A comparison of the short and long term effects of insecticidal lectins on the activities of soluble and brush border enzymes of tomato moth larvae ( Lacanobia oleracea)

Abstract

When fed in semi-artificial diet in short- and long-term bioassays, the lectins from snowdrop ( Galanthus nivalis; GNA) and jackbean ( Canavalia ensiformis; Con A) affected the activities of soluble and brush border membrane (BBM) enzymes in the midgut of Lacanobia oleracea larvae. In the short term both lectins increased gut protein levels and BBM aminopeptidase activity. The lectins also increased trypsin activity, both in the gut (Con A) and in the faeces (GNA). GNA also increased the activity of α-glucosidase, but neither lectin had a significant effect on alkaline phosphatase activity. Trypsin mRNA levels were similar in lectin-fed and control larvae in the short term, showing that there is no direct effect on expression of the encoding genes. Larvae chronically exposed to GNA and Con A showed reductions in weight of 50–60%, and exhibited a significant reduction in α-glucosidase activity, but little change in other enzyme activities. Con A bound to many BBM and peritrophic matrix (PM) proteins in vitro, whereas GNA showed more specific binding, with strongest binding to a 94 kDa uncharacterised BBM protein. Both lectins accumulated in gut tissues of insects after chronic exposure in vivo, but Con A was present at higher levels than GNA.