Comparative Behavior and Competition Between Two Aphid Hyperparasites: Alloxysta victrix and Asaphes californicus (Hymenoptera: Cynipidae; Pteromalidae) 1

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Abstract
A series of laboratory experiments was conducted to study one of the possible explanations why the endoparasitic hyperparasite, Alloxysta victrix (Westwood), was numerically more abundant by a 2:1 ratio in previous field studies over the ectoparasitic hyperparasite, Asaphes californicus Girault. It was hypothesized that perhaps a time factor or the day of attack in reference to the developmental stage of the Alloxysta larva/pupa within the aphid mummy could influence the competitive success or failure of the female Asaphes in her attempt at hyperparasitization as a tertiary. The host aphid was the pea aphid, Acyrthosiphon pisum (Harris), and the primary parasite was Aphidius smithi Sharma & Subba Rao. The developmental time of the 1st hyperparasite, Alloxysta, inside the aphid mummy was long enough to permit 11 test-days for attack by the 2nd hyperparasite, Asaphes. Results of these laboratory experiments on hyperparasite competition indicated that 89.3% of the hyperparasites which emerged from mummies containing Alloxysta and attacked by Asaphes during the 1st half of the test-period (Days 1–6) were Asaphes, and only 10.7% were Alloxysta. However, during the 2nd half of the test-period (Days 7–11), successful hyperparasitization by Asaphes decreased to 33.4%, and conversely 66.6% of the Alloxysta survived this attack and emerged as adults. Thus, the ectoparasitic Asaphes does not invariably dominate the endoparasitic Alloxysta when the 2 hyperparasites come into direct association, as had been supposed. The numerical abundance and apparent competitive superiority of Alloxysta over Asaphes in previous field studies is due not merely to its greater specificity and higher searching efficiency, but to its ability to compete successfully with Asaphes by increasingly surviving attack the later this occurs during its development inside the mummy.

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