An investigation into the robustness of insectary-reared Anopheles Arabiensis for use in the Sterile Insect technique for controlling malaria.

Abstract

Human malaria is one of the deadliest vector-borne diseases in the world and is caused by parasites of the genus Plasmodium that are transmitted via mosquitoes of the genus Anopheles. The highest impact of malaria can be seen in Africa, where 90% of worldwide deaths occur. Although current vector control strategies include biological control, chemical application and environmental management, there is renewed interest in the Sterile Insect Technique (SIT). SIT involves the mass production of the target population, in this study Anopheles arabiensis Patton, sterilizing the males with ionizing radiation and, thereafter, the mass release of these sterile males into the natural environment. The subsequent mating of the sterile males with the wild females should result in a decrease, and ultimately the elimination, of the natural An. arabiensis population. However, for SIT to be successful, the insectary-reared males need to compete effectively with their wild counterparts for female insemination. This study was conducted to determine if the laboratory-reared males would be able to compete successfully with the wild male population in northern KwaZulu-Natal. Standard testing protocols were taken from the Malaria Research Unit, World Health Organization, as well as methods proposed by the National Health Laboratory Services. The collection of mosquitoes from the target area indicated that An. arabienis is a seasonal species with populations increasing during warmer conditions. The mating compatibility between the three tested strains of An. arabiensis, namely the Old Mamfene strain (laboratory strain), New Mamfene Strain (wild strain) and the Genetic Sexing Strain, proved favorable due to statistically non-significant insemination rates. However, the results indicated that the laboratory-reared colony displayed greater fecundity and mean numbers of larvae hatched than the wild colony. Within strains, overcrowding of larvae affected the size of the male adults, although reduced size did not affect mating within each strain, as insemination rates were not statistically affected (p>0.05). Dyes were tested to track mating between sterile males and wild females. However, dye transfer from male to female during copulation resulted in mating compatibility being negatively affected. Further investigations are thus needed to determine a better approach to tracking females that have copulated with released males. Although the results indicate that laboratory-reared males can compete successfully with their wild counterparts, field studies are required to verify these laboratory results.