Management of cotton bollworms Helicoverpa armigera and Earias vittella by ento mopathogenic nematodes

Background: The bollworm complex consisting of Helicoverpa armigera and Earias vittella is a major threat in cotton production globally. The habit of developing resistance to many insecticides including Bt transgenic cotton necessitates the exploration of an alternate strategy to manage bollworms. The entomopathogenic nematodes(EPN) Steinernema carpocapsae strain APKS2 and Heterorhabditis bacteriophora strains KKMH1 and TRYH1 at different concentrations of 1 × 10^(9) infective juveniles(IJs)·hm^(-2), 2 × 10^(9)IJs.hm^(-2), and 3×10^(9)IJs·hm^(-2) in 500 L of water were evaluated as a foliar spray in fields naturally infested with H.armigera and F.vittella located at Eastern Block and and Cotton Research Farm of Tamil Nadu Agricultural University, Coimbaotre, India during October 2010–February 2011 and October 2011–February 2012, respectively.Results: In general, all three tested EPN strains reduced the larval population of H. armigera and E. vittella;reduced square and boll damage;and subsequently increased cotton yield compared with the untreated control. The S. carpocapsae APKS2 is most e ective against H. armigera whereas both S. carpocapsae APKS2 and H. bacteriophora KKMH1 were equally effective against E. vittella. The higher dose of 3×10^(9)IJs·hm^(-2) was highly significant in the reduction of H. armigera larvae. However, the doses 2×10^(9)IJs·hm^(-2)and 3×10^(9)IJs·hm^(-2) were equally effective for E. vittella control. The S. carpocapsae APKS2 at 3×10^(9)IJs·hm^(-2) caused a 62.2% reduction of H. armigera larvae, 34% reduction of square damage, 58.5% reduction of boll damage, and yielded 45.5% more seed cotton than the untreated control plots. In E. vittella infested field, S. carpocapsae strain APKS2 and H. bacteriophora strain KKMH1 at 2×10^(9)IJs·hm^(-2)resulted in 60.6%~62.4% larva reduction, 68.4%~70.7% square damage reduction, 66.6%~69.9% boll damage reduction and 45.9% yield increase over the untreated control. The effective EPN treatments were comparable to the chemical insecticide chlorpyriphos 20% emulsifiable concentrate spraying at 2 mL·L^(-1).Conclusions: This study has shown that EPN have great potential in the management of the bollworm complex in cotton. Foliar spraying EPN strain S. carpocapsae(APKS2) at 3×10^(9)IJs·hm^(-2) and S. carpocapsae(APKS2) or H. bacteriophora(KKMH1) at 2×10^(9)IJs·hm^(-2) five times at 10days intervals are the best for the management of H. armigera and E. vittella, respectively.

Laboratory evaluation of toxicity of selected insecticides against egg and larval stages of cotton pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae)

Background The cryptic nature of pink bollworm Pectinophora gossypiella(Saunders)larvae enables its reduced vul-nerability to insecticidal control.Further,the development of resistance against Bacillus thuringiensis(Bt)toxins posed a serious threat to transgenic cotton cultivation.This necessitated determining the critical timing of spray applications on the control effectiveness.This study assessed the influence of egg age(freshly laid vs.three-day-old)and the loca-tion of larvae(directly exposed to the insecticide residues on the boll rind vs.burrowed inside the bolls)on insecticide control efficacy.Results The results revealed a significant decrease in the ovicidal activity of tested insecticides with an increase in the age of eggs from one day old to three days old(paired t-test,P<0.05).The larvae directly exposed to the insec-ticide residues on the boll rind were more susceptible(>80%mortality)than the larvae exposed after they had bur-rowed inside the bolls(<49%mortality).The inhibitory effects of tested insecticides on developmental biology were more pronounced in the experiment on pre-larval release insecticide treatment compared with insecticide treatment given post-larval release and entry inside the bolls.Conclusion Egg age influences the insecticide susceptibility,as does the larval location,directly exposed vs bur-rowed inside the bolls.Older eggs and the larvae that had burrowed inside the green bolls of cotton were relatively less susceptible to the insecticide treatments.The toxic effects of insecticides on egg and larval stages were primar-ily ephemeral.These findings are significant for devising a comprehensive strategy for pink bollworm management on a sustainable basis.

