Int.A. G..J. Environ.S. Cuthbertson Sci. Tech. and A. K. Murchie European red spider mite - an ... © Autumn 2005, Vol. 2, No. 3, pp. 287-290

Review Paper

European red spider mite - an environmental consequence of persistent chemical pesticide application

1*A. G. S. Cuthbertson and 2A. K. Murchie

1Central Science Laboratory, Sand Hutton, York YO41 1LZ, UK

2Department of Agriculture and Rural Development for Northern Ireland and the Queen’s University of Belfast, Newforge Lane, Belfast BT9 5PX, UK *Corresponding Author, E-mail: [email protected]

Received 18 February 2005; revised 23 June 2005; accepted 22 August 2005; onlined 30 September 2005 The European red spider mite, Panonychus ulmi, between geographical regions, with for example, in is a major pest in almost all fruit growing regions of the UK up to five being usual for the south of England the world (Hardman et al., 1985). Spread of P. u l m i (Blair and Groves, 1952) but in the cooler climate of to most apple-growing areas has probably been Northern Ireland 2-3 generations is more common caused by the distribution of nursery stock carrying (Cuthbertson, 2000). winter eggs. This mite is stated to be an important Panonychus ulmi lays two types of eggs. secondary pest (due to the effects of chemical Summer eggs laid on the leaves of the host plant sprays killing natural enemies) of commercial are of the non-diapause type and develop without orchards throughout the United Kingdom (UK) and interruption. The winter eggs are deposited Europe (Cross and Berrie, 1994). A wide host range predominantly on the bark (Beament, 1951). Egg includes deciduous bushes and trees belonging to type is governed by photoperiod, temperature and the family Rosaceae, but it is in association with nutritional status of the female, as ‘summer’ females fruit trees such as apple, pear, plum, peach, prune exposed to cool conditions lay diapausing eggs (van and cherry that it reaches economic importance. In de Vrie et al., 1972). Mites feeding upon undamaged commercial orchards, the potential of P. u l mi to leaves are well nourished and the incidence of cause severe economic damage necessitates diapause is then determined solely by photoperiod chemical control several times a year (Croft, 1975). and temperature. Adult females are about 0.4 mm long; body oval, The mites feed on plant sap and unless they are strongly convex and dark red, with long setae arising crowded they will mostly be found alongside the from light-coloured pinacula (Alford, 1984). The male veins on the underside of the leaves (Blair and is similar to the female only smaller. Eggs are orange/ Groves, 1952). They puncture plant cells with their red and about 0.15 mm long. These hatch into six stylets and the contents are exuded due to turgor legged larvae with an average length of 0.17 mm pressure. The depth reached by the stylets is (Blair and Groves, 1952). approximately 70-120 µm (Avery and Briggs, 1968). Panonychus ulmi over-winter as diapausing Depth at which injury occurs is related to length of eggs laid on the bark of trees or smaller branches the stylet, the feeding time and population density. and spurs (Figure 1). During a heavy infestation, Continuous feeding leads to regular spots being areas of the bark may even appear red due to the formed and when these coalesce characteristic presence of many eggs. In UK Bramley orchards, chlorotic areas develop, often referred to as the and in particular Northern Irish orchards, eggs hatch ‘bronzing’ effect (Jeppson et al., 1975). At high from mid-April to the end of June depending on densities P. u l m i reduces the photosynthetic activity climatic conditions (Cuthbertson, 2000). On hatching, of leaves (Mobley and Marini, 1990). This damage juvenile mites move to the underside of the leaves can lead to current-year or second-year effects. and begin feeding. They reach maturity in Current-year damage, depending on the timing, approximately three weeks after undergoing three duration and severity, can reduce levels of foliar moults. The number of generations per year varies nitrogen, cause premature leaf fall (Baker, 1984), A. G.. S. Cuthbertson and A. K. Murchie European red spider mite - an ...

