Effects of snowdrop lectin (GNA) delivered via artificial diet and transgenic plants on the development of tomato moth (Lacanobia oleracea) larvae in laboratory and glasshouse trials

Abstract

The effects of snowdrop lectin (Galanthus nivalis agglutinin, GNA) on Lacanobia oleracea larval growth, development, consumption, and survival, were examined by 3 distinct binassay methods. Larvae were reared on artificial diet containing GNA at 2% (w/w) dietary protein; on excised leaves of transgenic potato expressing GNA at approx. 0.07% of total soluble proteins; and on transgenic potato plants expressing GNA at approx. 0.6% of total soluble proteins in glasshouse trials. Significant effects on larval growth were observed with all three treatments. At 21 days after hatch mean larval biomass was reduced by 32 and 23%, in the artificial diet and excised leaf bioassays respectively. In glasshouse trials a 48% reduction in insect biomass per plant was observed after 35 days. The artificial diet and excised leaf assays also showed that GNA significantly slowed larval development as assessed by instar duration. GNA caused a 59% overall reduction in mean daily consumption in the artificial diet assay, and a significant reduction in leaf damage in glasshouse trials. However, prolonged compensatory feeding by larvae in the excised leaf assay resulted in their consuming 15% more total leaf material than the control group. Adaptation to low levels of GNA, in terms of biomass recovery and compensatory feeding, was observed within one larval generation in the detached leaf assay. No significant effects of GNA on larval survival were observed in the artificial diet and detached leaf bioassays, whereas survival was decreased by approx. 40% in the glasshouse bioassay. The assays show that the insecticidal effects of GNA can be observed both in vitro when fed in artificial diet and in planta, and can be demonstrated in the glasshouse as well as under growth cabinet conditions.