Uncoupling physical and chemical cues: The independent roles of scale cover size and kairomone concentration on host selection byAphytis melinus DeBach (Hymenoptera: Aphelinidae) |
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Authors: | D J W Morgan J D Hare |
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Institution: | (1) Department of Entomology, University of California, 92521 Riverside, California |
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Abstract: | The ectoparasitoidAphytis melinus initially selects its host, California red scale,Aonidiella aurantii (Maskell) (Homoptera: Diaspididae), using characteristics of the host’s cover before assessing the quality of the scale body
beneath. Host suitability is known to increase with host size until the scale insect reaches maturity, after which it is no
longer available for parasitism. The wasp uses a combination of scale cover size and a kairomone,O-caffeoyltyrosine, in the cover for initial assessment. Under natural conditions these two factors are frequently coupled.
We quantified the relative importance of cover size and kairomone concentration independently by removing and selectively
reapplying controlled doses of syntheticO-caffeoyltyrosine to scale covers of known size. In the absence of the kairomone, wasps did not discriminate among scale covers
differing in size. Wasps showed a curvilinear response to kairomone dose for each scale cover age group. Wasps preferred low
doses ofO-caffeoyltyrosine on young, small scale covers, and high doses on old, large scale covers. The ability of wasps to respond
quantitatively to the kairomone may be used in the field to differentiate small second-instar from larger and more suitable
third-instar scale insect larvae. |
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Keywords: | O-caffeoyltyrosine parasitoid host quality scale cover Diaspididae |
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