Laboratory-based efficacy evaluation of Bacillus thuringiensis subspecies israelensis and temephos larvicides against larvae of Anopheles stephensi in Ethiopia

Background: Malaria, transmitted by the bite of infected female Anopheles mosquitoes, remains a global public health problem. The presence of an invasive Anopheles stephensi, capable of transmitting Plasmodium vivax and P. falciparum parasites was first reported in Ethiopia in 2016. The ecology of An. stephensi is different from that of An. arabiensis, the primary Ethiopian malaria vector, and this suggests that alternative control strategies may be necessary. Larviciding may be an effective alternative strategy, but there is limited information on the susceptibility of Ethiopian An. stephensi to common larvicides. This study aimed to evaluate the efficacy of temephos and Bacillus thuringiensis var. israelensis (Bti) larvicides against larvae of invasive An. stephensi. Methods: The diagnostic doses of two larvicides, temephos (0.25ml/l) and Bti (0.05mg/l) were tested in the laboratory against the immature stages (late third to early fourth stages larvae) of An. stephensi collected from the field and reared in a bio-secure insectary. Larvae were collected from two sites (Haro Adi and Awash Subuh Kilo). For each site, three hundred larvae were tested against each insecticide (as well as an untreated control), in batches of 25. The data from all replicates were pooled and descriptive statistics prepared. Results: The mortality of larvae exposed to temephos was 100% for both sites. Mortality to Bti was 99.7% at Awash and100% at Haro Adi site. Conclusions: Larvae of An. stephensiare susceptible to temephos and Btilarvicides suggesting that larviciding with these insecticides as vector control program may be effective against An. stephensi in these localities.