73 



all one way, and their pale youug would soon begia to get abundant. 

 However, they are not so very prolific, and produce at most half a 

 dozen young. These, without exception, are the true females, so far 

 as I have been able to make out, and develop slowly according to tem- 

 perature, the earliest produced only just now laying. About the time 

 the winged females begin to die the winged males take their places 

 and fecundate the wingless females so soon as these are sufficiently 

 mature. The appearance of the winged males settling in all positions, 

 and restless, is quite in contrast with that of the more plump and 

 sedate winged females. 



'"This means that the last generation from Hop gives us the winged 

 parthenogenetic female (return migrant) and the winged male — the lat- 

 ter somewhat later than the former and representing the remnant or 

 devitalized residuum — the closing nutrient power of Humulus being 

 sufficient to produce a male, but not a female ! So that only the true 

 sexual female is produced on Prunus in autumn. 



•' 'From appearances she will not lay more than five or six eggs, and 

 these are placed as in pruni, mali, etc., by preference around base of 

 nascent or latent buds and in cracks and crevices of last year's growth, 

 though sometimes (destined to perish) on leaf or smooth, green stem. 

 They are smooth and olive-green at first, becoming darker. * # * 

 The essential facts which I have published are all verified. 



" 'The true females are all white at first and indistinguishable from 

 young of other generations, but they gradually grow more orange and 

 then olive, the head and members getting darker, and the anus, espe- 

 cially after coition, black.' " 



The statements therefore in my paper of a year ago are substantially 

 correct, and the principal facts ascertained since may be thus briefly 

 summarized: 



(1) The insects begin getting wings in autumn irrespective of genera- 

 tion. These winged females may either come from the fifth generation 

 of the year or as much as the thirteenth, thirteen generations having 

 been followed during the j^ear 1887. 



(2) The males uniformly appear after the females and after the hop 

 crop is harvested. Hence it becomes extremely important to destroy 

 b3' fire or by thorough drenching with a strong kerosene emulsion all 

 the hop-vines as soon as possible after the crop is harvested. This 

 would cut ofi:' the larger bulk of the males so that there would be no im- 

 pregnation of the sexual females, which are for the most part at that 

 time already on the Plum. 



Another interesting fact is worthy of record here ; it is the small 

 proportion of eggs which survive the winter. In the fields and orchards 

 where my observations were made in England some trees were literally 

 covered with eggs, and I brought a number of them with me to this 

 country. The same was true of the plum trees in New York, which 

 were under observation by my assistants. Some of them were literally 



