40 THE REPORT OF THE No. 36 



doubtless will be found in Ontario and the Maritime Provinces in a suitable 

 environment. Practically all of the injurious species of thrips are contained 

 within the family Thripidse, and they all appear to have similar feeding habits 

 though the parts of plants they affect may differ. The average length of North 

 American species is about 1 mm., and their mouth parts are suctorial. There 

 is a forward and a backward movement of the head which enables the minute 

 styliform mandibles to pierce the epidermal cells of the plant, after which the 

 mouth parts are inserted into the opening formed, pressed down to the labrum 

 and sucking commences. A minute or so is apparently sufficient to remove all 

 the available sap within reach, after which a new location is taken up and the 

 same process of insertion proceeds again. It will not be necessary for me to 

 describe in detail the mouth parts of these minute insects. This has been done 

 on former occasions by several writers. It is only necessary to receive an im- 

 pression on the general motions undertaken and to appreciate the nature of the 

 injuries.. In addition to the often pronounced injuries caused by direct feeding, 

 which may cause "blasting" of the buds and flowers, leaves and seed pods, the 

 oviposition habits must also be noted. Members of the Thripidse are provided 

 with a saw-like ovipositor which is used to cut a cavity in the delicate portions 

 of plant growth, such as the pistils, stamens, developing ovules, fruit and leaf 

 petioles, before an egg is inserted. Microtome sections of such plant portions 

 may frequently disclose as many as 8-10 egg cavities. This habit naturally 

 greatly weakens the plant tissue and it is not surprising to find developing fruits, 

 seed pods, etc., failing to mature or dropping off completely as the season ad- 

 vances, due to oviposition injuries alone. More injury is caused by the feeding 

 habits than by oviposition but, in examination, the latter form of injury must 

 not be ignored. 



There is a third consideration worthy of mention at this point that relates 

 to the plant breeders. I have seen supposedly careful experiments conducted 

 in the cross-breeding of vegetables under cheesecloth and cheap calico screens 

 which, if they were not entirely negatived, were at least severely endangered 

 by the presence of innumerable thrips within the cages to which the screening 

 presented practically no obstacle. Thrips, particularly on bright sunny days, 

 may be observed passing in and out through the screen meshes and although 

 no immediate examination has been made at the time under the binoculars, it 

 is certain that they carried pollen grains attached to their measurably hairy 

 bodies and fringe-like wings, for pollen grains may be quite commonly seen on 

 live thrips gathered from blossoms under somewhat similar conditions. 



It is strange that up until the present time in Canada we can only record 

 one crop which is severely affected by Frankliniella tritici and its allied species, 

 despite the fact that these insects occur so commonly. This crop is alfalfa, 

 and Mr. H. L. Seamans, of the Dominion Entomological Branch, is now making 

 an exhaustive study of the economic relationship of F. occidentalis to alfalfa in 

 the alfalfa seed-producing areas of Alberta. He has already found that in cer- 

 tain seasons fully 80 per cent, of the young florets and seed pods are destroyed 

 or fail to mature by reason of the activities of this species. It seems possible 

 that the future may show these insects to be of more than passing interest in 

 Canada. There are, however, some observations made in the United States. 

 In California, Arizona and Montana, both F. tritici and occidentalis are known 

 to cause much damage to alfalfa, much in the manner already mentioned, 

 wherein the floral parts are attacked, causing the premature falling of the flower, 

 or the ovaries or tender stigmas are injured, preventing the development of the 

 seed pod. In New York State, F. tritici is not usually injurious though a com- 

 mon species in orchards. Parrott, however, in 1909, noted very extreme injury 



