55 



uals remain apterous and produce a fourth generation, most of which 

 become winged toward the end of the month or early in June. Some of 

 the winged fourth generation deposit a few larva' on the tree on which 

 they were born before leaving in search of other suitable plants. 



On warm days during the swarming period of the third generation 

 the air is often filled toward evening in the neighborhood of the in- 

 fested trees with the winged individuals searching for suitable plants 

 upon which to settle. 



The few remaining apterous females of the third generation have 

 now a hard struggle to escape their enemies, which by this time have 

 become extremely numerous, so much so that very few escape to estab- 

 lish colonies of the fourth generation. Still fewer escape to form the 

 fifth. Some of both the fourth and fifth become winged. Natural ene- 

 mies or a prevalent fungous disease destroy so many that the last few 

 stragglers may be seen on the trees early in June, and this appears to 

 be the extreme limit of the spring generations on the peach or plum, at 

 least in the vicinity of Washington. 



In the meantime, however, the migrating forms have been able, as 

 stated before, to establish and distribute their progeny on a number of 

 different plants over a wide area of country, often miles away from 

 any peach or plum trees, raising immense colonies, many individuals 

 of which become again winged from time to time, till the raids of their 

 enemies reduce them more and more, so that from the 10th to the 20th of 

 July hardly an individual is to be found on any of the infested plants. 

 They apparently disappear completely, though there can be no doubt 

 that they still exist in one form or another either above or below the 

 surface of the ground on different kinds of plants. No trace of their 

 whereabouts has been found so far. 



After an intermission of four or five months, after leaving the peach 

 and plum, the winged female return migrants suddenly make their 

 appearance again on the trees, from about the first of October till 

 toward the middle of November, so that at times all the leaves and 

 twigs are literally covered with them and with their larva 1 . All the 

 larva 1 which are now produced belong to the true sexual generation, 

 and are composed exclusively of apterous females, which, however, 

 differ considerably in appearance from all other apterous generations, 

 the oldest of which reach full maturity by the end of the month or the 

 first of November, by and after which time, for about two or three 

 weeks, a large number of migrants appear. These are almost entirely 

 males, which at once commence to pair with the females, after which. 

 in about a day, the latter deposit their eggs, to tin- number oi' from 5 to 

 8, on buds, twigs, and trunk. The plants from which these return 

 migrants come are in part those on which they settled in spring after 

 deserting the plum and peach. There seems to be. however, some 

 influence at work which prevents many from acquiring wings and 

 forces them to remain where they were born. These last, one would 



