12,2 



Journal of Agricultural Research 



Vol. XVI. No. 9 



The writer has removed a larva from its mine and watched it form a 

 new one. At first the larva cuts a short slit in the epidermis of the leaf. 

 Then by inserting the mouth hooks in this slit and working them back 

 and forth the lower and upper epidermises are separated. The larva 

 then pushes the anterior end of its body into the small opening which 

 it has made. After the first two segments have been forced into the 

 leaf, it is only a matter of a few minutes before the larva works its way 

 completely within it. This operation is accomplished with many vig- 

 orous twists of the body as it is drawn into the leaf. Larvae of the third 

 instar bury themselves completely in the leaf in less than 20 minutes. 



The feeding habits of the larvae are most interesting and can be very 

 conveniently watched under a microscope by means of transmitted light. 

 The pharyngeal skeleton (fig. i, A-D) bearing the mouth hooks, is 

 loosely joined within the first and second segments and is capable of 

 great freedom of movement. These move very rapidly when the larv^a 

 is feeding and are very effective tools for tearing away the parenchyma 

 of the leaf. There are two distinct types of movement which the mouth . 

 hooks possess. First, a lateral movement ; the mouth hooks are turned 

 perpendicular to their normal position and work in the plane of the mine. 

 They strike to the right for a short time, then to the left, separating the 

 upper and lower epidermises but not tearing away any of the tissue. 

 The second movement of the hooks is a vertical one. As the hooks are 

 held in their normal position, they are thrust downward, and pieces of 

 the parenchyma are torn loose from the bottom of the mine. In the first 

 case the two epidermal layers are only separated, while in the second the 

 parenchyma of the leaf is actually removed. 



Table II. — Length of the larval period of Pcgomyia calyptrata 



Experiment No. 



A 126 

 A 129 

 A 13s 

 A 35 

 A 225 



Eggs hatched. 



May- 

 May 

 May 

 July 

 Oct. 



Puparium 

 formed. 



June 7 



June 10 



June 8 



July 12 



Oct. 21 



Length 



of 

 larval 

 period. 



Days. 



16 

 10 



9 

 13 



From Table II it will be seen that the larval period varies somewhat. 

 This variation is undoubtedly due to weather conditions. During warm 

 weather the larvae mature rapidly, but during cooler weather the miners 

 become inactive, and the larval period may be prolonged several days. 

 Unfortunately the table is not complete enough to show this. How- 

 ever, it shows a tendency for a longer larval period in early May and 

 October than in the latter part of May and July. 



