Comparison of kinetic properties of a hydrophilic form of acetylcholinesterase purified from strains susceptible and resistant to carbamate and organophosphorus insecticides of green rice leafhopper (Nephotettix cincticeps Uhler)

A hydrophilic form of acetylcholinesterase (AChE) was purified from N-methyl carbamate susceptible (SA) and highly N-methyl carbamate-resistant (N3D) strains of the green rice leafhopper (GRLH), Nephotettix cincticeps Uhler. Both of purified AChE from SA and N3D strains displayed the highest activities toward acetylthiocholine (ATCh) at pH 8.5. In the SA strain, the optimum concentrations for ATCh, propionylthiocholine (PTCh), and butyrylthiocholine (BTCh) were about 1 × 10⁻³, 2.5 × 10⁻³, and 1 × 10⁻³ M, respectively. However, in the N3D strain, substrate inhibition was not identified for ATCh, PTCh, and BTCh to 1 × 10⁻² M. The K_m value in the SA strain was 51.1, 39.1, and 41.6 μM and that in the N3D strain was 91.8, 88.1, and 85.2 μM for ATCh, PTCh, and BTCh, respectively. The K_m value in the N3D strain indicated about 1.80-, 2.25-, and 2.05-fold lower affinity than that of the SA strain for ATCh, PTCh, and BTCh, respectively. The V_max value in the SA strain was 70.2, 30.5, and 4.6 U/mg protein and that in the N3D strain was 123.0, 27.0, and 14.5 U/mg protein for ATCh, PTCh, and BTCh, respectively. The V_max value in the N3D strain was 1.75- and 3.15-fold higher for ATCh and BTCh than that in the N3D strain. However, it was 1.13-fold lower for PTCh. The increased activity of AChE in the N3D strain is due to the qualitatively modified enzyme with a higher catalytic efficiency. The bimolecular rate constant (k_i) for propoxur was 27.1 × 10⁴ and 0.51 × 10⁴ M⁻¹ min⁻¹ in the SA and N3D strain and that for monocrotophos was 0.031 × 10⁴ and 2.0 × 10⁴ M⁻¹ min⁻¹ in the SA and N3D strain. AChE from the N3D strain was 53-fold less sensitive than SA strain to inhibition by propoxur. In contrast, AChE from the N3D strain was 65-fold more sensitive to inhibition by monocrotophos than AChE from the SA strain. This indicated negatively correlated cross-insensitivity of AChE to propoxur and monocrotophos.     

Non-target toxicology of a new mosquito larvicide, trypsin modulating oostatic factor

Trypsin modulating oostatic factor (TMOF), a peptide hormone originally isolated from the ovaries of adult Aedes aegypti, is currently under commercial development as a new pesticide chemistry with a novel mode of action for the control of larval mosquitoes. The objective of the current research is to evaluate potential risks of the use of TMOF as an insecticide on non-target organisms. TMOF (YDPAP₆) was degraded in vitro (as determined by HPLC and LC/MS) to DPAP₆, PAP₆, and then AP₆ by leucine aminopeptidase, a pancreatic enzyme found in the digestive system of vertebrates. The rate of degradation of TMOF and PAP₆ was significantly greater than that of DPAP₆, while no metabolism of AP₆ was found. TMOF technical insecticide was produced on a commercial scale by recombinant yeast (heat-killed before application). The technical TMOF when administered in a single dose by gavage to male and female mice at 2000 mg dry weight/kg body weight produced no negative effects as compared to controls up to 12 days after treatment. When male and female mallard ducks were treated by gavage with 1250 mg dry weight of technical TMOF/kg body weight each day for 5 days, again no toxic effects were noted through 35 days after the last treatment. TMOF technical insecticide was also applied to the shaved skin of male and female rabbits at the rate of 2000 mg/kg for 1-2 days, with no effect. The end point observations in these in vivo experiments were mortality; changes in growth rate, behavior, body structure, and color; and possible lesions observed during necropsy. Finally, Daphnia incubated with technical TMOF in rearing water at the level of 1.0 × 10⁶ yeast cells/ml (10 mg/ml) also demonstrated no negative effects on mortality, growth, molting, time to first brood, and production of viable neonates. It appears from these studies that TMOF can be degraded by vertebrate digestive proteases and technical TMOF is not toxic to the non-target organisms examined.     

Development of resistance to insecticides in the invasive mealybug Phenacoccus solenopsis (Hemiptera: Pseudococcidae) in Pakistan

The mealybug Phenacoccus solenopsis has been a serious pest of cotton, vegetables, ornamentals and other plants since its invasion into Pakistan in 2005. Its susceptibility to commonly-used insecticides was monitored during 2005–2013 by a nymphal dip bioassay. Initially, P. solenopsis was found susceptible to a range of insecticide classes. Lethal concentration values were particularly low for organophosphates and pyrethroids. After a year of its exposure to insecticides, P. solenopsis developed moderate to high levels of resistance to pyrethroids. After two years, resistance to organophosphates methidathion and chlorpyrifos also rose to moderate to high levels. After five years of use, resistance to pyrethroids, organophosphates, neonicotinoids, endosulfan, carbosulfan, and thiocyclam was generally high to very high. Acetamiprid resistance was slow to develop, as it reached moderate level of resistance after seven years of its extensive applications. Insecticide resistance in P. solenopsis could have been managed in Pakistan if the effective and diverse insecticides were used in rotation, along with other integrated pest management tactics, at the initial stages of resistance development.     

