Insects in Relation to Prickly Pear Control.
In view of the menace to agriculture in South Africa from prickly-pear (Opuntia spp.) and the importance of promptly tackling the problem of its eradication, the author reviews the biological means of dealing with it that have proved so successful in Australia. The principal species occurring in South Africa are O. decumana, O. decumana var. spinosa (the former being obtained from the latter by selective cultivation and being a very valuable fodder plant) and O. aurantiaca, which is the most dangerous species and is spreading rapidly. In 1913, Dactylopius ceylonicus, Green (indicus, Green) was introduced into South Africa. It confined its attack to O. monacantha and within a few years practically exterminated that species. About five years ago, Cactoblastis cactorum, Berg, which has been the outstanding success against Opuntia in Queensland [R.A.E., A, xviii, 287], was introduced, and, although effective in destroying O. decumana var. spinosa and O. aurantiaca, proved equally destructive to the valuable O. decumana, and also showed a tendency to feed to a slight extent on economic plants other than cactus. All the colonies were therefore destroyed, and while developments in Australia are being carefully watched, landowners in South Africa are advised for the present to resort to chemical methods of destroying Opuntia.