Studies were conducted to determine if any adverse effects ensued when larvae of Heliothis virescens (F.) survived various feeding periods on cotton treated with Bacillus thuringiensis Berliner. Some of the 2nd instars that were fed B. thuringiensis -treated terminals for 6, 18, or 30 h and then transferred to an untreated diet survived. The ability of larvae to recover decreased with increases in dosage rate or exposure time. After feeding periods of 18 or 30 h, duration of the larval stage was significantly increased. Effects on pupae were similar. No effects on adult longevity, fecundity, egg viability, or F1 larval survival were detected.