Impacts Of Transgenic Bt Cotton On Cotton Ecosystem And Its Ecological Risks

One of the major debates on the biosafety of transgenic crops focuses on their potential risks on beneficials or on the ecological serves in the ecosystem. The arthropod community in cotton field is a complex system including various pests, natural enemies and neutral species, with cotton as the centre. Transgenic Bt cotton in northern China depressed densities of the cotton bollworm, but also caused changes and rearrangements in the arthropo.d assemblages. In particular, the density of herbivores that were traditionally considered secondary pests such as sucking bugs, whiteflies, aphids and leafhoppers, increased, thus serving as important prey resources for the predators in transgenic cotton fields. In this study, the structure and seasonal dynamics of plant-dwelling arthropods in transgenic cotton were surveyed. Key factors affecting the population dynamics of the target pest Helicoverpa armigera and non-target pest Aphis gossypii in transgenic cotton field were analyzed by establishing their life tables. Impacts of transgenic cotton on non-target natural enemies (ladybirds, lacewings and wolf spider) were studied in laboratory by feeding experiments. Besides, to establish the IPM strategies in transgenic cotton fields, the biological control efficacy and the ecological effects of mass-releasing Trichogramma chilonis were examined, migration of ground-active invertebrate natural enemies in transgenic cotton field and adjacent crops were studied, and effects of agroecosystem structure on the arthropod community were compared. Based on these studies and relevant reports, guidelines for the risk assessment and risk management of trangenic cotton were drafted. Detailed results are as follows:1. Structure and seasonal dynamics of arthropods in transgenic cotton fildsStructure and seasonal dynamics of arthropods in transgenic cotton (cv. SGK321, with inserted genes of CrylAc and CpTI) and population dynamics of pests and natural enemies were studied in Nanpi County, Hebei Province in 2002, with the non-transgenic parental cotton (Shiyuan321) as control. It showed that arthropod diversity in SGK321 was similar to that in Shiyuan321, and the Shannon-Weiner diversity index was 0.975 and 0.967, respectively. Whereas the total number of arthropods in SGK321 decreased by 53.9%, which was mainly caused by the reduction of basal species. The composition of pest and predatory species was similar between the plots of SGK321 and the control, but the accumulated numbers of each species were different. SGK321 had good control not only to cotton bollworm (89.5%), but also to some non-target pests, such as cotton aphid Aphis gossypii, grean leaf bug Lygus lucorum, tobacco whitefly Bemisia tabaci and green leafhopper Ernpoasca flavescens, and their accumulated numbers decreased by 64.5%, 21.8%, .15.6% and 33.7%, respectively. For the dominant natural enemy species, the accumulated numbers of Propylaeajaponica and Chrysopa sinica increased by 34.0% and 9.1%, respectively; but those of Harmonia axyridis, Orius minutus, Campylomma diversicornis, Lysiphlebiajaponicus and spiders decreased by 28.6%, 6.5%, 43.1%, 44.7% and 14.0%, respectively. It indicated that SGK321 had good control not only to cotton bollworm, but also to some non-target pests. SGK321 had some negative effects on certain natural enemy populations. But it had no significant impacts on the arthropod diversity in the fields.2. Ecological impacts of transgenic cotton on target and non-target pestsBy cage experiments, life tables of the second generation cotton bollworm Helicoverpa armigera and cotton aphid Aphis gossypii in transgenic Bt cotton field (cv. GK12) and transgenic CrylAc + CpTI cotton (cv. SGK321) were established to evaluate key factors affecting their populations. These studies were carried out in Nanpi County, Hebei Province in 2004, with their non-transgenic parental cotton varieties (cvs. Simian3 and Shiyuan321) as control. It showed that: (1) Both GK12 and SGK321 had good control over the first instar CBW larvae, because of the Bt protein expression. But impacts of GK12 and SGK321 on the survival of cotton bollworm eggs were different. Compared to that in the respective control, egg survival was lower in GK12, but was higher in SGK321. Predation was also the key factor affecting the population dynamics of cotton b011worm, because its good control over the eggs and larvae. And predation efficacy in transgenic cotton (both GK12 and SGK321) had no significant difference to that in their parental cotton field. (2) Transgenic cotton had no significant impacts on natural control efficacy of cotton aphids, i.e. predation, rain and wind, parasitism by insects and pathogens, intrinsic physiology, etc. Predation was the key factor affecting cotton aphid population, both in transgenic cotton (GK12 and SGK321) and in the corresponding parental cotton fields. And predation efficacy in transgenic cotton was similar to that in the control. Except that cotton aphid had longer developmental period in SGK321 field, transgenic cotton