Because of their host-tree permanency pests and diseases may remain present in the orchard throughout the year. This
favours the increase in infestation or infection levels from one year to another, with the need for a continuous protection, namely, a recurrent use of pesticides to control them. Fruit tree protection is highly intensive and requires far more pesticide amounts than other crops. In 2006, an average of 36.5 treatments were sprayed in French apple orchards (Sauphanor et al., 2009). In all producing countries, current apple production systems resort to such intensive use of pesticides. Moreover, the trend is for an increase in the yearly number of treatments because of the development of
resistant strains in some pests, low surface areas planted with resistant or low susceptibility cultivars, and ‘zero default fruit’ market standards. Global warming is also likely to increase voltinism and the period of risks for some pests, and to
introduce new pests. From green tip to harvest, i.e. during a 6-to 8-month period, apple orchards are thus under pest and disease management regimes based on the use of pesticides. The side effects of their use on organisms living or foraging within the orchard may be direct through mortality and/or lower fecundity, or indirect through biomass (i.e. prey or host) reduction or host-plant suppression in the food-web.
In orchards the effect of pesticides and pest management regimes on arthropods is well documented for a few taxonomic groups, amongst which are spiders and ground-living beetles but it is more seldom studied for the total arthropod community. The use of pesticides has anegative effect on hunting spiders, ground living arthropods and insects parasitis-ing leaf miners (Prokopy et al., 1996) but, surprisingly, the total arthropod diversity or richness of the tree canopy is not or very little affected by the use of broad-spectrum insecticide programmes compared with more environmentally friendly
methods. Hypotheses that are likely to explain such results may be related to: the resilience of the orchard
system ; a high immigrating rate of arthropods in small-sized orchards within mosaic landscapes ; and/or
the inadequacy of synthetic diversity indices to give information on a whole community composed of groups with incon-
sistent responses. However, even though the diversity measured by classical ecological indices such as the Shannon index is not always affected, the abundance of arthropods is always negatively affected by intensive pest management regimes, as are soil micro-arthropods.