上海地区甜菜夜蛾的抗药性及防治

通过浸渍法测定上海地区甜菜夜蛾(Spodoptera exigua)对有机磷、拟除虫菊酯类、昆虫生长调节剂类(IGRs)以及一些新型药剂的抗性,结果表明:甜菜夜蛾对乙酰甲胺磷和氰戊菊酯的抗性分别为2 731.2和619.5倍的超高抗水平。昆虫生长调节剂如抑太保、米满等药剂对甜菜夜蛾抗性表现较好,是防治甜菜夜蛾的理想药剂,但近几年的敏感性有所下降,应注意抗药性抗性的产生和加剧。田间药效与室内毒力测定结果显示趋势一致。除尽、安打、氟铃脲、甲胺基阿维菌素苯甲酸盐和病毒制剂等是目前防治甜菜夜蛾的良好药剂。     

海南不同地区香蕉假茎象甲对几种杀虫剂的敏感性测定

采用虫体浸渍法,测定了海南澄迈和儋州两地的香蕉假茎象甲成虫对480克/升毒死蜱EC、77.5%敌敌畏EC、40%辛硫磷EC、40%丙溴磷EC、25%丙溴?辛硫磷EC、20%三唑磷EC等6种杀虫剂对的敏感性。结果表明,6种药剂对澄迈和儋州两地区的香蕉假茎象甲的毒力大小顺序相同,毒死蜱＞丙溴?辛硫磷＞丙溴磷＞三唑磷＞敌敌畏＞辛硫磷;儋州地区的香蕉假茎象甲对6种药剂的敏感性均高于澄迈地区。     

苹果黄蚜对杀虫剂的敏感性变化及混配增效作用研究

为了解苹果黄蚜药剂敏感性变化及药剂混配的增效作用, 采用FAO推荐的微量点滴法, 测定了苹果黄蚜在白天不同时间对杀虫剂啶虫脒、氟氯氰菊酯、马拉硫磷、溴氰菊酯的敏感性, 及不同作用机理的杀虫剂混配对苹果黄蚜的增效作用。结果表明, 苹果黄蚜在白天对所试药剂的敏感性呈规律性变化, 在9∶30am和4∶30pm对各药剂均出现敏感性高峰, 为喷药的最佳时间, 而在2∶30pm敏感性最低, 应减少在此时向区域内用药; 混配增效试验结果表明, 溴氰菊酯与马拉硫磷以有效成分1∶9, 吡虫啉与马拉硫磷以1∶10和1∶15, 啶虫脒与马拉硫磷以1∶10和1∶15混配对苹果黄蚜均有明显的增效作用。     

侧柏毒蛾幼虫酯酶对马桑毒素及4种杀虫剂的应激性反应

在比较马桑毒素及４种杀虫剂对虫体内酯酶活力影响的基础上,分析了酯酶应激性反应的异同性。结果表明,马桑毒素Ｂ及４种药剂处理后试虫酯酶相对活力发生了显著变化。其酯酶基因的表达有３种类型,即稳定型、应激型和可抑型。同工酶谱分布频率、相似系数Ｒｉｊ、聚类分析及基因表达率分析结果表明,马桑毒素Ｂ与其它４种药剂处理间的相关性较小,但处理１２ｈ后马桑毒素Ｂ与捕杀特的Ｒｉｊ值为０．８７６４,即由马桑毒素Ｂ所引起的     

荔蝽中乙酰胆碱酯酶活性与自然抗药性的关系

本文研究了荔蝽头部乙酰胆碱酯酶(AChE)活性的季节性变化与自然抗药性的关系,以及敌百虫对AChE的影响,同时运用聚丙烯酰胺凝胶电泳的方法,探讨了荔蝽酯酶同功酶的变动情况。结果表明:荔蝽正常成虫头部AChE活性在新羽化成虫中最高,比活力达3.5μmol min~(-1)mg~(-1)蛋白质,越冬期最低,仅1.17μmol min~(-1)mg~(-1)蛋白质,到生殖期又上升为2.67μmol min~(-1)mg~(-1)蛋白质。经敌百虫处理后,在新羽化成虫期和生殖期AChE活性有明显被抑制现象,其比活力分别为2.21μmol min~(-1)mg~(-1)蛋白质和2.04μmol min~(-1)mg~(-1)蛋白质,而在越冬期AChE活性几乎不受敌百虫影响,为1.24μmol min~(-1)mg~(-1)蛋白质,同功酶谱也显示AChE在不同季节中无明显变化。     

不同方法提取淡色库蚊总RNA的定量比较分析

采用异硫氰酸胍法、Trizol法、Trizol改良法、CTAB法及Trizol+ CTAB 5种方法提取的淡色库蚊总RNA,以期得到最优方法.提取总RNA并用电泳及紫外分光光度计检测,经过Dnase I消化后反转录成cDNA,以此为模板,用CYP6F1引物作定量表达分析.结果表明,与其他几种方法相比,CTAB法提取的效果最好,提取的样品纯度高,完整性好,杂质较少,DNA残留少,降解不明显.CTAB法提取的RNA可以作为eDNA合成和基因克隆的模板,能够满足后续研究的需要.     

杆状病毒在害虫控制中的应用策略

杆状病毒被视为安全和可供选择的生物杀虫剂,已经被广泛应用于防治多类害虫。限制杆状病毒使用的主要因素包括杀虫谱狭窄,杀虫速度缓慢,在试验商品生产中存在技术和经济困难,频繁监测其应用效果比较耗时,气候变化导致其田间药效变化不定等。科学家针对杆状病毒的缺点,尤其是其缓慢的作用速度,正在研究一系列策略,包括增加化学或生物物质的表达量及通过基因工程手段表达其毒素或荷尔蒙。此类策略能提高病毒的活动量和增加其作用速度,并且能够减少幼虫的进食量和进食速度。杆状病毒用于控制鳞翅目昆虫的功效正在接受检验。