184 I-IYMENOPTEKA (GALL-WASPS). 



in abundance around the larvae of the Large Cabbage-white 

 {Pieris brassiere) in the autumn are the cocoons of one of the 

 BraconidsB, Microf/asfer glomeratus, which aids so much in 

 destroying these noxious larvse on our cabbages. Vide also 

 fig. 95, 5. 



These insects vary much in size : some are microscopic, while 

 others are quite large. All, however, are equally beneficial, and 

 worthy of our protection. 



The Hessian-fly is largely parasitised by these insects ; so are 

 Aphides. "We can nearly always find some dead plant-lice on 

 every tree — pearly looking bodies, often with a minute round 

 hole, showing where the parasite has escaped. 



GaLIj-WASPS or CYNIPIDiE. 



Gall-wasps produce a great variety of deformities upon trees 

 and plants. There are many interesting features in these 

 insects, and their life-histories are often very complex. They 

 are mostly small, with apodal grub-like larvae (fig. 88, d). They 

 are subject to great numbers of parasites, and have other harm- 

 less guests (inquilines) called Synergi living in their galls. 

 The thorax is humped and the abdomen short. The females, 

 which have the ovipositor curved upwards from the ventral 

 surface, deposit their eggs in plants and trees. The eggs are 

 sometimes placed on long stalks or peduncles, usually in groups 

 or clusters (b), but sometimes singly. Those here figured are 

 of Biorhiza terminalis laid in the terminal buds of the oak. 

 The larvse, which are curved, white, footless grubs, pupate in 

 the galls, some developing in a few days (catkin galls), others 

 taking a long time to mature (woody galls). The "galls" were 

 at one time said to be formed by an irritating venom ejected 

 into the wound. This is not the case. The galls are produced 

 by the irritation set up by the larva;. We find, as a rule, two 

 forms, a sexual form and an agamic form. The galls of each 

 differ Those whose galls appear in the autumn are always 

 asexual. A\'e thus get an alternation of an asexual autumn 



