June, 1922 bionomics of alphelinus semiflavus 227 



Larva. 



Description. — The larva when first hatched has practically 

 the same size and form as the egg, but slightly shorter and 

 broader. As growth proceeds the anterior and middle segments 

 enlarge to accommodate the increasing mesenteron, giving it 

 at first a spindle form and later a distinct top shape; the head 

 forming a knob on the broad rounded anterior end, and the 

 posterior tapering to a rounded point. When the larva reaches 

 maturity it is contracted more in a longitudinal direction, 

 becoming almost globular in general shape. (Fig. 7, Plate I). 



In the younger stages the color is almost absent, except the 

 dark mesenteron which stands out against the general trans- 

 parency. Later on the accumulating fat body lends a light 

 yellow color to the larva. 



The segmentation of the larva is rather obscure, but with 

 careful search thirteen may be counted. The head is distinct, 

 supported by a visible tentorium, and bearing a mouth opening 

 in the anterior ventral portion. This mouth is armed with two 

 sharp dark mandibles which are situated well back in the cav- 

 ity, but are capable of protrusion sufficient for grasping pur- 

 poses. A peculiar botryoidal structure may be also observed 

 covering the front and vertex. (Fig. 8, Plate I). This is prob- 

 ably a group of sensory organs. The entire digestive tract may 

 be traced from mouth to anus in transmitted light; though 

 the fore and hind guts-are indistinct. Several other internal 

 organs were slightly visible, but no attempt was made to iden- 

 tify them. Spiracles are observable on segments five to nine 

 inclusive, but could not be seen on any of the others. Small 

 trachcce lead off from these, but it was not determined whether 

 they function or not. 



Position in Host. — During most of the growing period the 

 larva occupies no definite position in the host, but moves 

 freely about in the fluid of the body cavity. However, when it 

 has devoured most of the internal organs of the host and has 

 become large enough to fill the abdominal cavity it assumes 

 a position with its primary axes similar to those of the host. 

 Just before pupation this position is exactly reversed, so that 

 the primary axes of the parasite are opposite to those of the 

 host, both anterior-posteriorly and dorso-ventrally. 



