Bt对棉铃虫天蚕素抗菌肽基因(HacD)转录的影响

抗菌肽是昆虫体液免疫的重要组成部分, 对抵御外源致病微生物的侵染具有重要作用。明确苏云金芽胞杆菌Bacillus thuringiensis(Bt)诱导下棉铃虫天蚕素抗菌肽基因(HacD)转录的空间特征和时序特征, 有利于进一步了解昆虫体液免疫与棉铃虫抗Bt发展的关联性。本研究测定了HacD cDNA序列, 对序列进行了蛋白质翻译, 并通过RT-qPCR技术研究了棉铃虫HacD基因在Bt诱导下的转录规律。结果表明, 棉铃虫HacD cDNA全长189 bp, 其中GC含量为48.15%, 肽链由63个氨基酸组成。Bt诱导后棉铃虫幼虫HacD相对转录水平整体呈显著上调趋势, 其中脂肪体中HacD的相对转录水平上调最高, 其次为血淋巴。Bt对棉铃虫幼虫进行短期诱导后, 脂肪体和血淋巴中的HacD基因的相对转录水平均呈持续上调趋势, 分别在诱导24 h和18 h时达到最高, 随后均持续下调。对幼虫进行持续诱导后, F0代初孵幼虫、5龄幼虫、蛹和成虫的HacD基因均可以保持上调的转录特性;传代培养获得的F1代初孵幼虫、5龄幼虫、蛹和成虫的HacD基因转录较F0代下调, 但均高于对照组。综上所述, Bt能够诱导棉铃虫HacD基因转录水平上调。     

Impact of seed blend and structured maize refuge on Helicoverpa zea (Lepidoptera: Noctuidae) potential phenological resistance development parameters in pupae and adults

BACKGROUND

Helicoverpa zea, an economic pest in the south-eastern United States, has evolved practical resistance to Bacillus thuringiensis (Bt) Cry toxins in maize and cotton. Insect resistance management (IRM) programs have historically required planting of structured non-Bt maize, but because of its low adoption, the use of seed blends has been considered. To generate knowledge on target pest biology and ecology to help improve IRM strategies, nine field trials were conducted in 2019 and 2020 in Florida, Georgia, North Carolina, and South Carolina to evaluate the impact of Bt (Cry1Ab + Cry1F or Cry1Ab + Cry1F + Vip3A) and non-Bt maize plants in blended and structured refuge treatments on H. zea pupal survival, weight, soil pupation depth, adult flight parameters, and adult time to eclosion.

RESULTS

From a very large sample size and geography, we found a significant difference in pupal mortality and weight among treatments in seed blends with Vip3A, implying that cross-pollination occurred between Bt and non-Bt maize ears. There was no treatment effect for pupation depth, adult flight distance, and eclosion time.

CONCLUSION

Results of this study demonstrate the potential impact of different refuge strategies on phenological development and survival of an important pest species of regulatory concern. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Susceptibility pattern and development of resistance in the diamondback moth,Plutella xylostella L,to Bacillus thuringiensis Berl var kurstaki in India

Base‐line susceptibility for six‐day‐old larvae of the diamondback moth, Plutella xylostella, against Bacillus thuringiensis var kurstaki (Biobit^®) was studied by a cabbage leaf disc dip bioassay technique. Diamondback moth from 13 locations in seven different states spread over a distance of about 3000 km longitudinally was used for these studies. Forty‐eight‐hour LC₅₀ values varied from 1.0 to 10.97 mg AI litre⁻¹. Further investigations on the development of resistance under laboratory conditions showed an increase in LC₅₀ from 2.76 (for unselected F₁ generation) to 5.28 mg AI litre⁻¹ (for selected F₉ generation), using a selection concentration of 6.4 mg AI litre⁻¹. This suggested a possibility of the development of resistance under field conditions if there were to be extensive and indiscriminate use of B thuringiensis. These findings are discussed in relation to integrated pest management and the mechanisms of resistance in resistance management tactics. © 2000 Society of Chemical Industry     

Laboratory evaluation of fipronil,a phenylpyrazole insecticide,against adult Anopheles (Diptera: Culicidae) and investigation of its possible cross‐resistance with dieldrin in Anopheles stephensi

Adult mosquitoes from two strains of Anopheles gambiae and from three strains of Anopheles stephensi were exposed to 0.25% fipronil‐treated papers in WHO test kits or to 500 mg fipronil m⁻² impregnated mosquito netting in bioassay spheres. For comparison, tests were also carried out with the pyrethroid permethrin, using the same methods and doses, and on papers treated with 0.4 and 4% of the cyclodiene insecticide dieldrin. Compared with the same doses of permethrin, fipronil showed less and delayed activity. Two of the An stephensi strains were resistant to fipronil and dieldrin. To investigate whether this was due to a resistance mechanism in the An stephensi strains acting against both insecticides, the most fipronil‐ and dieldrin‐tolerant strain was further selected in two separate lines with one of the insecticides, followed by tests with the insecticide that the line had not been selected with. This indicated a concomitant rise of resistance to dieldrin in the fipronil‐selected line and vice versa. Repeated back‐crossing of the two lines with a susceptible strain and re‐selection with either dieldrin or fipronil gave evidence for the involvement of a single resistance mechanism to both insecticides. Permethrin resistance in both lines declined with selection for dieldrin or fipronil and confirms the absence of cross‐resistance between fipronil and pyrethroids. © 2001 Society of Chemical Industry     

Bio-potency of serine proteinase inhibitors from Acacia senegal seeds on digestive proteinases, larval growth and development of Helicoverpa armigera (Hübner)

Proteinase inhibitors (AsPIs) with high activity against serine proteinases were purified from seeds of the tree legume, Acacia senegal by ammonium sulfate precipitation followed by DEAE-Sephadex A-25 column and evaluated against Helicoverpa armigera larvae by in vitro and in vivo methods. The molecular weight of AsPIs was found to be approximately 19.58 ± 1.00 and 21.23 ± 1.00 kDa for PI and 18.16 ± 1.00 kDa for PII on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The AsPIs (5 μg/ml) inhibited approximately 70% of midgut trypsin and 61% of elastase-like chymotrypsin. In vitro studies showed that AsPIs have remarkable inhibitory activity towards total gut proteolytic enzymes followed by trypsin and chymotrypsin. The IC₅₀ of AsPIs for midgut trypsin was 0.1 μg/ml and for chymotrypsin was 2.0 μg/ml. The inhibition of gut proteinase enzymes was of the non-competitive type. In larval feeding studies, AsPIs were found to retard growth and development of H. armigera and also affects the fecundity of the pest. The results advocate the use of AsPIs in transgenic technology to develop plant resistance to H. armigera.