BIOLOGICAL EFFECTS OF PLANT-LECTINS ON THE COWPEA WEEVIL

Plant lectins have been implicated as antibiosis factors against insects, particularly the cowpea weevil, Callosobruchus maculatus. In the present investigation, 17 plant lectins were screened in an artificial seed system to determine if biological activity toward C. maculatus is widespread among lectins. Five of the 17 plant lectins screened caused a significant delay in C. maculatus developmental time at dietary levels of 0.2 and 1.0% (w/w). These lectins could be classed into one of two groups: lectins with specificity for N-acetylgalactosamine/galactose (GalNAc/Gal) and lectins with specificity for N-acetylglucosamine (GlcNAc). The GalNAc/Gal lectins included osage orange lectin and peanut agglutinin. A dose-response analysis of peanut agglutinin indicated that for every 0.1% increase in dose there was a 0.49 day delay in developmental time. The GlcNAc lectins included potato lectin, jimson weed lectin and wheat germ agglutinin (WGA). The most potent lectin was WGA; the dose-response analysis indicated that for every 0.1% increase in dose there was a 1.47 day delay in developmental time. Additionally, for every 0.1% increase in WGA there was a 2.79% increase in mortality. The results of this investigation indicate that there exists in C. maculatus physiological/biochemical systems vulnerable to selected plant lectins. The genes coding for the effective plant lectins could, in principle, serve as antibiosis factors to use in host plant resistance programs designed to bring resistance into cowpea through recombinant DNA technologies. © 1990.