106 Psyche [June 



in the case of temperature conditions, if the quantity of avail- 

 able food has any tendency at all to change the method of repro- 

 duction in aphids, the effect does not become apparent immediately. 

 This question, however, needs further investigation before very 

 definite conclusions can be reached. 



Summary. 



1. The sexual type of reproduction is the only one kno^vn to 

 occur in the Aphididse. This process takes three forms in this 

 family: (a) amphigony; (b) parthenogenesis; and (c) pedo- 

 genesis. 



2. Amphigony is considered as the more primitive method in 

 insects. Parthenogenesis has practically supplanted it in aphid 

 reproduction. 



3. Parthenogenesis in aphids is apparently continuous and un- 

 interrupted under favorable environmental conditions, amphigony 

 occurring only under the influence of low temperatures and, as 

 certain authors claim, inadequate food supply. 



4. Aphids in tropical and other warm climates appear to have 

 the tendency to reproduce exclusively by parthenogenesis. The 

 same condition apparently obtains among greenhouse aphids in tem- 

 perate climates. 



5. Aphids in colder climates undergo heterogony as an adap- 

 tation to adverse environmental conditions. In certain species, 

 the appearance of the amphigonous generation seems to be a rh3rth- 

 mic process, which continues to occur at definite cyclical intervals 

 for some time after the influence of low temperature has been 

 eliminated. 



6. Nothing very definite is known about the relation of food 

 and heterogony. If the quantity of food has any influence at all 

 on the determination of amphigony in a parthenogenetic mother, 

 the effect does not become manifest in the immediate offspring. 



Literature Cited. 

 Baker, A. C. 



1920. Generic classification of the hemipterous family x\phi- 

 didse. U. S. Department of Agriculture Bull. No. 826. 

 109 pp. 16 pi. 



