Life on the margin: rainwater tanks facilitate overwintering of the dengue vector,Aedes aegypti, in a sub-tropical climate

Abstract

1 Life on the margin: rainwater tanks facilitate 2 overwintering of the dengue vector, Aedes aegypti, in a sub-3 tropical climate. Abstract 23 A key determinant of insect persistence in marginal habitats is the ability to tolerate 24 environmental extremes such as temperature. Aedes aegypti is highly invasive and little is 25 known about the physiological sensitivity of the species to fluctuating temperature regimes at 26 the lower critical threshold. This has implications that limit establishment and persistence of 27 the species in sub-optimal regions. Daily winter temperatures were measured in common 28 Australian larval habitats, replicated in environmental chambers, and used to investigate the 29 effect of fluctuating temperatures on the development and survival of tropical and subtropical 30 strains of Australian Ae. aegypti. Development was slow for all treatments but both strains 31 were able to complete development to the adult stage, suggesting previous models 32 underestimate the potential for the species to persist in eastern Australia. Results suggested that 33 thermal buffering in large volume habitats, and water that persists for greater than 32 days, will 34 facilitate completion of the life cycle during sub-tropical winters. Furthermore, we provide a 35 non-linear estimate of the lower critical temperature of Ae. aegypti that suggests the current 36 threshold may be incorrect. Our study demonstrates that the current re-introduction of water 37 storage containers such as rainwater tanks, into major Australian population centres will 38 increase the risk of Ae. aegypti establishment by permitting year-round development south of 39 its current distribution.40 Keywords: Aedes aegypti, Australia, survival and development, temperature fluctuation, water 41 storage, rainwater tank, thermal buffering. 42 Introduction 43 A key determinant of insect distribution and persistence is the ability of a species to tolerate 44 micro-climates at a local scale (1). Conditions within the core distribution of a species will be 45 near-optimal and less stable populations will persist around the margins of an insect's 3 46 distribution; the permanency mediated by access to food sources, the availability of suitable 47 oviposition and resting sites and the abiotic factors associated with these micro-habitats (2-4).48 In recent years there has been renewed interest in predicting the spread of the mosquito Aedes 49 aegypti (L.) into cool range margins, primarily due the increased variability in temperature and 50 rainfall associated with climate change and the importance of the species as a disease vector 51 (4). In particular, rising temperatures, unpredictable rainfall and urban landscapes that are 52 evolving in response to climatic changes may impact mosquito distributions, daily activity 53 patterns and peak annual population abundance in marginal habitats (2, 3, 5-8).54 Aedes aegypti is a highly anthropophilic species (2, 9). The continuous availability of 55 oviposition sites and blood meals afforded by intra-domi...

Simulating an invasion: unsealed water storage (rainwater tanks) and urban block design facilitate the spread of the dengue fever mosquito, Aedes aegypti, in Brisbane, Australia

“…Future applications of this modelling framework should consider this intra-suburb variation on the rate of invasion spread at finer spatial scales. Our findings are conservative, however, as it was assumed the species could not persist long-term in Brisbane until recently (Trewin et al 2019). Over a 5-year period, invasions extended to a radius of approximately 500 m and area of 0.7-0.9km 2 , a conclusion which concurs with results from other modelling approaches with seasonal variation (Hancock et al 2018).…”

Releasing incompatible males drives strong suppression across populations of wild and Wolbachia -carrying Aedes aegypti in Australia

“…In the Australian context, the effects of climate change and our adaptation to it may increase the risk of this species establishing (and re-establishing) in towns and cities. In particular, the warming and dryer climate in much of Australia means our adaptation to drought-proof towns and cities with rainwater tanks are potentially providing ideal thermally buffered niches for the larvae, and the species may once again exist beyond the tropical biology restriction observed in the 20th century (21,55). Additionally, the more temperate-adapted Ae.…”

Eliminating Aedes aegypti from its southern margin in Australia: insights from genomic data and simulation modeling

“…aegypti persistence across Australia predicts high natural vulnerability of subtropical populations (such as those in WBBR) due to suboptimal climate (42,43). However, this vulnerability depends strongly on the availability of large larval breeding sites like rainwater tanks (7,42). The removal/sealing of non-compliant rainwater tanks should therefore significantly increase the probability of Ae.…”

“…The removal or sealing of rainwater tanks is thought to have been a major factor in the elimination of Ae. aegypti from the southeast distribution margin, including the city of Brisbane, where they provided key habitat for continual larval development during the cold and dry winter months (6,7).…”

“…The elimination of Ae. aegypti populations from the southern margin would not only benefit the towns involved but would also decrease the risk of southward re-incursion into the highly populated areas of southeast Queensland, including metropolitan Brisbane, where there are now over 300,000 rainwater tanks (7).…”