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.

Impact of warmer constant and fluctuating temperatures in the male Jamaican field cricket, Gryllus assimilis (Fabricius, 1775) (Orthoptera: Gryllidae).

Ectotherms, such as insects, are susceptible to climate changes because their body temperature is not physiologically regulated. Forecasts indicate a worldwide temperature rise of 1.4-6 °C by 2100, and an increase in heatwave frequency is expected. This study investigated the effects of constant temperatures (CT; 27, 34, 39, 40 and 41 °C) and fluctuating temperature (FT; 27/34 °C: 12/12 h) on the survival, metabolic rate, locomotor activity, gas exchange pattern, heat loss and water content of the male Jamaican field cricket, Gryllus assimilis (Fabricius, 1775) (Orthoptera: Gryllidae). It was found that 39 °C was the estimated lethal temperature for 50% of the population and that 41 °C was considered the thermal limit, causing 100% mortality in 96 h. Furthermore, FT caused slightly higher mortality (8.9 ± 3.8%) than CT27 (0%) and CT34 (1.43 ± 1.43%). FT caused a greater increase in the metabolic rate and locomotor activity than CT27. It was found that G. assimilis males had a continuous gas exchange as a standard at CT27; however, CT34 changed the gas exchange pattern from continuous to cyclic in 27% of crickets. FT decreased heat loss in crickets more than CT34; however, no significant differences were found in locomotor activity and metabolic rate. In addition, no significant differences between CT27, CT34 and FT were observed in terms of water content, thus suggesting no difference in water loss. Thus, it is suggested that FT, despite involving a modest warming, increased the climate sensitivity of G. assimilis males and led to a change in their optimum temperature, pushing it beyond its usual thermal limits. However, higher mortality in FT compared to CT27 (control) and CT34 must be interpreted with caution. In addition, the risk of higher mortality of G. assimilis males is predicted, especially in South America, where this cricket is widely distributed.

Reproductive Status Modulates Mortality Rate, Lifespan and Egg Production, but Do Not the Physiological Aging in the Field Cricket Gryllus assimilis (Fabricius, 1775) (Orthoptera: Gryllidae).

The effects of reproduction are variable among insects, as well as the time of mate. In animals, a trade-off is usually observed between reproduction and self-maintenance, mostly in females because of egg producing costs. In the present investigation, manifestations of aging and senescence at population and cellular levels were studied associated with the mating opportunities. The main goal of this study was to evaluate the effect of mating on lifespan and also on the physiological aging in adult Jamaican field cricket females, Gryllus assimilis (Fabricius, 1775). Three experimental groups were set: virgin, normal-mated (14 days old), and late-mated (30 days old) insects. Lifespan, age-specific mortality rate, number of eggs laid, and in situ amount of the age-pigment neurolipofuscin were quantified. Results showed a trade-off between reproductive females and lifespan, with the strongest effects found in late-mated. Age-specific mortality showed a faster increase for late-mated females from 35 to 50 days old, followed by normal-mated females (35 to 60 days old). Virgins had the lowest age-specific mortality of all, increasing just from 65 to 73 days old. Normal-mated had the highest number of eggs laid, followed by late-mated and virgins, respectively. Neurolipofuscin accumulation rate was similar among groups, which was reflected in similar physiological rate of aging. Results indicate that reproductive status did affect the life-history of these field cricket females.