Abundance and diversity of arthropods in transgenic Bt and non-Bt cotton fields under Indian conditions

Genetically engineered cottons expressing ä-endotoxins from Bacillus thuringiensis have been adopted on a large- scale worldwide. Therefore, we studied the efficacy of Bt cottons for the management of bollworms, their effects on non- target insects, and seedcotton yield under insecticide protected and unprotected conditions. Helicoverpa armigera and Earias vittella damage was significantly lower in Bt than in non-Bt cottons, while no significant differences were observed in egg-laying by H. armigera. The populations of major non-target sucking insect pests such as Amrasca biguttula biguttula, Bemisia tabaci, Aphis gossypii, Oxycarenus laetus, Dysdercus koenigii and Nezara viridula and the generalist predators, viz Cheilomenes sexmaculatus, Chrysopa spp., and spiders did not differ significantly between Bt and non-Bt cottons. Insecticide application resulted in resurgence of cotton aphid and whitefly, possibly because of elimination of natural enemies or better growth of plants uder protected conditions. Abundance of bollworms, non-target pests, and generalist predators was significantly greater before insecticide sprays than after insecticide application, except in a few cases. Bollworm damage was lower and seedcotton yields higher in Bt than in non-Bt cottons. The present studies indicated that Bt cotton hybrids are effective for the management of bollworms and yield more, and do not have any adverse effects on the abundance of generalist predators.

The effects of two insect-resistant transgenic cotton strains (transgenic Bt pest-resistant cotton Zhongkangza 5 and Lumianyan 23, transgenic Bt+CpTI pest-resistant cotton sGK958 and Zhongmiansuo 45) on the growth and reproduction of Tetranychus cinnabarinus was examined in comparison with non-transgenic cotton (K836) at 70% relative humidity and 30±0.5 ℃. The results showed that T. cinnabarinus fed on transgenic Bt cotton and transgenic Bt+CpTI cotton differed significantly from those on conventional cotton in development time of various stages. Furthermore, the development times of mites on transgenic Bt cotton and transgenic Bt+CpTI cotton were the same, but the development times of T. cinnabarinus fed on transgenic Bt pest-resistant cotton Zhongkangza 5 and Lumianyan 23 were different, as well as the development times of T. cinnabarinus fed on transgenic Bt+CpTI pest-resistant cotton sGK958 and Zhongmiansuo 45. The pre-oviposition period, oviposition period and the female mite life span were longer (1.44 d, 12.71 d, and 14.11 d respectively) on non-transgenic cotton than on transgenic cotton. The maximum fecundity was 75.61 eggs per female on non-transgenic cotton and the minimum fecundity (54.68 eggs per female) was observed in mites fed on sGK958. The net reproductive rate (R0) was the highest (55.000) on non-transgenic cotton, but was the smallest (37.219) on Zhongkangza 5. The intrinsic rate of increase (rm) was the highest (0.454) on non-transgenic cotton, but was the smallest (0.246) on Zhongkangza 5. The finite rate of increase (λ) was the highest (1.575) on non-transgenic cotton, but was the smallest (1.278) on Zhongkangza 5. The population doubling time (DT) was the shortest (1.526 d) on non-transgenic cotton, but was the longest (2.823 d) on Zhongkangza 5. The results of this study indicated the negative effects of transgenic cotton on the development and reproduction of T. cinnabarinus was significant: the larvae had the lowest survival rate after feeding on five kinds of cotton, while deutonymphs had the highest survival rate; the hatching rate and deutonymph survival rate of T. cinnabarinus fed on CK were the highest, while the hatching rate and larval survival rate of the sGK958 were the lowest. Transgenic insect-resistant cotton basically showed significant effects on the development period of each stage and the whole generation of T. cinnabarinus, but there were no significant differences between univalent transgenic Bt cotton and bivalent transgenic Bt+CpTI cotton.

Transgenic crops are increasingly prevalent worldwide, and evaluating their impact on soil microbial communities is a critical aspect of upholding environmental safety. Our previous research demonstrated that overexpression of ScALDH21 from desiccant-tolerant moss, Syntrichia caninervis, in cotton revealed multi-resistance to drought, salt, and biotic stresses. We conducted metabarcoding using high-throughput sequencing to evaluate the effect of ScALDH21 transgenic cotton on soil microbial communities. We further conducted soil tests to analyze the chemical properties of transgenic and non-transgenic cotton, including the total content and availability of chemical elements (K, P, and N), organic matter, and pH value. Both transgenic and non-transgenic cotton fields exhibited soil pH values higher than 8. The presence of transgenic cotton significantly enhanced the availability of available K and the total content of total P in the soil. Alpha and beta diversity indices of soil microbiota showed no difference between two transgenic and non-transgenic cotton groups. Dominant clades of fungal and bacterial genera were equivalent at the phylum and genus levels in all three groups. The correlation analysis of microbial communities and soil environmental factors revealed the absence of significant differences between transgenic and non-transgenic cotton genotypes. Functional predictions of soil microbial communities indicated that microbial community function did not show significant differences between transgenic and non-transgenic cotton samples. These findings are essential for evaluating the environmental effects of transgenic crops and supporting the secure implementation of transgenic cotton.

