Ecophysiological Responses of the Lesser Mealworm Alphitobius diaperinus Exposed to Desiccating Conditions.

In order to improve predictions of the impacts of climate change on insects, this study aimed to uncover how exposure to dry conditions can affect the biology of the invasive pest beetle Alphitobius diaperinus in terms of longevity, activity, water content, metabolic profiles, and fecundity. We measured desiccation resistance in adults of A. diaperinus by recording the time the beetles could survive desiccation stress. We found that the species was highly desiccation resistant, with about 50% of the insects exposed to desiccation being able to survive for 30 days, and some individuals even survived for up to 50 days at 10% ± 2 relative humidity. There was no evidence of active upregulation of sugars or other metabolites which the beetles could have used to better tolerate desiccation. Food deprivation affected both control (food deprivation, no desiccation) and treatment (food deprivation, desiccation) groups, as their metabolic phenotypes changed similarly after 1 week of treatment. Also, the activity of beetles from both control and desiccation treatments was similarly increased 2 weeks after the experiment had started. Even if there were no changes in the metabolic phenotypes of the insects experiencing desiccating conditions, beetles exposed to desiccation for 8 days had a significantly reduced reproductive output as compared with control insects. This result indicated a physiological cost of drought resistance or repair of stress-incurred damages. The exact nature of that effect (e.g., direct or indirect physiological costs) has not yet been described for tenebrionid beetles and should be investigated in future studies.

Thermal plasticity and sensitivity to insecticides in populations of an invasive beetle: Cyfluthrin increases vulnerability to extreme temperature.

Climate change increases average temperatures and the occurrence of extreme weather events, in turn accentuating the risk of organism exposure to temperature stress. When thermal conditions become stressful, the sensitivity of insects toward insecticides can be exacerbated. Likewise, exposure of insects to insecticides can subsequently influence their ability to handle stressful temperatures. Here, we investigated the effects of constant temperature and daily heat spikes, in presence/absence of insecticide treatment (cyfluthrin), on the condition (impairment of mobility) and thermal tolerance to cold (-6 °C) and heat (42.5 °C) of the terrestrial beetle Alphitobius diaperinus. The responses of insects from four populations (three farm-collected populations, one laboratory population) to different durations of extreme temperature exposure were compared. The results showed that the laboratory population was generally more sensitive to extreme cold and heat temperatures, with less than 50% of adults recovering after an exposure at -6 or +42.5 °C for 3h. Significant differences in the level of thermal tolerance were also found among insects from poultry farms. Cyfluthrin exposure incurred detrimental effects to insects' condition in all but one population. For two out of the four populations, mobility impairment was increased when adults were exposed to daily heat spikes (6 h per day at 38 °C) and cyfluthrin simultaneously, compared to cyfluthrin exposure at constant temperatures; yet, no significant interaction between the two stressors was found. Finally, using one farm collected population, effects of pre-exposure to cyfluthrin on extreme temperature tolerance provided another example of the toxicant-induced climate sensitivity in insects.