Multiplication of ice embryos by ice-whisker shedding.

have been made in field olfactometers with brevicomin, which was identified in the frass of female D. brevicomis (6). The material has consistently given indifferent results or been totally ineffective. However, when a representative assortment of natural terpenes was tested in conjunction with brevicomin, 3-carene proved to be effective in activating the substance. 3-Carene was superior to myrcene and other terpenes in tests made'dirii`ng the summer of 1968 (7). The failure of brevicomin alone to compete with natural sources of attractants in the forest is distinctly different from the results reported by Bedard et al. (8). The, brevicomin released from a tree in their experiments was probably associated with some natural component of the host. Their data show that myrcene might serve in this capacity, but it would be more logical to assume that 3-carene was responsible since it is a predominant component of oleoresin in ponderosa pine (averaging 38 percent) as compared to myrcene (averaging 15 percent) and is more active unit for unit than the latter. The ultimate utilization of pheromones of D. brevicomis in forest management would not appear to be so bleak as the data of Bedard et al. would indicate. As we have reported and discussed in a seminar at the U.S. Forest Service Southwest Experiment Station in January 1969, male D. brevicomis produce frontalin. The material is effective in aggregating populations when used alone, but is strongly enhanced by 3-carene. Whereas a mixture of brevicomin and 3-carene attracts a high proportion of males, frontalin with 3-carene attracts a preponderance of females. Since the female is the key to attack density, the use of a three-component mixture of frontalin, brevicomin, and 3-carene may be the ultimate answer to manipulation of D. brevicomis populations. It is not clear whether brevicomin will be an essential component in the mixture, but it is being retained for the time being to reinforce aggregation of males in predetermined spots. GARY B. PITMAN Boyce Thompson Institute, Yonkers, New York