Biological control of phytophagous mites in apple orchards in the Elgin area of South Africa using the predatory mite, Neoseiulus californicus (McGregor) (Mesostigmata: Phytoseiidae): A benefit-cost analysis
Neoseiulus californicus has been the dominant mite predator in the Elgin district of the Western Cape Province, South Africa, since the 1994/95 season when it was first recorded. During the 2002/03 season relatively high numbers of Euseius addoensis, a local specialist pollen feeder/generalist predator, were also recorded. While N. californicus has been present, population levels of the phytophagous mites, Tetranychus urticae and Panonychus ulmi, have declined steadily. N. californicus usually appeared when there were between two and four phytophagous mites per leaf. However, during the 2001/02 and 2002/03 seasons, it was recorded before the phytophagous mites appeared. The population peak of phytophagous mites usually varied between an average of two to 13 mites per leaf, while during the 2001/02 and 2002/03 seasons the phytophagous mite population peaked at less than one mite/leaf. Prior to the appearance of N. californicus, apple orchards in the Elgin area received at least one acaricide spray per season. Acaricides are no longer used on apples. A benefit-cost analysis was conducted in the Elgin district, where there are approximately 8000 ha bearing apples. Two scenarios were analysed. In the first, the cost of acaricides was fixed during each year at R60.00/ha. In the second, the 1993 price of an acaricide was set at R250.00 and was escalated using index values for sprays and dips. In the first scenario the benefit-cost ratio was 34, 52 and 69 for a reduction of 1, 1.5 and 2 acaricides per season, respectively. In the second scenario it was 189, 284 and 378 for the same season.