1931] Uichanco — Reproduction in the ApTiididce 103 



at the Cornell Agricultural Experiment Station, at which locality- 

 winter is more or less severe, and this species is known, tinder 

 natural conditions, to undergo an alternation of generations during 

 the year. It should be noted, however, that Myzus achyrantes is 

 a common pest of the gi-eenhouses in Ithaca, as Slingerland him- 

 self admits in his paper. It is highly probable, although he does 

 not specifically say so, that he obtained his material of this species 

 from stock which had been in existence in the greenhouse for 

 generations, and, as was the case with Myzus persicce in the present 

 experiments, the progenitors of the nymph with which he started 

 his cultures might have come from a strain that had been repro- 

 ducing exclusively by parthenogenesis as a result of prolonged 

 seclusion from the untoward effects of winter. Under these cir- 

 cumstances then, Slingerland's results would tend to corroborate 

 mine, instead of contradicting them. ISTor would E wing's (1916) 

 eighty-seven continuous parthenogenetic generations of Aphis 

 avence disprove my results, in view of the fact that the source of his 

 material was the Pacific Coast of the United States, where tliis 

 aphid has been known to reproduce normally by parthenogenesis 

 for indefinite periods. This author himself states in his paper 

 that he was unal^le to find amphigonous forms of the species out- 

 doors during the entire time that his experiments were in progress. 

 The results reported by earlier investigators, like Bonnet (1745) in 

 France, on nineteen continuous parthenogenetic generations of 

 Aphis sambuci Linna?us, and Kyber (1815) in Germany on parthe- 

 nogenetic reproduction during a four-year period by Macrosiphum 

 roscB Linnaeus {^^Siphonophora rosce Koch) and Myzus persicce 

 Sulzer (^Rhophalosiphum ddantJii Schrank), may have to bo 

 classed in the same category as Ewing's or Slingerland's, for the 

 reason that (1) at least one species, Myzus persicce, as I have 

 stated, is a common greenhouse pest, and (2) the material with 

 which they worked might have come from stocks which, in their 

 respective localities, had been reproducing outdoors normally by 

 parthenogenesis throughout the year, cases of which have been 

 reported lately from both countries (Gaumont, 1913, and Borner, 

 191-1). In this event, their results would not tend to contradict 

 mine. 



It would not be safe, on the basis of the foregoing evidence, to 



