of the unfolded but still immature leaves which are on the oaks at that season.
The constancy of this life history thruout nearly all of the genus Cynips is a remarkable testimonial to the hereditary stability of physiologic characters. This precise combination of characters is found nowhere else among the gall wasps. Its nearest approach is in the genus Disholcaspis, which is certainly a close relative of Cynips. But the agamic Disholcaspis emerges in the late fall, ovipositing in the veins of the embryonic leaves instead of in the bud scales; the bisexual Disholcaspis females do not emerge until mid-summer, and they oviposit in the bark of younger twigs of oak.
The life history of any cynipid is determined by a variety of physiologic characteristics of the insect. The date at which the adult matures depends both upon the season at which it started development and upon its rate of development. The place of oviposition of the female depends upon the inherent reflex and tropistic responses of the insect to factors which lead them to particular parts of particular species of plants and which inspire oviposition in those places. The length of the dormant period thru which each egg goes before it finally hatches must depend on the nature of the egg materials and on the reactions of those materials to external factors. In Cynips the eggs go thru a mid-winter dormancy of say 16 weeks before they hatch. The eggs of Disholcaspis require about 22 weeks. In each group the date of hatching is, however, a matter of long standing.
The mid-winter emergence of the agamic Cynips deserves further consideration. It is an interesting fact that we have bred most of our 17,000 insects of this genus out-of-doors at temperatures never more than perhaps fifteen degrees above freezing, and in many cases ten or fifteen degrees (Fahrenheit) below freezing. When these agamic forms are at room temperature they emerge later than normally, if they emerge at all. Active insects brought indoors become more active for a few minutes, but soon they are killed by such stimulated activity.
The cause of mid-winter emergence is not satisfactorily explained, altho it has been generally accepted as inherent in some way within the species. Miss Payne's studies (1925-1926) on the behavior of insect tissues at low temperatures
