The Cattle Grub Problem in Arizona. II. Phenology of Common Cattle Grub Infestations and Their Effects on Weight Gains of Preweaning Calves12

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Abstract
Studies were comlucted to determine dates of cessation of adult Hypoderma lineatum (de Villers) activity and effects of larval infestations on weight gains of cattle. The cattle were maintained on un supplemented range pastures at 5000 feet elevation in east-central Arizona. The numbers of hypo dermal grubs ill calves of known age born in 1965, 1967, 1968, and 1969 were ascertained during the winter and spring following their births. All calves born after a certain date each year (fly-free date) were free or hypodermal grubs when examined and obviously were born after oviposition activity of H. lineatum had ceased. fly-free dates ranged from Apr. 1 to May 4, and all preceded the recommended date, May 28, for treatment with systemic insecticides at this elevation. Several systemic insecticides were applied to calves born in 1967, 1968, and 1969 to evaluate effects of common cattle grub infestations on average daily weight gains (ADG). Each year. about 375 calves were selected randomly for insecticidal treatment or retained as untreated controls. Treatment dates were about June 1 and coincided with the usual practice of spring vaccinations. Calves ranged from 6 to 126 days old when treated. Individual weights were obtained when treated, at weaning in mid-November, and again when 12, 20, and 24 months old. No signs of insecticidal toxicity were observed. Statistically and economically significant increases in ADG were obtained at weaning in treated calves born in 1967 and 1969. Variations in ADG response to grub control between sexes and insecticides also were noted. Of the systemic insecticides used, trichlorfon produced the best results ill terms of increased ADG and resulted in 0.08 and 0.09 pounds per day in 1967 and 1969, respectively, over the preweaning periods of about 162 days. No significant alterations of ADG were noted in 1968 or at any of the post weaning weighing periods. Control of common cattle grubs in preweaning calves is safe and economically advantageous, provided the calves are treated soon after the fly-free date and if the treatment date coincides with other management practices.

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