Presence-absence sequential sampling plan for northern fowl mite, Ornithonyssus sylviarum (Acari : Macronyssidae), on caged-layer hens

Caged-layer hens were scored as infested or uninfested by visual examinatio n of the vent region, and the number of northern fowl mite, Ornithonyssus s ylviarum (Canestrini & Fanzago), per hen was estimated. The proportion infe sted and average number of mites per hen were shown to have a highly signif icant, positive relationship (r = 0.936). Sampling among houses within a fl ock. and rows and sections within houses were analyzed to determine the rel iability of sampling a representative portion of a flock. Low- and moderate -tolerance treatment thresholds, based on percentage of hens infested with mites, were developed From sampling 1 wk before and 1 wk after acaricide tr eatments determined necessary by the producer. These thresholds were used t o compare a fixed (single) sampling plan, a curtailed procedure of the fixe d sampling plan, and a sequential sampling plan based on a sequential proba bility ratio test, by sampling 174. hens (the maximum number needed for the single sampling plan). The sequential sampling plan required fewer hen exa minations on average fd reach a treatment decision than did the other plans , depending on the infestation tolerance limits. Using a low tolerance appr oach in which infestations below 15% are considered noneconomic (safe thres hold) and infestations above 25% are considered economically important (act ion threshold), as few as 5 hens required examination to reach a treatment decision. Sequential sampling plan graphs are presented for 2 tolerance thr eshold scenarios (a 15% safe threshold paired with a 25% action threshold a nd a 35% safe-threshold paired with a 45% action threshold). These sequenti al sampling plans using presence absence assessments should greatly Facilit ate monitoring and treatment decisions for this important pest.