Effects of cow dung and selected medicinal plants on anopheles species as a strategy for malaria vector control in Ahero rice irrigation scheme, Kenya

The control of malaria is complex and has previously focused on the use of drugs and chemicals targeting the parasite and the vectors respectively. However, this has been a challenge because the parasite and the vectors have developed resistance. However, integrated approaches that incorporate use of cow dung and plants products could increase the chances of malaria control. Deliberate organic contamination as a measure against mosquitoes has been shown to have a larvicidal effect but the findings have not been tested in semi-field conditions. For a long time, neem has been reported to possess larvicidal properties against mosquitoes. However, the combined effect of cow dung and neem on immature stages of Anopheles has not been investigated. This research was therefore designed to investigate the effect of cow dung alone and a combination of cow dung and neem on the immature stages of Anopheles mosquitoes. Despite the wide use of Artemisia annua in manufacture of malarial drugs little is known about its effect on the adult Anopheles species, the vector of malaria. This study was therefore undertaken to. investigate the effects A. annua on adult Anopheles mosquitoes. In the laboratory experiments, 10 individuals of each immature stage were placed in bowls containing either cow dung, neem alone or neem and cow dung combined. Mortality was recorded after 24 hours. Semi-field experiments were conducted in a screen house where sub-plots measuring 1.5 x 0.5 m were created. Cow dung, neem alone or cow dung combined with neem was added. 50 individuals of each immature stage were then introduced in each subplot and then mortality was recorded. In testing the effects of A. annua on adult Anopheles mosquitoes, crude extacts of A. annua were smeared on hands of human volunteers and subjected to 30 starved females. The number of mosquitoes that landed on hand with and without A. annua were counted and recorded after every 5 minutes for a period of I hour. Also the number of mosquitoes whose abdomens appeared reddish and dilated were counted and recorded at the end of the experiment. Analysis of variance tests was performed to determine the effect of cow dung, neem alone and a combination of neem with cow dung on the immature stages of Anopheles species in both the laboratory and the semi-field conditions. In evaluating the effect of A. annua against adult Anopheles mosquitoes, t-tests were performed to compare mean numbers of mosquitoes that landed and the means of fed and unfed mosquitoes. Results for laboratory experiments indicated that cow dung and neem individually caused significant mortality of immature stages of mosquitoes. Also, a combination of cow dung and neem caused higher mortality than cow dung, neem alone but the difference was not significant. In semi-field experiments, there was a significant difference in mortality between all the immature stages in sub-plots containing cow dung alone. The mortality was higher in sub-plots applied with a combination of cow dung and neem but as reported in the laboratory experiments the difference was not significant. In evaluating the effect of A. annua on Anopheles mosquitoes, the results showed that higher number of females landed and fed on the hands without A. annua than on hands applied with A. annua. However, efficacy of the latter reduced as time progressed. The findings of this study have demonstrated that cow dung, neem alone and a combination of neem and cow dung caused mortality of the immature stages and can thus be used to reduce abundance of larval stages in the mosquito breeding sites. It was also evident that, A. annua reduced the landing and feeding response of mosquitoes and could therefore be used to reduce human -vector contact.