Complex delayed and transgenerational effects driven by the interaction of heat and insecticide in the maternal generation of the wheat aphid, Sitobion avenae.

BACKGROUND: Experience of an earlier environment plays an important role in the induction of delayed and even intergenerational phenotypes of an organism. Evidence suggests that rapid adaptation to an environmental stressor can change the performance of organisms, and even enable them to deal with other stressors. The goal of this study was to determine the effects of adult imidacloprid exposure on life-history traits within and between generations of the cereal aphid, Sitobion avenae, under three developmental conditions: constant temperature, 22°C; a low-intensity thermal condition, 22 + 34°C for 2 h per day; and a high-intensity thermal condition, 22 + 38°C for 2 h per day. RESULTS: Early thermal experience not only changed the tolerance of S. avenae to the insecticide, imidacloprid, but also caused adults to incur fitness costs: the higher the heat intensity, the higher the costs. Negative transgenerational impacts of combined heat and insecticide stressors were limited to the developmental stage, whereas positive stimulation of heat intensity was observed during the adult stage. Overall, nymphal thermal experience exacerbated the detrimental effects of adult insecticidal exposure on the intrinsic rate of population increase in the maternal generation, but stimulated a net reproductive rate in the succeeding offspring generation. CONCLUSION: These findings underpin the importance of considering the experience of the early developmental environment, but also enhance our understanding of the transgenerational effects of combined thermal and insecticide stressors on the population fate of S. avenae. They also help to assess the efficacy of chemical control in a warming world. © 2021 Society of Chemical Industry.

Effects of developmental acclimation on fitness costs differ between two aphid species.

Most ectotherms are able to increase their tolerance to heat stress via the acclimation response. However, there is ongoing debate about whether the acclimation response is associated with fitness costs, and what factors can affect the consequences of acclimation are still unclear. To elucidate this, we sought to determine whether fitness costs varied with acclimation conditions in two cereal aphids, Sitobion avenae and Rhopalosiphum padi. Thus, the basal and inducible thermal tolerances (maximum critical temperature [CTmax]) and fitness traits (proportion of adult emergence, adult longevity, fecundity, and population parameters) of adult aphids were measured under three conditions of developmental acclimation: 1) 22 °C constant temperature (no acclimation), 2) 22 °C + 34 °C for 2 h per day (low daytime temperature), and 3) 22 °C + 38 °C for 2 h per day (high daytime temperature). We found that the thermal tolerances of both species were significantly higher following developmental acclimations, where higher basal and inducible thermal tolerances were observed in R. padi than in S. avenae. Low daytime temperature acclimation conditions (34 °C) resulted in negligible reproductive costs and improved the intrinsic rates of population increase in both species. In contrast, substantial fitness costs were detected in both species in response to high daytime temperature acclimation (38 °C), especially for S. avenae. Our results indicate that the effects of acclimation conditions on fitness costs differ between the two aphid species. These findings will not only enhance our understanding of species dynamics in the context of climate change but could also potentially improve pest control efforts.