Observations on circular purple scaleChrysomphalus aonidum (Linn.), and two introduced parasites in western Transvaal citrus orchards

Circular purple scale,Chrysomphalus aonidum (Linn.) is localized in its appearance in South African citrus orchards. It mainly occurs along the Natal Coast, the Western Transvaal and the Transvaal Lowveld. In the Western Transvaal its importance was highlighted by the development of biological and integrated programmes chiefly directed against red scale Aonidiella aurantii (Mask.)]. This paper reports on an attempt at the biological control of circular purple scale in the Western Transvaal by introducingComperiella bifasciata. The eggs ofC. aonidum, at 26.7°C and 50% relative humidity, hatches within two to three days. The female has two and the male four moults. The first eggs are laid approximately 43 days after settling of the crawler.C. aonidum has 4 broods a year. C. bifasciata, circular purple scale strain, is uniparental. The adults can live for only one day without food, but from 3–22 days in the laboratory when fed on honey. The photopositive adults lay the eggs internally in female scales, male scales being seldom parasitized. The eggs hatch in 3–4 days of which a female parasite lays an average of 37. The larval stages occupy 13–15 days and the pupal stage 7 days. Superparasitism does occur in which case only one larva reaches maturity. The length of the life cycle varies in various stages ofC. aonidum, the shortest was in scales 25–35 days old. ThoughC. bifasciata was established after release in citrus orchards, it maintained itself at very low levels or disappeared in competition withAphytis holoxanthus.