294 Miss Haviland, Note on the Life History of Lygocerus 



Lygocerus cameroni was fairly common round Cambridge in 

 1919, from mid-July to the end of August. The female selects an 

 aphis-cocoon containing a full-grown larva or newly transformed 

 pupa of Aphidius, and runs round it with much excitement, 

 tapping it with her antennae. Oviposition takes from 30-60 

 seconds, the insect meanwhile standing either on the top of the 

 cocoon facing the anterior end, or on the leaf behind, with her back 

 to it. Either way, the ovipositor is brought into the angle of the 

 host's body, as it lies curled inside. Sometimes two or three eggs, 

 the result of successive ovipositions by different females, are 

 found on the same host. 



The egg, which is laid on the upper surface of the abdomen of 

 the Aphidius, measures -25 x -10 mm. It is translucent, white, 

 and elliptical, with marked longitudinal striae of the chorion, and 

 a minute stalk at one end. Treatment of the egg with lacto-phenol 

 and cotton-blue showed the presence of bodies resembling the 

 symbiotes from the pseudovitellus of Aphides. The egg hatches in 

 about twenty hours. 



The larva of the first instar is a maggot shaped form, with 

 thirteen body segments and a head furnished with two minute 

 papillae. The mouth, which is circular and very small, contains 

 two simple chitinous mandibles set well behind the hood-hke 

 labrum and the labium. The mid-gut, which at this stage does not 

 communicate with the rectum, is large and globose, and its con- 

 tents tinge the transparent body pale yellow. Later on, when the 

 host dies, they become brown. The tracheal system consists of two 

 lateral longitudinal trunks, united by an anterior and posterior 

 commissure. When newly hatched, there are two open spiracles 

 between the first and second and on the fourth segments, but 

 soon afterwards the spiracles of the third and fifth segments 

 become functional. The larva is active and crawls over the host's 

 body. This instar lasts from twenty to twenty-four hours, and the 

 dimensions are about -45 x -22 mm. 



The larva of the second instar differs from that of the first 

 chiefly in the size, which is -70 x -35 mm., and in the tracheal 

 system. The ramifications of the latter are more numerous, the 

 dorso- ventral branches of the second segment become visible, and 

 the spiracular trunks of segments six, seven, and eight appear, 

 though their spiracles are not open. The duration of this instar is 

 about thirty-six hours, and at this time the host usually dies, and 

 its body becomes blackened and shrunken. 



In the third instar, the papillae on the head disappear, the body 

 becomes more globose, and the greater proportionate development 

 of the three first segments causes the head to be bent round to the 

 ventral side. The dimensions are about 1-00 x -75 mm. The spiracles 

 of the sixth, seventh and eighth segments open, and the spiracular 



