418 BIOLOGICAL CONTROL 



believed from the neighbouring Island of Reunion. The insect 

 spread so rapidly under the prevailing conditions that, in about 

 two 3"ears, the Opuntia was virtually destroyed and the cochineal 

 insect itself became no longer evident. Decary has more recently 

 suggested the introduction of some spineless species of Opuntia 

 suitable to take the place of 0. dillenii, and which, at the same 

 time, is resistant to the Dactylopius. 



Control of Clidemia. An experiment has been carried out in 

 Fiji for the purpose of attempting to control the noxious shrub 

 Clidemia hirta. In Trinidad the plant is not regarded as a pest, 

 and is kept under restraint by a combination of various factors, of 

 which phytophagous insects are but one of them. Studies carried 

 out in Trinidad showed that the Thrips, Liothrips urichi, is common 

 on this plant throughout the Island. It apparently causes its host 

 to become stunted and to flower less freely. It therefore appeared 

 to be a suitable insect for introduction into Fiji, provided that it 

 were proved to exhibit no tendency to attack plants of economic 

 importance. In October, 1929, W. H. Simmonds visited Trinidad 

 and studied the Thrips on the spot. It was found to be attacked 

 by a number of natural enemies which had to be excluded in any 

 effort made to introduce the insect into Fiji. He was able to send 

 a large consignment of the species to Suva, where a proportion of 

 its individuals were released in the field in 1930 and the remainder 

 kept for breeding further stock. The Liothrips has taken readily 

 to Fijian conditions and has continued to spread. To-day it is 

 claimed that it has brought Clidemia definitely under control in 

 large areas. This has been attained not by killing the plant, but 

 by so inhibiting its growth that it is no longer able to compete with 

 dominant local plants. 



Problems in New Zealand. A campaign was inaugurated in 

 1927 in order to attempt the control of four kinds of pest-plants 

 — gorse {Ulex eiiropoeus), blackberry (Ruhus fruticosus), ragwort 

 (Senecio jacobea') and piri-piri (Acama spp.). In the case of gorse 

 the plant is by no means wholly injurious, and for this reason only 

 control of its ultimate spread through seeding was aimed at. In 

 this connection the introduction from England of the pod- 

 infesting weevil, Apion ulicis, shows promise of success and its 



