M. Bonnet had repeated experiments of this kind, as far as the sixth generation, which all uniformly presented the observer with fruitful virgins, when he was engaged in a series of new and tedious experiments, from a suspicion imparted by M. Trembley in a letter to him, who thus expresses himself: “I have formed the design of rearing several generations of solitary pucerons, in order to see if they would all equally bring forth young. In cases so remote from usual circumstances, it is allowed to try all sorts of means; and I argued with myself, Who knows but that one copulation might serve for several generations?” This “WHO KNOWS” persuaded M. Bonnet that he had not sufficiently pursued his investigations. He therefore now reared to the tenth generation his solitary aphides, having the patience to keep an exact account of the days and hours of the birth of each generation. The result of this pursuit was, his discovering both males and females among them, whose amours were not in the least equivocal; the males are produced only in the tenth generation, and are but few in number; these soon arriving at their full growth, copulate with the females, and the virtue of this copulation serves for ten successive generations; all these generations, except the first from fecundated eggs, are produced viviparous, and all the individuals are females, except those of the last generation, among whom some males appear, to lay the foundation of a fresh series.
In order to give a further insight into the nature of these insects, I shall insert an extract of a description of their different generations, by Dr. Richardson, as published in the Philosophical Transactions for the year 1771.
The great variety of species which occur in the insects now under consideration, may make an inquiry into their particular natures seem not a little perplexing, but by reducing them under their proper genera, the difficulty is considerably diminished. We may reasonably suppose all the insects, comprehended under any distinct genus, to partake of one general nature; and, by diligently examining any particular species, may thence gain some insight into the nature of all the rest. With this view Dr. Richardson chose out of the various sorts of aphides the largest of those found on the rose-tree, not only as its size makes it the more conspicuous, but as there are few others of so long a duration. This sort appears early in the spring, and continues late in the autumn; while several are limited to a much shorter term, in conformity to the different trees and plants from whence they draw their nourishment.