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Aphytis melinus, an ectoparasitoid of California red scale, Aonidiella aurantii, replaced A. lingnanensis, another ectoparasitoid, in certain California citrus areas during the 1960's following the form~r's introdu~tion i~ _1956-1957. We show that, although both species attack a similar range o~ host slZes, A. melm~ _utiltz:s a smaller threshold scale size for the production of daughters. Size differences of scales Withm a cttrus tree (largest scales occur on fruits, smallest on wood, and intermediate on leaves), seasonal variation in scale age structure, multivoltinism of the scale and parasitoid populati'?ns, seasonal availability of citrus fruits (the substrate that supports the largest scales), dif-feren~s m the ~emp:ratur~.tolerances oft~e two par~sitoid species (A. lingnanensis is less tolerant), and differences m thetr vagtltty (A. melmus ts more vagtle), probably all favor A. melinus in competition with A. lingnanensis. A. lingnanensis does not realize its fecundity advantage in female progeny when these species compete because A. melinus preempts California red scale before it grows into the size range preferred by A. lingnanensis. Collection records through 1972 show that A. melinus continued to extend its geographical range coastally in southern California through 1972.

1. The ovipositional and egg allocation behaviour of individual females of Aphytis melinus DeBach and A.lingnunensis Compere were compared.2. Both Aphytis species exhibit the same behavioural sequence during oviposition.3. Aphytis melinus laid most of its female eggs on the dorsum of a scaleinsect beneath its cover, and most of its male eggs under the scale-insect's body. Aphytis lingnanensis also oviposited both dorsally and ventrally on scale-insect hosts, but female and male progeny arose with equal frequency from eggs laid in both locations.4. Both Amelinus and A. lingnanensis are facultatively gregarious parasitoids. The degree of gregariousness depends on host size, i.e. the larger the host, the more the Iikelihood that several eggs will be deposited at each visit by the parasitoid.5. When two eggs were laid during the same host visit, both Amelinus and A.lingnanensis laid one female and one male egg more often than would be expected under an assumption of random allocation of sexes.6. Because A.melinus successfulIy utilize smaller hosts than A h p a n e n s i s to produce progeny, these parasitoids should not be considered ecological homologues, as suggested by DeBach & Sundby (1963).

C. chinensis larval amylase is activated by Ca(2+) and inhibited by Cl(-) and EDTA (K(i) 6.7x10(-3)m). GSH and 2-mercaptoethanol activate, presumably at different sites, as 2-mercaptoethanol interferes with Ca(2+) activation, whereas GSH enhances it. The inhibition by iodoacetic acid and N-ethylmaleimide (K(i) 1.55x10(-2)m) suggest that free thiol groups are essential for activity. The pH optimum of 5.2-5.4 is moved to 5.6-5.8 by Ca(2+) and 2-mercaptoethanol. The activation energy is 7270 cal/mol, and is not affected by Ca(2+) and 2-mercaptoethanol. K(m) for soluble starch is 2.3mg/ml.

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