Negative bioenergetic responses to pesticides in damselfly larvae are more likely when it is hotter and when temperatures fluctuate

Abstract

To make more realistic predictions about the current and future effects of pesticides, we need to better understand physiological mechanisms associated with the widespread higher toxicity of many pesticides under increasing mean temperatures and daily temperature fluctuations (DTFs). One overlooked, yet insightful, mechanism are bioenergetic responses as these provide information about the balance between energy gains and costs. Therefore, we studied how the bioenergetic responses to the insecticide chlorpyrifos were affected by a higher mean temperature and a higher DTF in Ischnura elegans damselfly larvae. To quantify bioenergetic responses we measured energy availability (Ea), energy consumption (Ec) and total net energy budget (cellular energy allocation, CEA). Exposure to chlorpyrifos considerably reduced CEA values when a high mean temperature was combined with a high DTF (up to -18%). Notably, chlorpyrifos had little effect on CEA at a constant 20 °C, meaning that the bioenergetic impact of chlorpyrifos would have been underestimated if we had only tested under standard testing conditions. The chlorpyrifos-induced reductions in CEA under warming were driven by reductions in Ea (up to -16%, mainly through large reductions in sugar and fat contents) while Ec was unaffected by chlorpyrifos. Treatment groups with a lower CEA value showed a higher mortality and a lower growth rate, indicating bioenergetic responses are contributing to the higher toxicity of chlorpyrifos under warming. Our study highlights the importance of evaluating the effects of pesticides under an increase in both mean temperature and DTF to improve the ecological risk assessment of pesticides under global warming.

The Exposure Order Strongly Modifies How a Heat Spike Increases Pesticide Toxicity

“…Assays were done on one pooled set of five larvae per jar, and the jar means of the three to four technical replicates were used in the statistical analyses (exact sample sizes per treatment combination are given in Figure A,B and SI Figure S4 in Appendix S6). All assays were based on spectrophotometry as described in Delnat et al and Verheyen and Stoks . The detailed assay protocols can be found in SI Appendix S4.…”

Risks to the stability of coral reefs in the South China Sea: An integrated biomarker approach to assess the physiological responses of Trochus niloticus to ocean acidification and warming

“…The cellular energy allocation (CEA) measures a net cellular energy budget of the organisms at a cellular level of biological organization, by quantifying the available energy reserves and energy consumption in tissues (Erk et al, 2011). Presently, the CEA has been widely used as a biomarker reflected the metabolic processes of an organism under stressful conditions (Verheyen and Stoks, 2020;Gandar et al, 2017;Kühnhold et al, 2017). In terms of the available energy reserves, only exposure to OW led to an increase in total lipid content and a decrease in glycogen content in the muscles of T. niloticus.…”

Modeling the synergistic effects of toxicant mixtures

“…With such a bio-energetic approach, the higher toxicity of many pesticides under increasing mean temperatures and daily temperature fluctuations could be associated with a reduced cellular energy allocation [40]. Nevertheless, the question remains as to how these sublethal responses can be integrated to predict individual mortality in natural conditions, the most integral-and hence pivotal-endpoint when assessing the fitness of individuals and higher levels of biological organization.…”