Entomotoxic Properties of White Kidney Bean and Soybean Lectins and their Effects against Two Digestive Enzymes of the Spiny Bollworm, Earias insulana (Boisd.)

Abstract

Plant lectin, a heterogeneous group of carbohydratebinding proteins, is a direct defensive mechanism in plants against the attacking insects. Lectins from the leguminous plants Glycine max (GML) and Phaseoulus vulgaries (PhVL) were tested for their entomotoxic and growth inhibitory effects against the spiny bollworm (SBW), Earias insulana Boisd. The impact of the examined lectins on the two digestive enzymes of SBW, α-amylase and total proteases, was also investigated. Bioassay studies conducted on second-instar larvae over five and six days showed that GML (LC50 values of 72.22 and 33.45 µg/gm diet) was more hazardous than PhVL (LC50 = 299.05 and 182.91 µg/gm diet). GML and PhVL at LC25 equivalent concentrations (8.97 and 34.43 µg/gm diet) significantly (p < 0.05) reduced the larval weight to 24.9 and 27.4 mg / larva compared with 55.3 mg / larva in control after 9 days of treatment. The average time for SBW larvae to pupate increased when GML and PhVL were added at LC10 and LC25 in comparison to the control. In addition, the tested lectins significantly (p < 0.05) reduced pupal mean weight, pupation, adult emergence, fecundity and fertility. Tested lectins demonstrated significant inhibition of α-amylase and total protease enzyme activity in larvae of SBWs fed on diets containing concentrations comparable to LC10 and LC25. These findings imply that GML and PhVL are appropriate proteins to add to the cotton plant's DNA in order to control SBW.