Unique fine scale village spatial-temporal distributions of Anopheles farauti differ by physiological state and sex

Abstract

Background: The ecology of many mosquitoes, including Anopheles farauti, the dominant malaria vector in the southwest Pacific including the Solomon Islands, remains inadequately understood. Studies to map fine scale vector distributions are biased when trapping techniques use lures that will influence the natural movements of mosquitoes by attracting them to traps. However, passive collection methods allow the detailed natural distributions of vector populations by sex and physiological states to be revealed.

Methods: The barrier screen, a passive mosquito collection method along with human landing catches were used to record An. farauti distributions over time and space in two Solomon Island villages from May 2016 to July 2017.

Results: Temporal and spatial distributions of over 15,000 mosquitoes, including males as well as unfed, host seeking, blood-fed, non-blood fed and gravid females were mapped. These spatial and temporal patterns varied by species, sex and physiological state. Sugar-fed An. farauti were mostly collected between 10-20 m away from houses with peak activity from 18:00 to 19:00 h. Male An. farauti were mostly collected greater than 20 m from houses with peak activity from 19:00 to 20:00 h.

Conclusions: Anopheles farauti subpopulations, as defined by physiological state and sex, are heterogeneously distributed in Solomon Island villages. Understanding the basis for these observed heterogeneities will lead to more accurate surveillance of mosquitoes and will enable spatial targeting of interventions for greater efficiency and effectiveness of vector control.

Keywords: Anopheles farauti; Barrier Screen; Males; Solomon Islands; Sugar-feds.

Fig. 1

Map of Solomon Islands and showing Haleta village on Nggela Sule Island in Central Province and Jack Harbour village on Kolombangara Island in Western Province

Fig. 2

Village maps of Jack Harbour (a) and Haleta (b) showing all locations where barrier screens (red) and human landing catch stations (green) were located, as well as houses (circles) and primary larval habitat (blue)

Fig. 3

Densities of An. farauti on barrier screens by time. a Unfed females. b Blood-fed females. c Sugar-fed females. d Males

Fig. 4

Densities of An. farauti on barrier screens in proximity to the closest house. a Unfed females. b Blood-fed females. c Sugar-fed females. d Males

Fig. 5

Locations of significant mosquito foci (shown in orange) in Haleta village, Central Province, Solomon Islands, collected by barrier screens (a unfed female An. farauti; b blood-fed female An. farauti; c sugar-fed female An. farauti; d male An. farauti; e female culicine species) and human landing catch (f blood-seeking female An. farauti)

Fig. 6

Locations of significant mosquito foci (shown in orange) in Jack Harbour village, Western Province, Solomon Islands, collected by barrier screens (a unfed female An. farauti, b blood-fed female An. farauti, c sugar-fed female An. farauti, d male An. farauti, and e female culicine species) and human landing catch (f blood-seeking female An. farauti)

Fig. 7

Relationships between weather parameters and average total female resting An. farauti per half night with linear trendline. a Average wind speed and average total female resting An. farauti per half night. b Average humidity and average total female resting An. farauti per half night. c Average temperature and average total female resting An. farauti per half night. d Average wind speed and average total female biting An. farauti per half night. e Average humidity and average total female biting An. farauti per half night. f Average temperature and average total female biting An. farauti per half night