Efficacy of the insect parasitic nematode, Romanomermis iyengari, for malaria vector control in Benin West Africa

Background

The intensive use of chemical insecticides against mosquitoes has led to the development of widespread insecticide resistance. Control of Anopheles mosquitoes in malaria-endemic areas of Sub-Saharan Africa has become increasingly difficult [1]. There is an urgent need for malaria control programs to adopt more integrated mosquito management approaches that include sustainable, non-chemical solutions. In this perspective, insect parasitic nematodes specific to mosquitoes [2, 3] may be considered as alternatives, to help reduce reliance on insecticides, and concurrently help insecticide resistance management. The present work has tested the effect of the Mermithid nematode, Romanomermis iyengari, against Anopheles gambiae s.s. Giles in laboratory and field conditions in Benin, West Africa.

Materials and methods

The nematodes R. iyengari were mass produced and the pre-parasitic juvenile (J2) were used in all laboratory and field experiments. Under laboratory conditions, 2 different concentrations of pre-parasitic nematodes (5 and 10 J2 per larvae) were tested against first to third instar (L1, L2 and L3) larvae of An. gambiae. In field, the pre-parasitic nematodes were monthly sprayed into 2 different Anopheles natural breeding sites in Cotonou, south Benin; 3500 and 5000 J2 per square meter of stagnant water were released, respectively in site 1 and 2.

Results

Results indicated that in laboratory, 100% L1 larvae died within 24 hours post-infection and 100% of both L2 and L3 larvae died within 7 days post-infection, regardless of nematode concentration. In field, Anopheles larval density 5 days post-application decreased from 35 larvae per liter to 4 larvae, and from 17 larvae to 1, respectively in site 1 and 2. During a whole rainy season in 2011, monthly nematodes spraying resulted in suppression of larval An. gambiae in treated sites.

Conclusions

The present study indicated that the Mermithid nematode R. iyengari is effective for malaria vector control in Benin, West Africa. R. iyengari mass production using local materials is easy. Integrating this nematode into An. gambiae management system is therefore possible.