Mepraia spinolai, (Porter) 1934, is a diurnal triatomine endemic to Chile and a wild vector of the protozoan Trypanosoma cruzi, (Chagas) 1909, which causes Chagas disease. Behavioral changes in M. spinolai induced by this parasite have been reported previously, which include detection of a potential host, defecation latency, and some life history traits. In this study we assessed changes in locomotor and daily activity due to infection with T. cruzi. No difference was detected in distance traveled between infected and uninfected individuals. However, the groups differed in their daily activity patterns; infected individuals showed significant reduction of movements during the light phase and concentrated their activity in the dark phase. Uninfected individuals showed no differences in locomotor activity between the phases. The results suggest that T. cruzi induces a displacement in the activity of M. spinolai toward the dark phase of the circadian cycle, which may improve its vector competence.

In small mammals, huddling appears as an efficient response to low temperature with important consequences in energy saving, which in turn affect individual fitness. It has been proposed that this behavior is a self-organized process. However, to prove self-organization, it is necessary to study the dynamics of huddling, ruling out the presence of leaders. The objectives of this study were to determine the dynamics of huddling at different temperatures in Octodon degus, documenting the presence or absence of leaders, and to study the consistency of this behavior in two contrasting seasons. We found that huddling dynamics did not indicate the presence of leader initiators of the clustering at lower temperatures. There was no deterministic pattern in huddling dynamics, in any period or at any temperature, suggesting a behavior triggered spontaneously without any order, hierarchy, or recipes. The effect of temperature on huddling behavior was marked and similar in both seasons. The variability of the huddled groups was greater at higher temperatures, which is explained by a greater movement of individuals and more frequent variations in the number and size of the groups at higher temperatures. The results describe huddling as a self-organized behavior, more economical than other physiological processes and therefore preserved by natural selection. This increases its importance for survival and fitness given the significant reduction in energy expenditure achieved under conditions of low temperatures and reduced availability of food, such as during the breeding season of O. degus.

Loxoscelism is a health problem caused by the bite of spiders of the genus Loxosceles. In Chile all cases are attributable to Loxosceles laeta. It has been suggested that the spitting spider Scytodes globula may be a predator of L. laeta and control its population, which is only possible if they share the microhabitat. This study compared the thermal preferences and tolerances of the two species. Later, spiders acclimated to 15 °C and 25 °C were exposed to decreasing and increasing temperatures to determine the lower and upper critical temperatures. The preferred temperatures were lower during the morning, but there were no differences between the species. The thermal niche breadths were similar for the species, with a large overlap. Both species showed tolerance to extreme temperatures, but L. laeta showed greater tolerance to low temperatures. Both species showed acclimation of the lower critical temperatures to changes in acclimation temperatures. The similarity of preferred and tolerated temperatures was partly an expected fact, since the species share the same macrohabitat; these spider species are very common in domestic environments of central Chile. However, the results imply that their microhabitat choices are also very similar, indicating a high probability of meeting and predation, which could have important consequences in loxoscelism epidemiology.

There are two vectors of Chagas disease in Chile: Triatoma infestans and Mepraia spinolai. We studied the feeding behavior of these species, looking for differences which could possibly explain the low impact of the latter species on Chagas disease. Both species used thermal cues to locate their feeding source and consumed a similar volume of blood which was inversely related to the body weight before the meal and directly related to the time between meals. The average time between bites were 6.24 and 10.74 days. The average bite of M. spinolai lasted 9.68 min, significantly shorter than the 19.46 min for T. infestans. Furthermore, while T. infestans always defecated on the host, this behavior was observed in M. spinolai in only one case of 27 (3.7%). The delay between the bites and defecation was very long in M. spinolai and short in T. infestans. These differences may affect the reduced efficiency of transmission of Chagas infection by M. spinolai.

Preferred temperature and activity patterns of Triatoma infestans Klug and Triatoma spinolai Porter were studied, both are vectors of Chagas' disease in Chile. In the laboratory, 24 T. spinolai and 18 T. infestans were exposed to a temperature gradient between 50 and 15 degrees C and a photoperiod of 14:10 (L:D) h. Temperature and hourly position of bugs in an experimental chamber were recorded for 24 h. Both species showed a cycle of preferred temperature, and both selected higher temperatures beginning at 1600 hours, although T. infestans maintains this preference over a longer period. For both species, activity patterns were synchronized with the light-dark cycle, although these activity rhythms were significantly different. T. spinolai had higher activity during the photophase, and T. infestans showed a lower activity in the photophase and a higher one during the scotophase. The similar pattern of preferred temperatures may facilitate the selection of similar environments in the event of colonization of houses by T. spinolai. Diurnal activity of this species might be a disadvantage (in terms of more exposure to defensive responses of the vertebrate hosts) but may allow T. spinolai to share the same habitat with T. infestans without competitive interference.

The population effects of known fluctuations in fecundity and mortality of T. infestans was studied through simulation using Leslie matrices. The effect of mortality and fecundity cycles was a stepped cycling through the growing phase, with no significant population decreases. Density dependent regulation stabilizes changes during the steady phase. The main effect is on population composition with the establishment of a regular annual cycle in the proportion of different age groups. Cycles with high number of larvae may be misinterpreted as an adult plague.

Fecundity and mortality in population of insects is relevant to the epidemiology of insect transmitted diseases. These variables were studied for T. infestans during 5 years under constant conditions of temperature, relative humidity, light periods and individual density. Mean fecundity was 0.96 +/- 0.69 eggs/female-week, range 0 to 4. Minima were observed in april and maxima in october and november. Mean mortality of intermediate forms was 0.058 +/- 0.031/individual-week, range 0.009 to 0.135, similar for females and males. Minima for mortality were observed in june and july, maxima from november to march. Fluctuations of fecundity are attributed to endogenous cyclic changes related to mating and egg laying. Possible explanations for fluctuations in mortality include the action of infectious agents. The secondary mortality cycle may be related to delayed effect of population density or to differential mortality of cohorts born under different environmental conditions.