EFFECT OF CRYIC TOXIN FROM BACILLUS-THURINGIENSIS ON LARVAL FEEDING-BEHAVIOR OF SPODOPTERA-EXIGUA

The lack of data on the effect of Bacillus thuringiensis (B.t.) toxins on larval feeding behavior of the pest Spodoptera exigua (Hubner) (No ctuidae: Amphypyrini) prompted us to investigate the effect of three d elivery systems of CryIC, a commercial formulation, inclusion bodies, and the activated CryIC toxin. The commercial formulation was the leas t and CryIC toxin the most lethal form to neonates of susceptible colo nies. All but two of the treatments in choice tests with neonates and third instars showed significant avoidance of B.t. treated diet, with greater proportion of larvae from susceptible (UCR-S and AUBURN-S) and resistant (AUBURN-R) colonies on untreated diet than on diet treated with any of the CryIC forms and concentrations tested. Furthermore, th ird instars consumed significantly more control than treated diet for all CryIC forms, colonies and concentrations. The avoidance of CryIC t oxin by neonates and third instars strongly suggests that CryIC, which also is present in the commercial formulation and in the inclusion bo dies, is responsible for eliciting avoidance behavior by S. exigua lar vae. Behavioral observations of third instars in a no-choice test on e ither treated or control diet indicated that questing behavior in susc eptible larvae appears to be positively related with presence of CryIC toxin in the diet. Furthermore, resistant third instars were on the w hole more active than susceptible thirds on both treated and control d iet. Resistant thirds raised on CryIC treated diet (AUBURN-RC) spent m ore time eating treated diet than resistant larvae raised on control d iet (AUBURN-R), suggesting that diet conditioning plays an important r ole on feeding behavior of S. exigua. The implications of these result s are discussed.