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Johnston (T. H). Biological Control of the Prickly-pear Pest. — 



Queensland Agric. J I., Brisbane, xvi, no. 2, August 1921, pp. 65-68. 



A few years ago it was estimated that over 22,000,000 acres in eastern 

 Australia were infested with prickly pear, or one-third more than the 

 total cultivated area in the continent. 



Attempts have been made to control this pest by legislation, by 

 mechanical methods, by chemical means, and, to a slight extent, by 

 biological agencies. The most effective, so far, has been the chemical 

 method, but its cost is frequently prohibitive, and it does not afford 

 protection against fresh invasions of the plant. 



The biological method has not yet been given a fair trial. As a 

 result of the work of the Travelling Commission appointed by the 

 Queensland Government, two natural enemies, Dactylopius [Coccus) 

 confusus indicus and D. (C.) confusus capensis were introduced [R. A.E., 

 A, iii, 125] and became established. It is unfortunate that they attack 

 Opimtia monacantha only, to which the former is so injurious as to 

 effect eradication in all districts where it has access to this cactus. 

 It is possible that D. (C.) confusus indicus may be a native of South 

 America, and that the species described from Argentina, Coccus 

 argentinus, may be synonymous. It is also possible that D. confusus 

 indicus may not normally attack 0. monacantha in South America, 

 but that it may infest some other species of cactus in a less injurious 

 manner. 



The above-recorded success led the Commonwealth Institute of 

 Science and Industry to invite the co-operation of the Governments 

 of the Commonwealth, New South Wales and Queensland, and a 

 scheme, which came into operation officially in June 1920, was devised 

 to provide for the collection and shipment of desired material from 

 North and South America. 



The author brought some natural enemies from South America, 

 the chief being two fungi, Sclerotinia cactacearum and Montagnella 

 opuntiarum, and a Syrphid fly. The fungi are being experimented 

 with ; the flies that were bred from the imported Syrphid larvae 

 have failed to reproduce themselves. 



A collection of cactus insects, fungi and bacteria that has been 

 recently received from southern Florida and Texas includes the moth- 

 borer, Melitara prodenialis ; the weevils, Gerstaeckeria hubbardi, G. 

 nobilis, G. porosa, G. clathrata, and G. basalis ; the bugs, Chelinidea 

 vittigera and another species of this genus ; one or two kinds of wild 

 cochineal insects ; three or four species of scavenging flies which 

 breed in injured plants — Volucella esuriens, V. fasciata, Copestylum 

 marginatum and a large dark-coloured species of Hermetia ; four 

 fungi, Gloeosporium lunatum, Hendersonia opuntiae, Phoma sp. and 

 Perisporium wrighti ; and a bacterial rot. 



A consignment of material from Argentina, which should reach 

 Brisbane shortly, contains the Argentine cochineal insect, as well as 

 the fungi, Sclerotinia and Montagnella, mentioned above, and the moth- 

 borer, Cactoblastts (Zophodia) cactorum, the attempted introduction of 

 which by the Queensland Travelling Commission had been unsuccessful. 



The laborator}^ has also received some wild cochineal, Coccus 

 tomentosus, from California. It is apparently the same as the Texan 

 form recently received and has attacked three Queensland prickly 

 pears : the common prickly pear, the spiny pear of the Burnett and 

 Rockhampton districts, and the tree pear (0. tomentosa). Up to the 



