Symbiotic Micro-organisms of Aphids and Fixation of Atmospheric Nitrogen

Abstract

MANY insects have associated with them specific micro-organisms, often present in special organs, which are passed on from generation to generation. Their function is in most cases unknown. In many instances where it has been possible to rear sterile insects lacking their symbionts, these have been stunted in growth and deformed, in other cases such insects have been found to develop in an apparently perfectly normal manner¹. Fraenkel and Blewett² have shown that the poor growth of sterile larvæ of certain beetles, without their usual symbionts, may be restored to normal by the addition of certain factors of the vitamin B complex. In this case the role of the symbionts appears to be to provide the insect with these substances. It has been suggested from time to time, and more recently by Toth, that the symbionts are in many cases capable of assimilating gaseous nitrogen from the atmosphere. In his monograph³, Toth concludes that a large number of insect species, including aphids, are able to fix nitrogen with the aid of their symbionts.