Assessing the utilization of a carbohydrate food source and the impact of insecticidal proteins on larvae of the green lacewing, Chrysoperla carnea

A concern with the widespread use of insecticidal transgenic crops is their potential to adversely affect non-target organisms, including biological control agents such as larvae of the green lacewing, Chrysoperla carnea (Neuroptera: Chrysopidae). Since the insecticidal proteins expressed by the current transgenic plants are active only after ingestion, dietary bioassays are required to test direct effects on non-target organisms. After showing that C. carnea larvae utilize carbohydrate foods, we exposed them to insecticidal proteins dissolved in a sucrose solution. Feeding on snowdrop lectin (Galanthus nivalis agglutinin, GNA) as a model compound, the larvae were negatively affected in a number of life-table parameters. Interestingly, GNA caused a prolongation in first instar development, but had no effect on subsequent utilization of prey resulting in an increased weight of second instars. Comparable studies with avidin, a biotin-binding protein, revealed strong effects on C. carnea survival at the concentration tested. Despite the fact that the proteolytic digestion of C. carnea larvae is reported to be dominated by serine proteases, ingestion of soybean trypsin inhibitor (SBTI) did not cause any detrimental effects. Similarly, two Cry proteins derived from Bacillus thuringiensis (Cry1Ac and Cry1Ab) did not cause negative effects on C. carnea, what is consistent with earlier studies. The here presented bioassay provides a valuable tool to assess direct impacts of insecticidal proteins to C. carnea larvae and other predators that are known to feed on carbohydrate solutions.