ORIGINAL PAPER Increased lipid accumulation but not reduced metabolism explains improved starvation tolerance in cold-acclimated arthropod predators Kim Jensen 1 & Jakob V. Michaelsen 2 & Marie T. Larsen 2 & Torsten N. Kristensen 3 & Martin Holmstrup 1 & Johannes Overgaard 2 Received: 8 June 2018 /Revised: 31 October 2018 /Accepted: 3 November 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Predatory arthropods are used for biological control in greenhouses, but there is increasing interest to extend their use to the outdoor environment where temperatures are typically lower. Acclimation at low temperature increases the ability of ectotherms to cope with subsequent more extreme cold, but may involve costs or benefits to other performance traits. A recent study in mesostigmatid mites (Gaeolaelaps aculeifer) showed that starvation tolerance was improved following a period of cold exposure. However, the physiological mechanisms that underlie improved starvation tolerance following cold exposure were not investi- gated. To examine whether cold acclimation would also improve starvation tolerance in an insect, we repeated the starvation study in another arthropod predator, the pirate bug Orius majusculus, as well as in G. aculeifer . Before tests, the two species were acclimated at 10, 15, or 20 °C for 7 (G. aculeifer) or 16 (O. majusculus) days. We then analyzed the effects of thermal exposure on body composition, consumption, and basal metabolic rate in both species. Our results confirmed that exposure to low temperature improves starvation tolerance in these arthropod predators. Body composition analyses revealed that both species had accumu- lated larger lipid stores during exposure to colder temperature, which at least in part can explain the larger starvation tolerance following cold exposure. In contrast, consumption and basal metabolic rate were not changed by thermal acclimation. Our study indicates that predatory arthropods exposed to cold increase their physiological robustness and ability to endure environmental challenges, including low temperature and low prey availability. Keywords Cold acclimation . Gaeolaelaps aculeifer . Lipid storage . Orius majusculus . Starvation tolerance Introduction Biological control agents are successfully implemented for pest management in greenhouses in many countries in the northern hemisphere (Vreysen et al. 2007). Under field condi- tions, however, they encounter variable and sometimes stress- ful conditions including low temperature (Ghazy et al. 2016; Hart et al. 2002), which may reduce their performance as predators. Survival under stressful conditions is essential for the functioning of biological control agents in the field, and increasing robustness of agents before release might therefore be advantageous (Sørensen et al. 2012; Terblanche 2014). It is well known that cold acclimation, even on a short time scale, increases cold tolerance of arthropods (e.g., Alemu et al. 2017; Chown and Terblanche 2007; Kristensen et al. 2008; Overgaard and MacMillan 2017). We have previously shown that cold acclimation increased cold tolerance in the predatory mite Gaeolaelaps aculeifer Canestrini (Mesostigmata: Laelapidae), and there we also found that starvation tolerance was raised following cold acclimation (Jensen et al. 2017). However, cold and starvation tolerance appeared to trade-off with predation rate and reproduction (Jensen et al. 2017). Similarly, the pirate bug Orius majusculus Reuter Communicated by: Rumyana Jeleva * Kim Jensen kj@bios.au.dk 1 Department of Bioscience, Section for Soil Ecology and Ecotoxicology, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark 2 Department of Bioscience, Section for Zoophysiology, Aarhus University, C.F. Møllers Allé 3, Building 1131, 8000 Aarhus C, Denmark 3 Department of Chemistry and Bioscience, Section for Biology and Environmental Science, Aalborg University, Fredrik Bajers Vej 7H, 9220 Aalborg E, Denmark The Science of Nature (2018) 105:65 https://doi.org/10.1007/s00114-018-1593-6