CHAPTER XXI 



THE LIFE HISTORY OF INSECTS 



SECTION XVII. LIFE HISTORY OF A PLANT-LOUSE 



(FAMILY APHIDIDAE) 



Material. The family Aphididae probably furnishes some of the best ex- 

 amples for the study of incomplete metamorphosis of insects. It does not 

 matter much what particular species is selected for this work, as any of the 

 ordinary aphids attacking greenhouse plants will be found quite satisfactory. 

 Among the forms most easily managed may be mentioned the lettuce aphis and 

 the rose aphis. These may almost always be secured at any time of year. For 

 work on the lettuce aphis each student should be provided with a flowerpot 

 in which is growing one small lettuce plant. The instructor should keep on 

 hand a supply of aphids. These should be grown on lettuce under a large bell 

 jar, to prevent the escape of the winged forms. Each student should be given 

 one wingless, viviparous female just before the insect reaches maturity. 



It will be recalled that the life history of the Aphididae may vary 

 considerably with the different species. Nearly all of them, how- 

 ever, have two forms of reproduction, known as viviparous repro- 

 duction (in which the living young are brought forth without the 

 fertilization of the female by the male) and oviparous reproduction 

 (in which eggs are deposited by fertilized females). The sexual 

 forms are usually brought forth in the fall by a viviparous female, 

 and after mating, the oviparous female deposits eggs which are not 

 hatched until the next spring. From these eggs are hatched the 

 viviparous females, this form of reproduction continuing throughout 

 the summer. It will also be recalled that of the viviparous forms 

 part may be winged and part wingless. 



Exercise 44. Watch the viviparous female carefully and write up a detailed 

 set of notes, including the following observations : 



1. Date of birth of first young, giving the hour when the observation was made. 



2. Date of birth of subsequent young, giving the number of young, the day, 

 and the hour when observed. Be sure that only one viviparous female is present 

 on each culture, and keep careful track of all the offspring. 



298 



