Snowdrop lectin (GNA) has no acute toxic effects on a beneficial insect predator, the 2-spot ladybird (Adalia bipunctata L.)

Two-spot ladybird (Adalia bipunctata L.) larvae were fed on aphids (Myzus p ersicae (Sulz.)) which had been loaded with snowdrop lectin (Galanthus niva lis agglutinin; GNA) by feeding on artificial diet containing the protein. Treatment with GNA significantly decreased the growth of aphids. No acute t oxicity of GNA-containing aphids towards the ladybird larvae was observed, although there were small effects on development. When fed a fixed number o f aphids, larvae exposed to GNA spent longer in the 4th instar, taking 6 ex tra days to reach pupation; however, retardation of development was not obs erved in ladybird larvae fed equal weights of aphids. Ladybird larvae fed G NA-containing aphids were found to be 8-15% smaller than controls, but ate a significantly greater number of aphids (approx. 40% to pupation). GNA was shown to be present on the microvilli of the midgut brush border membrane and within gut epithelial cells in ladybird larvae fed on GNA-dosed aphids, although disruption of the brush border was not observed, It is hypothesis ed that GNA does not have significant direct toxic or adverse effects on de veloping ladybird larvae, but that the effects observed may be due to the f act that the aphids fed on GNA are compromised and are thus a suboptimal fo od. (C) 2000 Elsevier Science Ltd. All rights reserved.