Evidence of an extractable semiochemical produced by Rhopalosiphum padi acting on Psammotettix alienus

It has previously been shown that the aphid Rhopalosiphum padi (L.) (Homopt era: Aphididae) adversely affects the biology of the leafhopper Psammotetti x alienus (Dahlbom) (Homoptera: Cicadellidae) (Alla et al., 2001). In this work, we demonstrate that this effect was due to chemical components produc ed by the aphid. The increase in the number of aphids in the presence of the leafhopper on w heat caused nymphal mortality, an extended duration of the development and a decrease in nymph production of the leafhopper. Extract of aphids in meth anol-water (50/50: v/v), applied on plants significantly increased the mort ality in the leafhopper nymphs at both 3AE (3 Aphid Equivalent) and 7AE dos es. At the same doses, both the honeydew and water extract of aphids did no t have any effect. At the 20AE dose, aphid extracts in methanol-water led t o a longer development time and strong mortality in leafhopper nymphs. In f emale adults of the leafhopper, neither the aphid extracts in methanol-wate r nor the honeydew showed a conclusive result, but generally, daily nymph p roduction decreased with the increase in the extract doses. These results confirmed the depressive effect of R. padi on P. alienus and showed that this interaction was chemical. The active component(s) is parti ally extracted in a blend of methanol-water (50/50: v/v). Further studies t o identify this component(s) will be undertaken.