THE MARGUERITE FLY. 51 



Injury and Seriousness of the Pest. 

 The injury is caused by the larvse or maggots mining within the leaves, 

 and living upon the mesophyl or fleshy portion of the same. The mining 

 is seen on the surfaces of the leaves as irregular, whitish lines or patches, 

 the latter often extending to take in the whole surface, and causes the 

 death of part or the whole leaf. The activity of the larva or maggot 

 results in a serious interference with normal growth, in checking flowering 

 or in the reduction of the number of flowers normally produced, and in a 

 reduction in the size of the flowers. Small plants may be killed in a com- 

 paratively short time if exposed continually to attack. The depredations 

 of the insect are often very serious. In many instances the commercial 

 growing of marguerites and other Compositse have been given up on 

 account of it. 



Life History and Habits. 

 The adult insect is a small, grayish fly, only 2 millimeters, or ^V of an 

 inch, long, with a comparatively broad yellow stripe or band on each side 

 of the abdomen, and may be seen resting, or crawling lazily about, or 

 making its way from plant to plant in a skipping or hopping flight. The 

 female fly, as a rule, lives longer than the male. Females confined with 

 males upon leaves on plants in the laboratory lived as long as a month and 

 a half. One female may lay between 125 and somewhat over 150 eggs 

 during her lifetime. The eggs are laid singty in horizontal incisions made 

 by the ovipositor, between the parenchyma, or flesh, and epidermis, or 

 skin, of the leaf, — principally between the parenchyma and epidermis of 

 the lower surface. ^ Similar incisions are made, but mostly between the 

 parenchyma and epidermis of the upper surface, for purposes of feeding 

 on the juices of the leaf. The eggs hatch in from slightly over four and 

 a half to somewhat over five and a half days. The larvse do most of their 

 feeding immediately beneath the epidermis of the upper surface of the 

 leaf, owing to the better food conditions afforded by the palisade paren- 

 chyma, and may feed as long as seventeen and eighteen days. Pupation 

 takes place within the larval mine, and more often in those immediately 

 above the epidermis of the lower surface of the leaf. The pupa stage 

 lasts, as a rule, from thirteen to fifteen days, inclusive. The mean or 

 average length of a complete life cycle or generation is about thirty-three 

 and one-half days. The lengths of the different stages vary also with 

 the temperature to which they are subjected. The above periods are for 

 a temperature at which marguerites are usually grown. (See temperature 

 in connection with length of egg stage.) 



Control. 

 The insect may be controlled by spraying with the nicotine solutions 

 "Black Leaf 40," "Nico-Fume" Liquid and "Nicoticide," diluted from 

 400 to 450 times in water, and applied at intervals of eleven or twelve 



