The importance of water balance for terrestrial insects distribution

SCHILMAN, P.E.

Simposio; 8th International Symposium on the Environmental Physiology of Ectotherms and Plants; 2019

Temperature and humidity are the most important abiotic factors determining insect´s geographical distribution; most of the current studies are based on insect´s thermotolerances as their physiological limitations for their distribution. However, other physiological limitations are also important. Because of their large body surface area to mass ratios, terrestrial insects are especially susceptible to dehydration. This is particularly true for water loss through the cuticle, but other sources may also contribute to desiccation (e.g., water loss through the spiracles when insects exchange gases). John Lighton and I developed the ?hyperoxic switch?, a technique that allow straightforward estimation of respiratory water loss rates (RWLR) in arthropods lacking discontinuous gas exchange, and estimated RWLR for Drosophila melanogaster. Using this technique, we demonstrated that the invasion of the Argentine ant, Linepithema humile, is limited by water availability because its lower tolerance to dehydration due to its higher water loss rate through the cuticle and its critical water content (by gravimetric measurements) compared with five common ant species native to southern California. Also by gravimetric measurements, de la Vega and I showed a high tolerance to desiccation in seven kissing bug species, including the two most important Chagas disease vectors. We generated and used a derived vapor pressure deficit (VPD) measurement, and hypothesized that their desiccation tolerance could be reflected in their distribution, which is limited by areas with high relative VPD (e.g., hot and dry). We found that the maximum VPD limits the western and southern distribution of three of these bug species. This approach indicates that most of these triatomine bugs could be exploiting the dryness dimension of their fundamental niche. Incorporating such species-specific traits in studies of distribution, range, and limits under scenarios of changing climate could enhance predictions of movement of invasive species or disease causing vectors into novel regions.