Predatory Mites Not All Mites Are Equal

Naturally occurring predatory mites

Euseius rubicolus (previously called Amblyseius addoensis or Euseius addoensis) and Euseius citri (family Phytoseiidae) are indigenous mites that are common in fruit orchards (Figure 1). They are around 1 mm in size, white or cream with a smooth round body. When scouting for them, look on the inner canopy leaves. They hide from the sun and come out early morning or late afternoon to find their prey. They feed on spider mites and thrips and require pollen to supplement their diet. Thus, they are most effective in spring when flowers are blooming, and pest populations have not yet peaked. Anystis baccarum (family Anystidae) should be a common sight in orchards under Integrated Pest Management (Figure 2). They are small (1-1.5 mm) bright red mites that run in a spiral pattern, commonly known as “whirligig mites”. They are extremely fast, and will run away or drop to the ground as soon as the plant canopy is disturbed. This mite is a voracious predator, eating any small, soft-bodied prey that they find, including mites, small insects (such as thrips, aphids or immature mealybugs and scales) and eggs. Various species of Stigmaeidae predators can be found in IPM orchards where the use of pesticides is limited. The most common species in SA is Agistemus africanus, particularly abundant in deciduous fruit orchards. They are typically orange or red and smaller and slower than the other predatory mites, making them harder to spot. They are generalist predators, preying mostly on eggs and immature stages of mites.

Commercially available biocontrol agents

All commercial biocontrol predators in SA belong to the Phytoseiidae family. Each species has specific crop, prey and climate requirements, so be sure that you purchase and release the correct species for your needs. These are a few of the most commonly used species. Neoseiulus californicus is an exotic species that can be applied commercially, but is also established in many parts of the Western and Eastern Cape. It is a general predator, and will prey on spider mites, flat mites, broad mites, thrips or insect eggs. It is well-suited to higher temperatures, and works best if released into an orchard early in the season. Phytoseiulus persimilis is a specialised predator of web-spinning spider mites, such as Tetranychus urticae (two-spotted spider mite) – see Figure 3. It has special structures on its legs that allow it to move through webbing with ease. This mite is voracious and can quickly deplete a spider mite population, after which they will disperse or starve. It will not attack alternate prey, and cannot survive on pollen. Therefore, it is best used for outbreaks of Tetranychus spp. It thrives in high humidity and enclosed landscapes, such as greenhouses and under nets. Although it is adapted to high temperatures, extremely hot, dry summers may slow development or kill it. Neoseiulus cucumeris, Amblyseius swirskii, Transeius montdorensis and Galendromus occidentalis are commercially available for control of thrips, whiteflies, spider mites and broad (or silver) mites. All will survive on pollen when prey is not available. As above, be aware that not all species are suitable for all crops, all pests, or all climates.

Enhancing biocontrol with predatory mites

Most predatory mites are sensitive to pesticides. Therefore, in order to conserve the natural predators within the orchard, it is essential to limit pesticide usage. Secondly, many predators require pollen to reproduce, or will survive on pollen when pest numbers are low. Thus, the use of a cover crop, which flowers at a different time to the fruit tree, may be of benefit in conserving predators when pest populations are low. Choosing when and how to release an additional predatory mite is case-specific. Know which pests are present (see the previous two articles in this series), and if there are effective predators available. Make sure that predators are suitable to the crop and climate in which you plan to release them. Speak to your consultant regarding timing and density of releases. Finally, be patient. A predator may take time to bring a pest population under control, being influenced by factors such as predator:prey ratios, preying on immature stages, or interaction with other prey or predator species. Biocontrol is part of a complete management system, not a single-shot quick-fix. Tables 1 and 2 provide a glimpse of the most common mite predators in SA.

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Important

• Don’t panic if you see mites on your crop – it may be one of the good guys.
• Make sure you can tell the difference between a pest and a predator.
• To encourage natural predatory mites, keep flowering plants and spray fewer pesticides.
• If you release predatory mites, make sure you chose the correct predator for your pest, crop and climate.