416 BIOLOGICAL CONTROL 



fact is all the more remarkable for the reason that only 2,500 eggs 

 (from the Argentine) of the insect were introduced into Australia, 

 yet between 1928-30 about three thousand million eggs, laid by 

 descendants of insects issuing from the original batch, have been 

 distributed in the great prickly pear areas. The eggs are laid by the 

 moth in " sticks," averaging seventy-five eggs in each : these sticks 

 are readily collected and artificially attached to the cladodes of the 

 host-plants. The resulting larvae are gregarious, internal feeders 

 which tunnel in companies through the tissue of the plant, thus 

 also providing for the ingress of disease organisms. In this way 

 the prickly pear ultimately becomes so completely destroyed that 

 it is reduced to a rotting mass of pulp. The various insects, 

 established prior to the Cactoblastis, have either been largely 

 suppressed or their activities nullified, owing to competition with 

 its larvae. It is only locally, and in relation to a few species of 

 Opuntia of lesser importance, that the Cactoblastis has proved 

 more or less ineffective. Such problems, however, are being dealt 

 with through the operations of other phytophagous insects, 

 including cochineal (Dactylopius) and Ccrambycid beetles. To-day, 

 the enormous rate of increase of the prickly pear has been arrested 

 and less than 10 per cent, of the former great body of infestation 

 survives : the whole of the primary pear in Queensland and much 

 in New South Wales has broken down and collapsed. Approxi- 

 mately 25 million acres of good land are now" cleared and are being 

 developed and brought under production. 



Control of Prickly Pear in other Lands. The spectacular success 

 attending the control of prickly pear in Australia has rather 

 masked the efforts made to check Opuntias in other lands. In 

 Ceylon an extensive area of the Northern Province was formerly 

 infested by Opuntia monocantha, but was ultimately almost 

 completely exterminated by the cochineal Dactylopius ceylonicus, 

 which is stated to have come from Madras. This insect, it may 

 be added, has exercised a high degree of control over 0. monocantha 

 in many parts of India for a number of years past. According to 

 Jepson (1930) the cochineal insect has not maintained the same 

 efficiency in controlling this species of prickly pear in the Southern 

 Province of Ceylon. Another Opuntia, viz. 0. dillenii, has become 



