Enumerative and binomial sampling plans for armored scale (Homoptera : Diaspididae) on kiwifruit leaves

The spatial dispersion of armored scale insects; seedy scale, Hemiberlesia rapax (Comstock); and latania scale, Hemiberlesia lataniae (Signoret), was investigated on kiwifruit, Actinidia deliciosa (A. Chevalier) C. F. Liang e t A. R. Ferguson, leaves in New Zealand. A universal description for disper sion was determined using Taylor's power law, which encompassed a wide rang e of different orchards, blocks. block sizes, sampling times, scale control practices, regions and seasons, scale density significantly altered disper sion, especially at the high densities found on unsprayed kiwifruit. Most c ommercially managed kiwifruit blocks had low densities of <0.5 scale per le af and had a slightly aggregated scale dispersion. Wilson and Room's binomi al model, which incorporates a clumping pattern as a function of density, g ave a significant relationship between the proportion of infested leaves an d scale density. The optimal leaf sample sizes were estimated for predeterm ined levels of sampling reliability. Where population estimates require a h igh degree of precision and enumerative sampling methods are used, 2,500 le aves should be sampled when scale densities are near the current spray thre shold of 4% infested leaves and 500 leaves at 20% infested leaves. For mana gement-decision sampling, where a lower level of precision was acceptable, enumerative sampling would require that 400 leaves be sampled at 4%; or 85 leaves at 20% infested leaves. With binomial sampling to achieve an equival ent level of precision an increased sample size of 6-11% is required.