Background: In the 1970s, Anopheles farauti in the Solomon Island responded to indoor residual spraying with DDT by increasingly feeding more often outdoors and earlier in the evening. Although long-lasting insecticidal nets (LLINs) are now the primary malaria vector control intervention, only a small proportion of An. farauti still seeks blood meals indoors and late at night where they are vulnerable to being killing by contract with the insecticides in LLINs. The effectiveness of LLINs and indoor residual spraying (IRS) in controlling malaria transmission where the vectors are most exophagic and early biting will depend on whether the predominant outdoor or early biting phenotypes are associated with a subpopulation of the vectors present.
Methods: Mark-release-recapture experiments were conducted in the Solomon Islands to determine if individual Anopheles farauti repeat the same behaviours over successive feeding cycles. The two behavioural phenotypes examined were those on which the WHO recommended malaria vector control strategies, LLINs and IRS, depend: indoor and late night biting.
Results: Evidence was not found for subpopulations of An. farauti regarding time (early evening or late night) or location (indoor or outdoor) of blood feeding. Individual An. farauti did not consistently repeat the behavioural phenotype expressed for their original blood meal (e.g., while most mosquitoes that fed early and outdoors and would repeat those behaviours, some fed late at night and indoors in the next feeding cycle).
Conclusions: The finding that An. farauti is a homogeneous population is significant as all individual vectors can potentially be exposed to the insecticides used in insecticide treated nets (ITNs) or IRS. Across the multiple feeding cycles required to complete the extrinsic incubation period, individual females may enter houses late at night and potentially be exposed to insecticides in ITNs and IRS. This may explain, in part, the degree of control that LLINs and IRS have exerted against a predominantly outdoor feeding mosquito such as An. farauti. These findings may be applicable to the outdoor feeding vectors that dominate transmission in much of the malaria endemic world and justifies continued distribution of LLINs. However, the population-level tendency of mosquitoes to feed outdoors and early in the evening will require complementary interventions if malaria control can be accelerated towards elimination.e-recapture experiments were conducted in the Solomon Islands to determine if individual Anopheles farauti repeat the same behaviours over successive feeding cycles. The two behavioural phenotypes examined were those on which the WHO recommended malaria vector control strategies, LLINs and IRS, depend: indoor and late night biting.