The Coccidae of the Prickly-pear in South India and their economic Importance.
AbstractPreviously recorded observations on the Coccids attacking prickly-pear (Opuntia spp.) in South India, and attempts to use them for the biological control of Opuntia are briefly reviewed. The species growing in South India are O. monacantha, 0. dillenii and O. nigricans. The three species of Coccids present, which are exclusively cactus-feeders, are Diaspis echinocacti, Bch., which does very little damage to the plant, possibly owing to the activities of a Chalcid parasite; Dacty-lopius ceylonicus, Green (indicus, Green), which was introduced into India in 1795, feeds exclusively on O. monacantha and has reduced this plant to almost negligible areas; and D. opuntia, Ckll. (tomentosus, auct.), which is of recent introduction and which feeds only on O. dillenii. This is the commonest species of Opuntia in South India and as D. opuntia is being sent to different parts of the country where it is most needed, it is hoped that within the course of a few years prickly-pear will be rare in the country. In introducing the insects to fresh districts they should be liberated in shady parts of prickly-pear clumps in fine, calm weather; within a week under favourable conditions the larvae will spread over the plants and soon begin to show the white cottony pubescence, the life-cycle requiring about 45 to 50 days. Within a few months, large clumps of the plant die away. In view of the fact that O. monacantha still occurs in isolated spots and its specific enemy, D. ceylonicus has become extremely rare, it is suggested that both species of prickly-pear with their respective Coccids should be cultivated at some centre for use in any future need. The original introduction of D. opuntia was apparently made by a private individual, and it is suggested that the Government alone should have the right to make such introductions and that a strict system of baggage examination and quarantine should be instituted at all ports of entry.
Descriptions are given of the characters distinguishing the Coccids discussed.