What cues do parasitoids use to find host caterpillars on host plants?

What is it about?

Neither the size or local density of host plants (shore groundsel / Senecio lautus), nor the location of the host pupa (in the stem or flower head) seems to influence the chance that the tephritid fly (Sphenella fascigera) is parasitized.

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Why is it important?

OPENING PARAGRAPH: "About a quarter of all insects are parasites or parasitoids. Tri-trophic interactions between plants, their insect herbivores and parasitoids are among the most ubiquitous and important components of larger, more complex food webs (Schoonhoven et al. 2007 Schoonhoven LM, van Loon JJA, Dicke M 2007). Parasitoids are capable of controlling populations of herbivorous insects. They have the potential to act as biocontrol agents for agricultural pests (i.e. crop-damaging insect herbivores) (Aebi et al. 2006) or they may inhibit the success of insect herbivores that act as biocontrol agents (Paynter et al. 2010). Despite studies of the interactions between parasitoids, their hosts and the host plant, a lack of knowledge remains for a great number of tri-trophic interactions (reviewed in Lewinsohn et al. 2005; Paynter et al. 2010). Major differences between ecologically similar or taxonomically related taxa have made it difficult to determine universal tri-trophic interaction patterns, so further species-specific work is needed (Sasakawa et al. 2013)." FURTHER INFO Tephritid flies include well-known pests such as the Mediterranean fruit-fly. Here we studied a related species and found that parasitoids were able to locate tephritid pupae equally-well regardless of where they were located on the plant and regardless of other plant attributes. Understanding how parasitoids interact with their prey is an important step towards better biocontrol of pest species.