Colorado Potato Beetle (Coleoptera: Chrysomelidae) Larval Mortality: Operative Effects of Bacillus thuringiensis subsp. san diego

Percentage mortalities for different Colorado potato beetle instars were equal when equivalent concentrations of Bacillus thuringiensis subsp. san diego were administered on a body weight basis. When late first instars were placed on treated foliage and held under different temperatures, 100% mortality occurred at 28-33°C, whereas at 18°C mortality was only 45%. Fifty percent of second instars recovered from feeding on treated foliage, if they were placed on untreated foliage within 2.8 h of first exposure to treated foliage. Fourth instars did not avoid treated foliage in a choice test, nor did they leave treated foliage when untreated foliage was in contact with the treated foliage. Field applications of B. thuringiensis subsp. san diego need to be timed so larvae are exposed to treated foliage for at least 6-8 h, when temperatures exceed 24°C.