Understanding indirect, trophic-level effects of genetically engineered plants, expressing insecticidal proteins derived from the bacterium, Bacillus thuringiensis (Bt), is essential to the ecological risk assessment process. In this study, we examine potential indirect, trophic-level effects of Bt-sensitive prey using the predator, Harmonia axyridis (Pallas), feeding upon Spodoptera frugiperda (J.E. Smith) larvae, which had delayed development (lower body mass) following ingestion of Cry1Ab maize leaves. We found no adverse effects on development and survival when H. axyridis larvae were fed S. frugiperda larvae that had fed on Cry1Ab maize tissue. Presence of Cry1Ab in H. axyridis decreased considerably after switching to another diet within 48 h. In a nochoice assay, H. axyridis larvae consumed more Bt-fed S. frugiperda than non-Bt-fed larvae. Preference for S. frugiperda feeding on Bt maize was confirmed in subsequent choice assays with H. axyridis predation on Bt-fed, 1'5-d-old S. frugiperda larvae. We suggest that H. axyridis preferred prey, not based on whether it had fed on Bt or non-Bt maize, but rather on larval mass, and they compensated for the nutritional deficiency of lighter larvae through increased consumption. Pest larvae with variable levels of resistance developing on Bt diet are often stunted versus sensitive larvae developing on non-Bt diet. It is possible that such larvae may be preferentially removed from local field populations. These results may have implications for insect resistance management and may be played out under field conditions where seed blends of Bt and non-Bt hybrids are planted.
Bibliographical noteFunding Information:
We are grateful to Michael Meissle (Agroscope, Switzerland) for discussion about ELISA measurement, preparation of samples for ELISA tests, and for reviewing a previous version of the manuscript. We also thank Richard L. Hellmich (USDA-ARS, Iowa State University, United States) for comments on the manuscript. We acknowledge Syngenta Seeds, Inc., for providing maize seeds. Research was promoted with institutional support from the Institute of Entomology, Biology Centre CAS (RVO:60077344 and L200961652), Department of Entomology, University of Minnesota, and the Minnesota Agricultural Experiment Station, St. Paul, MN.
- Fall armyworm
- Harmonia axyridis
- Multicolored Asian lady beetle
- Resistance management