77 



The larva gains an entrance at an areole 

 and mines into the surrounding tissues, stimu- 

 lating them to activity so that there is produced 

 a small tumour rather paler in -colour than the 

 general plant surface. Some of the attacked 

 joints had, in spite of the presence of galls, main- 

 tained normal growth, while in the case of others 

 a decay had set in which either might be local 

 or might spread from the site of insect attack so 

 as to involve the entire segment. Occasionally 

 a similar decay was seen in joints which did not 

 contain any galls. Under the conditions of the 

 glass-house, death commonly follows. Owing to 

 the ravages Dr. Britton had lost about 150 plants 

 — all of them flat Opuntias or Nopaleas, any of 

 which seemed to be susceptible to attack, though 

 no other plants were observed to have been 

 infected. An examination of the bundle of 

 labels, which belonged to dead prickly-pears, 

 showed that amongst others the following species 

 had succumbed: — 0. tomentosa (which is the 

 Helidon tree-pear in Queensland) ; 0. inermis 

 (the common pest pear of Queensland) ; 0. 

 streptacantha (a species related to the " West- 

 wood Pear " of the Rockhampton district, 

 Queensland) ; 0. dillenii and 0. tuna (both rela- 

 ted to 0. inermis) ; 0. microdasys and 0. nigri- 

 cams (both of which occur naturalised in New 

 South Wales) ; and Nopalea cochinelifera (one 

 of the tree-pears at Gayndah). 



Since this insect had proved itself to be so 

 destructive to prickly-pears in cultivation and 

 was, as far as known, restricted not only to the 

 Cactaceffi, but to the flat Opuntias within that 

 natural order, a visit was paid to Albany in order 

 to consult Mr. E. P. Felt, the New York State 

 Entomologist, who is a recognised authority on 

 the CecidomyiidEe, and who is the author of the 

 original description of the insect (1910, p. 10; 

 1914). 



With regard to the general food relations of 

 the Cecidomyiidse, Mr. Felt referred to two 

 papers — (1) "A Summary of Food Habits of 

 American Gall Midges " (Annals Ent. Soe. 

 America, 4, 1911, pp. 55-62), and (2) " Hosts 

 and Galls of American Gall Midges " (Journal 

 of Economic Entomology, Oct., 1911, pp. 451- 

 475) — in which the information relating to this 

 subject is condensed. The observations of him- 

 self and of other specialists in this insect group 

 pointed to the fact that these flies, in establish- 

 ing relations with plants, either confined their 

 attention to single plant-species or to the mem- 

 bers of single genera. When, exceptionally, this 

 was not so they attached themselves to closely 

 allied plants in a single natural order. Thus 

 Asphondylia monacha attacked the flowers of 

 two Compositae, Aster and Solidago, while Geci- 

 domyiia {Phytophaga) destructor confined its 

 attacks to the two grasses, Hordeum (barley) and 

 Triticum (wheat). 



Pour kinds of Cecidomyiid flies attacked 

 prickly-pear — i.e., three species of Asphondylia 

 that were fruit-lovers and the one that is now 

 under notice. These four gall-midges were quite 

 distinct from any other insects of the group, and 

 it was almost a certainty that no plants other 

 than the Caetacese would serve as hosts for them. 

 Of the eight or nine hundred different kinds of 

 CecidomyiidEe in North America, Mr. Felt had 

 examined specimens of most of them, and of 

 these he had reared about five hundred himself. 

 His opinion is thus based upon a wide knowledge 

 of the gall-midges and their plant relations. 



The group Itonida?, which included the New 

 York pricldy-pear midge, was a fairly large one, 

 and in the majority of cases its members laid 

 their eggs in and developed in the buds of plants. 

 The species of the type genus Itonida itself, as 

 shown by his recorded rearings, had very varied 

 plant connections, but notwithstanding only 

 three species were associated with any of the 

 cultivated or economic plants of Australia — viz., 

 Itonida tritici, found in the heads of rye and 

 wheat; I. cucurbita', on rough squash; and I. 

 manihot, forming small leaf -scales on Cassava. 



Cecidomyiids formed swellings on twigs, 

 galls in or on leaves, &c., and sometimes injured 

 terminal buds, but, as a rule, they did not destroy 

 plants. The Hessian fly and sorghum midge were 

 exceptions. 



He concurred with the Commission in con- 

 cluding that whatever injury to the prickly-pear 

 accompanied the presence of Itonida opuntim 

 was most probably due to the action of fungoid 

 or bacterial organisms whose presence and 

 development were made possible by the insect 

 attacks, simple galls being formed, but no further 

 lesions or abnormalities being caused in the 

 absence of these organisms. 



Influenced by these and other general con- 

 siderations he remarked that he did not see how 

 anything adverse could develop from these insects 

 when in Australia, and that faced by a similar 

 problem to that which confronted the Commis- 

 sion he would not hesitate at all in attempting to 

 establish it there. At the same time, he could 

 not definitely predict any advantageous outcome 

 resulting from such procedure, since it was a 

 matter for experiment. The climatic conditions 

 that this Opuntia gall-midge would encounter on 

 its introduction to Queensland might or might 

 not be favourable to its development and to its 

 destructiveness. He would not expect it to 

 destroy prickly-pear there unless relatively moist 

 climatic conditions were prevalent. On the other 

 hand, it might meet with circumstances to which 

 it might react by ataining great vigour and 

 undergoing such numerical increase as to become 

 very plentiful. He considered that the Commission 

 was quite justified in deciding to advocate the 

 introduction into Australia, and the maintenance 

 there under proper safeguards for the time being, 

 of any insect which fed on Opuntia, and which 

 was not at the same time associated with, much 

 less an enemy of, any of the economic plants 

 that were already grown or might be grown there. 

 He doubted, however, if any man could predict 

 from observations in the field alone how an msect 

 would comport itself under novel conditions. 



Owing to the special interest that attaches to 

 this particular gall-midge by reason of its 

 destructiveness under certain conditions, the lol- 

 lowing account taken from the Annual Report of 

 the New York State Entomologist for 1913 (not 

 yet available) may be appended:— 



Cactus Midge— J^owda opunticz, Felt. 

 "Species of Opuntia, the flat-leaved, oval 

 Cacti, not the columnar forms, may be injured 

 bv the deep-red larvas of this midge and most 

 seriously affected by a bacterial or fungous 

 trouble which gains access to the inner tissues 

 through the injuries. The fungus or bacterium 

 is by far the most destructive, and is apparently 

 dependent for favourable media, so far as Cacti 

 are concerned, upon the work of the midge larvae. 



