67 



crevices around the buds, of different varieties and species of Prunus, both wild and 

 cultivated From this winter-egg there hatches a stem-mother (Fig. 35), which is char- 

 acterized by being somewhat stouter, with shorter legs 

 and honey tubes than in the individuals of any other 

 generation." 



" Three parthenogenetic generations are produced upon 

 Prunus, the third becoming winged (Fig. 36). This last is 

 called the Pseudogyna or the migrant,- and it instinctively 

 flies to the hop-plant, which is entirely free from attack 

 during the development of the three generations upon Plum. 

 A number of parthenogenetic generations are produced 

 upon the Hop, until in autumn, and particularly during 

 the month of September, winged females are again produced. 

 This is the pupifera or return migrant, and she instinctively 

 returns to the Plum. . Here she at once settles and in the 

 course of a few days, according as the weather permits, pro- 

 duces some three or more young. These are destined never 

 to become winged and are true sexual females (Big. 37). 

 Somewhat later, on the Hop, the true winged male (Fig. 

 38), and the only male of the whole series is developed, and 

 these males also congregate upon the Plum, on the leaves of which toward the end of 



Fig. 



Stem-iriother, enlarged ; head 

 and antenna still more enlarged. 



Fig. 36: 

 First migrant from the plum, third generation, enlarged ; head at side still more enlarged. 



the season they may be found pairing with the wingless 

 females, which stock the twigs with the winter eggs (Fig. 

 39). Such, briefly, is the life-history. Twelve generations 

 may be produced during the year, but there is great irre- 

 gularity in the development of these generations and the 

 return migrant from the Hop is produced at the end of 

 the season whether from individuals of the fourth or fifth 

 generation, or of the twelfth - " 



" Each parthenogenetic female is capable of producing 

 on an average one hundred young (the stem-mother pro- 

 bably being more prolific), at the rate of one to six, or an 

 average of three per day, under favourable conditions. Each 

 generation begins to breed about the eighth day after birth, 

 so that the issue from a single individual easily runs up, 

 in the course of the summer, to trillions. The number of 



Fig. 37. 

 True sexual female, enlarged. 



