Impacts on the predatory carabid beetle Ctenognathus novaezelandiae of pure and mixed diets of natural field-collected prey and Spodoptera litura fed control or transgenic avidin tobacco

Abstract The potential compatibility with biological control of transgenic insecticidal plants expressing the biotin-binding protein avidin was investigated in tri-trophic experiments with the predatory carabid beetle, Ctenognathus novaezelandiae . Beetles were provided with pure and mixed diets of 33%, 67% or 100% of Spodoptera litura larvae, fed either avidin-expressing or isogenic control tobacco, and invertebrates field-collected from the forest floor. Beetles given only tobacco-fed S. litura , whether avidin was present or not, had lower fecundity, egg fertility, body mass and male survival than beetles that received some field food. Fewer of the avidin tobacco-fed prey were consumed than the control tobacco-fed, whatever mixture or proportion offered, probably as a result of the reduced quality of biotin-deprived prey. Beetles consuming 100% avidin tobacco-fed prey had lower fecundity than those given 100% control tobacco-fed prey, although predation on eggs as well as reduced prey quality could have contributed to this result. Despite the nutritionally limiting nature of an exclusive diet of tobacco-fed prey, there was no effect of avidin on fecundity in beetles consuming 67% or 33% avidin prey, or any effect on female or male mass, survival or egg fertility, even in the 100% avidin prey treatment. Fecundity in beetles fed 33% field food with 67% tobacco-fed prey was lower than in those fed 67% or 100% field food. However, there was no added impact of avidin on fecundity, mass or survival, or egg fertility of the 33% field food diet, suggesting that under field conditions, where a mixture of prey is available, negative impacts of avidin-fed prey are unlikely.