Direct effects of snowdrop lectin (GNA) on larvae of three aphid predators and fate of GNA after ingestion

Abstract

Plants genetically modified to express Galanthus nivalis agglutinin (GNA) have been found to confer partial resistance to homopteran pests. Laboratory experiments were conducted to investigate direct effects of GNA on larvae of three species of aphid predators that differ in their feeding and digestive physiology, i.e. Chrysoperla carnea, Adalia bipunctata and Coccinella septempunctata. Longevity of all three predator species was directly affected by GNA, when they were fed a sucrose solution containing 1% GNA. However, a difference in sensitivity towards GNA was observed when comparing the first and last larval stage of the three species. In vitro studies revealed that gut enzymes from none of the three species were able to break down GNA. In vivo feed-chase studies demonstrated accumulation of GNA in the larvae. After the larvae had been transferred to a diet devoid of GNA, the protein stayed present in the body of C. carnea, but decreased over time in both ladybirds. Binding studies showed that GNA binds to glycoproteins that can be found in the guts of larvae of all three predator species. Immunoassay by Western blotting of haemolymph samples only occasionally showed the presence of GNA. Fluorescence microscopy confirmed GNA accumulation in the midgut of C. carnea larvae. Implications of these findings for non-target risk assessment of GNA-transgenic crops are discussed.