Browsing by Author "Justinian, Amos"

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Evaluation of autodissemination technique using novaluron against anopheles arabiensis under semi-field conditions in south-eastern Tanzania
(NM-AIST, 2022-08) Justinian, Amos
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.
Susceptibility status of major malaria vectors to novaluron, an insect growth regulator South-Eastern Tanzania
(Pan African Medical Journal, 2022-04-05) Justinian, Amos; Muyaga, Letus; Ngowo, Halfan; Urio, Naomi; Vianney, John‑Mary; Lwetoijera, Dickson
Introduction: application of Insect Growth Regulator (IGR) such as pyriproxyfen has shown a promising result in controlling malaria transmitting mosquitoes through autodissemination technique. Novaluron that inhibits the chitin development at mosquito larval stage present a promising candidate IGR for rotation with pyriproxyfen to prevent a chance of resistance development. This study assessed the susceptibility of immature stages of Anopheles arabiensis, Anopheles gambiae and Anopheles funestus to novaluron. Methods: susceptibility bioassays using technical grade novaluron (98% active ingredient) were performed inside the semi-field system using first instar larvae of Anopheles species. For each tested species, a total of 1500 larvae were used in the bioassay. Concentration range 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 by using log-dose response analysis. Results: of the tested mosquitoes, Anopheles 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, 0.332 and 2.001 respectively. For An. arabiensis were 0.026, 0.546 and 2.013; and for An. funestus were 0.032, 1.00 and 5.580. High larval mortality was recorded at high concentration (2mg/L), with 80% mortality within 3 days post exposure. Conclusion: the study demonstrates the efficacy of novaluron in controlling Anopheles mosquito species at immature stages via larval mortality. These findings warrant further testing of novaluron for autodissemination by different vector species for its inclusion in rotation to prevent development of resistance.