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Insects exposed to low temperature stress can experience chill injury, but incorporating fluctuating thermoprofiles increases survival and blocks the development of sub-lethal effects. The specific parameters required for a protective thermoprofile are poorly understood, because most studies test a limited range of thermoprofiles. For example, thermoprofiles with a wave profile may perform better than a square profile, but these two profiles are rarely compared. In this study, two developmental stages of the alfalfa leafcutting bee, Megachile rotundata, eye-pigmented pupae, and emergence-ready adults, were exposed to one of eight thermoprofiles for up to 8 weeks. All the thermoprofiles had a base of 6°C and a peak temperature of either 12°C or 18°C. The duration at peak temperature varied depending on the shape of the thermoprofile, either square or wave form. Two other treatments acted as controls, a constant 6°C and a fluctuating thermal regime (FTR) with a base temperature of 6°C that was interrupted daily by a single, 1-h pulse at 20°C. Compared with constant 6°C, all the test thermoprofiles significantly improved survival. Compared with the FTR control, the thermoprofiles with a peak temperature of 18°C outperformed the 12°C profiles. Bees in the eye-pigmented stage exposed to the 18°C profiles separated into two groups based on the shape of the profile, with higher survival in the square profiles compared with the wave profiles. Bees in the emergence-ready stage exposed to 18°C profiles all had significantly higher survival than bees in the FTR controls. Counter to expectations, the least ecologically relevant thermoprofiles (square) had the highest survival rates and blocked the development of sub-lethal effects (delayed emergence).

 

Megachile rotundata exhibits a facultative prepupal diapause but the cues regulating diapause initiation are not well understood. Possible cues include daylength and temperature. Megachile rotundata females experience changing daylengths over the nesting season that may influence diapause incidence in their offspring through a maternal effect. Juvenile M . rotundata spend their developmental period confined in a nesting cavity, potentially subjected to stressful temperatures that may affect diapause incidence and survival. To estimate the impact of daylength and nest cavity temperature on offspring diapause, we designed a 3D printed box with iButtons that measured nest cavity temperature. We observed nest building throughout the season, monitored nest cavity temperature, and followed offspring through development to measure diapause incidence and mortality. We found that daylength was a cue for diapause, and nest cavity temperature did not influence diapause incidence. Eggs laid during long days had a lower probability of diapause. Siblings tended to have the same diapause status, explaining a lot of the remaining variance in diapause incidence. Some females established nests that contained both diapausing and nondiapausing individuals, which were distributed throughout the nest. Nest cavities reached stressful temperatures, which decreased survival. Mortality was significantly higher in nondiapausing bees and the individuals that were laid first in the nest. In conclusion, we demonstrate a maternal effect for diapause that is mediated by daylength and is independent of nest box temperature. 

Abstract Variation in body size has important implications for physical performance and fitness. For insects, adult size and morphology are determined by larval growth and metamorphosis. Female blue orchard bees, Osmia lignaria, (Say) provision a finite quantity of food to their offspring. In this study, we asked how provision-dependent variation in size changes adult morphology. We performed a diet manipulation in which some larvae were starved in the final instar and some were given unlimited food. We examined the consequences on adult morphology in two ways. First, allometric relationships between major body regions (head, thorax, abdomen) and total body mass were measured to determine relative growth of these structures. Second, morphometrics that are critical for flight (wing area, wing loading, and extra flight power index) were quantified. Head and thorax mass had hyperallometric relationships with body size, indicating these parts become disproportionately large in adults when larvae are given copious provisions. However, abdominal mass and wing area increased hypoallometrically with body size. Thus, large adults had disproportionately lighter abdomens and smaller wing areas than smaller adults. Though both males and females followed these general patterns, allometric patterns were affected by sex. For flight metrics, small adults had reduced wing loading and an increased extra flight power index. These results suggest that diet quantity alters development in ways that affect the morphometric trait relationships in adult O. lignaria and may lead to functional differences in performance.