Toxicity of Bacillus thuringiensis CrylAb Toxin to the Predator Chrysoperla carnea (Neuroptera: Chrysopidae)

Abstract

Laboratory feeding studies were carried out to determine the effects of the Bacillus thuringiensis (Berliner) CrylAb toxin on developmental time and mortality of Chrysoperla carnea (Stephens) larvae. A bioassay technique was developed that allowed for incorporation of the CrylAb toxin into a liquid diet that was then encapsulated within small paraffin spheres. Because only 2nd and 3rd instars can penetrate the surface of the paraffin spheres, 2 different methods were used to rear chrysopid larvae through the 1st instar. The 1st method used small foam cubes soaked in non-encapsulated, liquid diet (with or without CrylAb). The 2nd method used Ephestia kuehniella (Hübner) eggs as prey during the first instar (no CrylAb exposure). After reaching the 2nd instar, all larvae received encapsulated, artificial diet with or without CrylAb, respectively. When reared only on artificial diet containing CrylAb toxin, total immature mortality was significantly higher (57%) than in the respective untreated control (30%). Also, significantly more chrysopid larvae died (29%) that received CrylAb later during their larval development compared with the respective control (17%). Although mortality was consistently higher, no or only small differences in developmental times were observed between CrylAb-treated and untreated C. carnea larvae. C. carnea larvae required significantly more time to complete larval development when reared on artificial diet only than when reared first on E. kuehniella eggs followed by encapsulated artificial diet or on only E. kuehniella eggs, regardless of exposure to CrylAb. These results demonstrate that CrylAb is toxic to C. carnea at 100 μ mg/ml of diet by using encapsulated artificial diet.