Ecological and physiological thermal niches to understand distribution of Chagas disease vectors in Latin America.

In order to assess how triatomines (Hemiptera, Reduviidae), Chagas disease vectors, are distributed through Latin America, we analysed the relationship between the ecological niche and the limits of the physiological thermal niche in seven species of triatomines. We combined two methodological approaches: species distribution models, and physiological tolerances. First, we modelled the ecological niche and identified the most important abiotic factor for their distribution. Then, thermal tolerance limits were analysed by measuring maximum and minimum critical temperatures, upper lethal temperature, and 'chill-coma recovery time'. Finally, we used phylogenetic independent contrasts to analyse the link between limiting factors and the thermal tolerance range for the assessment of ecological hypotheses that provide a different outlook for the geo-epidemiology of Chagas disease. In triatomines, thermo-tolerance range increases with increasing latitude mainly due to better cold tolerances, suggesting an effect of thermal selection. In turn, physiological analyses show that species reaching southernmost areas have a higher thermo-tolerance than those with tropical distributions, denoting that thermo-tolerance is limiting the southern distribution. Understanding the latitudinal range along its physiological limits of disease vectors may prove useful to test ecological hypotheses and improve strategies and efficiency of vector control at the local and regional levels.

Temperature preference in Rhodnius prolixus, effects and possible consequences.

The present work examines the thermal preference of adult Rhodnius prolixus along a temperature gradient. The mean preferred temperature differed slightly between sexes: 25.0 degrees C for males versus 25.4 degrees C for females. This preference was not constant, but varied daily by about 0.2 degrees C for both sexes, and reached its highest value at the onset of the dark phase and was lowest during the light phase. A change in the preferred temperature with the level of starvation was also observed (about 1 degrees C lower after 20 days of starvation). Changes in environmental temperature strongly affected the rate of weight loss for both sexes. When insects were maintained for 20 days in a chamber at 32 degrees C, they lost significantly more weight than when kept at 24 degrees C; both water loss and nutrient conversion processes are involved. This increase in weight loss rate with increasing temperature would cause a higher biting rate and consequently higher probability of Chagas' disease transmission. Females oviposit across a range of temperatures from 22 to 33 degrees C with a peak at 25-26 degrees C. These results are compared with patterns of thermopreference in other species of triatomine, as related to differences in their distribution and tolerance to starvation.

Dynamics of thermopreference in the Chagas disease vector Panstrongylus megistus (Hemiptera: Reduviidae).

The thermopreference of resting P. megistus (Burmeister, 1834) adults was studied in a temperature gradient. We also determined the thermopreference for oviposition and ecdysis. Thermopreference of resting individuals depended on the feeding state of the insects. Results demonstrated an initial resting preference of approximately 290 degrees C, which gradually changed to 26-27 degrees C with increasing starvation. A daily variation in thermopreference was also observed with this species. The insects showed a daily maximum preference at the beginning of the dark phase, and a minimum preference during the first half of the light phase. Ecdysis took place all along the gradient, but exhibited a maximum frequency at 30 degrees C. Most eggs were found between 25 and 29 degrees C. Results are discussed in relation to the ecology of P. megistus as compared with other related species, and the existence of mechanisms of behavioral thermoregulation in the group.

Two different vibratory signals in Rhodnius prolixus (Hemiptera: reduviidae).

In this study the substrate-borne stridulatory vibrations produced by Rhodnius prolixus females were recorded and analysed in two different behavioural contexts. In the context of sexual communication females spontaneously stridulated to reject copulatory attempts performed by males. These male-deterring stridulations were fully effective: out of 61 attempts, no copulation occurred. These stridulations consisted of short series of repetitive syllables, each one composed by a single chirp. In the context of defensive behaviour, bugs stridulated if they were clasped or restrained. These disturbance stridulations consisted of long series of repetitive syllables, each one composed by a series of short chirps and a long one. Male-deterring and disturbance stridulations differed in their temporal pattern and frequency spectra, having a main carrier frequency of about 1500 and 2200 Hz, respectively. As no differences in the inter-ridge distances along the whole stridulatory organ were found, the differences in the frequency between both signals could be explained on the basis of a different velocity of rubbing of the proboscis against the prosternal stridulatory organ. It was found that R. prolixus and the related species Triatoma infestans rubbed only the central region of the stridulatory groove (around 1/3 of the total length) to produce disturbance stridulations. The results are discussed in relation to previous work on vibrational sensitivity in R. prolixus and are also compared with results reported for T. infestans.