Use of Bt-resistant caterpillars to assess the effect of Cry proteins on beneficial natural enemies

Authors: SHELTON, ANTHONY - Cornell University; ROMEIS, JOERG - Agroscope; Naranjo, Steven; Hellmich Ii, Richard; TIAN, J - Zhejiang Academy Of Agricultural Sciences

Submitted to: IOBC/WPRS Bulletin (Abstract for Conference Proceedings)
Publication Type: Proceedings
Publication Acceptance Date: 6/14/2016
Publication Date: 6/16/2016
Citation: Shelton, A.M., Romeis, J., Naranjo, S.E., Hellmich Ii, R.L., Tian, J.C. 2016. Use of Bt-resistant caterpillars to assess the effect of Cry proteins on beneficial natural enemies. IOBC/WPSR Bulletin. 114:51-55.

Interpretive Summary: Genetically engineered (GE) insect-resistant crops, producing insecticidal crystal (Cry) proteins from the bacterium Bacillus thuringiensis (Bt), have revolutionized insect control and become a major tool for integrated pest management (IPM) programs. There are concerns, however, about the ecological risk of GE crops, especially potential risk to insects that provide biological control services. Our team has studied natural enemies from multiple orders and families of insect predators and parasitoids, and an entomopathogenic nematode. These natural enemies are exposed to Bt proteins when they consume prey that have fed on a Bt crop. The challenge in studying these tri-trophic interactions is that the prey itself is often harmed by the Bt protein, which makes it difficult to separate the effects of prey quality from Bt effects on the natural enemy. The prey-quality problem was addressed by using pest caterpillars that are resistant to the Bt proteins found in GE cotton and maize. Numerous biological attributes of the natural enemies were examined including immature development and survival, and adult longevity and reproductive output. The study results provide unambiguous evidence of the lack of effects of these Cry proteins on important natural enemies and provide guidance for future non-target studies. These data confirm the large and sound body of literature demonstrating that the Cry proteins currently used in Bt crops for control of caterpillar pests are not harmful to natural enemies that are important for biological control of these and other pest species. The results are of interest to regulatory bodies that oversee the approval of GE crops, agricultural producers, and to many other stakeholder groups including the general public concerned with environmental safety and biodiversity.

Technical Abstract: A concern related to the use of insect-resistant Bt-transgenic plants is their potential to harm non-target organisms, especially natural enemies of important crop pests. A few studies purporting to show negative effects of Bt plants on non-target organisms had tremendous negative effects on the perception of Bt plants and on regulatory decisions. Focusing on the tri-trophic non-target studies it became evident that the design of these studies often did not account for the quality of the hosts being fed to the natural enemies. This occurred when Bt-susceptible hosts that had ingested Bt (Cry) proteins and became compromised were fed to natural enemies, causing indirect prey/host-quality mediated effects. We here review studies that overcame this methodological problem in testing Cry proteins against natural enemies by feeding them strains of pest insects that had evolved resistance to Cry proteins expressed in the Bt plants. The studies utilized natural enemies from multiple orders and families of insect predators and parasitoids, and an entomopathogenic nematode. The study results provide unambiguous evidence on the lack of effects of these Cry proteins on important natural enemies and provide guidance for future non-target studies. These data confirm the large and sound body of literature demonstrating that the Cry proteins currently used in Bt crops for control of Lepidoptera are not harmful to natural enemies that are important for biological control of these and other pest species.