Environmental Health and Ecological Sciences Department, Ifakara Health Institute, P.O. Box 53, Ifakara, Tanzania.
Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, UK.
Sci Rep. 2024 Jan 10;14(1):1002. doi: 10.1038/s41598-024-51152-1.
Effective larviciding for malaria control requires detailed studies of larvicide efficacies, aquatic habitat characteristics, and life history traits of target vectors. Mosquitoes with brief larval phases present narrower timeframes for biolarvicidal effects than mosquitoes with extended periods. We evaluated two biolarvicides, VectoBac (Bacillus thuringiensis israelensis (Bti)) and VectoMax (Bti and Bacillus sphaericus) against Anopheles funestus and Anopheles arabiensis in shaded and unshaded habitats; and explored how larval development might influence retreatment intervals. These tests were done in semi-natural habitats using field-collected larvae, with untreated habitats as controls. Additionally, larval development was assessed in semi-natural and natural habitats in rural Tanzania, by sampling daily and recording larval developmental stages. Both biolarvicides reduced larval densities of both species by >98% within 72 h. Efficacy lasted one week in sun-exposed habitats but remained >50% for two weeks in shaded habitats. An. funestus spent up to two weeks before pupating (13.2(10.4-16.0) days in semi-natural; 10.0(6.6-13.5) in natural habitats), while An. arabiensis required slightly over one week (8.2 (5.8-10.6) days in semi-natural; 8.3 (5.0-11.6) in natural habitats). The findings suggest that weekly larviciding, which is essential for An. arabiensis might be more effective for An. funestus whose prolonged aquatic growth allows for repeated exposures. Additionally, the longer residual effect of biolarvicides in shaded habitats indicates they may require less frequent treatments compared to sun-exposed areas.
有效控制疟疾需要对杀幼虫剂的功效、水生栖息地特征和目标病媒的生活史特征进行详细研究。幼虫期较短的蚊子比幼虫期较长的蚊子对生物杀幼虫剂的作用时间更窄。我们评估了两种生物杀幼虫剂，VectoBac（苏云金芽孢杆菌以色列亚种（Bti））和 VectoMax（Bti 和球形芽孢杆菌）对致倦库蚊和阿巴蚊在遮荫和非遮荫栖息地的效果；并探讨了幼虫发育如何影响重复处理间隔。这些测试是在半自然栖息地中使用野外收集的幼虫进行的，未处理的栖息地作为对照。此外，在坦桑尼亚农村的半自然和自然栖息地中评估了幼虫发育情况，每天采样并记录幼虫发育阶段。两种生物杀幼虫剂在 72 小时内将两种蚊的幼虫密度降低了>98%。在阳光照射的栖息地，功效持续一周，但在遮荫的栖息地仍保持>50%两周。致倦库蚊化蛹前最长需要两周（半自然中 13.2(10.4-16.0)天；自然中 10.0(6.6-13.5)天），而阿巴蚊则略超过一周（半自然中 8.2(5.8-10.6)天；自然中 8.3(5.0-11.6)天）。这些发现表明，每周进行一次杀幼虫处理对于阿巴蚊是必要的，而对于致倦库蚊可能更为有效，因为其延长的水生生长允许重复暴露。此外，遮荫栖息地中生物杀幼虫剂的残留效果较长表明它们可能比阳光照射的区域需要更频繁的处理。