棉花无蜜腺性状抗棉铃虫及红铃虫效果研究

棉花无蜜腺性状抗棉铃虫及红铃虫效果研究郑冬官，方其英（安徽农业大学合肥２３００３３６）郑厚今（安徽省农业厅，合肥２３０００１）Ｒｅｓｉｓｔａｎｃｅｏｆｃｏｔｔｏｎｎｅｃｔａｒｉｌｅｓｓｃｈａｒａｃｔｅｒｔｏｂｏｌｌｗｏｒｍａｎｄｐｉｎｋｂｏｌｌｗｏｒ...

Selection of Homozygous Cotton Lines Transformed with Two Insect-Resistant Genes

A plant expression vector containing a chimeric Bt29K gene coding for the activated Cry1Ac protein and the arrowhead proteinase inhibitior gene API B were introduced into the cotton cultivar Jihe321 mediated by Agrobactertium tumefaciens. Based on the results of kanamycin resistant testing, PCR detection for both foreign genes and insect bioassay using Heliethis armigera , nine transgenic homozygous cotton lines with insect resistance of more than 90% and better agronomic traits were bred through six generations from the original transgenic plants. Results from insect bioassay and sequence analysis of the PCR products of plants from some homozygous lines indicated that the chimeric Bt29K gene was stably inherited in these transgenic cotton lines. The main agronomic characters of these homozygous cotton lines, such as boll productivity and fibre strength, were better than that of the original cotton cv. Jihe321.

Performances of the cotton bollworm,Heliothis armigera (Hubner) at different temperatures and relative humidities

The cotton bollworm, Heliothis armigera (Hubner) is an important insect species at-tacking many crops. Their performances have been examined at temperatures from 15℃ to 35℃ and relative humidities (RH) between 22.5% and 100%, respectively, in order to assess possible effect of climate in future on its occurrence and infestation. Durations of all developmental stages of the insect shortened with increasing temperature. The temperature favoring population growth ranged from 25℃ to 30℃.Larval duration and adult longevity decreased as relative humidity increased, but development of other stages was independent of RH. At RH of over 64%, their survival rate, egg production and oviposition rate varied a little, and all the population parameters of the insect remained at a relative constant level.

Characterization of circRNAs associated with resistance to defoliating insects in soybean

Circular RNAs (circRNAs) are new type of non-coding endogenous RNA characterized by presence of covalent bond linking 3′ and 5′ ends recently. Various endogenous circRNAs with potential biological functions have been identified in animals and plants.However, little is known regarding circRNAs in soybean. In this study, we have performed genome-wide profiling of circRNAs that associate with insect resistance in soybean through bulk segregant RNA-seq and bioinformatics analysis. In total, 5,367 circRNAs were identified,of which 3,377 and 3,457 ones were detected from resistant and susceptible bulks respectively. These circRNAs showed diverse expression patterns, and 199 circRNAs were found to be differentially expressed between resistant and susceptible samples under stress of defoliation-damage by cotton bollworm feeding. Functional categorization of circRNA-hostgenes revealed that various biology processes were triggered to be active during chewing injury. Intriguingly, some circRNAs were predicted to involve in insect resistance processes,such as tropane, piperidine and pyridine alkaloid biosynthesis, and monoterpenoid biosynthesis.Furthermore, 1,118 circRNAs were predicted to have enrichened miRNA binding sites in soybean. This research provid not only circRNAs resources, but also useful clues about their biological insights in response to defense biotic stress in plant.

Efficiency of cotton bollworm (Helicoverpa armigera Hübner) control of different Bt cotton varieties in North China

Background： The cotton bollworm （Helicoverpa armigera） is one of cotton＇s most destructive insect pests in terms of yield and quality. Since 1997, China has grown commercially available transgenic Bacillus thuringiensis （Bt） cotton. We aimed to investigate the variation in resistance of transgenic Bt cotton varieties to cotton bollworm in North China. Methods： Populations of cotton bollworm were monitored from 2008 to 2015 in environments where Bt cotton was planted adjacent to other non Bt crops. The study included 197 Bt cotton varieties planted in 42 counties/locations in three provinces （Hebei, Shandong and Henan） of North China, which were evaluated through field investigations, bioassays, and enzyme linked immunosorbent assays （ELISA）. Results： The average number of cotton bollworms never exceeded the action threshold （10 larvae per 100 cotton plants）, however, their number reached 19.55 per 100 cotton plants in 2011. The ratios of damaged plants to total Bt cotton stem tips, buds, and bolls was low except in 2010, when the ratios reached 1.82%, 2.09%, and 10.63%, respectively. The results of bioassay showed that the corrected mortality were higher at the second generation cotton bollworm stage than the third and fourth germination stages. Totally, Bt protein content declined sharply at the seedling stage from 2008 to 2015. Conclusions： This study indicated that almost all Bt cotton varieties were capable to effectively control the populations of cotton bollworm in North China.

