Insecticidal effect of ethnobotanical plant extracts against Anopheles arabiensis under laboratory conditions.

BACKGROUND: The emergence and spread of resistant strains of malaria vectors to chemical insecticides are becoming major problems for malaria vector management. Natural plant products have a vital role to play in the current challenge of malaria control. The current study was conducted to evaluate insecticidal effect of ethnobotanical plant extracts against the primary malaria vector, Anopheles arabiensis in northwestern Ethiopia. METHODS: Primarily, ethnobotanical plants used for Anopheles mosquito control were surveyed in Dangur district, northwestern Ethiopia. Insecticide-susceptible strains of Anopheles arabiensis mosquito were reared in the insectary of the Tropical and Infectious Diseases Research Centre, Assosa University. After surveying plants used for mosquito control in local people, four frequently used plants were identified for extraction. The larvicidal and adulticidal potential of frequently used plant extracts against susceptible strains of the laboratory colony were evaluated. RESULTS: A total of 15 plants were identified as ethnobotanical plants that help local people with mosquito control. Azadirachta indica, Ocimum lamiifolium, Ocimum americanum, Moringa olifeira leaf, and Moringa olifeira seed species of local plants were found to be frequently used to kill and/or repel mosquitoes in the study district. All the plant extracts were found to have potential larvicidal activity against fourth instar larvae of An. arabiensis and only ethanol and methanol extract of Azadirachta indica and Ocimum lamiifolium were found to have potential adulticidal effect against adult of An. arabiensis. The highest larvicidal activity was observed in ethanol extract of Azadirachta indica with 95% larval mortality and lowest Lethal Concentration 50 (LC 50) of 40.73parts per million (ppm) and LC90 of 186.66 ppm. The highest adulticidal activity was observed in methanol extract of Azadirachta indica with 75% adult mortality at 300 ppm and lowest LC50 of 106.65 ppm and LC90 of 1,293 ppm. The lowest larvicidal and adulticidal activity was observed in methanol extracts of Ocimum lamiifolium with 63.35% larval mortality and leaf extract of Moringa olifeira with 50% adult mortality at 300 ppm, respectively. CONCLUSION: Ethanol extract of Azadirachta indica exerted a remarkable larvicidal effect against An. arabiensis and thus it can be used for botanical mosquito insecticide development. Since the current finding is based on susceptible strain of An. arabiensis, further work on wild mosquitoes is recommended.

An update on the distribution, bionomics, and insecticide susceptibility of Anopheles stephensi in Ethiopia, 2018-2020.

BACKGROUND: Anopheles stephensi, an invasive malaria vector, was first detected in Africa nearly 10 years ago. After the initial finding in Djibouti, it has subsequently been found in Ethiopia, Sudan and Somalia. To better inform policies and vector control decisions, it is important to understand the distribution, bionomics, insecticide susceptibility, and transmission potential of An. stephensi. These aspects were studied as part of routine entomological monitoring in Ethiopia between 2018 and 2020. METHODS: Adult mosquitoes were collected using human landing collections, pyrethrum spray catches, CDC light traps, animal-baited tent traps, resting boxes, and manual aspiration from animal shelters. Larvae were collected using hand-held dippers. The source of blood in blood-fed mosquitoes and the presence of sporozoites was assessed through enzyme-linked immunosorbent assays (ELISA). Insecticide susceptibility was assessed for pyrethroids, organophosphates and carbamates. RESULTS: Adult An. stephensi were collected with aspiration, black resting boxes, and animal-baited traps collecting the highest numbers of mosquitoes. Although sampling efforts were geographically widespread, An. stephensi larvae were collected in urban and rural sites in eastern Ethiopia, but An. stephensi larvae were not found in western Ethiopian sites. Blood-meal analysis revealed a high proportion of blood meals that were taken from goats, and only a small proportion from humans. Plasmodium vivax was detected in wild-collected An. stephensi. High levels of insecticide resistance were detected to pyrethroids, carbamates and organophosphates. Pre-exposure to piperonyl butoxide increased susceptibility to pyrethroids. Larvae were found to be susceptible to temephos. CONCLUSIONS: Understanding the bionomics, insecticide susceptibility and distribution of An. stephensi will improve the quality of a national response in Ethiopia and provide additional information on populations of this invasive species in Africa. Further work is needed to understand the role that An. stephensi will have in Plasmodium transmission and malaria case incidence. While additional data are being collected, national programmes can use the available data to formulate and operationalize national strategies against the threat of An. stephensi.