August, '16] CORY: COLUMBINE LEAF-MIXER 423 



stout; two pairs of dorsocentrals; disc sparsely setose, two erect scutellar bristles. 

 Abdomen setose on lateral margins. Front concave, proboscis light yellow, palpi 

 inconspicuous, black and globular. Cheeks 

 light brown, mesonotum shining black, pleu- 

 ral sutures outlined with light yellow. 

 Wings iridescent, base of veins light yel- 

 low to white, halteres light yellow to white. \^^^ - — ■^'■:lsK ^ ' 



Abdomen black, legs broAvn, yellowish at 

 joints. Venation as in Fig. 26. Ovipositor, 

 brown ^^^- ^^- ^olumbme leaf -miner, wing. 



The Period of Incubation 

 The length of time required for hatching of the egg varies with 

 the different generations. Probably the temperature is the deter- 

 mining factor. Eggs of the first generation require an average of 

 5^ days. Eggs of the second, third and fourth generations average 2 

 days. Averages for the year are of no value. 



Length of Larval Stage 



The length of larval stage seems to be less dependent on temperature 

 than the egg stage. This is shown by the fact that the longest larval 

 period observed in May was 11 days while in June, 12 days was the 

 longest, with an average for the two months, however, of 10.5 days, 

 the same as the average for May. The principal limiting factor is a 

 reduction of the food supply such as occurs when too many eggs have 

 been deposited in a given leaf. Under such circumstances the length 

 of the larval period may be reduced to six days. The normal average 

 for all generations is 10.5 days. 



The Pupal Stage 



The larva emerges from a crescent-shaped cut on the under side of 

 the leaf, remaining attached thereto. In only two instances have lar- 

 vae been noticed pupating on the upper surface of the leaf. The pupal 

 stage of the first and second generations occupj^ an average of 14 days. 

 The third generation may take 19 days for the pupal stage, or, there 

 may be a period of aestivation lasting from the first week in June to 

 the second week in September. The fourth generation winters over as 

 pupae on and in the ground and the compost at the base of the plants. 



Puparia, sifted from the first half inch of soil beneath plants on 

 March 3, gave adults and parasites on April 9, in the insectary. The 

 first individuals appeared out of doors on April 22. 



Parasites 



Thirteen species of parasites have been reared from the columbine 

 leaf-miner.^ As mentioned before, they exert a decided influence at 



1 The author is greatly indebted to Mr. A. B. Gahan for the determination of the 

 parasites. 



