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Wyatt Collins
Wyatt Collins

Azederach



Synthetic insecticides are employed in the widely-used currently favored malaria control techniques involving indoor residual spraying and treated bednets. These methods have repeatedly proven to be highly effective at reducing malaria incidence and prevalence. However, rapidly emerging mosquito resistance to the chemicals and logistical problems in transporting supplies to remote locations threaten the long-term sustainability of these techniques. Chinaberry (Melia azederach) extracts have been shown to be effective growth-inhibiting larvicides against several insects. Because several active chemicals in the trees' seeds have insecticidal properties, the emergence of resistance is unlikely. Here, we investigate the feasibility of Chinaberry as a locally available, low-cost sustainable insecticide that can aid in controlling malaria. Chinaberry fruits were collected from Asendabo, Ethiopia. The seeds were removed from the fruits, dried and crushed into a powder. From developmental habitats in the same village, Anopheles arabiensis larvae were collected and placed into laboratory containers. Chinaberry seed powder was added to the larval containers at three treatment levels: 5 g m-2, 10 g m-2 and 20 g m-2, with 100 individual larvae in each treatment level and a control. The containers were monitored daily and larvae, pupae and adult mosquitoes were counted. This experimental procedure was replicated three times.




azederach



In this study we confirm and quantify the potency of Chinaberry in preparation for such a study. We present laboratory evidence that the powdered seed of the Chinaberry tree (Melia azederach) can decrease mosquito numbers through a strong growth-inhibiting larvicidal effect when applied to aquatic developmental habitat of the common African malaria vector Anopheles arabiensis. The result is a method of malaria mosquito population control that does not depend on outside support, and may provide villagers with a sustainable, ecologically sound means of reducing mosquito abundance. The abundant Chinaberry tree may therefore offer a potential sustainable additional malaria control tool that does not suffer from the aforementioned problems with ITN and IRS.


The presented results show that the Chinaberry tree (Melia azederach) has highly significant growth-inhibiting larvicidal effects on the malaria vector An. arabiensis, the most abundant malaria vector in Asendabo, Ethiopia. The inhibition of emergence (IE) was 100% or near 100% for all of the trials in both experimental replicates. These results are encouraging, and will support the design of a field trial in Asendabo to ascertain efficacy when this technique is applied within a village. The IE is expected to be lower in a field trial than in the carefully controlled, idealized laboratory setting. This may be partly due to wind gusts blowing the powdered seeds on the surface of larger pools to one side of the pool, leaving areas of pool surface without seed. In smaller pools this is not likely to be a significant problem. IE in the field may also be lower than in the laboratory because alternative particulate nutrient sources (such as wind-dispersed maize pollen, for example) can collect on the surface film, reducing the likelihood that anopheline larvae will take the powdered Chinaberry seed as a food source. The presence of such alternate, non-toxic nutriment sources may reduce the uptake of the powdered seed by the immature larvae. Nevertheless, the strong results of this laboratory study confirm that Chinaberry seed is a powerful growth-inhibiting larvicide when used against Anopheles arabiensis. The next step in this research is a field trial, conducted in Asendabo.


The presented laboratory tests have shown that powdered Chinaberry (Melia azederach) seed has very potent growth-inhibiting larvicide properties against Anopheles arabiensis, the dominant malaria vector in the region of Jimma, Ethiopia as well as much of Africa. At moderate treatment levels of 5 grams per square meter of water, the inhibition of emergence was 93%, and at 10 grams per square meter, laboratory tests with 100 individuals showed complete inhibition of emergence. No adult mosquitoes emerged from treated water. A rudimentary survey suggests that enough Chinaberry seed exists in the study village of Asendabo to suppress mosquito populations and thus diminish vectorial capacity. Both of these observed results suggest that field trials using Chinaberry seed are necessary, feasible and likely to succeed. Although this method will most likely not (and probably should not) replace currently employed malaria control strategies, it may offer an additional tool to be used in an integrated approach to combat malaria that is completely sustainable. Future field studies will seek to confirm the efficacy of Chinaberry seed to combat Anopheles arabiensis mosquitoes at the village scale.


One of the most interesting (rent-paying) deciduous trees for small gardens is Melia azederach, the 'chinaberry', 'bead tree' or 'Persian Lilac'. It is native to the warm-temperate belt stretching from the Middle East, through India to China and South East Asia and down to Australia. 041b061a72


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