Mortality, metabolic rate, and oviposition of Gryllus (Gryllus) assimilis (Fabricius, 1775) (Orthoptera: Gryllidae) females under constant and fluctuating warm temperatures

The global average temperature will increase by up to 5.7 °C, under high greenhouse gas emissions, consequently increasing the frequency of heatwaves, according to recent IPCC forecasts. These especially impacts ectotherms, such as insects, which are the most susceptible animals to changes in environmental temperature, affecting their physiology and reproduction. Thus, we investigated the effects of a 96-h exposure to constant temperatures (CT: 27, 30.5, 34, 39, 41, or 43 °C) and fluctuating temperatures (FT: 27/34 °C, 12/12 h) on the survival, metabolic rate, and oviposition of the female cricket Gryllus (Gryllus) assimilis (Orthoptera: Gryllidae). Mortality, body mass and water content of females and males were quantified and compared. It was found that CT27, CT34 and FT27/34 do not cause mortality in females of G. (G.) assimilis. CT30.5 (average temperature between 27 and 34), despite causing mortality of 5.0 ± 3.5%, do not differ from CT27, CT34 or FT27/34. CT39 causes a mortality of 8.3 ± 5.5%. Estimated lethal temperature for 50% of the population of females (LT50Temp) is 40 °C, and 43 °C promotes 100% mortality in 96 h. Comparing mortality between sexes, females present higher LT50Temp and thermotolerance than males. In addition, FT27/34 and CT34 do not differ in the metabolic rate, but both have higher values than CT27. CT34 strongly reduces oviposition in females, however FT27/34 does not. We suggest that CT34 reduces oviposition in females in two ways: by affecting the endocrine system related to egg production, or by causing behavioral egg retention, as a strategy to survive thermal stress. Moreover, females had a higher wet body mass and present a lower average weight loss than males. In conclusion, despite females present a higher mortality at temperatures above 39 °C, they are more thermotolerant than males. Furthermore, CT34 is detrimental to the oviposition of G. (G.) assimilis. •Gryllus (Gryllus) assimilis females present higher wet body mass and lower average weight loss than males.•Constant temperature of 40 °C promotes 50% of mortality in of G. (G.) assimilis females.•G. (G.) assimilis females are more thermotolerant than males.•Constant temperature of 34 °C strongly decreases oviposition in G. (G.) assimilis females.