Prickly Pear and Cochineal Insects.
AbstractAt various dates from 1795 to 1836, Dactylopius ceylonicus, Green (indicus, Green) was introduced into India [cf. R.A.E., A 19 535], apparently in mistake for the true cochineal insect, D. coccus, Costa (cacti, auct.). It proved inferior to D. coccus in the production of cochineal, and the industry died out. D. ceylonicus, however, spread rapidly on Opuntia monacantha throughout India, and by the middle of the nineteenth century it had practically eradicated it from northern and central India. About this time, it was taken from Madras to Ceylon, where it rapidly brought the cactus under control [15 100], It has also spread to the sub-Himalayan tract of the Punjab, where it periodically destroys the cactus. Attempts in the late nineteenth century to use D. ceylonicus to control Opuntia in South India failed, because the commonest species there were O . dillenii and 0. nigricans, on which D. ceylonicus does not feed. In 1913, it was sent to Queensland against 0. monacantha [3 126]. In 1924, consignments of the American species, D. opuntiae, Ckll. (tomentosus, auct.) were received from Australia and liberated against 0. dillenii, which was a pest in the north of Ceylon, and in 4 or 5 years it had completely destroyed it [21 262; etc.]. From Ceylon it was unofficially introduced into South India in 1926, whence it has spread rapidly to adjacent districts, occurring throughout an area of over 40, 000 sq. miles by 1930.
For control, heavily infested pieces of the species of Opuntia concerned should be placed in the cactus clumps, preferably on the shady side and in the absence of rain and wind. The young larvae spread on to the healthy cacti, and within 7-10 days begin to cover themselves with a white cottony secretion. Gradually the whole plant becomes covered with a close mass of this secretion, and eventually small tubular cases are formed from which the winged males emerge. The life-cycle of the female lasts about 45-50 days. Dactylopius feeds throughout the year and is free-living for only a short period during the early stages, so that a continuous food-supply is necessary. It is incapable of living on plants other than Opuntia.