Abstract
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.
Highlights
Changes in the frequency and/or intensity of dry spells and heat waves threaten terrestrial biodiversity by increasing the likelihood of individuals’ desiccation (Trenberth, 2011; IPCC, 2014)
Survival of the Insects Exposed to Desiccating Conditions To measure the survival capacities of adult A. diaperinus continuously exposed to desiccating conditions and food deprivation, in comparison to controls, groups of 10 beetles were transferred to 24 round plastic containers (5 cm diameter, 4 cm tall), without food
Desiccation significantly reduced the survival probability of the beetles (P < 0.001), with about 50% of the individuals being dead after 30 days of the experiment, while almost no mortality was recorded in the controls (ND) after 30 d (Figure 1)
Summary
Changes in the frequency and/or intensity of dry spells and heat waves threaten terrestrial biodiversity by increasing the likelihood of individuals’ desiccation (Trenberth, 2011; IPCC, 2014) This is true for smaller animals such as insects which have a large surface-to-volume ratio and are highly susceptible to evapotranspiration and dehydration (Hadley, 1994). They have developed a wealth of behavioral, morphological, and physiological adaptations aiming at limiting loss of body water and/or detrimental consequences thereof (Hadley, 1994; Hidalgo et al, 2014, 2018; Mamai et al, 2014, 2016; Thorat and Nath, 2018). The main physiological responses to desiccation include (i) limiting the rate of body water loss (desiccation resistance) (Ahearn, 1970; Zachariassen, 1991), (ii) increasing tolerance to water loss (desiccation tolerance) (Arlian and Staiger, 1978; Hadley, 1994), and (iii) controlling the main routes of water loss (excretion, transpiration, and respiratory loss) (Chown et al, 2011)
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