Biological control of tetranychid mites in South African apple orchards

摘要

There are three apple producing regions in the south western area of South Africa. These are around Elgin, Ceres and in the Langkloof centered around Joubertina. The spider mites, Tetranychus urticae Koch and Panonychus ulmi (Koch), are found in theElgin area while only T. urticae causes damage in the Ceres area and the Langkloof. A variety of indigenous predatory mites, mainly phytoseiids, and two predatory beetles have been found. However, their contribution to biological control of these two spider mites is negligible. During 1989 Galendromus occidentalls (Nesbitt) was imported and released in the Ceres and Elgin areas. It established in the former but not in the latter however, biological control achieved by this predator in the Ceres area was disappointing. Phytoseiulus persimilis Athias-Hennot appeared in apple orchards dunng 1989 and was distributed for biological control during 1990. However, successful biological control was erratic and largely dependent on the presence of certain weedsin the cover crop, To counter this, experimental importations and releases from a European insectary were conducted. These were not successful. During 1994 Neoseiulus califomicus (McGregor) was recorded in apple orchards. It was very widespread and hasresulted in a marked reduction in miticide sprays. In addition, no adverse effects on the local predators have been detected.