Many species of predatory mites are found on unsprayed apple trees but, in selectively sprayed orchards, the most common and important species is the orchard predatory mite Typhlodromus pyri.
- This species has developed strains resistant to organophosphorus and carbamate insecticides.
- It is the key natural enemy of the fruit tree red spider mite and apple rust mite and effectively regulates populations of these pest mites such that outbreaks rarely occur.
- This predatory mite is crucial to successful Integrated Pest Management. Unless the predator is established, regular outbreaks of fruit tree red spider mite and apple rust mite are inevitable and these can be very damaging and difficult and costly to control.
- Once the predator is established and the biological equilibrium between the predatory mite and the pest mite has stabilised, fruit tree red spider mite and apple rust mite seldom cause problems, providing the equilibrium is not disturbed by the use of pesticides harmful to the predatory mite.
Typhlodromus pyri overwinters as a fertilised adult female underneath loose bark and in crevices etc. on fruit trees.
- They emerge in spring and invade the foliage and commence laying eggs in May.
- The development time from egg through larval and nymphal development stages to adult takes about 7 days at 26°C and 14 days at 20°C.
- There are 3‑4 generations per year.
It is important to ensure that Typhlodromus pyri is present at adequate levels in every apple orchard.
- This can be done by inspecting the undersides of fully expanded leaves for the presence of the mite in summer.
- The predatory mite often occurs along the main vein often at the point where the main vein joins with a side vein, sheltering in the groove between the veins and the leaf lamella.
- The predatory mite is a pale whitish-straw coloured, sometimes with red gut when a red spider mite has been consumed and is pear shaped with a smooth body with 17 pairs of setae. It often moves rapidly over the leaf.
The predatory mite will establish naturally in apple orchards but this can be a slow process. Pest mite infestations can develop rapidly on newly planted trees which do not have established populations the predatory mite (often because they have been sprayed with predator-harmful pesticides in the nursery e.g. with frequent sprays of carbendazim to control canker).
- Where the orchard predatory mite is absent, e.g. in newly planted orchards, it should be introduced in summer by transferring extension shoots from established orchards where the predatory mite is abundant.
- Summer prunings may be used.
- Ideally, at least one shoot should be placed amongst the foliage in each tree of the orchard where the predator is to be introduced.
Although Typhlodromus pyri is resistant to many insecticides, other insecticides and some fungicides are either very, moderately or slightly harmful.
- Synthetic pyrethroid insecticides (bifenthrin (Talstar), cypermethrin (various products), deltamethrin (Decis), lambda-cyhalothrin (Hallmark), are particularly harmful, especially those products recommended for mite control.
- Use of synthetic pyrethroids on apple should be avoided except as a last resort.
- Several fungicides are harmful or moderately harmful to the orchard predatory mite, especially when programmes of multiple sprays are applied. Carbendazim (Bavistin), dinocap (Karathane), mancozeb (Karamate), maneb (Manex) and sulphur fall into this category.
- Use of these products should be avoided if possible but where use is necessary the number of sprays applied should be minimised.