Colorado potato beetle (Coleoptera : Chrysomelidae) feeding, development, and survival to adulthood after continuous exposure to Bacillus thuringiensis subsp tenebrionis-treated potato foliage from the field

Colorado potato beetle, Leptinotarsa decemlineata (Say), feeding, developme nt, and survival to adulthood were examined after continuously exposing lar ge larvae to Bacillus thuringiensis subsp, tenebrionis-treated. potato foli age from the field. In laboratory assays, the overall consumption and the l ength of period to become prepupae were determined for larvae, which began as 3rd and 4th instars, that were offered potato leaf disks with naturally declining levels of B. thuringiensis residue. In small-cage field experimen ts, survival to adulthood and the period to adult emergence for beetles con fined to potato plants treated with B. thuringiensis beginning as 3rd and 4 th instars also were examined. Third instars remaining on plants after a B. thuringiensis application were unlikely to feed and 4th instars consumed o nly approximate to 50% as much foliage as those fed untreated foliage. Many late instars subjected to B. thuringiensis-treated foliage failed to survi ve to adulthood; 58-83% of these beetles died during the larval stage. Redu ced feeding and poor survival of late instars suggest that counts of large larvae after application do not provide a complete picture of the efficacy of the B. thuringiensis treatment. Late instar Colorado potato beetles that were exposed continually to naturally declining levels of B. thuringiensis -treated potato foliage took an average of 1.8 - 4.5 d longer to become pre pupae and. 4-8 d longer to emerge as adults compared with those provided wi th untreated foliage. Delayed emergence of adults that fed on B. thuringien sis-treated potatoes as late instars indicated that development was prolong ed in these insects because of ingestion of a sublethal dose of B. thuringi ensis.