Abstract
The aphid parasitoid Aphidius ervi was collected and subsequently reared on Sitobion avenae on wheat or Acyrthosiphon pisum on alfalfa. Parasitoids from both origins were exposed in an olfactometer to alfalfa or wheat volatiles after plant experience (wheat or alfalfa) or after oviposition experience (S. avenae on wheat or A. pisum on alfalfa). The results showed the importance of adult experience, conditioning and innate preferences on the responses of A. ervi toward volatiles and provided a mechanistic explanation to the high prevalence of A. ervi on aphids on cereals and legumes in central Chile.
Highlights
Aphid parasitoids may use a variety of chemical cues for habitat and host location (Mackauer et al, 1996; Poppy et al, 1997)
When the parasitoids were reared on the pea aphidalfalfa system, both experience on the host-plant and oviposition experience on pea aphids on alfalfa resulted in a significant parasitoid preference toward alfalfa volatiles in relation to wheat volatiles (Table 1)
The results with parasitoids collected on alfalfa and reared on alfalfa or wheat and subjected to oviposition experience on a host-plant complex, agreed with previous work reporting the importance of associative learning for A. ervi (Du et al, 1996, 1997; Powell et al.,1998), as well as for other aphid parasitoid species (Sheehan & Shelton, 1989; Grasswitz & Paine, 1993a, 1993b) and parasitoids of other insects (Vet & Dicke, 1992; Turlings, 1993)
Summary
Aphid parasitoids may use a variety of chemical cues for habitat and host location (Mackauer et al, 1996; Poppy et al, 1997). A. ervi is known to be attracted by host-plant volatiles (Powell & Zhang, 1983) and by pea aphids feeding on Vicia faba (host-plant complex) (Du et al, 1996) This parasitoid was introduced as a biocontrol agent in Chile during three consecutive years (1976-1978). As suggested earlier by Starý (1993), the occurrence of the parasitoid in cereals and legumes may be due to the proximity with which these crops are grown We tested this hypothesis by investigating the attraction of the parasitoid toward wheat or alfalfa mediated by host plant semiochemicals, and the effect of previous experience of the foraging parasitoid upon this attraction to the volatiles. Parasitoid behaviour was assessed using olfactometric assays, following expo sure to host plants (wheat and alfalfa) and oviposition experience on Sitobion avenae Fabr. on wheat and A. pisum on alfalfa
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