Proper identification

*Present address: Dr Andrew G. S. Cuthbertson, Central Science Laboratory, Sand Hutton, York Y041 1LZ, U.K. Tel.: +44 (0)1904 462201; Fax: +44 (0)1904 462111; E-mail: a.cuthbertson@csl.gov.uk

A Bramley apple orchard in Northern Ireland, receives on average 2-3 sprays of insecticide or acaricide per annum. While this is a small expenditure compared with costs of fungicide application, or with the amount of insecticide/acaricide applied in other parts of the UK, there are several reasons for avoiding unnecessary sprays.

Attractive to customers – the low usage of insecticide/acaricide in Northern Ireland orchards could attract certain customers.

Environmental – there is a growing awareness among consumers about side effects of pesticides on the surrounding habitat and wildlife.

Resistance – unnecessary applications of pesticides can foster pest resistance to the chemical making it useless.

Cost – unnecessary spays are a waste of money. There may be a need to get away from the ‘calendar spraying’ regime.

Creating new pest problems – within a comparatively stable ecosystem like orchards, the ability of natural enemies to control pests, completely or partly, is well known. Indiscriminant use of pesticides may kill valuable predators and parasites which in turn may allow non-pest species to develop economically-damaging populations. For example, overuse of broad-spectrum pesticides killed natural enemies of the fruit tree red spider mite and allowed this mite to flourish unhindered.

A vast array of insect species are known to feed on apple. The majority of these cause little damage or occur only sporadically, and out of this considerable complex only four species show signs of reaching pest status in Northern Ireland (Mowat & Clawson, 1996):

(1) The fruit tree red spider mite (Panonychus ulmi (Koch), Acarina: Tetranychidae);

(2) The apple rust mite (Aculus schlechtendali (Nalepa), Acarina: Eriophyidae);

(3) The fruit tree tortrix moth (Archips podana (Scopoli), Lepidoptera: Tortricidae);

(4) The apple-grass aphid (Rhopalosiphum insertum (Walker), Homoptera: Aphididae).

A wide range of natural enemies have been exploited, or have the potential to be exploited, as biological control agents against pests of fruit. In the British Isles, these include mirid bugs, flower bugs and several mite families including the species Typhlodromus pyri or, as commonly known to growers, ‘Typhs’. However, within local Bramley apple orchards, the most commonly-occurring natural enemy is the predatory mite species Anystis baccarum. No common name exists for this species, although the family is often referred to as ‘whirli-gig’ mites, due to the random running behaviour of the individuals.

Anystis baccarum is red/orange in colour and thus could be mistaken for fruit tree red spider mite by the untrained eye. However, certain characteristics enable it to be identified in the field:

1) Anystis baccarum ranges in size from 1.0-1.5 mm in diameter (Figure 1). This is a lot larger than the fruit tree red spider mite, which when fully grown is about 0.4 mm in diameter (Figure 2).

Figure 1: The predatory mite Anystis baccarum camouflaged on tree bark. Bar is 1mm

Figure 2. The fruit tree red spider mite, Panonychus ulmi on Bramley apple leaf. Bar is 1 mm

2) Anystis baccarum moves rapidly over the branches and foliage of the trees, whereas, red spider mite is relatively sedentary and only found on the under-side of leaves.

3) Eggs of red spider mite are visible on the twigs of the trees during the winter months. Anystis baccarum lays its eggs under loose bark on the trunk or in the soil surrounding the tree base.

Anystis baccarum does not cause any damage to fruit or foliage. It will attack and kill a range of insect prey (Figure 3) including the pests found in the Bramley orchards. This predatory mite offers varying degrees of control over apple rust mite in non-pesticide sprayed orchards (Cuthbertson et al., 2003a) and is a predator of apple-grass aphid (Cuthbertson et al., 2003b). Anystis baccarum is most abundant in the orchards during May, which coincides with the hatching of red spider mite eggs and the migration of apple rust mites from their over wintering sites

Figure 3: Anystis baccarum attacking collembola prey.

Consultation with a number of local growers revealed that some had encountered this mite species, but mis-identified it as fruit tree red spider mite and actively sprayed against it. In doing so, they not only removed a natural pest control agent which predated red spider mite in their orchards, but also wasted money on sprays. Additional research has shown A. baccarum to be compatible with certain fungicides that are regularly used within the orchards to control apple scab (Cuthbertson and Murchie 2003c). Therefore, consideration of this important predatory species needs to be made before applying insecticide/fungicide sprays within the orchards and steps taken to conserve their populations.

Cuthbertson, A.G.S., Bell, A.C. and Murchie, A.K. (2003a). The impact of the predatory mite Anystis baccarum on apple rust mite (Aculus schlechtendali) populations in Northern Ireland Bramley orchards. Annals of Applied Biology 142: 107-114

Cuthbertson, A.G.S., Fleming, C.C. and Murchie, A.K. (2003b). Detection of Rhopalosiphum insertum (apple-grass aphid) predation by the predatory mite Anystis baccarum using molecular gut analysis. Agricultural and Forest Entomology 5: 219-225.

Cuthbertson, A.G.S. and Murchie, A.K. (2003c). The impact of fungicides to control apple scab (Venturia inaequalis) on the predatory mite Anystis baccarum and its prey Aculus schlechtendali (apple rust mite) in Northern Ireland Bramley orchards. Crop Protection 22: 1125-1130.

Mowat, D.J. and Clawson, S. (1996). The need for pest control in Northern Ireland Bramley apple orchards. Crop Protection in Northern Britain 2: 225-230.