Study on Insect-resistant Transgenic Cotton Harbouring Double-gene and Its Resistance to Insect Pests

By using the method of pollen tube pathway, the synthesized GFM CryIA gene and modified CpTI gene were transfered into the elite cotton( Gossypium hirsutun L. ) varieties(lines). Through the field and lab identifications, the insect-resistant transgenic plants were obtained. PCR analysis indicated that both the synthesized GFM CryIA gene and modified CpTI gene presented positive reaction. In R1 the boliworm resistance of each transformant was different, and the insect-resistance of R3 of ZGK9708 was stable.

Does cotton bollworm show cross-resistance to the Bacillus thuringiensis toxins Cry1Ac and Cry2Ab? A mini review

Since 1996, transgenic Bacillus thuringiensis(Bt) cotton has been commercially grown in numerous countries in an effort to stem the losses caused by key lepidopteran pests. However, the development of pest resistance to Bt toxins has jeopardized the continued utilization of Bt cotton. As a strategy designed to circumvent the development of resistance, Bt cotton varieties expressing two or more toxins targeting the same pest have been introduced. Nevertheless, from the perspective of long-term planting of Bt cotton, the potential risk of cross-resistance to these Bt toxins is a threat that cannot be ignored. In this paper, we review current research(including that based on the analysis of protein binding sites and resistance genes) on the resistance of cotton bollworm(Helicoverpa armigera) to the Bt toxins Cry1 Ac and Cry2 Ab and the interrelationship between these toxins. On the basis of existing evidence, we assume that the actions of Cry1 Ac and Cry2 Ab against cotton bollworm are not completely independent, and then propose the "resistance-associated gene mutation potential hypothesis". Although the mechanisms underlying the resistance of pests to Bt toxins are yet to be comprehensively elucidated, this hypothesis could undoubtedly have important implications for adopting "pyramid" strategy in the future. Further research is recommended to devise strategies to retard the development of H. armigera resistance to Bt cotton, either using different Bt toxins or their various combinations.

Impact Analysis of Genetically Modified (Bt) Cotton Genotypes on Economically Important Natural Enemies under Field Conditions

Field studies were conducted at Hisar during Kharif, 2009-2010 and 2010-2011 under natural and unsprayed condition. RCH 134 Bt, HS 6 (non Bt), H 1117 and Ganganagar Ageti (non Bt) were selected for the studies. The experiment was laid down in Randomized Block Design replicated thrice having plant spacing 67.5 × 60 cm. Among the bollworms, Erias spp. exhibited positive correlation with rainfall, minimum temperature and relative humidity morning hours significantly at 5 percent level whereas Helicoverpa and Pectinophora displayed positive relations only with evening hours relative humidity significantly while Spodoptera were significantly positive correlated with relative humidity of morning and evening hours. Bollworm complex was negatively correlated with all the weather parameters employed to study although being non-significant in case of rainfall, maximum and minimum of temperature, morning and evening hours of relative humidity. Among the sucking pests, leafhoppers, whitefly, thrips and aphids population showed significantly negative correlation with weather parameters. The comparison of natural bio-agents in cotton hybrids under study revealed that overall mean population of natural enemies were higher in Bt cotton hybrid as compared to non-Bt. These results confirm that use of genetically modified (Bt) cotton in lieu of conventional genotypes could positively impact non-target and beneficial insect species by preserving their host populations.

Evaluation of Insecticides Targeting Control of Helicoverpa armigera(Hubner)(Lepidoptera:Noctuidae)

Insecticides from different chemical groups were tested by laboratory bioassay to verify the percentage mortality of Helicoverpa armigera (Hubner 1808) (Lepidoptera: Noctuidae). The experiment was conducted in the Crop Science laboratory—Prof. CinobelinaElvas Campus—UFPI, Bom Jesus, PI, from January to June, 2013. The populations utilized came from the University’s own insect breeding laboratories. Third instar larvae of H. armigera were used to conduct the bioassay. The experimental design was fully randomized, with 13 treatments and four replications. Five larvae were used per replication, with 12 insecticides from 9 different chemical groups and a control. Each treatment consisted of three doses. The methods of application used were topical contact and ingestion in artificial diet. According to the results the percentage mortality of H. armigera larvae varied among the treatments. The results demonstrated that chlorpyrifos and spinosad were effective against third instar H. armigera larvae both on contact and by ingestion. Flubendiamide, acephate, methomyl, Bacillus thuringiensis, dimethoate, chlorantraniliprole and fipronil had good responses to control of H. armigera.

