In vitro and in vivo binding of snowdrop (Galanthus nivalis agglutinin; GNA) and jackbean (Canavalia ensiformis; Con A) lectins within tomato moth (Lacanobia oleracea) larvae; mechanisms of insecticidal action

When fed in semi-artificial diet the lectins from snowdrop (Galanthus nival is: GNA: mannose-specific) and jackbean (Canavalia ensiformis: Con A: speci fic for glucose and mannose) were shown to accumulate in vivo in the guts, malpighian tubules and haemolymph of Lacanobia oleracea (tomato moth) larva e. Con A, but not GNA, also accumulated in the fat bodies of lectin-fed lar vae. The presence of glycoproteins which bind to both lectins in vitro was confirmed using labelled lectins to probe blots of polypeptides extracted f rom larval tissues. Immunolocalisation studies revealed a similar pattern o f GNA and Con A binding along the digestive tract with binding concentrated in midgut sections. Binding of lectins to microvilli appeared to lead to t ransport of the proteins into cells of the gut and malpighian tubules. Thes e results suggested that both lectins are able to exert systemic effects vi a transport from the gut contents to the haemolymph across the gut epitheli um. The delivery of GNA and Con A to the haemolymph was shown to be depende nt on their functional integrity by feeding larvae diets containing denatur ed lectins. Con A, but not GNA, was shown to persist in gut and fat body ti ssue of lectin-fed larvae chased with control diet for three days. Con A al so shows more extensive binding to larval tissues in vitro than GNA, and th ese two factors are suggested to contribute to the higher levels of toxicit y shown by Con A, relative to GNA, in previous long term bioassays. Crown C opyright (C) 2001 Published by Elsevier Science Ltd. All rights reserved.