Host‐related volatile cues used by a parasitoid wasp during foraging for its woodboring host

Abstract

Parasitoids rely mainly on infochemicals to search for their herbivore hosts to oviposit on. Megarhyssa nortoni (Cresson) (Hymenoptera: Ichneumonidae) is a parasitoid of siricid wasp larvae which are concealed inside tree stems of several coniferous tree species. This parasitoid is used as a biological control agent against the global pine pest Sirex noctilio Fabricius (Hymenoptera: Siricidae), which engages in an obligate nutritional symbiosis with the fungus Amylostereum areolatum (Chaillet ex Fr.) Boidin (Russulales). We explore the chemical cues that could be used by M. nortoni females while foraging for hosts on the two pine species most commonly planted in commercial forests in Patagonia, Argentina, Pinus contorta Douglas ex Loudon var. latifolia Engelm. ex S Watson and Pinus ponderosa Douglas ex C Lawson (Pinaceae). Behavioural assays were conducted in an olfactometer and the following odour sources were tested in pairwise combinations: (1) P. contorta, (2) P. ponderosa, (3) P. contorta with host fungal symbiont, (4) P. ponderosa with host fungal symbiont, and (5) air (control). Megarhyssa nortoni females discriminated the odours of infested wood (host fungal symbiont‐pine complex) from those of healthy trees, irrespective of the pine species. Additionally, when offered both pine species infested with the fungal symbiont, the parasitoids displayed a bias towards P. contorta. Even though the identity of the compounds responsible for the behavioural bias towards the symbiont was not established at this stage, our findings emphasize the relevance of chemical information derived from the fungal symbiont‐pine complex during parasitoids that forage for woodboring insect hosts.

Patch exploitation behaviour by a parasitoid of a forest pest: The influence of host cues and intra‐ and interspecific interactions

“…Additionally, females elicited probing behaviours solely on patches that held the fungus. These findings extend those of Madden (1968) and Fischbein et al (2018), who showed an olfactory response of M. nortoni to volatiles from A. areolatum . However, females showed a flexible response to host–fungal symbiont cues, since they spent the same time on patch when foraging together with a conspecific female, regardless of whether these patch billets had fungal growth.…”

“…The combination of this symbiotic fungus, a phytotoxic venom inoculated by ovipositing S. noctilio females, and the developing larvae cause the death of pine trees (Madden, 1988). Previous laboratory studies have shown that M. nortoni females are attracted to volatiles coming from A. areolatum (Fischbein et al, 2018;Madden, 1968). However, no studies have been explored yet into the patch exploitation behaviour of this parasitoid under different stimulus scenarios.…”

Chinese oak silkworm Antherae pernyi egg, a suitable factitious host for rearing eupelmid egg parasitoids

“…11 It is well known that various factors such as host species, host stage, host size or host-associated volatiles could affect not only host acceptance by adult female parasitoids but also the performance of their offspring. 6,22,26,29,30 Previous studies indicated that the fertilization status of host eggs affected host acceptance by some egg parasitoids. 21,28,31,32 The performance of parasitoid offspring was different on fertilized and unfertilized host eggs in several tested egg parasitoid species.…”

“…For example, A. orientalis detected chemical traces left by adult host L. delicatula while searching for host egg 11 . It is well known that various factors such as host species, host stage, host size or host‐associated volatiles could affect not only host acceptance by adult female parasitoids but also the performance of their offspring 6,22,26,29,30 . Previous studies indicated that the fertilization status of host eggs affected host acceptance by some egg parasitoids 21,28,31,32 .…”