ON p. 331 of NATURE of December 28, 1916, the writer of the review of the book entitled “Plants in Health and Disease” remarks:—“The accounts of such pests as the cabbage-root fly and the onion fly, which have been very active this year, are particularly clear. We could only wish that the measures whereby these pests are to be combated were half as good.” With reference to the cabbage-root fly, I am glad now to be able to report that an efficient measure for dealing with that widespread pest has been tested under my direction during the past season.