Parthenogenesis in some New Zealand crop aphids

Abstract

Three species of aphids occurring on cereals in New Zealand were examined for their production of sex forms at a photoperiod of less than the critical 14½ hours light noted in the literature, at a range of temperatures. In each experiment a 16-hour light period was used as a control. The aphid species were Macrosiphum euphorbiae, Rhopalosiphum padi, and Macrosiphum miscanthi. They were reared in cages on leaves of a homozygous line of wheat (Triticum aestivum), variety Arawa, using clones of aphids in the experiments, but also exposing wild populations a the same time. Reaction was according to species. Under a shortened (12-13 hours) photoperiod, M. euphorbiae changed to sex forms, while under a 10-hour photoperiod R. padi showed no change, and M. miscanthi produced approximately 1% sex forms, mostly males. This varied reaction of different species suggests that elements in the New Zealand aphid complex may have been drown from more than one source, even within the same species. It is suggested that the results of these experiments contain some evidence of a Pacific, sub-tropical source for certain species, or strains within species. The varied reaction of M. miscanthi within a clone, in the production of sex forms, is indicative of some interruptor mechanism within the system of genic control of this process. The hypothesis is put forward that this could be a side-effect of ecdysone as it promotes the regular moulting of the adult aphid. Attention is drawn to the further possibility of meiotic parthenogenesis being largely overlooked in the literature of the Aphidoidea.