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

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.