Temperature influences host instar selection in an aphid parasitoid: support for the relative fitness rule

Abstract

The relative fitness rule states that parasitoid females should adopt risk‐prone reproductive behaviours when expecting low reproductive success. Temperature influences the reproductive success of insects by affecting their basal metabolic rate during development, their egg load at emergence, and their life expectancy as adults. Using an aphid–parasitoid model system, we investigated the influence of developmental and adult temperature on the risk‐sensitive decision‐making of females. We considered the use of a low‐quality host nymphal instar by the aphid parasitoid Aphidius ervi to be a risk‐prone behaviour. Immature females were reared at 12, 20 or 28 °C and had access to the four nymphal instars of the potato aphid Macrosiphum euphorbiae for oviposition at one of these temperatures. Host selection behaviour was continuously recorded during exploitation of an aphid patch. We observed that warm‐developed females and parasitoids foraging at high temperature attacked low‐quality hosts more frequently than females from other treatments. These results support the hypothesis that a decrease in expected parasitoid reproductive success resulted in risk‐prone behaviours. To our knowledge, this is the first experimental evidence suggesting that temperature influences host stage selection and risk‐sensitive making decision in parasitoids, and the present study is the first to support the relative fitness rule. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●●, ●●–●●.

Size-induced phenotypic reaction norms in a parasitoid wasp: an examination of life-history and behavioural traits

“…Alternatively, concentrating reproduction in early life could still be advantageous for small individuals even if females of all sizes experience the same high level of environmental stochasticity. In accordance with the ‘relative fitness rule’ (Giraldeau & Boivin, ; Moiroux, Boivin & Brodeur, ), being able to maximally exploit the first patch of hosts encountered could increase the fitness of small individuals relative to larger individuals, in the event that there is a stochastic mortality event that affects the entire population. Small individuals are advantaged by such stochastic mortality because their loss of future fitness gain (proportional offspring contribution to the next generation) is lower relative to that of large individuals (Giraldeau & Boivin, ).…”

Behavioural effects of temperature on ectothermic animals: unifying thermal physiology and behavioural plasticity

“…For example, insect parasitoids that are smaller as a result of developing at higher temperatures may have altered fecundity, basal metabolic rates, and life expectancy, changing the efficiency with which they interact with hosts and exploit host patches (Colinet et al 2007;LeLann et al 2011). Due to their smaller size, warm-developing parasitoids tend to be less capable of subduing larger hosts (LeLann et al 2011;Wu et al 2011;Moiroux et al 2015) and may adopt more risk-prone behaviour (Moiroux et al 2015), possibly representing adaptive behavioural plasticity in response to developmental temperature-induced size variation. Oviposition rate was higher, and patch residence time and host handling time were shorter in females reared at low temperature than females reared at high temperature when foraging at a common temperature.…”

Rapid responses of winter aphid-parasitoid communities to climate warming

“…Modifications of the parasitoid guild could also be due to shifts in competition for hosts following the addition of new species. Indeed, female parasitoids show seasonal variations in foraging behavior (Roitberg et al, 1992) and can adapt their foraging strategies to competition or host-patch quality (Barrette et al, 2010;Le Lann et al, 2008;Moiroux et al, 2015;Outreman et al, 2005). In winter, it has been demonstrated that female parasitoids adopt generalist strategies due to shortage of optimal hosts, leading to high competition, whereas spring parasitoids usually display specialist strategies by selecting optimal host species (Eoche-Bosy et al, 2016).…”