Long-term exposure of Aedes aegypti to Bacillus thuringiensis svar. israelensis did not involve altered susceptibility to this microbial larvicide or to other control agents
Long-term exposure of Aedes aegypti to Bacillus thuringiensis svar. israelensis did not involve altered susceptibility to this microbial larvicide or to other control agents
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DOI：
10.1186/s13071-018-3246-1
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发表时间：
2018-12-29
影响因子：
3.2
通讯作者：
Neves Lobo Silva-Filha, Maria Helena
中科院分区：
文献类型：
--
作者：
Carvalho, Karine da Silva;Crespo, Monica Maria;Neves Lobo Silva-Filha, Maria Helena
研究背景苏云金芽孢杆菌Israelensis（Bti）是一种有效、安全的防治埃及伊蚊的生物农药。它的行动模式的基础上，四个protoxins不利于阻力，但是，控制在流行地区，全年显示高蚊子侵扰需要连续的杀幼虫剂的应用，这施加了强大的选择压力。因此，本研究的目的是调查的影响，一个密集的Bti暴露的Ae。Aegypti菌株（RecBti），关于其对Bti的敏感性和单独测试的两种其原毒素，对其它控制剂替美磷和灭幼脲，以及其解毒酶的概况。采用生物测定法和催化测定法分别测定了幼虫对杀幼虫剂的敏感性和解毒酶的活性。洛克菲勒菌株是用于这些evaluations.ResultsBti曝光产生的平均74%的死亡率在每一代的参考。在30个世代的7个时间点评估的幼虫对Bti晶体敏感（抗性比RR 2.8），并且对其单独的毒素Cry 11 Aa和Cry 4 Ba敏感（RR 4.1）。在最近的评估中检测到对Cry 11 Aa敏感性改变的早期迹象，表明这种毒素是施加选择压力的标志。RecBti幼虫也对其他控制剂，灭幼磷和灭幼脲敏感（RR 1.6）。解毒酶和-酯酶，谷胱甘肽-S-转移酶和混合功能氧化酶的活性被归类为不变的幼虫从两个世代（F-19和F-25），除了A -酯酶增加F-25。埃及伊蚊幼虫对Bti没有进化成对晶体的抗性，也没有记录到与替美磷和灭幼脲的交叉抗性，这支持它们与Bti一起可持续地用于综合防治实践。大多数解毒酶的活性不变，表明它们可能在Bti毒素的代谢中不起主要作用，因此通过这种机制产生的耐药性不太可能发生。这项研究还强调，需要建立适当的标准来分类幼虫的易感性/抗性的状态。
BackgroundBacillus thuringiensis svar. israelensis (Bti) is an effective and safe biolarvicide to control Aedes aegypti. Its mode of action based on four protoxins disfavors resistance; however, control in endemic areas that display high mosquito infestation throughout the year requires continuous larvicide applications, which imposes a strong selection pressure. Therefore, this study aimed to investigate the effects of an intensive Bti exposure on an Ae. aegypti strain (RecBti), regarding its susceptibility to Bti and two of its protoxins tested individually, to other control agents temephos and diflubenzuron, and its profile of detoxifying enzymes.MethodsThe RecBti strain was established using a large egg sample (10,000) from Recife city (Brazil) and more than 290,000 larvae were subjected to Bti throughout 30 generations. Larvae susceptibility to larvicides and the activity of detoxifying enzymes were determined by bioassays and catalytic assays, respectively. The Rockefeller strain was the reference used for these evaluations.ResultsBti exposure yielded an average of 74% mortality at each generation. Larvae assessed in seven time points throughout the 30 generations were susceptible to Bti crystal (resistance ratio RR 2.8) and to its individual toxins Cry11Aa and Cry4Ba (RR 4.1). Early signs of altered susceptibility to Cry11Aa were detected in the last evaluations, suggesting that this toxin was a marker of the selection pressure imposed. RecBti larvae were also susceptible (RR 1.6) to the other control agents, temephos and diflubenzuron. The activity of the detoxifying enzymes - and -esterases, glutathione-S-transferases and mixed-function oxidases was classified as unaltered in larvae from two generations (F-19 and F-25), except for a -esterases increase in F-25.ConclusionsProlonged exposure of Ae. aegypti larvae to Bti did not evolve into resistance to the crystal, and no cross-resistance with temephos and diflubenzuron were recorded, which supports their sustainable use with Bti for integrated control practices. The unaltered activity of most detoxifying enzymes suggests that they might not play a major role in the metabolism of Bti toxins, therefore resistance by this mechanism is unlikely to occur. This study also highlights the need to establish suitable criteria to classify the status of larval susceptibility/resistance.