Effects of Bt transgenic Chinese cabbage on the herbivore Mamestra brassicae (Lepidoptera: Noctuidae) and its parasitoid Microplitis mediator (Hymenoptera: Braconidae)

We investigated the effects of a diamondback moth-resistant Chinese cabbage (Brassica campestris subsp napus variety pekinensis Makino), expressing the insecticidal protein CrylA(c) toxin derived from Bacillus thuringiensis, on the nontarget herbivore Mamestra brassicae (L.) (Lepidoptera: Noctuidae) and its parasitoid wasp Microplitis mediator (Haliday) (Hymenoptera: Braconidae). A decreased survival rate at neonate stage was observed in M. brassicae when reared on Bt cabbage, although overall development was not significantly affected. According to enzyme-linked immunosorbent assay test using CrylA(c) antibody, the Cry toxin was only detected in the alimentary canal, not in the hemolymph or remaining body parts of M. brassicae, indicating that the ingested Cry toxin is neither distributed inside the body nor transferred through the trophic level. As expected, no Cry toxin was found in the larvae and cocoons of M. mediator. In addition, no significant changes were observed in the parasitization rate, larval period, pupal period, cocoon weight, or adult emergence rate when M. mediator wasps were reared on the M. brassicae larvae fed with transgenic Chinese cabbage. In summary, no direct or indirect adverse effects of transgenic Chinese cabbage on the two nontarget insect species were observed, suggestive of low risk in herbivore-parasitoid food chain.