Abstract
BackgroundThe larvicidal efficacy of the naturally derived insecticide spinosad, for control of immature stages of Anopheles albimanus and associated culicids, was compared to that of synthetic and biological larvicides. Effects on non-target insects were also determined.MethodsA field trial was performed in replicated temporary pools during the rainy season, in southern Mexico. Pools were treated with 10 ppm a.i. spinosad (Tracer 480SC), Bti granules applied at 2 kg/ha (VectoBac WDG, ABG-6511), and 100 ml/ha temephos (50 EC), or an untreated control. Numbers of immature mosquitoes, and aquatic insects in pools were monitored for 20 weeks.ResultsSamples of immature mosquitoes comprised approximately 10% An. albimanus, 70% Culex spp. (mostly Cx. melanoconion and Cx. coronator) and 20% Uranotaenia lowii. The most effective larvicides were spinosad and temephos that eliminated An. albimanus in 16 out of 20 post-treatment samples, or 9 weeks of continuous control of immature stages, respectively. These larvicides resulted in 15 and 5 weeks of elimination of Culex spp., respectively, or 20 and 4 weeks of continuous elimination of U. lowii, respectively. Bti treatment provided little consistent control. Aquatic insects were recorded comprising 3 orders, 20 families, 40 genera and 44 species. Shannon diversity index values (H’) for aquatic insects were highest in the control (0.997) and Bti (0.974) treatments, intermediate in the spinosad treatment (0.638) and lowest in the temephos treatment (0.520). Severely affected non-target insects in the spinosad and temephos treated pools were predatory Coleoptera, Hemiptera and Odonata, which in the case of spinosad was likely due to the high concentration applied. Bti had little effect on aquatic insects.ConclusionsThe spinosad treatment retained larvicidal activity for markedly longer than expected. Spinosad is likely to be an effective tool for control of anopheline and other pool-breeding mosquitoes in tropical regions. Non-target effects of spinosad on aquatic insects merit further study, but were likely related to the concentration of the product used.
Highlights
The larvicidal efficacy of the naturally derived insecticide spinosad, for control of immature stages of Anopheles albimanus and associated culicids, was compared to that of synthetic and biological larvicides
In previous studies we reported that spinosad at concentrations between 1 and 10 parts per million was a highly effective larvicide against Aedes aegypti, Aedes albopictus and Culex spp. that develop in water containers or abandoned car tires in urban or peri-urban habitats in Mexico [12,13,14,15]
We addressed the issue of the impact of these products on aquatic insect diversity, including species that predate immature mosquitoes, in the temporary pools
Summary
The larvicidal efficacy of the naturally derived insecticide spinosad, for control of immature stages of Anopheles albimanus and associated culicids, was compared to that of synthetic and biological larvicides. Temporary freshwater pools are island habitats that vary widely in the diversity of their macroinvertebrate fauna. Many species of anopheline and culicid mosquitoes exploit temporary pools as oviposition sites across a diversity of natural, agricultural and urban environments. The rapid warming of water temperatures in pools and the presence of organic matter, such as leaf litter or algae, provide conditions suitable for the rapid development of mosquito immature stages [4]. Such pools attract a number of mosquito predators, including amphibians, insects and crustaceans for which immature mosquitoes can be an important component of their diet. To improve the likelihood of offspring survival, mosquitoes tend to avoid oviposition in pools that contain predators [5], a process that appears to involve chemically-mediated detection of predator-related kairomones [6]
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