The influence of the parasite Comperiella bifasciata How. on the populations of two species of armoured scale insects, Aonidiella auramtii (Mask.) and A. citrina (Coq.), in South Australia

Abstract

C. bifasciata is an internal parasite of the armoured scales A. aurantii, red scale, and A, citrina, yellow scale. The red-scale race of this parasite stabilizes the population of A. citrina, buthas little influence upon populations of A. aurantii. Itis suggested that these different outcomes are due not to the population biology of the parasite, but rather to the different biological characteristics of itstwo hosts. Experiments show that, in the case of mature A. aurantii, the effects of parasitization are offset to some extent by the killing, through encapsulation, of a minimum of nearly 60% of the immature stages of C. bifasciata; 50% of these parasitized scale survive and reproduce. On the other hand, nearly 100% of the eggs of C. bifasciata laid in A, citrina develop normally, lead to successful eclosion, and thus kill their host. Field samples of scale corroborate this difference in the ability to encapsulate the immature stages of C. bifasciata. Parasites that feed externally on their hosts are not subject to the hosts' immune responses in the same way as C. bifasciata in A. aurantii, and for this reason may have a greater influence on populations of their hosts than internal parasites under the same conditions.