GK12 and SGK321 had no adverse impacts on development and fecundity of cotton aphid. It indicated that Bt protein expression in the cotton plant was the key factor affecting population dynamics of cotton bollworm in GK12 and SGK321. And predation ranked the second. Predation was also the key factor affecting population dynamics of cotton aphid.Population dynamics and damage of green leaf bug Lygus lucorum in Bt cotton (cv. NuCOTN 33B) fields under two control measures were investigated in Nanpi, Hebei in 2002. Inthe Bt cotton field sprayed with three times of biopesticides and once of low-toxic chemical, the occurence and damage of L. lucorum were more serious than those in the chemical controlled field. The population peak happened in early September and averaged 7.2 bugs per 10 plants, which was higher than the control action threshold. Cotton leaf damage rate by the second generation of L. lucorum was 19.4%. In the Bt cotton field with 7 times of chemical spray, the population peak happened in August and averaged 2.0 bugs per 10 plants. Leaf damage rate by the second generation of L. lucorum was 4,8%. It suggested that green leaf bug became an important pest in Bt cotton production. Its damage couldn't be effectively controlled when the pesticide usage in Bt cotton field decreased. So it is urgent to study the ecological control ofL. lucorum in Bt cotton field.3. Ecological impacts of transgenic cotton on non-target predatorsTo clarify the ecological effects of transgenic on polyphagous predator via the phytophagous pest preys, some case studies were carried out in laboratory by feeding experiments. The lacewings Chrysopa sinica, C. formosa, C. septempunctata, the ladybeetle Propylaeajaponica, and the wolf spider Alopecosa pulverulenta were involved as pred.ators. Bemisia tabaci and Aphis gossypii were involved as preys. Survival, development and fecundity parameters of the predators were evaluated.(1) Bemisia tabaci on GK12 had no significant adverse impacts on survival and development of immature C. sinica. Between the two GM-cotton varieties, C. sinica feeding on prey propagated on NuCOTN 33B had lower survival in larval and cocoon stages, longer developmental period, and imbalanced sex ratio of more females.(2) Bemisia tabaci on GK12 had no significant impacts on larval development and adult body mass of P. japonica. And larval mortality was lower than that in the control. Between the two GM-cotton varieties, P. japonica feeding on prey propagated on NuCOTN 33B had lower mortality in larval stage. (3) Aphis gossypii on GK12 had no significant impacts on immature survival, development, cocoon b.ody mass and adult sex ratio of C. formosa for two generations. But the oviposition period was shorter and number of eggs laid per female was less for the first generation, and the egg viability of the second generation was lower. Between the two GM-cotton varieties, the first generation of C. formosa feeding on prey propagated on NuCOTN 99B had shorter larval and cocoon stages, lower cocoon body mass, and lower egg viability. But there were no differences in development and reproduction of the second generation of C. formosa.(4) Compared to control, GK12-originated aphid prey had no significant impacts on immature survival, larval and cocoon developmental time, adult sex ratio, female lifespan, or egg viability of the emerged female C. septempunctata. But cocoon body mass was higher, female ratio was higher, and females laid more eggs. Between the two GM-cotton varieties, when C. septempunctata lavae fed on prey propagated on NuCOTN 99B, there were less females emerged and female laid less eggs. In the treatment of mixed feeding of cotton aphids from the two GM-cotton and one non-GM cotton, C. septempunctata developed longer in cocoon stage, had higher cocoon body mass, and higher female ratio.(5) Aphids reared on SGK321 vs. non-GM cotton were both poor quality food for the wolf spider A. pulverulenta spiderlings, in terms of growth and mortality. But spiderlings showed higher survival and developed better when they were fed with aphids and fruit flies alternatively. Among the treatment of different combination of SGK321-originated aphid vs non- GM-originated aphid, unlimited feeding vs. unlimited feeding, single diet vs. mixed feeding of aphids and fruit flies, it didn't show significant adverse impacts on the survival and body mass increase ofA. pulverulenta spiderlings.These results indicated that impacts of transgenic cotton on predators varied according to cotton variety, pest species and predator species. Among the natural enemy species tested, we only found transgenic cotton cv. GK12 had some adverse effects on the oviposition of C. formosa through non-target prey cotton aphid.4. Bioligical and ecological control of phytophagous pests in transgenic cotton fieldsBiological control efficacy and ecological effects of mass-releasing Trichogramma chilonis in transgenic hybrid cotton (cv. Lumianyanl5) field were surveyed in Huimin county, Shandong province in 2002, with the chemically controlled cotton field as control. Trichogramma showed high control efficacy on cotton bollworm eggs after three times of release both in the second and in the third generation bollworm periods. The parasitism on the second and third generation bollworm eggs were 66.0%～70.7% and 76.0%～81.2%, respectively, which were significantly higher than that in the control (second generation'. 