Concanavalin A inhibits development of tomato moth (Lacanobia oleracea) and peach-potato aphid (Myzus persicae) when expressed in transgenic potato plants

The effects of concanavalin A (ConA), a glucose/mannose-specific lectin fro m jackbean (Canavalia ensiformis), on insect crop pests from two different orders, Lepidoptera and Homoptera, were investigated. When fed to larvae of tomato moth (Lacanobia oleracea) at a range of concentrations (0.02-2.0% o f total protein) in artificial diet, ConA decreased survival, with up to 90 % mortality observed at the highest dose level, and retarded development, b ut had only a small effect on larval weight. When fed to peach-potato aphid s (Myzus persicae) at a range of concentrations (1-9 mu M) in liquid artifi cial diet, ConA reduced aphid size by up to 30%, retarded development to ma turity, and reduced fecundity (production of offspring) by >35%, but had li ttle effect on survival. With both insects, there was a poor correlation be tween lectin dose and the quantitative effect. Constitutive expression of C onA in transgenic potatoes driven by the CaMV 35S promoter resulted in the protein accumulating to levels lower than predicted, possibly due to potato not being able to adequately reproduce the post-translational processing o f this lectin which occurs in jackbean. However, the expressed lectin was f unctionally active as a haemagglutinin. Bioassay of L. oleracea larvae on C onA-expressing potato plants showed that the lectin retarded larval develop ment, and decreased larval weights by >45%, but had no significant effect o n survival. It also decreased consumption of plant tissue by the larvae. In agreement with the diet bioassay results, ConA-expressing potatoes decreas ed the fecundity of M. persicae by up to 45%. ConA thus has potential as a protective agent against insect pests in transgenic crops.