Behavioural heterogeneity of Anopheles species in ecologically different localities in Southeast Asia:: a challenge for vector control

In Southeast Asia the biodiversity of Anopheles species in the domestic environment is very high. Only few species are considered major vectors throughout the region, whereas the vector status of other species varies from area to area. Often it is difficult to identify an Anopheles species as a malaria vector in areas with low malaria incidence. The behaviour of Anopheles species largely determines their vector status, and insights into their behaviour are essential to evaluate the appropriateness of vector control measures. This study was conducted in six ecologically different localities in Southeast Asia to rank the different Anopheles species in terms of anthropophily and endophagy in order to estimate their current epidemiological importance. Concurrently, the biting and resting behaviour of the vectors was analysed to evaluate the appropriateness of insecticide-impregnated bed nets and residual house spraying in vector control. Anopheles dirus A was highly anthropophilic at all sites where it occurred. By contrast, the degree of anthropophily exhibited by An. minimus A depended on availability of cattle. Anopheles campestris, An. nimpe, An. sinensis, An. maculatus, An. aconitus showed a high degree of anthropophily in certain villages, indicating their potential of participating in malaria transmission, although the actual incidence of malaria in the study villages can be fully explained by transmission of the major vectors (An. dirus A, An. minimus A and An. sundaicus). Late biting of An. minimus A and biting activity throughout the night of An. sundaicus favour bed nets as a control method for these species, whilst exophilic and outdoor biting in combination with early feeding behaviour of An. dirus A will make both insecticide-impregnated bed nets and indoor residual spraying less suitable for controlling this species. Spatial variation in biting and resting behaviour was observed within almost all Anopheles species. These heterogeneities may result in the differences in epidemiological importance and in response to vector control of Anopheles species in different areas. Moreover, environmental changes and changes in human practice are expected to influence the behaviour, hence the role of the different species in malaria transmission. The effect of environmental changes on vector behaviour should be followed up carefully.