Stagewise resolution of temperature-dependent embryonic and postembryonic development in the cowpea seed beetle Callosobruchus maculatus (F.)

Variation in Thermal Sensitivity of Diapause Development among Individuals and over Time Predicts Life History Timing in a Univoltine Insect

AbstractPhysiological time is important for understanding the development and seasonal timing of ectothermic animals but has largely been applied to developmental processes that occur during spring and summer, such as morphogenesis. There is a substantial knowledge gap in the relationship between temperature and development during winter, a season that is increasingly impacted by climate change. Most temperate insects overwinter in diapause, a developmental process with little obvious morphological change. We used principles from the physiological time literature to measure and model the thermal sensitivity of diapause development rate in the apple maggot fly Rhagoletis pomonella, a univoltine fly whose diapause duration varies substantially within and among populations. We show that diapause duration can be predicted by modeling a relationship between temperature and development rate that is shifted toward lower temperatures compared with typical models of morphogenic, nondiapause development. However, incorporating interindividual variation and ontogenetic variation in the temperature-to-development rate relationship was critical for accurately predicting fly emergence, as diapause development proceeded more quickly at high temperatures later in diapause. We conclude that the conceptual framework may be flexibly applied to other insects and discuss possible mechanisms of diapause timers and implications for phenology with warming winters.

Modeling the impact of temperature on the population abundance of the ambrosia beetle Xyleborus affinis (Curculionidae: Scolytinae) under laboratory-reared conditions

Modeling the impact of temperature on each life stage of a beetle population represents a continuing challenge. This study evaluates the effects of five temperature treatments (20, 23, 26, 29 and 32 °C) on population abundance and timing of a colony of ambrosia beetles Xyleborus affinis reared under laboratory conditions and use this data to develop demographic and phenological models. Abundances at each life stage (eggs, larvae, pupae and adult) were examined through periodic destructive sampling; given that it was not possible to track individuals. To assess the effects of temperature on oviposition, development and survival rates we developed a novel estimation strategy based on cohorts, which does not require individual developmental data. Since oviposition was entirely unwitnessed, we assessed competing empirical ovipositional models. Rates of development were computed using a modal rate curve for each life stage, and rates were projected to cohorts in life stages assuming log-normal developmental variance. Temperature-driven survival rates were assumed to be logistic with a quadratic exponent to capture modal temperature dependence. Parameters were estimated simultaneously using minimum negative log posterior likelihood, assuming Poisson distribution of observations and using priors to inform unobserved developmental rates and enforce mechanistic constraints on oviposition models. A parabolic function best described oviposition rate. Optimal developmental temperatures were 30.5 °C, 29 °C and 27.5 °C, with maximum developmental rates of 0.26/day, 0.12/day and 0.23/day for eggs, larvae and pupae, respectively. The survival rates in the range 20-29 °C were equal to 1 in the eggs-to-larvae transition, from 0.72 to 0.35 in larvae-to-pupae transition, and from 0.2 to 0.89 in pupae-to-adults transition. This procedure effectively characterized the direct thermal effects on development and survival of each life stage in the X. affinis under laboratory conditions and would be suitable for estimating temperature dependence for other species in which individual observations are not possible.