Validation of a binomial sequential sampling plan for the horn fly in pasture cattle

The horn fly is an extensive economic pest to cattle. Direct economic effects of high infestations have warranted the development of sampling procedures to incorporate better management practices among cattle producers. There is little research on determining a sampling plan for the horn fly based on the economic threshold (ET). A binomial sequential sampling (BSS) plan offers an efficient method for the classification of pest density and its infestation level above or below the ET. This sampling plan follows sequential analysis and integrating a binomial component will increase the speed of sampling by classifying fly density as presence (above threshold) or absence (below threshold). The objective of this study is to develop a binomial sequential sampling plan for horn flies based on cattle hide color and to determine reproductive losses at different horn fly infestation levels. Preliminary analysis of horn fly counts on cattle were categorized based on hide coloration of black hide and combined. Taylor’s Power Law (TPL) was calculated for horn fly dispersion patterns. For all groups, b values were greater than one (black hide b = 1.97, combined b = 1.81), corresponding to high aggregation of horn flies on cattle. Next, tally thresholds were developed, and it was determined a tally threshold of 350 horn flies/animal for black hide (R2 = 0.93) and the combined model (R2 = 0.92) are the best choice for determining fly density. After fitness and practicality of the model was examined, Wald’s sequential probability ratio test (SPRT) was used to develop upper and lower stop lines for sampling plans. Examination of reproductive performance in rangeland cattle found no significant effect of fly infestation level on calving periods and most reproductive variables tested. Preliminary findings of this study provide a dynamic sampling plan for H. irritans on cattle in pasture settings and implementation of this plan can significantly enhance pest management strategies against the horn fly, however, this study suggest horn fly infestations did not significantly impact most reproductive parameters evaluated in rangeland cattle.