Experimental evaluation of entomopathogenic fungi for the biological control of philebotomine sand flies (diptera psychodidae)

Abstract

The leishmaniases are some of the WHO's neglected tropical diseases which pose threat to human life in both the New and Old World. They are mostly transmitted through the bite of infected sand flies. The disease affects the poor from the third world. Disease control through chemotherapy is logistically difficult, toxic, expensive and out of reach for many. Entomopathogenic fungi (EPF) hold great potential as alternative vector control. These fungi infect the host through the cuticle. They are friendlier to non-target organisms than synthetic chemical insecticides. Although EPF are widely used to control agricultural pests, few attempts have been made to develop them as biocontrol agents of disease vectors like phlebotomine sand flies. The study had two phases: laboratory and field based studies. Isolates were cultured on Sabourand dextrose agar (SDA) in Petri dishes and incubated at room temperature (22-28 DC).In the laboratory, sand flies were exposed to 0.3 g of dry conidia evenly spread on a cotton velvet cloth covering the inner side of a cylindrical plastic tube (95x48 mm diam). Control flies were not exposed to any conidia. Mortality was recorded daily until all the sand flies died. The study tested 16 isolates of Metarhizium anisopliae and 3 of Beauveria bassiana to adult sand fly spp of Phlebotomus duboscqi in the laboratory. All the fungal isolates were pathogenic to the test-insect, causing mortality of between 76.8 and 100%. The (LTso) and (LT90) ranged from 3.0-7.8 days and from 5.3-16.2 days, respectively. One of the most virulent isolates of M anisopliae was tested in the field at Rabai in Marigat Division, Baringo County. Dry conidia of the fungi (2.0 x 1014 ) were introduced into ten termite mounds through the shafts using a modified foot pump. Preliminary results indicate that application of the fungus in termite mounds resulted in three to ten-fold reduction in the population of sand flies after 8 weeks. Two weeks after introduction of the conidia, the longevity of sand flies collected from treated termite mounds was shorter than those in the control mounds. Sand flies from the treated mounds died within 9 days whereas over 90% of sand flies collected from the untreated control termite mounds survived for more than 21 days. These results clearly demonstrate the potential of EPF as a biological control of phlebotomine sand flies. Further studies to determine the best methods for delivery and application in the diverse ecological settings of various leishmaniasis vectors are therefore recommended.