Effects of Variable Doses of Permethrin on Heliothis zea (Lepidoptera: Noctuidae) Growth and Development

Heliothis zea (Boddie) larvae reared on artificial diet were treated with permethrin using a topical or dip bioassay at 3, 5, and 7 days post-hatch. Forty-eight-hour survival and weight gain in survivors, percent pupation, and percent adult eclosion were measured in one experiment. Generally, larval weight gain after 48 hours among survivors decreased with increasing dose. A high proportion of individuals surviving after 48 hours went on to pupate and emerge as adults regardless of dose, age, and reduction in growth at 48 hours post-treatment. In a second experiment, pupal and adult weights and development times of larve and pupae were measured after topical treatment of larvae with permethrin. Pupal weights of survivors decreased with increasing dose in all age classes. Adult weights decreased with increasing dose only in the 7-day-old treatment. Development times were protracted with increasing dose in the 5-day-old and 7-day-old treatments, but not the 3-day-old treatment. In both experiments, smaller larvae were more tolerant of permethrin than larger larvae per unit body weight.