Efficacy of the mermithid nematode, Romanomermis iyengari, for the biocontrol of Anopheles gambiae, the major malaria vector in sub-Saharan Africa

Abstract

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. There is an urgent need for malaria control programmes to adopt more integrated mosquito management approaches that include sustainable, nonchemical solutions. The mermithid nematode Romanomermis iyengari is one of several natural control alternatives to synthetic pesticides for mosquito suppression. This study evaluated the effectiveness of the nematode R. iyengari for control of Anopheles gambiae . Methods The nematode R. iyengari was mass-produced, and pre-parasitic stage (J2) were used for laboratory and field experiments. In laboratory experiments, two concentrations of pre-parasitics (5 and 10 J2 per larva) were tested against first- (L1), second- (L2) and third-instar (L3) larvae of An. gambiae . Infected larvae were observed daily to determine their mortality rate and the number of post-parasitic nematodes emerging from dead larvae. In field experiments, 3500, 4000 and 5000 J2/m 2 were sprayed in separate natural Anopheles breeding sites. After treatment, the larval mosquito density in the breeding sites was assessed every 5–7 days. Results Laboratory results showed that larval An. gambiae is susceptible to nematode infection: 100% L1 larvae died within 24 hours post-treatment, and 100% of both L2 and L3 larvae died within 7 days, regardless of nematode concentrations. The average number of post-parasitic nematodes emerging per larva increased with increasing nematode concentration. In field experiments, the monthly applications of 3500 to 5000 pre-parasitic nematodes per m 2 eliminated larval mosquito development in Anopheles - and mixed breeding sites. Larval mosquito density dramatically decreased five days after the first treatment in all treated sites and was maintained at a very low level during the whole experimental period. Basically, only early instar larva were detected in treated sites throughout the test period. The average number of post-parasitic nematodes emerging per larva collected in treated sites was 1.45, 2, and 5.7 respectively for sites treated with 3500, 4000, and 5000 J2/m 2 . Conclusions Malaria mosquito larvae is susceptible to R. iyengari infection in West Africa. Parasitism intensity depends on tested nematode concentrations. Monthly application of 3500 J2/ m 2 was enough to control effectively larval An. gambiae in wetlands and f...

The need for new vector control approaches targeting outdoor biting anopheline malaria vector communities

“…For example, laboratory and field tests conducted in Benin showed that treatment of larval breeding sites with eggs of the nematode Romanomermis iyengari significantly reduced An. gambiae larvae density [94]. Early larval stages are more susceptible to infection, hence nematode control should be applied shortly after rainfall and relies on extensive surveying of breeding sites.…”

Mosquito-Borne Diseases Emergence/Resurgence and How to Effectively Control It Biologically

“…quinquefasciatus, and An. gambiae [226][227][228][229]. As they are naturally adapted to their host, such nematodes are highly specific to theirs hosts, which they can kill by producing high levels of parasitism.…”

The parasitic impact of Romanomermis iyengari Welch (Nematoda: Mermithidae) on the survival and biology of the common mosquito, Culex pipiens L. (Diptera: Culicidae)

“…They are obligate endoparasites of at least 100 species of mosquito larvae (Platzer 2007). The ease of application, environmental safety, host specificity, lethality, practical methods of in vivo mass rearing and achievability of long-term recycling make mermithid nematodes ideal biological control agents (Abagli et al 2019).…”

“…Likewise, Pérez-Pacheco et al (2015) examined the susceptibility of culicine mosquito larvae to R. iyengari. In laboratory experiments, Abagli et al (2019) showed that all Culex quinquefasciatus Say, 1823 instar larvae were susceptible to R. iyengari infection. Moreover, Pérez-Pacheco et al ( 2015) demonstrated that the 3 rd instar larvae of Aedes aegypti (Linnaeus, 1762), Anopheles pseudopunctipennis Theobald and Cx.…”