Humidity and temperature preference in two Neotropical species of sand flies

Abstract

Background: Arthropods vector a multitude of human disease-causing organisms, and their geographic ranges are shifting rapidly in response to changing climatic conditions. This is, in turn, altering the landscape of disease risk for human populations that are brought into novel contact with the vectors and the diseases they carry. Sand flies in the genera Lutzomyia and Pintomyia are vectors of serious disease-causing agents such as Leishmania (the etiological agent of leishmaniasis) and may be expanding their range in the face of climate change. Understanding the climatic conditions that vector species both tolerate physiologically and prefer behaviorally is critical to predicting the direction and magnitude of range expansions and the resulting impacts on human health. Temperature and humidity are key factors that determine the geographic extent of many arthropods, including vector species.

Methods: We characterized the habitat of two species of sand flies, Lutzomyia longipalpis and Pintomyia evansi. Additionally, we studied two behavioral factors of thermal fitness-thermal and humidity preference in two species of sand flies alongside a key aspect of physiological tolerance-desiccation resistance.

Results: We found that Lu. longipalpis is found at cooler and drier conditions than Pi. evansi. Our results also show significant interspecific differences in both behavioral traits, with Pi. evansi preferring warmer, more humid conditions than Lu. longipalpis. Finally, we found that Lu. longipalpis shows greater tolerance to extreme low humidity, and that this is especially pronounced in males of the species.

Conclusions: Taken together, our results suggest that temperature and humidity conditions are key aspects of the climatic niche of Lutzomyia and Pintomyia sand flies and underscore the value of integrative studies of climatic tolerance and preference in vector biology.

Keywords: Leishmania; Lutzomyia; Pintomyia; Climate change; Desiccation; Humidity preference; Leishmaniasis; Psychodidae; Sand fly; Temperature preference.

Fig. 1

Environmental conditions during the collection period in two sampling locations. The trend lines depict median temperature and humidity conditions during the collection period at both localities; polygons around the trend line show variation among specific trap sites at each location. A Temperature in Colosó. B Relative humidity (RH) in Colosó. C Temperature in Ricaurte. D RH in Ricaurte. Red: traps that yielded sand fly specimens. Blue: traps that yielded no specimens

Fig. 2

Temperature preference variation in sand flies. A Lutzomyia longipalpis and Pintomyia evansi differ in their temperature preference. B Tetracycline affects the temperature preference in Lu. longipalpis females. Note that the distribution of temperature preference in Lu. longipalpis females is shown in both panels

Fig. 3

Humidity preference differs between the two species of sand fly. Lutzomyia longipalpis and Pi. evansi differ in their RH preference in laboratory experiments. Sex was not a significant factor within species

Fig. 4

Survival plots of two species of sand flies in extreme desiccation conditions. All experiments were conducted for 10 h, or until all individuals had died. We ran experiments for at least three replicates per genotype. The two species of sand flies differ in their physiological tolerance to desiccating conditions, and within Lu. longipalpis, males were especially resistant to desiccation

Fig. 5

Sand flies that prefer more humid temperatures are more sensitive to desiccating conditions. The two species show intraspecific phenotypic variation in desiccation resistance and humidity preference that is negatively correlated (i.e., individuals that prefer more humid conditions are more likely to die early in desiccating conditions). Histograms show Pearson’s correlation tests of 1000 bootstrapped samples. A Pi. evansi females. B Pi. evansi males. C Lu. longipalpis females. D Lu. longipalpis males