Why is there no impact of the host species on the cold tolerance of a generalist parasitoid?

Abstract

For generalist parasitoids such as those belonging to the Genus Aphidius, the choice of host species can have profound implications for the emerging parasitoid. Host species is known to affect a variety of life history traits. However, the impact of the host on thermal tolerance has never been studied. Physiological thermal tolerance, enabling survival at unfavourable temperatures, is not a fixed trait and may be influenced by a number of external factors including characteristics of the stress, of the individual exposed to the stress, and of the biological and physical environment. As such, the choice of host species is likely to also have implications for the thermal tolerance of the emerging parasitoid. The current study aimed to investigate the effect of cereal aphid host species (Sitobion avenae, Rhopalosiphum padi and Metopolophium dirhodum) on adult thermal tolerance, in addition to sex and size, of the aphid parasitoids Aphidius avenae, Aphidius matricariae and Aphidius rhopalosiphi. Results revealed no effect of host species on the cold tolerance of the emerging parasitoid, as determined by CT and Chill Coma, for all parasitoid species. Host species significantly affected the size of the emerging parasitoid for A. rhopalosiphi only, with individuals emerging from R. padi being significantly larger than those emerging from S. avenae, although this did not correspond to a difference in thermal tolerance. Furthermore, a significant difference in the size of male and female parasitoids was observed for A. avenae and A. matricariae, although, once again this did not correspond to a difference in cold tolerance. It is suggested that potential behavioural thermoregulation via host manipulation may act to influence the thermal environment experienced by the wasp and thus wasp thermal tolerance and, in doing so, may negate physiological thermal tolerance or any impact of the aphid host.

Cold tolerance and diapause within and across trophic levels: endoparasitic wasps and their fly host have similar phenotypes

“…For example, the greater tendency of D. alloeum and U. canaliculatus to avert diapause may result in poor energy reserve accumulation (Hahn and Denlinger, 2011) and higher mortality due to energy drain at mild winter temperatures. Conversely, characteristics of host physiology, such as diet or whether the host is in diapause, can have strong effects on parasitoid cold tolerance physiology (Li et al, 2015; Tougeron et al, 2019; but see Alford et al, 2017). Given that all the wasps in our cold tolerance experiments were collected from the same population of hawthorn-infesting R. pomonella , many of the wasps likely had access to similar host-related resources, resulting in similar overwintering success (Hahn and Denlinger, 2011; Toxopeus and Sinclair, 2018).…”

“…Endoparasitoids feed and develop to adulthood within a single host organism, usually killing the host in the process (Godfray, 1994; Hood et al, 2021). The parasitoid cold tolerance literature is dominated by studies of wasps (Hymenoptera) that parasitize insect pests from many different insect orders, including Diptera (e.g., drosophilids; Amiresmaeili et al, 2020; Li et al, 2015; Murata et al, 2013), Lepidoptera (e.g., pyralid moths; Carrillo et al, 2005; Foray et al, 2013), Coleoptera (e.g., emerald ash borer; Hanson et al, 2013), and Hemiptera (e.g., aphids; Alford et al, 2017; Colinet and Hance, 2010; Tougeron et al, 2018). However, studies that examine multiple parasitoids that attack a single host are rare (e.g., Hanson et al, 2013), and in these cases the immature life stages of multiple parasitoid species may never interact due to distinct geographic distributions (e.g., Murata et al, 2013) or strong differences in life history timing (e.g., Le Lann et al, 2011).…”

Bet-hedging in parasitoids: when optimization is not the best strategy to cope with climatic extremes

“…In parasitoids, koinobionts keep the host alive until the parasitoid reaches the nymphal instar, while idiobionts paralyze or kill the host arresting its development at the time of egg laying. In koinobiont parasitoids, the overwintering site may not be a site where the host typically overwinters, due to the manipulation of the host's behaviour by the parasitoid ( Alford et al 2017 ). The parasitoid then forces the host to move to a more favorable site for parasitoid overwintering.…”

Cold tolerance and diapause within and across trophic levels: Endoparasitic wasps and their fly host have similar phenotypes

“…Endoparasitoids feed and develop to adulthood within a single host organism, usually killing the host in the process (Godfray, 1994;Hood et al, 2021). The parasitoid cold tolerance literature is dominated by studies of wasps (Hymenoptera) that parasitize insect pests from many different insect orders, including Diptera (e.g., drosophilids; Amiresmaeili et al, 2020;Li et al, 2015;Murata et al, 2013), Lepidoptera (e.g., pyralid moths; Carrillo et al, 2005;Foray et al, 2013), Coleoptera (e.g., emerald ash borer; Hanson et al, 2013), and Hemiptera (e.g., aphids;Alford et al, 2017;Colinet and Hance, 2010;Tougeron et al, 2018). However, studies that examine multiple parasitoids that attack a single host are rare (e.g., Hanson et al, 2013), and in these cases the immature life stages of multiple parasitoid species may never interact due to distinct geographic distributions (e.g., Murata et al, 2013) or strong differences in life history timing (e.g., Le Lann et al, 2011).…”