Ambient temperature affects mechanosensory host location in a parasitic wasp

Abstract

Certain parasitic wasps (Ichneumonidae, Pimplinae) use self-produced vibrations transmitted on plant substrate to locate their immobile concealed hosts (i.e. lepidopteran pupae). This mechanosensory mechanism, called the vibrational sounding, depends both on physical cues of the environment and physical activity of the parasitoid and is postulated to depend on ambient temperature. We analysed the influences of temperature on vibrational sounding by choice experiments using plant-stem models with hidden host mimics in the temperate species Pimpla turionellae. The results show a significant effect of temperature on host-location activity and on the success of this process. Outside an optimum range, the performance of the wasps decreased both at low and high temperatures. Below 10 degrees C and beyond 24 degrees C, the wasps displayed (1) substantial reduction in responsiveness, i.e. proportion of females showing ovipositor insertions, (2) reduction of quantitative activity with ovipositor insertions in the individuals, and (3) reduced precision of mechanosensory host location. Nevertheless, female wasps were able to locate their host over a surprisingly broad range of ambient temperatures which indicates that the wasps are able to compensate for temperature effects on vibrational sounding.

Superparasitism in gregarious hymenopteran parasitoids: ecological, behavioural and physiological perspectives

“…Idiobiont parasitoids may exploit mechanosensory stimuli characterizing an already paralysed, immobile host that has been previously attacked by a parasitoid. Endoparasitoid females may use vibrational cues, such as those used by ichneumonid wasps to locate their concealed host in a substrate (Otten et al ., 2001; Samietz et al ., 2006), to locate parasitoid progeny embedded in a host’s body. Further work is needed to understand parasitoid behaviour under different choice situations, and to elucidate stimuli used by gregarious species to assess host quality for superparasitism.…”

Temperature affects interaction of visual and vibrational cues in parasitoid host location

“…French 1985;Otten et al 2002;Fischer et al 2003a). The inXuence of temperature on vibrational sounding was recently demonstrated in P. turionellae as well as in the closely related tropical ichneumonid species Xanthopimpla stemmator (Thunberg) Samietz et al 2006). In both species the percentage of females responding to the vibrational cue and the quantitative insertion activity decreased down-and upwards of a temperature optimum.…”

“…This experimental set-up is comparable to a tritropic system with hidden host pupa and has been successfully used in a number of studies on visual and vibrational host location in this insect (e.g. Fischer et al 2004a;Kroder et al 2006;Samietz et al 2006).…”

“…The insertion precision was quantiWed by analogy with the insertion bias method of Samietz et al (2006) and Kroder et al (2006) by measuring the average devia-tion from the nearest cue centre. The insertion activity was expressed as the average number of insertions per responding female, and is therefore also an indicator for the general searching activity of the wasps.…”

“…Both are used in this species and seem to be equally important for reliable host location on the investigated spatial scale. However, reliability of vibrational cues may change with changing environmental temperature since the performance and precision of vibrational sounding is obviously negatively inXuenced by suboptimal, especially too low ambient temperatures of 10°C or less Samietz et al 2006). In insect vision, however, such negative temperature eVects are unknown.…”