hegner] 



GALL INSECTS AND INSECT GALLS 



203 



transient or accidental guests. These species of insects do not 

 emerge from the gall at the same time but become mature one 

 after another over a 

 large part of the spring 

 months. 



Making a study of 

 willow-cone gall in- 

 sects is a simple mat- 

 ter. The galls should 

 be collected about the 

 last of March and kept 

 in a covered glass 

 dish where they can 

 be observed easily, 

 or better, may be 

 placed in a breeding box such as is shown in the accom- 

 panying illustration (Figure 2). The insects as they emerge will 

 seek the light and w r ill therefore congregate in the glass tubes. 

 These tubes can be withdrawn and their inhabitants liberated or 

 preserved, if desired. If one wishes to determine from which eggs 

 or larva the adults develop, it is of course necessary to isolate them, 

 placing them in separate bottles. A few drops of water sprinkled occa- 

 sionally over the cones in the breeding cage will prevent the eggs and 

 larvae from drying. 



The Oak Hedgehog Gall 



A gall-fly that has a more complex life-history than that form- 

 ing the willow-cone gall has recently been studied by Trigger son. 

 The gall it makes is known as the oak hedgehog gall (Fig. 3 ) and 



Fig. 2. Breeding cage for rearing parasites 

 and gall insects. (After Banks) 



Fig. 3. Oak Hedgehog Gall. (After Beutenmiiller) 



