SCALE MORPHOLOGY EFFECTS ON FEEDING-BEHAVIOR AND BIOLOGICAL-CONTROL POTENTIAL OF RHYZOBIUS-LOPHANTHAE (COLEOPTERA, COCCINELLIDAE)

We compared the morphological characteristics of tile scale covers and bodies of 2 economically important scale species, California red scal e, Aonidiella aurantii (Maskell), and oleander scale, Aspidiotus nerii (Bouche), to determine their protective value against predation by th e coccinellid Rhyzobius lophanthae (Blaisdell). We also compared the m or phology of the mandibles of R. lophanthae with that of Chilocorus c acti (L.), a specific predator of diaspidid scales. A higher percentag e of R. lophanthae larvae survived when they fed on 2nd- and 3rd-insta r A. aurantii and all stages of A. nerii than when they fed on gravid and parturient A. aurantii. Adult R. lophanthae took longer to consume 3rd-instar A. aurantii than 3rd-instar A. nerii and were frequently u nable to penetrate the scale body of gravid and parturient A. aurantii . Predator preference for scale stage and species reflected the ease w ith which it was able to penetrate the scale cover and body of its pre y. The hardened scale cover of gravid and parturient A. aurantii when coupled with the sclerotized scale body provided the scale with substa ntial immunity to predation by R. lophanthae for approximately two-thi rds of the scale life span. We conclude that R. lophanthae is unlikely to suppress A. aurantii populations below those of economic concern w hen it is the sole biological control agent present. In contrast, the entire life span of A, nerii is vulnerable to predation, and this spec ies appears to be suppressed to low densities by R. lophanthae.