Interactions Between Bt-Bioinsecticides and Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae), a Predator of Plutella xylostella (L.) (Lepidoptera: Plutellidae)

Effects of a Bt-based insecticide on the functional response of Ceraeochrysa cincta preying on Plutella xylostella

Plutella xylostella, is the main pest infesting Brassica crops, and products based on Bacillus thuringiensis (Bt) are frequently used in strategies for its biocontrol. The present study aimed to evaluate whether a Bt-based bioinsecticide affects the predation behavior of Ceraeochrysa cincta when preying on P. xylostella. Three larval instars of the predator and the eggs and second-instar larvae of the moth were used, with the prey either untreated or treated with a Bt-based product (Xentari®). Results showed that, the first larval instar of C. cincta presented a type II functional response when preying upon untreated eggs, and a type III response when preying upon Bt-treated eggs, while the second and third instars presented type II and III responses, respectively, in both situations. The predator's first and third larval instars presented a type II functional response when preying upon untreated larvae and a type III response when preying upon Bt-treated larvae. However, the predator's second-instar larvae showed a type II response in both treatments. The results obtained allowed us to conclude that the Bt-based insecticide tested affects the predation behavior of the first-instar larvae of C. cincta on eggs and of both the first- and third-instar larvae of this predator on P. xylostella larvae.

Can Bacillus thuringiensis affect the biological variables of natural enemies of Lepidoptera?

ABSTRACT: The entomopathogen Bacillus thuringiensis (Bt) is widely used as one of the ingredients in pest control formulations, but researches conducted on its effect on non-target organisms are still in the nascent stage. This investigation aimed to uncover if Bt treated with Tenebrio molitor (Coleoptera: Tenebrionidae) larvae and pupae could affect the biological variables of Podisus nigrispinus (Hemiptera: Pentatomidae) and Palmistichus elaeisis (Hymenoptera: Eulophidae), all of which established natural enemies of leaf defoliator caterpillars in the eucalyptus culture. Larvae of T. molitor were fed on wheat bran containing different concentrations of B. thuringiensis (0.00; 0.25; 0.50; 1.00; 2.00 and 4.00 g Agree/kg bran). When the larvae attained size of about 2 cm, they were used as prey for P. nigrispinus (Bioassay I), and their pupae used as hosts for P. elaeisis (Bioassay II). Only the biological variables oviposition period and egg numbers by posture of the predator P. nigrispinus were altered. The biological variables of P. elaeisis were not altered, since it was possible to use these control methods within the integrated pest management.