Abstract
Cabbage looper, Trichoplusia ni (Hübner) is an important lepidopteran pest on many vegetable and greenhouse crops, and some field crops. Although there are no commercial transgenic Bt vegetable or greenhouse crops, T. ni is a target of Bollgard II cotton, which produces Cry1Ac and Cry2Ab. We expand on previous work that examined the effect of Bt crops on parasitoids using Bt-resistant lepidopteran populations as hosts. Cry1Ac/Cry2Ab-resistant T. ni larvae were used to eliminate host quality effects and to evaluate the direct effects of Bt cotton on the parasitoids Copidosoma floridanum (Ashmead) and Cotesia marginiventris (Cresson). These tri-trophic studies confirm that Bt cotton had no significant impact on development, success of parasitism, survival and adult longevity of C. marginiventris when using Bt-resistant T. ni fed on Bt cotton. Similarly, this Bt cotton had no significant impact on the development, mummy weight and the number of progeny produced by C. floridanum. Our studies verified that lyophilized Bt crop tissue maintained its insecticidal bioactivity when incorporated into an artificial diet, demonstrating that hosts and parasitoids were exposed to active Cry proteins. The egg-larval parasitoid C. floridanum, or similar species that consume their entire host, should be considered useful surrogates in risk assessment of Bt crops to non-target arthropods.
Highlights
The area planted to genetically engineered insect-resistant crops producing proteins from Bacillus thuringiensis (Bt) has expanded rapidly since their first commercial production in 1996
There were no significant differences in survival of the T. ni larvae when fed either Bt or non-Bt cotton incorporated diet (Table 1)
Initial studies to support risk assessment are conducted in the laboratory and provide information on whether a high dose of the biologically active insecticidal compound is toxic to the test species[8]
Summary
The area planted to genetically engineered insect-resistant crops producing proteins from Bacillus thuringiensis (Bt) has expanded rapidly since their first commercial production in 1996. This Bt-resistant T. ni strain was further selected on Bt cotton in the laboratory[21] and has been used in several studies to assess the potential effects of Cry1Ac/Cry2A cotton on natural enemies, including Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae)[22], Chrysoperla rufilabris Burmeister (Neuroptera: Chrysopidae)[23], Zelus renardii (Kolenati) (Hemiptera: Reduviidae)[24], Geocoris punctipes (Say) (Hemiptera: Geocoridae) and Orius insidiosus (Say) (Hemiptera: Anthocoridae)[25]. There were no significant differences in survival of the T. ni larvae when fed either Bt or non-Bt cotton incorporated diet (Table 1).
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