164 



infection to the next one invaded by them. The organism wovild also certainly 

 be transmitted by similar Pyralid larvae (Cactoblasfis cactornm and C hucyrus) 

 which attack cacti in South America. 



The boring larvae of the cactus longicorn beetles, Moneilcma spp., also 

 may act as transmitters as a result of contamination, and thus their action in 

 destroying old stems and underground parts of prickly pear plants may be 

 accelerated. 



The common ferment flies (Droso])hilidae) which invade ripe and rotting 

 fruit, decaying vegetation, etc., in Brisbane, are attracted to decomposing prickly 

 pear, in \\fcliich they readily breed and on which they feed. The flies are capable 

 of acting as transmitters of the disease by infecting injured surfaces of segments. 



A series of experiments was carried out, using the following four species 

 of cactus bugs: Cheliiiidcs vittigcra (Texas), C. vittigcra [?] (Florida variety), 

 C. ca)ivona, and C. tabiilata, which were allowed to feed on obviously diseased 

 segments for a few days and then transferred to healthy segments, but in no 

 case did infection result. Perhaps the outside of the rostrum of the bugs may 

 have become cleansed during the act of puncturing the tissues of the plant to 

 which they had been subsequently transferred. 



The effect of B. cacticidus on a variety of crops and fruits was tried out 

 in the laboratory. In the case of growing plants the surface of leaves was 

 scratched and material from an active culture was placed in the injuries, but 

 no disease developed. The plants so tested were wheat, barley, oats, maize, and 

 legumes. Direct inoculation as well as attempted infection of scratches was 

 tried in the case of banana plants, but without success. The organism was 

 inoculated, but failed to produce any disease, in the following fruits : apple, 

 pear, plum, peach, banana, mango, pineapple, custard apple ; also in carrots, 

 parsnips, beet, turnips, cabbage, cauliflower, lettuce, and sugar-cane. It was 

 found that hard cucurbitaceous fruits such as the pumpkin were not affected, 

 but that the more pulpy kinds such as squashes, melons, and marrows were, 

 the parenchyma completely breaking down into a liquid as a result of deep 

 inoculation even from an agar culture. Under ordinary conditions of tempera- 

 ture potatoes were not affected by inoculation, but if kept in an incubator at 

 37° C. then decomposition was produced. 



The disease was not encountered anywhere in the United States, except in 

 Miami, Florida, either by the senior author or by his colleague, Mr. J. C. Hamlin. 

 The garden from which the original material was obtained is primarily utilized 

 for growing tropical agricultural plants and various kinds of citrus fruits. As 

 any lesion on fruits would soon be observed, and if unknown to those in charge, 

 would be submitted for expert examination, it is reasonable to assume that citrus 

 fruits are not susceptible to attack. 



It seems as if B. cacticidus may play a very important role in prickly pear 

 eradication in Australia during the warm moist summer, by becoming associated 

 (as a result of contamination) with the larval stages of the moths Mclitara and 

 Mimorisfa especially, and. to a less extent, the adult Drosophilid flies and the 

 larvae of Moneilcma beetles, but without these aids the organism will at most 

 I)roduce only a local lesion on the plant, acting as a wound parasite. 



The following species of prickly pear occurring naturalized in Australia 

 are susceptible to attack, viz., Opuntia tomcntosa, 0. incrtnis, 0. stricta, O. 

 aurantiaca, 0. mcgacantha, 0. ficus-indica, and O. monacantha (vulgaris). It 

 can be safely assumed that the remaining species which occur more sparsely in 

 our continent are also susceptible. 



