Development and validation of a binomial sequential sampling plan for the horn fly (Diptera: Muscidae) in pastured cattle.

The horn fly (Haematobia irritans) (L.) is an extensive economic pest to cattle and annual high infestations warrant the development of sampling procedures to inform management practices for cattle producers. There is little research on developing a sampling plan for the horn fly and a binomial sequential sampling (BSS) plan offers a potentially efficient method for the classification of pest density. Analyses of horn fly counts within and among cattle across different pastures were quantified from 2023 to 2024. Taylor's power law (TPL) regressions indicated that the spatial distribution of horn flies is highly aggregated on cattle, and density estimation models based on the proportion of animals infested above selected tally thresholds revealed strong predictive relationships. A tally threshold of 350 horn flies/animal resulted in the strongest relationship for all herd types (R2 = 0.92). These relationships were validated with independent field data, and Wald's sequential probability ratio test was used to develop upper and lower sequential sampling stop lines based on ratios of infested cattle equating to estimated economic thresholds (ETs). Sampling plans were further validated, using resampling validation software, and average sample numbers along with operating characteristics among ETs were calculated. Sampling requirements for management decisions were low, indicating a high probability of adoption for our sampling program. This study is the first to develop and validate a BSS plan for H. irritans on cattle in pasture settings and implementation of this efficient plan has the potential for major economic returns from horn fly management.