Evaluation of autodissemination technique using novaluron against anopheles arabiensis under semi-field conditions in south-eastern Tanzania

Abstract

This study assessed the susceptibility of immature stages of An. arabiensis, An. gambiae and An. funestus to novaluron and the autodissemination technique using An. arabiensis. Susceptibility bioassays using technical grade novaluron (98% active ingredient) were performed inside the semi-field system using first instar larvae of the mosquito test species. A total of 1500 larvae were exposed to novaluron within three replicates of control and treatment assays. Concentration ranges of 0.01 mg/l to 2 mg/l of novaluron were tested to establish lethal concentration (LC) sufficient to kills 50%, 90% and 99% of the exposed larvae (LC50, LC90 and LC99) by using log-dose response analysis. The autodissemination experiment exposed 2500 mated female blood fed An. arabiensis mosquitoes (aged 6-7 days) to both contaminated and uncontaminated clay pots. In two each chambers in the semi-field tunnel cage; an artificial breeding habitats were provided in each chamber to assess the autodissemination. The successful autodissemination and contamination was assessed by comparing larval mortality from treated and untreated chambers. An. gambiae were highly susceptible to novaluron followed by An. arabiensis and then An. funestus. Lethal concentrations, LC50, LC90 and LC99 (95%CI) in mg/l for An. gambiae were 0.018 (0.016-0.020), 0.546 (0.374-0.719) and 2.001 (1.986-3.206) respectively. For An. arabiensis were 0.032 (0.027- 0.038), 0.332 (0.168-0.496) and 2.013 (1.997-4.491); and for An. funestus were 0.02561 (0.02140- 0.0299), 1 (0.4657-1.5347) and 5.580 (4.687-8.496). High larval mortality was recorded at high concentration (2mg/L) for all species, with 80% mortality within 3 days post exposure. Similarly, low larval mortality was observed at low concentration (0.1 mg/L) (for all species) with 80% mortality within 9 days post exposure. There were no evidence of autodissemination following adults’ exposure to novaluron. The results showed no significant difference between treatment and control cups when An. arabiensis larvae were exposed to the water samples from the breeding habitats. The study demonstrates the efficacy of novaluron against immature stages of susceptible and resistant Anopheles mosquito species. The findings present a promising candidate IGR for rotation to counteract the insecticide resistance development. Moreover, these results warrant further evaluation of novaluron for autodissemination by vector species for its inclusion in rotation to prevent evolution of resistance in both chemistries.