Cloning and Sequencing of Two Acetylcholinesterase cDNA Fragments from Cotton Aphid,Aphis gossypii Glover

Two acetylcholinesterase (AChE) genes cDNA fragments,Ag.acel and Ag.ace2,have been cloned from cotton aphid,Aphis gossypii Glover using degenerate primers with RT-PCR technique.Ag.acel gene cDNA fragment is of 282?bp encoding 94 amino acids,and Ag.ace2 gene cDNA fragment is of 264?bp encoding 88 amino acids.Both two putative AChE genes cDNA fragments share numerous similarities with those cloned from other insects.This is the first report of two AChE cDNA fragment sequences in the insect species,which provided the direct evidence of multiple AChE existence in insects.

Effect of Transgenic Bt plus CpTI Cotton on Carboxylesterase and Acetylcholinesterase of Cotton Aphid Aphis gossypii

[Objective] The research aimed to assess the effect of transgenic Bt plus CpTI cotton variety SGK321 on carboxylesterase and acetylcholinesterase of cotton aphid Aphis gossypii and provide theoretical basis for studying the biosafety of transgenic cotton.[Method] Cotton aphids were fed with SGK321 and Shiyuan321（normal parental varieties） for over 40 generations.Enzyme activities were compared between cotton aphids feeding on SGK321 for 1,2,3,41,42 and 43 generations with those on Shiyuan321.[Result] The carboxylesterase activity of cotton aphids feeding on SGK321 for 1 generation was significantly higher than those feeding on Shiyuan321.Acetylcholinesterase activity of cotton aphids feeding on SGK321 for 1,2 and 3 generations were significantly higher than those feeding on Shiyuan321 in the same generation.But there was no significant difference of enzyme activity between cotton aphids feeding on SGK321 for a long term and those feeding on parental cotton.[Conclusion] The cotton aphid that feeding on transgenic Bt plus CpTI cotton SGK321 for a long time has adaptivity to SGK321 by regulating the detoxifying enzyme.

释放异色瓢虫对甜瓜蚜虫的防控效果

为探究在设施栽培条件下,释放异色瓢虫(Harmonia axyridis)防治甜瓜蚜虫(Aphis gossypii Glover)的综合效果,按不同益害比释放异色瓢虫,评价其在设施条件下对甜瓜蚜虫的防控效果以及天敌和害虫的消长动态。结果表明:异色瓢虫对于甜瓜蚜虫具有良好的防控效果,特别是长期防控效果优于化学农药,益害比1∶5与益害比1∶10的投放密度对蚜虫的防控效果好,两者比较差异未达显著水平,在释放后28 d时防效仍在70%以上。但考虑到生产成本,益害比1∶10为甜瓜上异色瓢虫释放的最佳密度;前期异色瓢虫定殖量随着蚜虫数量增加而升高,14 d时天敌投放处理的瓢虫定殖量达到峰值,故应结合病虫害测报,在蚜虫发生高峰期前尽早释放。

内吸性杀虫剂对瓜蚜生物活性及种群实时增长率的影响

为探索新型精准施药方式,筛选防治瓜蚜(Aphis gossypii Glover)的高效内吸性药剂,采用茎部用药法,测定了9种内吸性杀虫剂对黄瓜(Cucumis sativus Linn.)瓜蚜的校正致死率及试验期间的种群实时增长率。结果表明,20%啶虫脒可溶液剂和10%氟啶虫酰胺散粒剂对瓜蚜的内吸活性最高,分别在施用杀虫剂后10、15 d达到100.0%的校正致死率,且施用杀虫剂后20 d校正致死率均稳定在95%以上。各杀虫剂中,10%氟啶虫酰胺散粒剂速效性最差,但持效性最好;其次为70%吡虫啉散粒剂和10%烯啶虫胺水剂,最大校正致死率分别出现在施用杀虫剂后10 d,分别为99.3%和95.0%,且施用杀虫剂后20 d均稳定在90%以上;25%噻虫嗪散粒剂、10%溴氰虫酰胺悬浮剂、25%吡蚜酮可湿性粉剂、20%呋虫胺散粒剂和22.4%螺虫乙酯悬浮剂所有浓度下的最大致死率均低于90%。中、高浓度处理下,20%啶虫脒可溶液剂和70%吡虫啉散粒剂在试验中期对瓜蚜种群增长有明显的阶段性抑制作用,10%氟啶虫酰胺散粒剂在后期持续抑制瓜蚜种群增长。这说明啶虫脒、吡虫啉和氟啶虫酰胺对黄瓜瓜蚜具有较高的内吸活性。

Differential mRNA expression levels and gene sequences of carboxylesterase in both deltamethrin resistant and susceptible strains of the cotton aphid, Aphis gossypii

Extensive use of insecticides on cotton has prompted resistance development in the cotton aphid, Aphis gossypii （Glover） in China, A deltamethrin-selected population of cotton aphids from Xinjiang Uygur Autonomous Region, China with 228,59-fold higher resistance to deltamethrin was used to examine how carboxylesterase conferred resistance to this pyrethroid insecticide. The carboxylesterase activity in the deltamethrin-resistant strain was 3.67-, 2,02- and 1.16-fold of the susceptible strain when using α-naphthyl acetate （α-NA）, β-naphthyl acetate （β-NA） and α-naphthyl butyrate （α-NB） as substrates, respectively, Carboxylesterase cDNA was cloned and sequenced from both deltamethrinresistant and susceptible strains. The cDNA contained 1581 bp open reading frames （ORFs） coding a 526 amino acid protein. Only one amino acid substitution （Val^87-Ala） was observed between deltamethrin-resistant and susceptible strains but it is not genetically linked to resistance by the catalytic triad and signature motif analysis. The real-time polymerase chain reaction analysis indicated that the resistant strain had a 6.61-fold higher level of carboxylesterase mRNA than the susceptible strain. The results revealed that up-regulation of the carboxylesterase gene, not modified gene structure, may be responsible for the development of resistance in cotton aphids to deltamethrin.

Ultrastructure of compatible and incompatible interactions in phloem sieve elements during the stylet penetration by cotton aphids in melon

Resistance of the melon line TGR-1551 to the aphid Aphis gossypii is based on preventing aphids from ingesting phloem sap. In electrical penetration graphs （EPGs）, this resistance has been characterized with A. gossypii showing unusually long phloem salivation periods （waveform El） mostly followed by pathway activities （waveform C） or if followed by phloem ingestion （waveform E2）, ingestion was not sustained for more than 10 min. Stylectomy with aphids on susceptible and resistant plants was performed during EPG recording while the stylet tips were phloem inserted. This was followed by dissection of the penetrated leaf section, plant tissue fixation, resin embedding, and ultrathin sectioning for transmission electron microscopic observation in order to study the resistance mechanism in the TGR. The most obvious aspect appeared to be the coagulation of phloem proteins inside the stylet canals and the punctured sieve elements. Stylets of 5 aphids per genotype were amputated during sieve element （SE） salivation （El） and SE ingestion （E2）. Cross-sections of stylet bundles in susceptible melon plants showed that the contents of the stylet canals were totally clear and also, no coagulated phloem proteins occurred in their punctured sieve elements. In contrast, electron-dense coagulations were found in both locations in the resistant plants. Due to calcium binding, aphid saliva has been hypothesized to play an essential role in preventing/suppressing such coagulations that cause occlusion of sieves plate and in the food canal of the aphid＇s stylets. Doubts about this role of E 1 salivation are discussed on the basis of our results.