Impact of feacal coliforms and interspecific cohabitation on the productivity of culicidae breeding sites, littoral-Cameroon

The demographic structure and emergence dynamics of Culicidae depend on biotic and abiotic interactions in the environment. The objective of this study is to determine the influence of bacteriological parameters, abundance, and interspecific cohabitation on the development of the pre-imaginal stages of Culicidae. Larvae were sampled using the “dipping” method and identified using dichotomous keys after rearing to adulthood; species of the Anopheles gambiae complex were distinguished using molecular techniques. The standard method for isolating and quantifying bacteria in water was used to quantify coliforms in water samples. The effect of density and interspecific cohabitation on the aquatic development of Culicidae was studied. The larvae were reared at different densities in a monospecific situation or in interspecific cohabitation. The number of individuals at each stage of development, the number of dead larvae, and the number of emergences were counted every 24 hours. The culicid fauna in Youpwé during the study period consisted of Culex quinquefasciatus (42.6%, n = 415), Anopheles coluzzii (39.8%, n = 388), and Aedes aegypti (17.6%, n = 171). Fecal coliforms were found at all breeding sites; the species identified were Enterobacter aerogenes (51.8%), Escherichia coli (6.5%), and Salmonella typhimurium (9.4%). A positive and significant correlation was observed between E. coli density and larval productivity of the genus Aedes (P-value = 0.002). In the laboratory, significantly slower pre-imaginal development was observed in a high-density interspecific cohabitation environment than in a monospecific environment. This was the case, for example, for the interspecific combination Anopheles gambiae/Culex quinquefasciatus, which had a significantly longer development time than Anopheles gambiae reared in a monospecific environment (P-value < 0.05). The same observation was made for the interspecific combination Anopheles culuzzii/Culex quinquefasciatus and Anopheles culuzzii in a monospecific environment (P-value ˂ 0.05). In addition, a bias in favor of females in interspecific cohabitation was noted. It would therefore be appropriate, based on the results of more specific work on the mechanisms influencing fecal coliforms, to move towards integrated vector management. This requires the integration of sex ratio and cohabitation into entomological surveillance programs.