Comparative susceptibility of transgenic Bt cotton hybrids to Earias spp. and other non-target insects

Transgenic cotton is very effective in controlling targeted pests such as cotton bollworm (Helicoverpa armigera). However, increases in spider mite (Acari: Tetranychidae) populations have been reported in fields of transgenic cotton. The objectives of our laboratory experiments were (i) to determine host plant preference (transgenic or non-transgenic cotton) of T. turkestani females and (ii) to compare the life table parameters of T. turkestani females reared on transgenic or non-transgenic cotton. Enzyme-linked immunosorbent assays indicated that T. turkestani females reared on transgenic cotton leaves contained 14.9±0.23 μg Bt toxic protein per gram fresh weight, about 57.4% toxin in the transgenic cotton leaves. Results of dual-choice disc tests showed that T. turkestani females preferred to feed and lay eggs on non-transgenic cotton. Food source (transgenic or non-transgenic cotton) had no significant effect on the life table parameters of T. turkestani females. We conclude that increases in the population of spider mites in fields of transgenic cotton cannot be attributed to host plant preference or to the effects of Bt toxic protein on the non-targeted arthropods life cycle. Additional studies should be done to determine if the increases are due to less insecticide application or less competition with primary insects in transgenic cotton fields.

The environmental impact of genetically modified crops has been extensively investigated. However, few reports on the influence of transgenic traits on genetic structure have been reported in the literature. It is unknown how or if transgenic cultivars have affected genotypic variation in upland cotton (Gossypium hirsutum L.) since its rise to dominance in cotton production. In this study, the genotypic variance components, g, of lint yield (LY) and fiber quality were compared among transgenic and nontransgenic cotton in the USDA Regional High Quality (RHQ) tests from 2002 through 2018. The popular transgenic and nontransgenic cultivars/lines developed by the major private and public cotton breeding programs in the United States during this period were included. Testing cycles within the RHQ protocol consist of standardized control cultivars plus experimental entries. Variance components were dissected in each testing year within six such testing cycles. Lint yield of the transgenic cotton was generally higher than nontransgenic cotton. Fiber quality of the nontransgenic cotton was generally higher than the transgenic cotton. For LY, the proportion of g to the total variance was lower in the transgenic cotton than in the nontransgenic cotton, but the difference diminished in the recent two cycles. The proportion of g was lower in the transgenic cotton compared with the nontransgenic cotton for fiber length, fiber strength, fiber uniformity, and micronaire. The discrepancy between the two types of cotton in the RHQ tests reflects the influences of differential breeding schemes in the private and public breeding programs on means and genotypic variance of LY and fiber quality.

In a 3-yr field experiment, possible effects of Bt transgenic cotton plants expressing cry1A(c) gene from Bacillus thrungiensis Berliner variety kurstaki on diversities of arthropod communities and pest and natural enemy sub-communities were assessed in insecticide treated and untreated cotton fields, as measured by the Shannon-Weaver diversity index. The treatments included: 1) nontransgenic cotton with no insecticide treatment (nontransgenic), 2) nontransgenic cotton with insecticide treatments (nontransgenic+insecticide), 3) transgenic Bt-cotton with no insecticide treatment (Bt-cotton), and 4) transgenic Bt-cotton with insecticide treatments (Bt-cotton+insecticide). The results indicated that Bt-cotton increased the diversity of arthropod communities and pest sub-communities; however, it decreased the diversities of natural enemy sub-communities. Insecticide treatments increased diversities of communities and sub-communities of arthropods in both transgenic Bt-cotton and nontransgenic cotton ...

