Effect of different thermal conditions on the pre-imaginal biology of Culex apicinus (Philippi, 1865) (Diptera: Culicidae).

The time of development and survival of the pre-imaginal period and the adult body size of Culex apicinus were analyzed in individuals reared from the 1st instar larva to adult emergence under laboratory and field conditions. In the laboratory, insects were exposed to three constant temperatures (15, 20, and 25 degrees C) and a photoperiod of 14:10 (L:D). In the field, temperature and photoperiod were not manipulated; during the study period water temperature ranged between 15.5 and 24.2 degrees C, and photoperiod changed from 13:11 to 14:10 (L:D). Survival to the imaginal stage at 15 degrees C (85.4%) and in the field (88.8%) was higher than that at 20 degrees C (45.8%) and 25 degrees C (8.3%). Based on femur and wing length measurements, the mosquitoes reared under field conditions (mean water temperature = 20.5 degrees C) were smaller than those laboratory-reared, even when the time of development in the field (29.5 - 36 days) was longer than that observed at 15 degrees C (24 days), 20 degrees C (15 days), and 25 degrees C (11 days). Male emergence was earlier than that of females (protandry) only in the field. Although laboratory conditions included a photoperiod and temperature range comparable with the observed values in the field, the disagreements between field and laboratory results suggest that the characteristics examined in this work could be affected by the joint variation of several factors not controlled in field conditions, such as photoperiod, temperature regime, and/or food quality of larval habitat.

Mortality rate and relative strain index in Buenos Aires city.

Thermal stress may seriously affect human health to the extent of provoking death in those human groups at high risk such as little children and elderly persons. This research studies the climatology of the relative strain index (RSI) in the city of Buenos Aires (Argentina). It is observed that the conditions at 1400 hours local time on more than 75% of summer days cause discomfort, though only on 25% of days are physiological failure levels reached. The nocturnal RSI values show 75% of nights to be comfortable, bringing relief and allowing physiological recuperation. Comparison between the RSI frequency distributions of different decades by the application of the Kolmogorov-Smirnov test shows a possible urban heat-island effect that increases nocturnal RSI values. The relationship between the RSI and the daily number of interments is also analysed. Because of the large number of different causes of mortality, only about 10% of the variance of the daily number of interments can be explained by the RSI value at 1400 hours local time 1 or 2 days before. Comparison of mortality figures with these RSI values shows deaths to be at a minimum for the interval 0.0-0.1 (the RSI comfort range), slightly increasing for negative values that could represent unexpected Summer cold waves. For values of RSI over 0.2 the increment is more abrupt, indicating an impact of a thermal strain on mortality. The relationship between the joint occurrence of the 1400 hour and 0200 hour (local time) RSI values and mortality shows a clear impact of prolonged exposure to uncomfortable conditions.