Abstract
During parasitoid development, the immature parasitoid is confined to the host species. As a result, any potential to modify the physiology or behaviour of the host could play an important role in parasitoid fitness. The potential for host manipulation by the aphid parasitoid Aphidius avenae to increase cold thermotolerance was investigated using the aphid host species Metopolophium dirhodum and Sitobion avenae. Aphids were parasitized at L3/L4 instar stage (5 d old) and allowed to develop into pre-reproductive adults (10 d old) containing a 5 d old parasitoid larva. A control group was created of non-parasitized pre-reproductive adults (10 d old). The inherent physiological thermotolerance (LT50) and potential behavioural thermoregulation (behaviour in a declining temperature regime) of parasitized and non-parasitized aphids were investigated. Results revealed no effect of parasitism on the physiological thermotolerance of S. avenae and M. dirhodum. Significant differences in the behaviour of parasitized and non-parasitized aphids were observed, in addition to differences between host species, and such behaviours are discussed in view of the potential for host manipulation.
Highlights
When subjected to unfavourable thermal conditions, an organism’s survival is governed by its inherent physiological thermotolerance
By comparing parasitized and nonparasitized aphids, the current study investigates the potential for the aphid parasitoid A. avenae to manipulate the physiological thermotolerance and behavioural thermoregulation of two species of its cereal aphid hosts, S. avenae and M. dirhodum
lethal temperature 50 (LT50) did not significantly differ between non-parasitized individuals and individuals parasitized by A. avenae of the cereal aphid species, M. dirhodum and S. avenae (Fig 1)
Summary
When subjected to unfavourable thermal conditions, an organism’s survival is governed by its inherent physiological thermotolerance. In addition to inherent physiological thermotolerance, organisms may employ behavioural mechanisms as a form of thermoregulation, such as habitat selection across large spatial scales, involving extensive seasonal migrations to suitable overwintering sites [3], or microhabitat selection such as basking or burying [4, 5]. Parasitoid insects, for example, which are largely dominated by the order Hymenoptera [6], lay their eggs on or within a host species and are intricately linked to their host during the immature instar stage [7]. Their ability to utilise behavioural thermoregulation during immature development is subsequently severely reduced. Any potential to modify the behaviour or physiology of the host could play an important role in parasite and parasitoid fitness [8]
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