Effects Of Insecticidal Protein From Bacillus Thuringiensis And Transgenic Cotton On Helicoverpa Armigera H(?)bner And The Parasitoid, Microplitis Mediator Haliday

Interactions among the cotton bollworm, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), its larval parasitoid Microplitis mediator (Haliday) (Hymenoptera: Braconidae), and CrylAc insecticidal protein of Bacillus thuringiensis Berliner or transgenic cotton expressing CrylAc and CrylA + CpTI (cowpea trypsin inhibitor) were evaluated under laboratory conditions. The following were results:1. Host (H. armigera) size had significant influence on oviposition of the female parasitoid, and the parasitization rate decreased as the host size became large. Host larvae over 14 mg were difficult to be parasitized. The host weight at time of parasitizationg was positively related with cocoon weight of the parasitoid, cocoon weight was positively related with adult weight of the parasitoid, and the longevity of the adult was positively related with the weight of the parasitoid adult, but the host weight at time of parasitization was negatively related with egg incubation and larval duration. However, the host weight did not significantly affect cocoon duration. The growth of H. armigera larvae was delayed and the pupation rate and pupal weight decreased when they were fed on diet containing CrylAc protoxin. Due to the slower growth rate of the host larvae, the time available for parasitization of H. armigera by M. mediator increased when the host larvae were reared on diet containing CrylAc protoxin.2. The effects of Bt protein on laboratory and field populations of H. armigera and the parasitoid were tested. When M. mediator parasitized hosts reared on diet containing CrylAc protoxin, their egg and larvae durations were delayed. Pupal weight, new emerging adult body weight and adult longevity were also significantly decreased. When hosts fed on diet containing CrylAc protoxin for 12 h before parasitism and after parasitism, the effects on M. mediator were similar to those which hosts were continually treated with Bt toxin. In comparison to control, the larval weight and pupal weight of cotton bollworms were decreased significantly when their larvae fed on diet containing Bt toxin. The cotton bollworm of both laboratory and field populations were susceptible to transgenic cotton expressing Cry 1A plus CpTI.3. When adult M. mediator parasitized the host larvae that fed on diet containing CrylAc toxin, their offspring's eggs and larvae were significantly delayed and pupal weight and adult weightwere also significantly less compared with the control. The F₂ female parasitoid from the host which fed on diet containing 8 μg/g CrylAc protoxin could oviposit on a healthy host, and her biological parameters (egg-larval period, pupal weight and adult weight), parasitism rate, abnormal pupal rate and adult emergence were not affected significantly. Phenoloxidase activity of parasitized or unparasitized host was inhibited significantly when host fed on Bt-diet(8 μg/g) Melanogenesis rate of parasitized host larvae was inhibited whether larvae fed on Bt-diet(8 μg/g) or normal diet when compared to unparasitized host. For both non-parasitized and parasitized host, the concentration of hemocytes of larvae fed on Bt-diet (8 μg/g) for 24 h and 48 h was decreased significantly when compared to control. CrylAc toxin was detected in larvae and hemolymph of H, armigera, but no CrylAc toxin was detected in the larvae of M. mediator.4. The longevity of female and male parasitoids was not significantly affected when newly emerging wasps fed on honey solutions containing three different concentrations of CrylAc protoxin (125, 250, 500 μg/ml). When female parasitoids fed on honey solutions containing CrylAc, their offspring's egg and larval development period, pupal weight, length of pupation, adult weight and adult longevity did not change significantly in most of the treatments compared with the control.5. Two major transgenic cotton cultivars used in Hebei province of northern China, DP99B (Bollgard), carrying the cryIAc gene, and SGK321, carrying both crylA and CpTI genes, were used for testing the effects on M. mediator. The results ind...