Location: Pest Management and Biocontrol ResearchTitle: Effects of Bt cotton on Thrips tabaci and its predator, Orius insidiosus) Author
Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/8/2014
Publication Date: 5/1/2014
Citation: Kumar, R., Tian, J.C., Naranjo, S.E., Shelton, A.M. 2014. Effects of Bt cotton on Thrips tabaci and its predator, Orius insidiosus. Journal of Economic Entomology. 107:927-932. Interpretive Summary: Transgenic cotton producing the target-specific insecticidal proteins of Bacillus thuringiensis (Bt) have been widely adopted and cultivated on millions of hectares globally. However, there remain concerns about the ecological risk associated with these crops, specifically the risk to non-target organisms. Of particular interest are non-target organisms that supply valuable ecosystem services such as natural enemies of pest insects. Insects that provide biological control services are typically exposed to the Bt proteins through the prey they consume that have fed on the Bt crop (tri-trophic interaction). Here we examine the interaction between Bt cotton producing two Bt proteins, a non-target pest (Thrips tabaci) and the insidious flower bug, Orius insidiosus. Both the Cry1Ac and Cry2Ab proteins produced in Bollgard-II cotton plants were acquired by the thrips and in turn the predator. The thrips contained 2-22% of the levels of the two proteins found in the plant while the predator contained only 0.3-4% of that found in the plant. The survival and development of immature O. insidiosus as well as the fecundity and longevity of adults were not affected when the predator consumed thrips that had fed on Bt cotton compared with non-Bt cotton. Our findings show that we would not expect this predator to be affected in the field and that it would continue to supply valuable biological control services regardless of the cultivation of Bt cotton. These results should be useful to governmental regulators, scientists interested in ecological risk assessment and others concerned about the risks of Bt transgenic crops.
Technical Abstract: Laboratory studies were conducted to investigate tritrophic transfer of insecticidal Cry proteins from transgenic cotton to a herbivore and its predator, and to examine effects of these proteins on the predator’s development, survival and reproduction. Cry1Ac and Cry2Ab proteins from the bacterium Bacillus thuringiensis (Bt) produced in Bollgard-II® (BG-II, Event 15985) cotton plants were acquired by Thrips tabaci Lindeman (Thysanoptera: Thripidae), an important sucking pest of cotton, and its generalist predator, Orius insidiosus (Say) (Hemiptera: Anthocoridae). The average protein titers in BG-II cotton leaves were 1,256 and 43,637 ng Cry1Ac and Cry2Ab per g fresh leaf tissue, respectively. At the second trophic level, larvae of T. tabaci reared on BG-II cotton for 48-96 hr had 22.1% and 2.1% of the Cry1Ac and Cry2Ab toxin levels expressed in leaves, respectively. At the third trophic level, O. insidiosus that fed on T. tabaci larvae had 4.4% and 0.3% of the Cry1Ac and Cry2Ab protein levels expressed in BG-II plants. Orius insidiosus survivorship, time of nymphal development, adult weight, pre-oviposition and post-oviposition periods, fecundity and adult longevity were not adversely affected due to consumption of T. tabaci larvae that had fed on BG-II cotton compared with non-Bt cotton. Our results indicate that O. insidiosus, a common predator of T. tabaci, is not harmed by BG-II cotton when exposed to Bt proteins through its prey. Thus, O. insidiosus can continue to provide important biological control services in the cotton ecosystem when BG-II cotton is used to control primary lepidopteran pests.