Dietary effects of transgenic MON810 Bt-maize pollen on fitness of Hippodamia variegata Goeze

Plant food such as pollen represents part of the diet of many predaceous coccinellids, exploited as a supplemental food source when prey is scarce. They can therefore suffer adverse effects when foraging on genetically modified plants expressing Cry1Ab toxin derived from Bacillus thuringiensis Berliner. The Variegated Lady Beetle, Hippodamia variegata Goeze, a very common and important aphid predator in the Mediterranean area, feeds preferably on aphids but can use plant pollen as a supplemental food source. Hence, it can be exposed to Cry proteins when foraging on insect-resistant Bt-maize. In the current study, an experimental methodology to provide pollen to the coccinellids and quantify the amount of pollen eaten was developed. Using this methodology, the potential effects of the consumption of Bt-maize pollen on the fitness of H. variegata were evaluated. Both standardized laboratory bioassays and demographic approach by means of an age-structured matrix population model were performed. Both biological and demographic parameters did not differ between coccinellids fed Bt- or non-Bt-maize pollen. However, demographic analyses showed that some effects of Bt pollen exposure on H. variegata occurred. Indeed, the Bt-pollen-fed females had a higher expected lifetime reproduction; however, a reduced life expectancy occurred early in life for their offspring. As a result, the consumption of Bt-maize pollen causes a lower increase in H. variegata population since a reduction of offspring survival seems only partially outweighed by increased female fecundity. Overall, this study shows that the consumption of Bt-maize pollen expressing Cry1Ab by adults of H. variegata does not significantly affect their fitness, but it also shows that this outcome is a result of a trade-off among vital rates such as age-specific fecundity and survival probability that are positively or negatively influenced. Moreover, the methodology proposed in this study provides a sound exposure system to supply pollen to the coccinellids and appears functional to quantify maize pollen consumption by H. variegata adults.