Environmental variation in physical and chemical cues used by the parasitic wasp, Aphytis melinus, for host recognition

Abstract

AbstractO‐caffeoyltyrosine is a host recognition kairomone for Aphytis melinus DeBach (Aphelinidae) found in the covers of its host, California red scale, Aonidiella aurantii (Maskell) (Diaspidae). This study tests the hypothesis that the concentration of O‐caffeoyltyrosine and scale cover size are reliable indicators of scale body size, an important component of host quality for A. melinus, over a range of scale rearing conditions. Both scale cover area and O‐caffeoyltyrosine concentrations were only qualitatively related to scale body size during the third instar, the scale life stage most suitable for A. melinus. Scale cover area and O‐caffeoyltyrosine concentrations were reduced, relative to scale body size, when scale were reared on bark and leaves compared to fruits. Scale cover area and O‐caffeoyltyrosine concentration were also relatively reduced when scales were reared in mid‐summer compared to spring and fall, and when reared on orange cultivars compared to lemon cultivars in the field. Finally, scale cover area and O‐caffeoyltyrosine concentration were reduced when scale were reared at 52% compared to 100% humidity in the laboratory. Scales appear to be chemically conspicuous to A. melinus for a short period of the time in which they are physiologically susceptible. Scales that minimize their cover size and maximize the incorporation rate of O‐caffeoyltyrosine into covers may minimize their conspicuousness to A. melinus. Minimizing scale cover size, but not necessarily incorporation rates, may make scales more vulnerable to predators, however.