Dosage/Mortality Response of Spodoptera frugiperda (Lepidoptera: Noctuidae) and Other Noctuid Larvae to Beta-exotoxin of Bacillus thuringiensis

Abstract

A β-exotoxin of Bacillus thuringiensis Berliner was tested on first-, third-, and fourth-instar Spodoptera frugiperda (J. E. Smith), Heliothis zea (Boddie), and Trichoplusia ni (Hübner). Larvae were placed on diet including 10–12 concentrations of the β-exotoxin ranging from 0 to 200 μg (AI)/ml of diet. LC50’s for first-, third-, and fourth-instar S. frugiperda were 0.4, 7.2, and 123.7 μg (AI)/ml, respectively. H. zea larvae were less sensitive to the toxin, with LC50’s for first, third, and fourth instars of 1.0, 14.2, and 127.3 μg (AI)/ml, respectively. T. ni was most sensitive, with LC50’s of 0.3, 5.2, and 14.4 μg (AI)/ml for first, third, and fourth instars, respectively. Dose/mortality response curves for fourth-instar S. frugiperda and T. ni were nonlinear throughout the assay period and indicated a possible feeding deterrent factor associated with the toxin. Fecundity of moths developing from larvae exposed to β-exotoxin was lower than fecundity of moths developing from larvae fed on untreated diet.