El Niño drought and tropical forest conversion synergistically determine mosquito development rate

Extreme warming events can profoundly alter the transmission dynamics of mosquito-borne diseases by affecting mosquito life-history traits (e.g. survival, growth and reproduction). At local scales, temperatures are determined largely by vegetation structure and can be dramatically altered by drivers of land-use change (e.g. forest conversion). Disturbance activities can also hinder the buffering capacity of natural habitats, making them more susceptible to seasonal climate variation and extreme weather events (e.g. droughts). In experiments spanning three years, we investigated the interactive effects of tropical forest conversion and climate on fine-scale temperature, and the consequences for mosquito larval development. This study was conducted in the northern Malaysian Bornean state of Sabah using local Aedes albopictus mosquitoes; important vectors of dengue, chikungunya and Zika viruses. We demonstrate that variation in temperatures due to forest conversion dramatically increases development rates in Ae . albopictus mosquitoes. However, this effect was mediated by an El Niño Southern Oscillation (ENSO) drought event. In normal years, mean temperatures did not differ between land-use types, however mosquitoes reared in oil palm plantations typically emerged 2–3 days faster than in logged forests. During an ENSO drought, mean temperatures did differ between land-use types, but surprisingly this did not result in different mosquito development rates. Driving this idiosyncratic response may be the differences in daily temperature fluctuations between the land-use types that either push mosquito larvae towards optimal development, or over the thermal optimum, thereby reducing fitness. This work highlights the importance of considering the synergistic effects of land-use and seasonal climate variations for predicting the thermal response of a key mosquito life-history trait driving disease transmission dynamics.