122 PHILOSOPHICAL TBANSACTIONS. [aNNO 1771. 



which appear early in the spring, to proceed from small black oval eggs, which 

 were deposited on the last year's shoots in autumn : though when it happens that 

 those insects make too early an appearance, he had observed the greatest part to 

 suffer from the sharp weather that usually succeeds; by which means the rose 

 trees are some years in a manner freed from them. 



Those which withstand the severity of the weather seldom come to their full 

 growth before the month of April ; at which time they usually begin to breed, 

 after twice casting off their exuviae, or outer covering. It then appears that they 

 are all females, which produce each of them a very numerous progeny, and that 

 without having intercourse with any male insect. As before observed, they are 

 viviparous; and what is equally uncommon, the young ones all come into the 

 world backwards. When they first come from the parent, they are enveloped 

 by a thin membrane, having in this situation the appearance of an oval egg ; 

 which probably induced Reaumur to suspect that the eggs discovered by Bennet, 

 were nothing more tiian abortions. This egg-like appearance adheres by one 

 extremity to the mother, while the young one contained extends the other ; by that 

 means gradually drawing the ruptured membrane, over the head and body, to 

 the hind feet. During this operation, and for some time after, by means of 

 something glutinous, the fore part of the head adheres to the vent of the parent. 

 Being thus suspended in the air, it soon frees itself from the membrane in which 

 it was confined, and after its limbs are a little strengthened, is set down on some 

 tender shoot, and then left to provide for itself. 



When the spring proves mild, and consequently favourable to this kind of 

 insect, Dr. R. has observed not only the rose-trees, but various kinds of fruit- 

 trees, to be greatly injured by them. Hence he was first induced to investigate 

 the nature of these insects ; in order to find out some expedient, by which so 

 great an evil might be prevented. To avoid being tedious by descending to par- 

 ticulars, he recommends the following general rule; viz. to lop off the infected 

 shoots before these insects are greatly multiplied ; repeating the same operation 

 before the time their eggs are deposited. By the first pruning, you will prevent 

 a very numerous present increase ; and by the second, may entirely cut off the 

 next year's supply. 



Sect. 1. In the spring months, there appear on the rose tree only 2 generations 

 of aphides, including those which immediately proceed from the last year's eggs ; 

 the warmth of the summer adds so much to their fertility, that no less than 5 

 generations succeed each other during that interval. One is produced in May, 

 which twice casts off its covering ; while the months of June and July each 

 supply 2 more, which cast off their coverings 3 or 4 times, according to the dif- 

 ferent warmth of the season. This frequent change of the outer covering is the 

 more extraordinary, as it is the ofteuest repeated when the insects come the 