7.0%～12.3%, third generation: 5.2%～7.4%). And the injury rate of cotton buds and bolls in the second and third generation bollworm were 2.2% and 3.1%, respectively, which were significantly lower than that in the control (second generation: 8.5%, third generation: 20.9%). In the second generation bollworm period, number of bollworm eggs or larvae in the Trichogramma released cotton field did not differ to that in the chemically controlled field. But in the third generation, there were significantly less bollworm eggs and larvae in the Trichogramma released cotton field. There were more predators in the Trichogramma released cotton field. These results indicated that cotton bollworm in the transgenic hybrid cotton field could be effectively controlled by mass-releasing of Trichogramma chilonis. And the biocontrol method was also beneficial to predator protection in the cotton fields.A pitfall trap survey for the ground-dwelling arthropod natural enemy community was carried out in transgenic hybrid cotton (cv. Jikang668) fields and their adjacent crops. Three kinds of ecotones were involved, i.e. wheat/corn-cotton, alfalfa-cotton, and cotton-cotton ecotones. It showed that number of species, number of individuals and community structures of ground-dwelling natural enemies in cotton fields differed significantly among the three ecotones. Seasonal dynamics of ground-dwelling natural enemies in cotton field and its adjacent wheat/corn or alfalfa field field were similar, indicating there was free migration between the adjacent fields. Among the three ecotones, wheat/corn-cotton ecotone favored the occurrence and development of ground-dwelling arthropod natural enemies, and there were the most natural enemy species (13.3) and relatively more individuals (75.1), and it showed the highest diversity (1.743). It indicated that number of natural enemies in the transgenic hybrid cotton field could be increased by adjusting its adjacent crop.Arthropod community structures in transgenic hybrid cotton (cv. Lurnianyanl 5) fields were compared. There were four crop arrangement styles involved, i.e. monocultured cotton, cotton adjacent vegetable, cotton adjacent orchard, and cotton adjacent peanut. It showed that arthropod community structures in cotton fields were affected by their adjacent crops. Cotton adjacent orchard was recommendable because the arthropod community in cotton field was more diverse thus more stable, and there were more natural enemies for the pest control. Cotton adjacent peanut should be cautious because there were more pest species and individuals, and the pest community was more diverse in cotton field. Cotton adjacent vegetable should be avoided since the population of pests increased and the arthropod diversity decreased.5. Guidelines for the risk assessment and management of transgenic Bt cottonAccording to the current studies and other published papers, guidelines for the risk assessment and management of transgenic cotton were constituted. It included: (1) basic information for risk assessment, (2) contents and methods for risk assessment of non-target effects, gene flow, herbivore resistance, and ecological adaption, (3) risk management in different phases of transgenic cotton production, i.e., laboratory test, environmental release, commercialization, and transfer over countries.To sum up, in this study, it took the leads in studying the impacts of transgenic CrylAc + CpTI cotton on cotton ecosystem and its ecological effects on polyphagous spider species. For the first time, it clearly defined that impacts of transgenic cotton on predators varied according to cotton variety, pest species and predator species, and found had some adverse effects of transgenic cotton cv. GK12 on C. formosa through non-target prey cotton aphid. It confirmed the migration of ground-dwelling natural enemies between cotton and its adjacent fields. It also confirmed the control efficacy of mass-releasing Trichogramma chilonis in transgenic cotton fields in mid- to late growing seasons, and verified the effects of adjusting agroecosystem structure on the arthropod community in cotton fields. It constituted the guidelines for the risk assessment and management of transgenic cotton, which were highly manipulatable. These results are helpful to reveal to the temporal and spatial relationship between host plants, herbivores and natural enemies, to reveal the harmonized control efficacy and intrinsic stability of different natural enemy guilds, to reveal the impacts of transgenic plants on the ecological services of ecosystem, to provide theoretical and practical evidences for the ecological and biological integrated pest management in transgenic cotton fields, and to provide guidance for the risk assessment and management oftransgenic cotton in China.