PROCEEDINGS, 1917. 41 



from the most susceptible variety (Gravenstein) this year showed a reduction to 20 

 per cent. 



Success in spraying depends on thoroughly covering the fruit with the poison so 

 as to force the flies to feed upon it and on the absence of important sources of infesta- 

 tion near at hand. 



SOME REASONS FOR STUDYING PUPAE. 



Edna Mosher. 



IN considering the metamorphosis of insects we usually think of them as be- 

 longing to two classes, in which the first are without metamorphosis, and the 

 second with two types of metamorphosis, the incomplete and the complete. We are 

 accustomed to think of these types as differing widely from each other. Although not 

 so defined, we are apt to gain the impression from our reading that in insects with in- 

 complete metamorphosis the early stages of a species resemble the adult so closely as to 

 make identification possible. This may be because we are usually given the grasshop- 

 per as an example of an insect with incomplete metamorphosis. The superficial re- 

 semblance is striking and the casual observer will perhaps think them identical except 

 for the smaller size and the absence of wings in the nymph. Most of us fail to realize 

 the changes that do take place in the grasshopper during the nymphal stages. There are 

 not only the changes connected with the growth of the wings and the consequent modi- 

 fications of the terga, but other changes are taking place in the thorax. The sclerites 

 of the sternum and pleuron are not all present in the early stages, but are gradually de- 

 veloped. The modification of the caudal end of the body, due to the development of the 

 reproductive system, is quite noticeable. The structures for making and receiving sound 

 are also gradually developed. These are by no means all of the changes which take 

 place during the nymphal life of the grasshopper, still the general appearance remains 

 the same. Very few people would have any difficulty in recognizing the young grass- 

 hopper as such. Little difficulty would be encountered in identifying the immature 

 stages of psocids, earwigs, white ants, bird lice, or thrips, but the difficulty increases as 

 we approach the Hemiptera. There are many families in this order in which the nymphs 

 show very little resemblance to the adulte. The nymphs of many Coreidae 

 are shaped very differently from the adults and often covered with spines, thus re- 

 sembling animated pin cushions. The nymphs of cicadas, and in fact, of very many 

 Homoptera, are strikingly different from the adult. The males of Coccidae are so dif- 

 ferent that many entomologists claim that they have complete metamorphosis. The 

 other orders of insects with incomplete metamorphosis including mayflies, stoneflies 

 and dragonflies have nymphs which differ markedly from the adult. A careful study 

 of these forms reveals the fact that the only good characters to separate insects with in- 

 complete metamorphosis are that the wings are developed externally instead of intern- 

 ally, and that there is no pupal stage. However, if some of Tower's investigations on 

 the origin and development of wings have been correctly interpreted, some of the Coleop- 

 tera have their wings developed in this way; so that we only have left the presence or 

 absence of the pupal stage to distinguish the two types of metamorphosis. 



The pupal stage is peculiar to those insects having complete metamorp hosis. We 

 usually think of insects with this type of metamorphosis as being very different in the 

 larval, pupal and adult stages. This again is due to the common example of this type 

 which is always given us, the butterfly. The butterfly is an extreme type as far as dif- 

 ferences between the three stages are concerned. When one studies the life histories of 

 insects belonging to other orders, or even within this same order, many examples are 

 found in which the larva and pupa, at least, resemble each other very closely. Many 



