Evaluation On The Ecological Safety Of Cry1Ab And Cry1Ac Toxin To The Oriental Armyworm, Mythimna Separata And Its Parasitoids

In China, before the insect resistant transgenic Bt crops being commerically plant, we lacked of ecological risk assessment to the sub-target migratory pest, the oriental armyworm Mythimna separata (Walker) (Lepidoptera:Noctuidae), and its parasitic natural enemies Microplitis pallidipes (Hymenoptera:Braconidae)and Exorista civilis Rondani (Diptera:Tachinidae). Because of this, the paper has systematically studied the effects of CrylAb and Cry1Ac insecticidal protein on the insecticidal effect, growth and development, reproduction and flight potential of the oriental armyworm by means of behavior, ecology, physiology and toxicology. Meanwhile we revealed the effects of CrylAb insecticidal protein on the growth and development of M. pallidipes and E. civilis. At the same time, this will help to improve the evaluation of ecological safety of Bt crops, and revealed the effects of transgenic Bt crops on integrated pest control. The main innovative results were as follows:The insecticidal effect of CrylAc toxin on the growth and development and reproduction of M. separata were systematically evaluated. The results showed that the mean head capsule width and body length of the larvae fed with diets containing 0,3,6, 12,24,48 and 96μg/g of CrylAc toxin for 6 d were significantly decreased as the toxin increased. Similarly, body weight, mortality rate and the developmental period of the larvae treated for 18 d were negatively and significantly affected as the CrylAc dosage increased. The larvae fed with diets containing more than 12μg/g of CrylAc toxin could not pupate, while the larvae fed with diets containing 0,3 and 6μg/g of CrylAc toxin could pupate and emergence normally. Furthermore, the pupal duration was extended, and the pupation rate decreased significantly as CrylAc concentration increased from 0 (ck) to 3, and 6μg/g. Reproductive potential of the moths resulting form the larvae fed with diets containing 0,3, and 6μg/g of CrylAc toxin was also significantly different. Preoviposition period of adults was significantly prolonged, and the number of eggs laid per female was significantly decreased as the dosage of CrylAc toxin increased. All these results showed that the CrylAc had a significant impact on the growth and development and reproduction of M. separata.The insecticidal effects of CrylAb toxin on the different instar of oriental armyworm were systematically researched. The main reason of causing death is the decrease of food ingestion and food utilization rate. We revealed the LC5o of Cry1Ab toxin on the different instars of oriental armyworm, it revealed that CrylAb toxin has a good insecticidal effect on the newly hatched larvae, but bad on larvae of 4-6th instars. The effects of CrylAb toxin on food ingestion, feces, weight gain, approximate digestibility (AD), efficiency of the conversion of ingested food (ECI) and efficiency of the conversion of digested food (ECD) of 6th instar larvae were measured by means of gravimetry. The results showed that the correction food ingestion, feces and weight gain of the 6th instar larvae, which were reared on artificial diets containing 0,12.5,25,50, 100 and 200μg/g CrylAb toxin, were significantly decreased as the dosage of CrylAb toxin increased. The ECI and ECD of the larvae fed on toxin protein diet were significantly lower than that fed on normal diet, and decreased as the dosage of CrylAb toxin increased. The ECI and ECD of which fed on diets containing more than 25μg/g toxin protein were negative, and the higher the concentration was, the lower the ECI and ECD were. However AD was significantly increased as the dosage of toxin protein increased, the AD of the larvae fed on toxin protein diet were significantly higher than that fed on normal diet. All these results revealed the insecticidal mechanism of CrylAb toxin on 6th instar larvae:inhibited its food ingested, decreased its food digestibility and utilization, so that inhibited the larvae's growth and development, and at last caused death.Effects of CrylAc toxin in the sub-lethal dose on the growth and development, reproduction and flight potential of M. separata were systematically researched. When the larvae of M. separata was fed on artificial diet containing sub-lethal dose Cry1Ac toxin, the larvae weight was significantly decreased as the dosage of Cry1Ac toxin increased, and the larvae duration was significantly extended; the pupal weight was significantly decreased as the dosage of Cry1Ac toxin increased, and the pupal duration was significantly extended; the fresh weight and dry weight of adult and the dry weight of thoracic dorsal longitudinal muscle were all significantly decreased as the dosage of Cryl Ac toxin increased; preoviposition period of the adults whose larvae fed on toxin protein diet was significantly prolonged compaired with the ck, although there was no significantly difference through various concentration; The fecundity, mating times and oviposition period of the moth have no significantly change as the dosage of Cry1Ac toxin increased; the flight potential (flight distance, duration and velocity) of 1-day-old adult was significantly decreased as the dosage of Cry1Ac toxin increased. All these results revealed that Cry1Ac toxin in the sub-lethal dose had a significantly negative impact on growth development and flight potential, but little on the reproduction of adult M.separata. Effects of CrylAb toxin on the growth and development of M. pallidipes were revealed in this paper. When adult M. pallidipes parasitized the larvae of M. separata that constantly fed on diet containing 1,2,4,8μg/g of CrylAb toxin, the results showed that, compared with ck, the egg-larval period which fed on diet containing CrylAb toxin were significantly prolonged, besides the cocoon weight and adult weight of M. pallidipes were significantly less than the ck, in despite of no significant effect on the cocoon period and the adult longevity. In addition, the egg-larval period was significantly increased and the cocoon weight and adult weight of M. pallidipes were significantly decreased as the dosage of CrylAb toxin increased, the adult longevity also decreased. But these dosages of CrylAb toxin had no significantly effect on the cocoon period. It showed that CrylAb toxin had a significantly negative effect on the growth and development of M. pallidipes, and the higher concentration of CrylAb toxin was, the more significantly negative effect.Effects of CrylAb toxin on parasitic behavior and population growth of E. civilis were revealed in this paper. It was firstly revealed that the population growth of E. civilis could be advanced by CrylAb toxin in suitable dosage, and had obvious synergism on control of the host pest. Compared with ck, Cry1Ab toxin had no significantly effect on the parasitism percentage and average number of eggs of E. civilis when M. separata fed on diet containing 6.25 and 25μg/g of CrylAb toxin. It showed that CrylAb toxin had no impact on the parasitic behavior of E. civilis. In addition, Percentage of E. civilis which grew in the M. separata fed on diet containing 3.13μg/g of CrylAb toxin was 40%, significantly higher than that on ck(6.7%),6.25(3.3%) and 25(3.3%)μg/g of CrylAb toxin. The percentages of E. civilis were not significantly different among ck, 6.25 and 25μg/g of CrylAb toxin. These results showed that low concentration (3.13μg/g) of CrylAb toxin could significantly increase the survival rate of the E. civilis. The mortality rate of the parasitized M. separata was significantly increased and the percentages of adult M. separata emerged after parasitism was significantly decreased as the dosage of CrylAb toxin increased. The mortality rate of the parasitized M. separata which fed on diet containing 3.13μg/g of CrylAb toxin was just 14%, but fed on diet containing 12.5μg/g of CrylAb toxin was 53%. All the results showed Cry1Ab toxin combined with parasitic fly have obvious synergism on control of the host pest. This could provide a new idea for solving the resistance of insects to transgenic Bt Crops.