|Wright Osment, Maureen|
Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2003
Publication Date: 1/2/2004
Citation: Brandt, S.L., Coudron, T.A., Habibi, J., Brown, G.R., Ilagan, O.M., Wagner, R.M., Wright Osment, M.M., Backus, E.A., Huesing, J.E. 2004. Interaction of two bacillus thuringiensis o-endotoxins with the digestive system of lygus hesperus. Current Microbiology. 48:1-9
Interpretive Summary: Tarnished plant bugs are now considered to be primary pests of many crops, including canola, strawberries, vegetables, seed alfalfa, and especially cotton. Although cultural and biological controls show promise in managing tarnished plant bugs in high value crops such as strawberries and seed alfalfa, pesticides remain the most cost-effective method available for controlling these pests in cotton, canola, and other row crops. The development of insect populations with resistance to a wide range of insecticides suggests that reliance on conventional chemical control to manage plant bugs may not be an economically or environmentally sustainable pest management strategy. Consequently, new methods of control for these insects are needed. Our studies focused on 2 toxins that are produced by a soil bacterium and that are toxic to caterpillar pests, but not to tarnished plant bugs. We found that when one of these toxins was ingested by the western tarnished plant bug some of the toxin was digested, but a portion of the toxin was able to bind to the gut lining of the insect - a necessary requirement for toxicity. Furthermore, our data showed that a portion of both toxins retained structural integrity while within the insect. This study presents findings that are important to researchers for the development of a bioactive protein for the control of these pests.
Technical Abstract: The active-toxin form of Cry1Ac (65 kDa) or Cry2Ab was fed to a non-susceptible insect, L. hesperus in an artificial diet. Biochemical and immunocytochemical methods were used to determine the distribution of ingested toxin. The toxins did not illicit a feeding deterrent response. Cry1Ac and Cry2Ab were ingested; small amounts were absorbed into the hemolymph as holoproteins, but most was excreted. SDS-PAGE analysis of Cry1Ac and Cry2Ab incubations with salivary gland homogenate showed a small decrease in the molecular weight of the active toxins. Proteolytic processing of the toxins also occurred in vivo, within the digestive system of L. hesperus. Excreted Cry1Ac and Cry2Ab retained activity toward lepidopteran larvae. Immunocytochemical in vivo localization studies showed negligible association of Cry1Ac with L. hesperus tissues. In contrast, strong extracellular association of Cry2Ab was observed with L. hesperus midgut brush border microvilli and basement membrane, as well as with cellular outlines within the hemolymph and fat body.