Food availability alters the effects of larval temperature on Aedes aegypti growth.

Variation in temperature and food availability in larval habitats can influence the abundance, body size, and vector competence of the mosquito Aedes aegypti. Although increased temperature has energetic costs for growing larvae, how food resources influence the developmental response of this mosquito species to thermal conditions is unknown. We explored how rearing temperature and food affect allometric scaling between wing size and epidermal cell size in Ae. aegypti. Mosquitoes were reared at 22 and 28 degrees C across a gradient of field-collected detritus designed to simulate commonly observed natural larval food resources. Overall, reduced temperature and increased food level increased wing size, but only temperature affected cell size. Females fed the least food had the longest time to maturation, and their increases in wing size induced by cold temperature were associated with larger, rather than more, cells. By contrast, males fed the most food had the shortest time to maturation, and their increases in wing size induced by cold temperature were associated with more, rather than larger, cells. Therefore, food levels can alter the underlying physiological mechanisms generating temperature-size patterns in mosquitoes, suggesting that the control of development is sensitive to the combination of nutrient and thermal conditions, rather than each independently. Conditions prolonging development time may favor increased cell division over growth. We suggest that understanding the effects of climate change on Ae. aegypti vectorial capacity requires an improved knowledge of how water temperature interacts with limited food resources and competition in aquatic container habitats.

Temperature induces trade-offs between development and starvation resistance in Aedes aegypti (L.) larvae.

Heightened temperature increases the development rate of mosquitoes. However, in Aedes aegypti (Diptera: Culicidae), the larvae of which commonly experience limited access to food in urban habitats, temperature effects on adult production may also be influenced by changes in the capacity of larvae to survive without food. We carried out experiments to investigate the effects of temperatures increasing at intervals of 2 °C from 20 °C to 30 °C on the growth, maturation rate and longevity of optimally fed larvae placed in starvation. Overall, both growth rate and starvation resistance were lower in the first three larval instars (L1-L3) compared with L4, in which growth of >75% occurred. Although increasing the temperature reduced the duration of each instar, it had a U-shaped impact in terms of the effect of initial growth on starvation resistance, which increased from L1 to L2 at 20 °C and 30 °C, remained constant at 22 °C and 28 °C, and decreased at 24 °C and 26 °C. Growth from L2 to L3 significantly increased starvation resistance only from 26 °C to 30 °C. Increased temperature (>22 °C) consistently reduced starvation resistance in L1. In L2-L4, increments of 2 °C decreased starvation resistance between 20 °C and 24 °C, but had weaker and instar-specific effects at >24 °C. These data show that starvation resistance in Ae. aegypti depends on both instar and temperature, indicating a trade-off between increased development rate and reduced starvation survival of early-instar larvae, particularly in the lower and middle temperatures of the dengue-endemic range of 20-30 °C. We suggest that anabolic and catabolic processes in larvae have distinct temperature dependencies, which may ultimately cause temperature to modify the density regulation of Ae. aegypti populations.

Ecological links between water storage behaviors and Aedes aegypti production: implications for dengue vector control in variable climates.

Understanding linkages between household behavior and Aedes aegypti (L.) larval ecology is essential for community-based dengue mitigation. Here we associate water storage behaviors with the rate of A. aegypti pupal production in three dengue-endemic Colombian cities with different mean temperatures. Qualitative, semi-structured interviews and pupal counts were conducted over a 7-15-day period in 235 households containing a water storage vessel infested with larvae. Emptying vessels more often than every 7 days strongly reduced pupal production in all three cities. Emptying every 7-15 days reduced production by a similar magnitude as emptying <7 days in Armenia (21.9 degrees C), has a threefold smaller reduction as compared to <7 days in Bucaramanga (23.9 degrees C), and did not reduce production in Barranquilla (29.0 degrees C). Lidding vessels reduced mosquito production and was most feasible in Barranquilla because of container structure. Vessel emptying strongly correlated with usage in Barranquilla, where many households stored water in case of interruptions in piped service rather than for regular use. In the cooler cities, >90% of households regularly used stored water for washing clothes, generating a weaker correlation between emptying and usage. Emptying was less frequent in the households surveyed in the dry season in all three cities. These results show that A. aegypti production and human behaviors are coupled in a temperature-dependent manner. In addition to biological effects on aquatic stages, climate change may impact A. aegypti production through human behavioral adaptations. Vector control programs should account for geographic variation in temperature and water usage behaviors in designing targeted interventions.

Application of the pupal/demographic-survey methodology in an area of Havana, Cuba, with low densities of Aedes aegypti (L.).

Between the April and December of 2004, an Aedes aegypti (L.) pupal/demographic survey was conducted in the Playa municipality of Havana. The aims were to identify the key types of container in the production of the adult mosquitoes (and so provide a basis for targeted control) and assess transmission risk in terms of the number of pupae/person. Pupal abundance, as measured in the survey, was compared with traditional Stegomyia indices. The immature stages of Ae. aegypti were only found in 70 of the 15,153 containers that were investigated and the pupae of this species were only seen in 52 of the containers. Ground-level water-storage tanks yielded 74.1% of all the pupae, with a further 19.0% found in miscellaneous small containers. The utility of the pupal/demographic-survey methodology in the evaluation of dengue risk in the study area, and other areas of Cuba with low densities of Ae. aegypti, is discussed.