Summer Each mite molts 3x Adults lay ‘summer’ eggs on leaves

Juvenile mites migrate to underside of leaves 3-5 generations per year

Mid-Sept. females lay ‘winter’ eggs

Eggs hatch at green cluster - pink bud Eggs deposited on twigs over-winter stage (mid-Apr. - early May) Winter

Figure 1: Life cycle of the European red spider mite, Panonychus ulmi reduce shoot growth (Briggs and Avery, 1968) and discontinued, the foliage in these orchards may be trunk diameter (Chapman et al., 1952) and most injured by disease or deficient in nutrients, so making importantly lower fruit yields (Hardman et al., 1985; the host plant less favourable for P. u l m i (Walde, Croft et al., 1983; Baker, 1984). It can also adversely 1995). It has been found that severe damage from affect fruit quality, for example, size (Hoyt et al., P. u l m i occurs on fruit such as apples or pears that 1979), skin colour, soluble solids, titratable acids and have a thin cuticle (Garman, 1923). Leaf surface firmness (Ames et al., 1984). Second-year effects texture and contours are important in the of mite damage are reduced bloom with consequent reproductive potential of spider mites. Such features reductions in numbers of apples and yield (Lienk et may serve as tough impediments to feeding (van de al., 1956; Baker, 1984). Panonychus ulmi was not Vrie et al., 1972). Blair and Groves (1952) stated considered to be of economic importance prior to that Bramley’s Seedling seemed to be the only the 1940’s (Chant, 1966). After the war, the cultivar which exhibited any degree of resistance. chlorinated hydrocarbons, particularly DDT, were The two layers of palisade mesophyll in the leaves widely used in orchard pest control (Baker, 1952). help mask damage caused by the mites. To date, These were broad spectrum in action and persisted little use has been made of any known host plant in the environment. During the 1960’s and 70’s P. resistance in developing commercial apple varieties. ulmi became resistant against many compounds like Cultivars tend to be selected because of their high omethoate and dimethoate (Sterk, 1994). The yielding potential and adaptability to modern growing detrimental effect of chemical spray compounds on systems rather than for their resistance to a particular the natural enemies of P. u l m i is considered a main pest or disease.With ever increasing public concern contributing factor to the sudden increase in red over the use of chemical pesticides in regard to fruit spider mite numbers across European orchards production, based on fears relating to build-up of (Huffaker et al., 1969). In addition, improved chemical residues and also effects on non-target management of orchards, including the use of species and the environment, is driving the need for artificial fertilisers, has increased the nutritional value fruit growers to devise new methods of pest control. of apple leaves leading to improved mite fecundity Integrated pest management is now the leading force (van de Vrie et al., 1972). Panonychus ulmi may behind insect pest control. This involves moving away therefore be considered a man-made pest. In from the reliance of chemical insecticides and unsprayed or abandoned orchards where natural encouraging the natural enemy biodiversity to help enemies are active, damaging levels of European control invertebrate pest species populations red mite are seldom reached (Croft and Hoying, (Cuthbertson et al., 2003a, b; Cuthbertson, 2004; 1977). Although researchers have attributed the Cuthbertson and Murchie, 2004a,b; Cuthbertson, decline of P. u l m i populations to predators that have 2005; Cuthbertson and Murchie, 2005). This will entered the orchard after toxic sprays are reduce the build-up of pesticide resistance within

288 A. G.. S. Cuthbertson and A. K. Murchie European red spider mite - an ... pest species and also reduce the amount of chemical Croft B. A. and Hoying S. A., (1977). Competitive pesticides required for their control, therefore helping displacement of Panonychus ulmi to form a more environmentally sustainable (Acarina:Tetranychidae) by Aculus schlechtendali ecosystem. (Acarina:Eriophyidae) in apple orchards. Can. Entomol., 109, 1025-1034.

Acknowledgement Croft B. A., Elfving D. C. and Flore J. A., (1983). IPM Dr. Andrew G. C. Cuthbertson was funded by and fruit-tree physiology and growth. In: Integrated a Department of agriculture and Rural Development management of insect pests of pome and stone fruits (Northern Irland) Studentship. (Croft, B. A. and S. C. Hoyt (Eds.)). Wiley and Sons. New York, 67-92.

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