Despite increasing reports and concerns about resistance development to public-health insecticides in malaria-vectors, significant steps have been put into the quest for novel strategies to disrupt the disease transmission cycle by targeting insect-vectors hence sustaining vector management. This study evaluates the toxicity potential of oils of insecticidal plants shortlisted in an ethnobotanical survey on the larvae and adult stages of Anopheles gambiae. Oils from leaves of Hyptis suaveolens, Ocimum gratissimum, Nicotiana tabacum, Ageratum conyzoides and fruit-peel of Citrus sinensis were extracted by steam-distillation using a Clevenger apparatus. Larvae and female adults of deltamethrin susceptible Anopheles gambiae were gotten from an already established colony in the Entomological Research Laboratory, University of Ilorin. Twenty-five third instar stage larvae were used for larvicidal assays while twenty 2-5 days old adults were used for the adulticidal assays in five replicates. After which, coupled gas chromatography-mass spectrometry analysis (GC-MS) was performed to determine the major chemical-constituents of plant oils. A. gambiae exposed to H. suaveolens and C. sinensis demonstrated significantly higher larval toxicity (94.7-100%) after 24 hours. At 48 hours, the mortality induced by the oils of the four plants peaked at 100%. N. tabacum (0.50 mg/ml) induced the highest percentage adult mortality (100%) on A. gambiae which compared favourably with the positive control Deltamethrin (0.05%). The lowest KdT₅₀ was observed with 0.25 mg/ml of N. tabacum (20.3 minutes) while the lowest KdT₉₅ was observed with 0.10mg/ml of A. conyzoides (35.97 mins) against adult A. gambiae. D-limonene is the key chemical-constituent in oils from C. sinensis and A. conyzoides. The significant larval and adult mortality rates, lower lethal concentration and knockdown times demonstrated by the evaluated plant oils showed promising outcomes that can be further developed for vector control management.

中文翻译：

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实验室条件下选定的杀虫植物油对冈比亚按蚊（双翅目：Culicidae）的毒性潜力

尽管关于疟疾媒介对公共卫生杀虫剂产生耐药性的报道和担忧越来越多，但已经采取了重要步骤来寻求新的策略，通过针对昆虫媒介从而维持媒介管理来破坏疾病传播周期。本研究评估了在冈比亚按蚊幼虫和成虫阶段的民族植物学调查中入围的杀虫植物油的毒性潜力。使用 Clevenger 装置通过蒸汽蒸馏提取来自Hyptis suaveolens、Ocimum gratissimum、Nicotiana tabacum、Ageratum conyzoides和Citrus sinensis果皮的油。溴氰菊酯易感冈比亚按蚊的幼虫和雌性成虫是从伊洛林大学昆虫学研究实验室的一个已经建立的群体中获得的。25 只三龄幼虫用于杀幼虫试验，而 20 只 2-5 天大的成虫用于 5 次重复的杀成虫试验。之后，进行气相色谱-质谱联用分析 (GC-MS) 以确定植物油的主要化学成分。A. gambiae暴露于H. suaveolens和C. sinensis在 24 小时后表现出显着更高的幼虫毒性 (94.7-100%)。在 48 小时时，四种植物的油引起的死亡率达到 100% 的峰值。N. tabacum (0.50 mg/ml) 对A. gambiae的成人死亡率百分比最高 (100%)与阳性对照溴氰菊酯 (0.05%) 相比具有优势。用 0.25 mg/ml 的普通烟草（20.3 分钟）观察到最低的 KdT ₅₀ ，而用 0.10mg/ml 的A. conyzoides（35.97 分钟）观察到最低的 KdT _95对成虫冈比亚。D-柠檬烯是C. sinensis和A. conyzoides 油中的关键化学成分。评估的植物油显示出显着的幼虫和成虫死亡率、较低的致死浓度和击倒时间，显示出可进一步开发用于病媒控制管理的有希望的结果。