Page:Phylogeny of cynipid genera and biological characteristics.pdf/21

 The alterilate generations of very niianiy Cynipidæ differ in their manners of reproduction, one generation reproducing agamically, the next from fertilized eggs. It will be generally believed that in such cases the sexual generation is nearer like the original formn of the species. It is true that Adler argued to the contrary. He said (1881, p. 155):

(1) Some species are only propagated parthenogenetically.

(2) No species of oak gall-fly is known to propagate itself exclusively in a sexual manner. They are only known to do so alternately with an agamous generation in a generation-cycle.

Therefore it seems to me reasonable to infer that the present agamous form is either itself the original form or, if not exactly identical with it, it is at least very nearly related to it.

But such reasoning is not likely to be followed by many stuidents. As we have shown earlier in this paper, the strictly agamnic species of (Cynipidae have been derived from normally bisexual species. If we were to follow Adler's reasoning, we would have to presume a group of strictly agamic Cynipids from which the dimorphic species miiight have arisen. But the most primitive of these dimorphic gall-wasps, species of the genus Neuroterus, show (in characters of radial cell, first abscissa of the radius, second segment of the abdomen, degree of complexity of gall-structure, etc.) closest relationship to the strictly bisexual genus Aulacidea rather than to Diastrophus, Rhodites, or other groups known to be largely agamic. Undoubtedly the bisexual forim of dinmorphic species is the original form.

The reason for the existence of agamic geneiationis may be the fact that in almost every known case the agamic is the winter generation of the species. The chances of survival of this generation are naturally reduced by the vicissitudes of climatic conditions. The agamic female often appears in mid-winter when the temnperature is far below freezing, or at least matures early in the spring when cliinatic conditions are still unfavorable. If it were necessary that the female of this winter generation meet a male of the species and that the eggs be fertilized, before they were capable of developing, the chances of survival would be greatly reduced.

This may be the whole explanation of the origin of the agamnic generation in these insects. If it is, the species found in warmer climnates, as in southern Europe and northern Africa, and in the southern United States and Mexico, should not have an againic generationl even though there may be an alternation of generations among the species. It is highly desirable that some student experiment in such regions and solve life histories of cvnipids of perpetual suminer climates.