~\y 



PSYCHE 



VOL. XXVIll AUGUST, 1921 No. 4 



EEPEODUCTION IN THE APHIDID^ WITH A CONSID- 

 ERATION OF THE MODIFYING INFLUENCE OF 

 ENVIRONMENTAL FACTORS.^ 



By Leopoldo B. Uichanco 



College of Agriculture, University of the Philippines, 



Los Baiios, P. I. 



Literature on aphids abounds in references to the existence of 

 an "asexual" and a "sexual" reproduction. As a matter of fact, 

 however, they reproduce sexually only, the term "sexual reproduc- 

 tion" being generally accepted by zoologists as meaning reproduc- 

 tion by means of special reproductive cells, and "asexual reproduc- 

 tion" that method which involves a direct division, or budding, of 

 an animal without the intercession of specific germ cells. 



Reproduction in aphids may be subdivided into two categories : 



1. Amphigony. This involves the union of reproductive cells of 

 both sexes, the female gamete, or egg, necessitating fertilization by 

 the male gamete, or spermatozoon, as a prerequisite to development, 



2. Parthenogenesis. In this mode of reproduction the male ga- 

 metes are dispensed with, the egg developing without having been 

 previously fertilized. Hertwig and Kingsley (1912, p. 130) char- 

 acterize parthenogenesis as "a sexual reproduction in which a degen- 

 eration of fertilization has taken place." In addition to the two 

 foregoing methods of reproduction, occasional cases of pcedogenesis 

 (e. g., in Aphis avenm Fabricius, as reported by Ewing, 1916, and 

 in Toxoptera graminum Rondani, Webster and Phillips, 1912) 

 have been reported. Pedogenesis is parthenogenesis occurring in 

 the preadult stages of animals. 



Amphigonous reproduction is considered as the more primitive 

 method in insects, parthenogenesis being the result of a later 

 specialization. The latter method of reproduction has become of 

 normal occurrence in aphids and has practically supplanted the 

 former, amphigony taking place only under the influence of ad- 

 verse conditions in the environment. We have thus in aphids a 



' Contribution from the Entomological Laboratories of the Bussey Insti- 

 tution, Harvard University. No. 191. 



