novel insecticides to determine if it has developed resistance to them. Pheromone trap data (2006) in Norfolk County suggested 2 peaks of adult flight in field tomatoes - July and August, while in Essex County there were 3 peaks - July, August and September. Direct contact toxicity bioassays were done using larvae from a laboratory culture established at the University of Guelph in late summer 2006 from larvae collected from tomato fields in both counties. Of the 4 insecticides registered for use, lambda-cyhalothrin was most toxic to 3rd-4th instar larvae > permethrin > chlorpyrifos > methomyl. Chlorantraniliprole was most toxic of the reduced risk insecticides tested. Spinosad and metaflumizone, which act primarily as stomach poisons, were less toxic by direct contact. Second instar larvae were most susceptible to permethrin > 3rd-4th > 5th instar. Comparison of results with 1977 published data showed that variegated cutworm had developed low level resistance to methomyl but not to chlorpyrifos or permethrin. Results of the study showed that pyrethroid insecticides will be effective so long as stage of larval development and climatic conditions are considered and insecticides are applied in a manner resulting in the most effective penetration of the plant canopy as possible.