Vectorial Capacity across an Environmental Gradient

Project Number 38 Back to projects

Start date

2017-04-05

End date

2017-05-30

Research areas

Ecology
Infectious Diseases
Microclimate

Data use

PhD Thesis

Rationale

Drivers of environmental change (e.g. climate change, land-use) dramatically impact species persistence and interactions central to mediating the transmission of a range of infectious diseases. Particularly responsive to environmental parameters are mosquito vectors, whose parasites exert enormous fitness and economic costs across the globe. Given that transmission intensity of mosquito-borne parasites is inextricably linked to vector biology, characterizing the response of mosquitoes to these environmental changes is critical for effective disease control. Current models of mosquito-borne disease transmission remain limited by static assumptions of mosquito ecology and environmental parameters, often resulting in over optimistic predictions of disease control effectiveness (Dye & Hasibeder 1986).Temperature directly influences transmission-relevant mosquito traits, including development rate, adult body size and duration of gonotrophic cycle (the period between blood feeding and ovipositing). Controlled laboratory manipulations and descriptions of ambient temperature typically correlate mosquito life-history traits with mean conditions, whereas in reality, mosquitoes experience daily temperature fluctuations. Additionally, the few available studies that consider temperature variation - transmission dynamics relationships have demonstrated greater magnitude of temperature effects on factors influencing vector competence, highlighting the need to further explore these relationships across ecologically realistic thermal regimes.
Using stage-specific, field-based methods, the proposed project seeks to characterize how key parameters of mosquito vectorial capacity vary across an environmental gradient. Specifically, I will use well-established field-based sampling methods to 1) characterize the per-capita impact of natural temperature variation on larval development rate and mortality for Aedes aegypti, a key vector species; 2) characterize the impact of larval temperature regimes on adult traits relevant to vectorial capacity (e.g. adult body size); and 3) establish baseline parameter values for adult survival in the field as a function of larval development rate and temperature regime.

Methods

Stage I: Egg collection
A set of infusion-baited oviposit traps will be established near the SAFE field house as source traps. Traps will consist of 10x25x15 cm black containers containing approximately 200ml of Tertafin fish food infusion and lined with paper towels to provide substrate for ovipositing female Aedes mosquitoes. Egg paper will be collected and replaced every 2 days. The number of eggs will be counted, papers dried and then stored in a plastic container under cool conditions until a sufficient number has been obtained (N = 100 per trap).Stage II: Larval rearing tanks
Three rearing tanks, each containing 300mL of Tertafin infusion, will be placed at each second-order sampling point across old growth, logged forest (Fragment B) and oil palm sites (N = 72; see Fig 1.). In each tank, mosquito eggs (N = 100) will be submerged in infusion to allow for embryonation and hatching.
Traps will be monitored daily and the proportion of each developmental stage recorded. Once larvae begin to pupate, a small wooden stick will be placed in each trap to provide a resting substrate for emerging adults. Traps will also be covered with muslin cloth to prevent adults escaping. The level of infusion in each container will be marked with permanent marker (at approximately 5cm) in an effort to standardize nutritional availability across tanks. Whilst previous work has included locally collected stagnant water in the bait solution, site-specific differences in water nutrients may limit our ability to later attribute larval development rates to microclimate alone. Data loggers (EL-USB 2 RoH8, temperature accuracy <±0.5 ◦C) will be placed approximately 10cm below ground at each trap and set to monitor ground temperature at intervals of 3 hours for duration of the sampling period.
Stage III: Adult survival (starvation assays)
When encountered, adult mosquitoes will be removed from traps and transferred to mesh cages, organised by day of emergence, at the field house. Adults will be monitored daily and the proportion of mosquitoes surviving recorded. Dead mosquitoes will be removed and identified to species (if possible). To quantify wing length, one wing will be removed from each adult female and mounted onto glass microscope slide using double-sided tape and cover slips. Wings will be measured using a stereomicroscope. Wing measurements will be taken from the tip of the wing (excluding fringe) to the distal end of the alula.
Project members
ResearcherProject roleProject contact
Lauren CatorSupervisor
Nichar GregoryPhD Student
Robert EwersSupervisor
Maria DickinsonCoordinator