The life history of the small chestnut weevil[9] is somewhat similar, except that in the vicinity of Beltsville the weevils leave the soil late in May or early in June, when the trees are in bloom. Several weeks later the females deposit eggs in the nuts. At Beltsville, egg laying begins late in August and continues for several weeks. After the nuts have fallen from the tree, the full-grown larvae leave them and enter the soil. Earthen cells are constructed at a depth of 4 to 12 inches, where some of the larvae remain for two winters.
The small chestnut weevil completes its life cycle in two years, and a small percentage requires three years, whereas the large chestnut weevil completes its transformation from egg to adult in one year. The large weevils pass the winter as larvae, whereas the small weevils pass one winter as larvae and the second winter as adults. With the few individuals of the small weevil which require three years for transformation, the first two winters are passed in the ground as larvae and the third in the same location as adults. This habit of the small weevil complicates control measures, as one season's spraying with DDT does not reduce the entire infestation of weevils.
[Footnote 8: +Curculio proboscideus+ Fab.]
+Proper Time for Spray Applications+
Application of DDT sprays at the proper time is very important. An examination in 1944 of many unopened chestnut burs disclosed the fact that eggs of the small chestnut weevil were being deposited many weeks before the burs would open. It was also noted that great numbers of the larvae were leaving the nuts soon after the burs cracked open. Evidently these full-grown larvae had hatched from eggs deposited several weeks before the burs split.
In 1945, 1946, and 1947, cloth bags were tied over developing burs at various intervals during the season to prevent further egg laying in the nuts. At harvest time, the bags were removed and the nuts examined. Occasionally adults were hidden among the spines of the burs and were inadvertently enclosed in the bags; therefore, all nuts in bags containing female adults that might have continued ovipositing were discarded. The data in Table 1 show the approximate time prior to which the nuts were infested.
Because of difficulty in obtaining sufficient burs for bagging, and other orchard conditions, the results of these studies were far from conclusive. They indicated, however, that many eggs had been deposited in the nuts before the burs had reached maturity. They also suggested that the seasonal histories of the two species are closely parallel. At Glenn Dale, Md., and Fairfax, Va., the small weevils predominated, constituting about 69 to 90 per cent of the total numbers taken. At Elkton, Md., only 42 per cent of the weevils were of the small species.
[Footnote 9: Curculio auriger Casey.]
Table 1. Results of studies to determine the time of oviposition of the chestnut weevils.
Nuts Infested with