Cynijpid hyperparasite of Aphides 237 



these two stages, or whether the change of form was due merely to 

 growth and absorption. In the fourth stage, the tail, appendages, 

 and papillae disappear, and the anus is proportionately smaller 

 than in the preceding instars. 



All this time, the parasite, with its head orientated towards 

 that of the host, lies in the haemocoele of the latter against the 

 distended mesenteron, which, under the pressure, becomes much 

 constricted. The Aphidius remains apparently healthy and retains 

 some power of movement when irritated. It secretes silk as usual; 

 but, immediately after the cocoon is woven, its development is in 

 some way arrested, for the contents of the gut are never voided 

 and metamorphosis does not take place. Death occurs only when 

 the Cynipid larva is almost fully fed, and to the last the tissues 

 remain fresh and undiscoloured. The Charips, which until then has 

 been apneustic, makes its way out through the host's thorax, and 

 its tracheal system becomes functional. Within the next twelve 

 hours the hyperparasite devours the remains of the host, and 

 prepares for metamorphosis within the cocoon inside the aphid's 

 skin already woven by the Aphidius. 



The full-grown larva is an apodous form with a well-developed 

 head and thirteen body segments tapering somewhat posteriorly. 

 The skin is soft and smooth, and the gut contents, seen through 

 the white fat-body, give it a greenish colour. The buccal armature 

 consists of labrum, mandibles, maxillae, and labium. The labrum 

 is crescentic and bears eight small papillae. The mandibles are 

 strongly chitinised, notched, and connected by powerful muscles 

 to the endoskeleton of the head. The maxillae each bears a raised 

 disc on which are three minute papillae, one of which terminates 

 in a short seta. The labium is large and oval, and is furnished with 

 two pairs of papillae. The salivary duct, which is conspicuously 

 dilated immediately below its orifice, opens on the floor of the 

 mouth under the U-shaped hypopharynx. There are six pairs of 

 open spiracles in the full-grown larva, namely, between the first 

 and second segments, and on segments 3, 4, 5, 7 and 9. Two larvae, 

 out of the considerable number examined, had, in addition, a pair 

 of spiracles on segment 8. 



Pupation lasts from three to four weeks, and the total period 

 of development seems to be from thirty to thirty-five days. The 

 imago, when ready to emerge, gnaws a hole in the aphid's skin and 

 creeps out. The adult insects feed on the honey dew of the aphides, 

 which is either sipped from the leaves where it has fallen or else 

 from the anus of the living insect. 



The economic importance of this hyperparasite is probably not 

 great, but to some extent it must be considered injurious, since it 

 checks the Aphidius in its destruction of plant-lice. The inter- 

 relations of aphides with their parasites and hyperparasites form a 



16—2 



