26 MASS. EXPERIMENT STATION BULLETIN 157. 



Phytomyza, but now raised to generic rank by some writers), but this is 

 clearly an error, as the keys in the literature referred to in the catalogue 

 place the insect in the older genus Phytomyza, the posterior cross vein 

 being absent in chrysanthemi. 



Sanders (Journal of Economic Entomology, Vol. V., No. 6, December, 

 1912, p. 472) has already referred to the insect by this catalogue name. 



INJURIES. 



(Plates II. and III., Figs. 9, 10, 12.) 



The first indications of the activity of the insect are seen in minute, pale 

 specks, blotch-like, and usually fan-shaped, on both surfaces of the leaves 

 (Fig. 9). As a rule, they are more numerous on the upper side. These 

 specks or blotches are produced by the adult female fly, which pierces the 

 epidermis and destroys the parenchyma beneath by means of her oviposi- 

 tor, for the purpose of feeding or egg laying. 



These blotches, however, do not long retain their original appearance. 

 In a few days, as a result of a reaction on the part of the injured paren- 

 chyma, they usually develop into wart-like protuberances or papillae 

 (Fig. 9) ; and when the flies are abundant, during a period of great activity, 

 the surfaces of the leaves may be literally covered with the papillse, or 

 papillce and blotches together. On the other host plants which were kept 

 under observation in the insectary the papillse developed less readily, and 

 as a rule, less perfectly. 



The real damage, however, is caused by the larva or maggot. Seem- 

 ingly possessed of a tireless energy and of appetites which never seem to be 

 satisfied, the maggots move slowly along beneath the epidermis (most of 

 the feeding is done immediately beneath the epidermis of the upper sur- 

 face) of the leaf, devouring the parenchyma in their course, and leaving a 

 whitish and usually irregular path — the external evidence of the mine 

 which lies directly beneath — in their wake, the white color of which con- 

 trasts sharply with the green color of the rest of the leaf surface (Fig. 10). 

 The mihe widens and becomes more distinct as the larva increases in size. 

 The part of the leaf thus mined (the petiole very often also), or the whole, 

 if it is badly attacked, gradually dries up, and in this withered condition 

 remains clinging to the plant (Fig. 12). Small plants may be kiUed in a 

 comparatively short time during a period of great activity of the flies. 



In reply to some questions of the writer in regard to the resulting injury, 

 Mr. Walker Holden, who kindly furnished the infested marguerites for 

 study, states that "the infestation reduces the number of flowers and 

 weakens the plants to a very great extent." Moreover, he is of the 

 opinion that, because of the reduced vigor of the plants, there is a ten- 

 dency towards a reduction in the size of the flowers. 



Of the plants (feverfews, yellow marguerites, and white marguerites) 

 attacked in Mr. Holden's greenhouse, the yeUow marguerites were the 

 most seriously affected — so seriously that he destroyed them. Of the 