THE FUNDAMENTAL STRATEGY FOR THE CONTROL OF COTTON BOLLWORM OUTBREAKS IN CHINA

on the basis of the analysis of the factors causing the cotton bollworm outbreaks and control failure, the authors recommend that the fundamental strategy for solving the problem of cotton bollworms in China should be to conduct area-wide unified controls rather than depend on insecticides. The unified control system is the guarantee for Integrated Pest Management (IPM) for small-scale crop owners at present. So the authors call on policymakers to put stress on organizing individual growers to carry out area wide unified controls.

How does atmospheric elevated CO2 affect crop pests and their natural enemies？ Case histories from China

Global atmospheric CO2 concentrations have risen rapidly since the Industrial Revolution and are considered as a primary factor in climate change. The effects of elevated CO2 on herbivore insects were found to be primarily through the CO2-induced changes occurring in their host plants, which then possibly affect the intensity and frequency of pest outbreaks on crops. This paper reviews several ongoing research models using primary pests of crops （cotton bollworm, whitefly, aphids） and their natural enemies （ladybeetles, parasitoids） in China to examine insect responses to elevated CO2. It is generally indicated that elevated CO2 prolonged the development of cotton bollworm, Helicoverpa armigera, a chewing insect, by decreasing the foliar nitrogen of host plants. In contrast, the phloemsucking aphid and whitefly insects had species-specific responses to elevated CO2 because of complex interactions that occur in the phloem sieve elements of plants. Some aphid species, such as cotton aphid, Aphis gossypii and wheat aphid, Sitobion avenae, were considered to represent the only feeding guild to respond positively to elevated CO2 conditions. Although whitefly, Bemisia tabaci, a major vector of Tomato yellow leaf curl virus, had neutral response to elevated CO2, the plants became less vulnerable to the virus infection under elevated CO2. The predator and parasitoid response to elevated CO2 were frequently idiosyncratic. These documents from Chinese scientists suggested that elevated CO2 initially affects the crop plant and then cascades to a higher trophic level through the food chain to encompass herbivores （pests）, their natural enemies, pathogens and underground nematodes, which disrupt the natural balance observed previously in agricultural ecosystems.

Expression of two insect-resistant genes cryIA (b&c)/GNA in transgenic tobacco plants results in added protection against both cotton bollworm and aphids

The synthesized Bacillus thuringiensis insecticidal protein gene crylA(b&c) and the synthesized gene GNA, (the mannose specific lectin from snowdrop ( Galanthus nivalis)), tumefaciens have been inserted into plant expression vector pGW4BAI. Leave stripes of Nico-tiana tabacum var. K326 have been transformed with Agrobacterium tumefaciens strain LBA4404 harboring the plant expression vector. 28 kanamycin resistant tobacco plants

Determining the major Bt refuge crops for cotton bollworm in North China

Evaluation of the effectiveness of refuge strategies involved in cotton boll- worm Bt resistance management would be aided by technologies that allow monitoring and quantification of key factors that affect the process under field conditions. We hy- pothesized that characterization of stable carbon and nitrogen isotopes in adult bollworm, Helicoverpa armigera （Htibner） （Lepidoptera： Noctuidae） moths may aid in determining the larval host that they developed upon. We found moths reared from larvae fed on peanut, soybean or cotton, respectively, could be differentiated using isotopic analyses that also corresponded to their respective larval host origins. These techniques were then used to classify feral second-generation bollworm moths caught in Bt cotton （Gossypium hirsu- rum） fields into different populations based on their isotopic signatures. In 2006-2007 feral moths captured in Bt cotton fields predominantly correlated with the peanut （Arachis hypogea） having served as their larval host, indicating this is the most important refuge crop for Bt-susceptible bollworm individuals （providing 58%-64% individuals） during independent moth peaks for the second generation in North China. The remaining feral moths correlated with soybean （Glycine max） （0-10%）; other C3 plant （20%-22%） and non-C3 plant （12%-14%） host types also provided some Bt-sensitive moths. Field obser- vations showed that peanut constitutes the primary refuge crop contributing to sustaining Bt-susceptible moths dispersing into cotton in North China. These results suggest that peanut may be a more effective refuge to sustain Bt-susceptible bollworm individuals and reduce the risk of development of a Bt-resistant biotype.