The effects of Bt transgenic cottons (Bt-I expressing cry1Ac and Bt-II expressing cry1Ab and cry2Ab or cry1Ab and cry1Fa) and non-Bt cottons on feeding, oviposition and longevity of adults, and development and survival of Liriomyza trifolii larvae were studied under laboratory conditions; and infestation on four Bt and two non-Bt cotton traits were investigated under field conditions. Laboratory choice and no-choice tests showed that L. trifolii adults were capable of distinguishing between Bt cottons and non-Bt cottons. In a choice test on younger plants (4-5 leaves), the adults were found more often and made more feeding punctures (FP) on non-Bt cottons than on Bt cottons. On older plants (8-9 leaves), adults made the most FP on non-Bt cotton followed by those on Bt-II cottons and the least on Bt-I cotton. The females oviposited more eggs (6.7 eggs per leaf) on non-Bt cotton than on Bt-I (1.7 eggs per leaf) and Bt-II (0.8 eggs per leaf) cottons on younger plants and oviposited similar numbers of eggs (0.7-1.3 eggs per leaf) on non-Bt and Bt cottons on older plants. In a no-choice test, the females also fed more FP on non-Bt cottons than on Bt cottons on both younger and older plants. The females oviposited more eggs (15.6 eggs per leaf) on non-Bt cotton than on Bt-I (8.2 eggs per leaf) and Bt-II (6.5 eggs per leaf) cottons on younger plants and similar numbers of eggs (2.5-3.3 eggs per leaf) on non-Bt and Bt cottons on older plants. Larval and puparial survivals were not different among Bt and non-Bt cottons. The occurrence and damage of leafminers on cottons in the field showed that L. trifolii infested more plants and leaves and had more mines on non-Bt cotton than on Bt cottons.

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Transgenic cotton has shown great promise for the control of target pest insects; however, frequent outbreaks of nontarget pest mirids has been recorded in recent years in northern China. To test the hypothesis that transgenic cotton contributes to nontarget pest outbreaks, we studied the impact of transgenic Bt cottons (both Bt and Bt + CpTI) on the fitness of nontarget pest Adelphocoris suturalis Jakovlev. No significant differences were detected between population densities of A. suturalis in unsprayed nontransgenic cottons and in unsprayed transgenic Bt cottons in 2007, 2008, and 2009. No difference in preferred oviposition site or egg production was detected between transgenic and nontransgenic cottons in both free choice and no choice tests. No difference in life table parameters was detected for A. suturalis between Bt cottons and nontransgenic cottons. All these results indicated that transgenic crops did not contribute to the nontarget pest outbreaks when being compared with their parental lines. The possible reasons for intensified pest status of A. suturalis, such as decrease of pesticide application, deficient natural enemies, and area-wide shift of cotton varieties, were discussed.

Being a new cultivar, the physiology of transgenic cotton, especially dual-toxin transgenic (Bt+CpTI) cotton, is not yet completely understood. Twelve elements in three organs of dual-toxin transgenic cotton seedlings were analyzed by ICP-MS. The distributions of the 12 elements were substantially different from those of non-transgenic cotton. In particular, the contents of B, Mg, P, K and Ca were the highest in leaves, while those of Si, Fe, Rb and Cu were the highest in roots; other elements had similar contents in the two organs, which were higher than those in the stem. Compared with non-transgenic cotton, the 12 elements could be classified into four groups according to their contents and distributions in the three organs: (a) P, K and Cu: their contents in transgenic cotton were remarkably lower, especially contents of P and K in leaves that were one times lower than those in leaves of non-transgenic cotton; (b) B, Mg and Mo: their contents in leaves and roots of transgenic cotton were higher, but lower in stems, compared with non-transgenic cotton; (c) Si, Mn, Fe, Rb and Zn: compared with non-transgenic cotton, these were lower in leaves and stems, but higher in roots of transgenic cotton; and (d) Ca: compared with non-transgenic cotton, its content was higher in all three organs of the transgenic counterpart. The decrease in soluble proteins and the expression of Bt and CpTI genes could be responsible for these changes. Further studies are needed to verify this hypothesis.

Insect pests constitute a considerable risk to global crop production. Although Bacillus thuringiensis (Bt) toxins produced in transgenic plants are effective against chewing insect pests, they do not protect plants against sucking insect pests, and continued use of Bt crops in the field can lead to the evolution of resistant pest species. However, several plant-derived mannose binding lectins are effective against sucking insect pests. To provide broad-spectrum and durable resistance against multiple insect pests, we produced a double gene construct harboring Cry2Ab (encoding a B. thuringiensis toxin) and PTA (Pinellia ternata leaf agglutinin, encoding a plant lectin). Nicotiana benthamiana and Arabidopsis thaliana were used as model plant systems for characterizing the double gene construct (Cry2Ab + PTA). Transgenic plants were made and evaluated to measure the efficacy of Cry2Ab + PTA against chewing and sucking insect pests. Molecular investigation of transgenic A. thaliana plants showed stable integration and expression of the Cry2Ab and PTA genes. On N. benthamiana expressing Cry2Ab + PTA, Myzus persicae (green peach aphid) mortality was 74%, compared to 25% on non-transgenic controls. Bemisia tabaci (whitefly) mortality was 78%, compared to 22% on non-transgenic controls. Spodoptera frugiperda (fall armyworm) showed 83% mortality when fed on transgenic A. thaliana plants expressing Cry2Ab + PTA, whereas 17% mortality was observed on non-transgenic control plants. The Cry2Ab + PTA construct protects plants against both sucking and chewing insects, suggesting that this construct can be introduced into cotton and other crops to control multiple insect pests.

