Comparing Visual and Digital Counting Methods to Estimate Horn Fly (Diptera: Muscidae) Populations on Cattle

Horn fly, Haematobia irritans (L.), population estimates often serve as a diagnostic tool prior to implementing managerial control options available to researchers and producers. Digital photographs taken of cattle infested with horn flies have been suggested to provide similarly accurate population estimates as compared with traditional visual assessments. The objective of this study was to compare visual and digital techniques used to estimate horn fly populations. Sixteen Angus × Hereford yearling heifers artificially infested with four levels of horn flies (Low = 0 flies; Medium = 250 flies; High = 500 flies; Extreme = 1,000 flies) were evaluated. Population estimates were taken visually by experienced (VE1) and inexperienced (VE2) technicians, as well as digitally, with photographs taken on both lateral sides of the south-facing animal. Horn flies were counted in both photographs and combined (CDC) for full body estimates. In addition, the highest photographed side population times two (DDC) was used for comparison. Estimations were made at 0700, 1200, and 1900 h the day following infestation. A time of observation × infestation level interaction (P < 0.01) was detected. On average, VE1 population estimates were greater (P < 0.01) than any other counting method observed. Morning estimates were greater (P < 0.05) than those taken at noon or in the early evening regardless of counting method. Further research regarding the standardization of these techniques to ensure more accurate population estimates is needed before these methods can be incorporated into integrated pest management programs.