The effects of Phaseolus vulgaris erythro- and leucoagglutinating isolectins (PHA-E and PHA-L) delivered via artificial diet and transgenic plants onthe growth and development of tomato moth (Lacanobia oleracea) larvae; lectin binding to gut glycoproteins in vitro and in vivo

Red kidney bean, Phaseolus vulgaris, contains a lectin phytohemagglutinin ( PHA) with toxicity towards higher animals. PHA exists in the isoforms PHA-E and PHA-L, which agglutinate erythrocytes and lymphocytes, respectively. L acanobia oleracea larvae were reared from hatch on artificial diets contain ing PHA-E or PHA-L at 2% (w/w) dietary protein, and on transgenic Arabidops is plants expressing either lectin at 0.4-0.6% of total soluble proteins. I n artificial diet bioassays neither lectin affected larval survival, develo pment, growth nor consumption. In transgenic plant bioassays both PHA-E and PHA-L promoted larval growth and development. This effect was greatest for PHA-E. Mean larval biomass of insects fed on plants expressing PHA-E was s ignificantly greater (up to two-fold) than controls during the final two in stars and the insects developed at a significantly greater rate so that aft er 26 days 83% of PHA-E exposed insects were in the final instar compared t o 44% for control insects. PHA-E and PHA-L were detected by Western blottin g in haemolymph, sampled from insects fed diets or plant material containin g the lectins. However, despite the demonstrated potential for both isolect ins to bind to gut glycopolypeptides in vitro neither was found to accumula te in vivo in the guts of exposed insects. Since lectin binding to gut poly peptides is thought to be necessary for insecticidal activity the failure o f PHA-E and PHA-L to bind in vivo may account for their lack of toxicity to L. oleracea. Crown Copyright (C) 2001 Published by Elsevier Science Ltd. A ll rights reserved.