The Detection of Bacillus thuringiensis in Mass Rearing of Cactoblastis cactorum (Lepidoptera: Pyralidae)

Verena-Ulrike Lietze, George Schneider, Pannipa Prompiboon, Drion G. Boucias

Abstract


A colony of the cactus moth, Cactoblastis cactorum Berg, suffered a die-off that involved 100% larval mortality in selected rearing containers. Preliminary microscope examination of wet mounts prepared from dead larvae revealed the presence of numerous uniform, highly refractive particles reminiscent of bacterial spores. Utilizing a combination of bacteriological, molecular, and chemical methods the causal agent responsible for this die-off was found to be a strain of the insecticidal Bacillus thuringiensis var. kurstaki. Significantly, larvae that were killed supported bacterial growth and sporulation. The gregarious feeding habit of this insect combined with the ability of this bacterium to amplify in dead larvae explains in part the observed rapid spread of sepsis in the rearing containers. Screening the various diet ingredients demonstrated that the cannellini bean flour harbored a variety of heat resistant bacilli including both Bacillus cereus and B. thuringiensis implicating it as the likely source of toxicity.

View this article in BioOne

Full Text:

PDF