Toxicity of Bacillus thuringiensis Cry1Ab toxin to the predator Chrysoperla carnea (Neuroptera: Chrysopidae)

Laboratory feeding studies were carried out to determine the effects of the Bacillus thuringiensis (Berliner) Cry1Ab toxin on developmental time and mortality of Chrysoperla carnea (Stephens) larvae. A bioassay technique was developed that allowed for incorporation of the Cry1Ab 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 Ist instar. The Ist method used small foam cubes soaked in non-encapsulated, liquid diet (with or without Cry1Ab). The 2nd method used Ephestia kuehniella (Hubner) eggs as prey during the first instar (no Cry1Ab exposure). After reaching the 2nd instar, all larvae received encapsulated, artificial diet with or without Cry1Ab, respectively. When reared only on artificial diet containing Cry1Ab toxin, total immature mortality was significantly higher (57%) than in the respective untreated control (30%). Also, significantly more chrysopid larvae died (29%) that received Cry1Ab 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 Cry1Ab-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 artifical diet or on only E. kuehniella eggs, regardless of exposure to Cry1Ab. These results demonstrate that Cry1Ab is toxic to C. carnea at 100 mu mg/ml of diet by using encapsulated artificial diet.