Mother’s choice of the oviposition site: balancing risk of egg parasitism and need of food supply for the progeny with an infochemical shelter?

Abstract

Oviposition site selection of herbivorous insects depends primarily on host plant presence which is essential for offspring survival. However, parasitoids can exploit host plant cues for host location. In this study, we hypothesised that herbivores can solve this dilemma by ovipositing within high plant diversity. A diverse plant species composition might represent an 'infochemical shelter', as a potentially complex volatile blend can negatively affect the host location ability of parasitoids. We examined this exemplarily for the egg-laying response of the generalist leaf beetle, Galeruca tanaceti, in relation to (1) host plant availability and (2) plant species diversity in the field. Further, we investigated the effect of odours from mixed plant species compositions on (3) leaf beetle oviposition site selection and on (4) the orientation of its specialised egg parasitoid, Oomyzus galerucivorus. In the field, egg clutch occurrence was positively related to the presence and quantity of two major host plants, Achillea millefolium (yarrow) and Centaurea jacea, and to the number of herbaceous plant species. In two-choice bioassays, female beetles oviposited more frequently on sites surrounded by an odour blend from a diverse plant species composition (including yarrow) than on sites with a pure grass odour blend. In the presence of yarrow odour and an odour blend from a diverse plant mixture (including yarrow) no difference in the oviposition response was recorded. Experienced parasitoid females were attracted to yarrow odours, but showed no response when yarrow odours were offered simultaneously with odours of a non-host plant. In conclusion, it could be shown in laboratory bioassays that the parasitoid responds only to pure host plant odours but not to complex odour blends. In contrast, the herbivore prefers to oviposit within diverse vegetation in the field and in the laboratory. However, the laboratory results also point to a priority of host plant availability over the selection of a potential 'infochemical shelter' for oviposition due to high plant diversity.

EAG-Active Herbivore-Induced Plant Volatiles Modify Behavioral Responses and Host Attack by An Egg Parasitoid

“…However, associative learning, i.e., association of hostspecific volatiles with the presence of hosts, is a possible solution to this problem (Vet and Groenewold 1990;Vet and Dicke 1992;Kaiser et al 2003;Randlkofer et al 2007;Schröder et al 2008). Compared to larval parasitoids, little is known on the learning capabilities of host-plant-derived cues in egg parasitoids.…”

Parasitism cost of living in a high quality habitat in the bog fritillary butterfly

“…(3) Alternatively, parasitoid search efficiency might be lower in suboptimal fen grassland habitat types because of specific features of the vegetation, such as taller or structurally more complex vegetation (Andow and Prokrym 1990;Randlkofer et al 2007;Obermaier et al 2008). (4) Higher habitat quality might also enhance caterpillar quality and survival, providing better prospects for parasitoid progeny (Van Alpen et al 2003), hence increasing their attractiveness for parasitoids if these latter are able to evaluate the quality of their hosts (Godfray 1994).…”

Does vegetation complexity affect host plant chemistry, and thus multitrophic interactions, in a human-altered landscape?

“…Herbivores might also select their host plant in response to the top-down pressure exerted by predators and parasitoids (e.g. Randlkofer et al 2007). Moreover, other toxic or anti-nutritive compounds, or primary metabolites, which were not considered in this study, might have affected abundances of the herbivores (Agrawal 2004).…”