SYSTEMIC TREATMENTS FOR CONTROL OF CATTLE GRUBS HYPODERMA SPP. IN AN ISOLATED RANGE HERD

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Abstract
The effect on infestation by cattle grubs Hypoderma species of six annual systemic insecticide treatments was studied in a range herd isolated by at least 10 miles from locations where adjacent herds could have dropped pupae. After two treatments the infestation was reduced from 30.2 to 1.6 grubs per untreated calf, remaining at approximately this low level until after the fifth treatment when it decreased to 0.2 grubs per untreated calf. After the sixth treatment the infestation persisted at 1.7 grubs per untreated calf, and, in the absence of insecticide treatment in the 7th year, increased to 10.2 grubs per untreated calf in the 8th year. Summer fly disturbance had been a long-standing herd management problem, but did not recur after the first systemic insecticide treatment. Herd management restricted sampling to calves. Failure to eliminate grubs was attributed to either high survival of grubs in the unsampled mature animals, or to migration of female Hypoderma into the spring range. These results provide little basis for optimism concerning projects in organized areas for control of grubs with single annual applications of currently available systemic insecticides.