Distribution, occurrence, and identification of mosquito species in the Tongatapu Island Group, Kingdom of Tonga
Thesis DisciplineWater Resource Management
Degree GrantorUniversity of Canterbury
Degree NameMaster of Water Resource Management
Mosquitoes pose a serious threat to the economy, health status, and biosecurity of countries around the world. Mosquitoes kill an average of 700,000 people per year. The global expansion of air, sea, and land transport networks has greatly enhanced the spread of mosquitoes internationally. In the Pacific, the number of mosquito-borne diseases occurring has been on the rise in recent years, possibly as a result of human-mediated dispersal of larvae and adult mosquitoes. The Kingdom of Tonga has had numerous outbreaks of dengue fever and chikungunya virus in recent years. Previous research has catalogued species occurrences and distributions throughout Tonga. However, it is unknown whether new species have arrived in Tonga, and if distribution of previously found species has changed since the last comprehensive survey in 2006. Present research aims to update the literature by conducting a mosquito survey at 84 sites across the four islands of Tongatapu, Pangaimotu, ‘Oneata, and ‘Eua to record the distribution and occurrence of mosquito larvae. Nine mosquito species were collected: Aedes aegypti Linnaeus, A. albopictus Skuse, A. tongae Edwards, A. horrescens Edwards, A. vexans nocturnus Theobold, Culex annulirostris Skuse, C. albinervis Edwards, C. quinquefasciatus Say and C. sitiens Wiedemann. The collection of A. albopictus is the second time that this species has been recorded in Tonga. Moreover, the spatial extent of this species throughout Tonga was far greater than previously recorded. A major outcome of this survey has been the creation of an identification key for the mosquito larvae species of Tonga. This key should increase the accuracy of positive mosquito larvae identifications in Tonga. Mosquitoes were more frequently collected in artificial (e.g., used car tyres, fuel drums, containers) than natural (e.g., pools, ponds, tree holes) habitats. Car tyres, water containers, fuel drums, fridges, washing machines, and ponds were the most common habitats in which mosquito larvae were found. Aedes aegypti, A. albopictus, and C. quinquefasciatus were the three most common mosquito species collected, whereas A. tongae, A. horrescens, A. vexans nocturnus, C. annulirostris, C. sitiens, and C. albinervis were less frequently found. Multiple logistic regression analyses indicated that habitat volume had a significant positive effect on the presence of A. albopictus and A. tongae, whereas conductivity had a significant positive effect on the presence of C. annulirostris. Additionally, the volume by temperature interaction was a significant predictor of species presence for A. aegypti, A. albopictus, and C. annulirostris (as habitat volume increases, the effect of temperature went from neutral to negative). This suggests that larger, cooler habitats favour colonisation by these species. The number of artificial habitats (particularly used car tyres) present may have significantly increased since previous studies. Management should therefore focus on implementing community-run mosquito projects aimed at reducing the number of artificial habitats capable of being colonised by mosquito larvae. Covering, tipping out water, and infilling these habitats with soil to prevent mosquito oviposition is a pragmatic and straightforward mosquito control solution. This should immensely reduce the abundance of mosquitoes and may prevent disease outbreak in Tonga.