2009—2013年Bt棉田节肢动物群落多样性动态变化

Field studies were conducted in 2000–2002 to compare foliage-dwelling arthropod populations on Bacillus thuringiensis Berliner (Bt) (Bollgard) cotton and non-Bt (conventional) cotton season-long in South Carolina, Georgia, northern Alabama, and southern Alabama. For each of these four regions, three or four paired fields were sampled weekly in each of the 3 yr. Each pair of fields consisted of a Bt and a non-Bt cotton field, both at least 5 ha in size. The dominant arthropod taxa collected included target pests (heliothine moths and Spodoptera spp.), nontarget pests (stink bugs and plant bugs), and generalist natural enemies [Geocoris spp., Orius spp., Solenopsis invicta (Buren), ladybeetles, and spiders]. Where target pests were present, particularly Helicoverpa zea (Boddie), their numbers were consistently significantly lower in the Bt cotton fields. Natural enemy populations generally were not significantly different between the Bt and the non-Bt cotton fields (50% of all comparisons) and, where significant differences were present, natural enemy abundance usually was higher in the Bt than the non-Bt cotton fields. These differences were correlated with lower insecticide use on the Bt than the non-Bt cotton fields, particularly in South Carolina, where target pest pressure was heaviest. When presented with insect eggs or larvae as prey items, the larger natural enemy populations in Bt cotton fields exhibited significantly higher predation rates. These results show that Bt cotton has no significant adverse impacts on the nontarget arthropod populations studied and, compared with insecticide-treated non-Bt cotton, Bt cotton supports higher natural enemy populations with significant positive impacts on biological control.

Transgenic Bt cotton BG II (cry1Ac +cry2Ab genes) in comparison with non-Bt cotton were evaluated for their effect on the development of Spodoptera litura in the IPM Laboratory of Department of Entomology, Punjab Agricultural University Ludhiana. The leaf and square of various Bt cotton cultivars viz. MRC 7017, BCHH 6488, BCHH 6588, Ankur 3028, NCS 855 and non-Bt cotton LH 2076 were fed to the neonates, first and second instars larvae of cotton leaf worm, S. litura. The neonates, 1st and 2nd instar larvae when fed on leaves of transgenic Bt cotton resulted in 100 per cent mortality as compared to non-Bt cotton (0.00). However, 2nd instar larvae fed on squares of Bt cotton resulted in 100 per cent mortality in most of the Bt cotton cultivars, MRC 7017, BCHH 6488, BCHH 6588 and Ankur 3028 except NCS 855 (82.16) and non-Bt (6.63). The developmental times of 2nd instar larvae of S. litura were different among Bt cotton cultivars and non-Bt cotton. The survived 3rd instar larvae fed on leaves in Ankur 3028 (11.11) followed by BCHH 6588 (7.14) and BCHH 6488 (7.4) continued to be 3rd instar even after 17 days, while those on non Bt cotton moulted to pupal stage (7.14). However, when larvae fed on squares of Bt cotton and non-Bt cotton, maximum pupation takes place in non Bt cotton cultivar, LH 2076 (93.33) followed by Bt cotton cultivar NCS 855 (17.85) after 24 days. The total developmental time of larvae in the Bt cotton was significantly longer than that of larvae on non-Bt squares. The higher weight of larvae fed on leaves was recorded in LH 2076 (19.72 mg). Similarly, after 10 days of release of S. litura on squares of different cotton cultivars higher weight of larvae was recorded in LH 2076 (25.671 mg) and lower in MRC 7017 (2.919 mg). The pupae that developed from the larvae that fed on non-Bt were heavier than those that developed from the larvae that fed on non-Bt cotton squares. After 27 days, 100 per cent adult emergence was recorded in non-Bt cotton cultivar, LH 2076 followed by single emergence in BG II cotton cultivar NCS 855. However, after 31 days, four adults were formed in case of NCS 855 but they were not able to survive for more than 2 days and all of them were males. It can be inferred that all BGII cotton cultivars were toxic to neonates, first and second instar larvae of S. litura under laboratory conditions.