. Bulletin of the Department of Agriculture. Agriculture; Agriculture. THE CATTLE GRUBS OR OX WARBLES 77 [stantially correct for that section in 1924. W. H, Brittain has sent the writers specimens collected by W. E. Whitehead at in- tervals during the spring of 1924 from cattle at Truro, Nova Scotia. In an examination of a large number of cattle by Doctor Whitehead on March 24 only 3 grubs were found. The largest one had been in the back about 10 days. Kecords sent the writers by C. J. Drake on collections of larvte made by E. W. Dunnam and others at Ames, Iowa, indicate that larvse of H.
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. THE CATTLE GRUBS OR OX WARBLES 77 [stantially correct for that section in 1924. W. H, Brittain has sent the writers specimens collected by W. E. Whitehead at in- tervals during the spring of 1924 from cattle at Truro, Nova Scotia. In an examination of a large number of cattle by Doctor Whitehead on March 24 only 3 grubs were found. The largest one had been in the back about 10 days. Kecords sent the writers by C. J. Drake on collections of larvte made by E. W. Dunnam and others at Ames, Iowa, indicate that larvse of H. Uneatum first reached the backs in 1923 about January 8, and in 1924 about January 20, Hundreds of collections have been made by the writers and by correspondents throughout the country, and with these records as a basis the dates of appearance of the earliest larvse of H. Uneatum have been estimated and the accompanying map (fig. 33) constructed. Unfortunately, as the number of accurate records of the time of first appearance is small, many discrepancies will be found, but it. Fig. -Hypoderma Uneatum: Date zones of first appearance of grubs in backs of cattle, in the United States is hoped that tlie data available will serve a useful purpose in control undertakings and also stimulate others to add to these much needed records. The date when the first larvae become matui-e and leave the host is an important one from an economic point of view. This date is necessarily closely correlated with the date when the first gi-ubs of the season reach the back. It seems extremely rare for these eai-liest grubs to complete their development in the minimum time, hence the first emei'gence of larvaj from the cattle should be expected to take place about 45 days after the grubs first reach (he back. At Dallas the earliest larvtc become mature and begin leaving the host between December 1 and IT) (hiring average years. The follow- ing are the appi-oxiinate dates when mature larviu licgan emer
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