1 Biological control by conservation of native natural enemies can, at its best, reduce the need for pesticides and prevent detrimental effects upon the environment. The present study investigated the role of ground-active generalist predators as natural enemies of two tortricid pests in apple orchards. 2 Predation rates were compared on the well established codling moth Cydia pomonella and the emerging oriental fruit moth Grapholita molesta, which has recently switched hosts to apples. 3 The present study hypothesized that the ground-active predators consumed the two tortricid pests in significant numbers without preference, and attacked the pests at different developmental stages. 4 Using diagnostic polymerase chain reaction on the gut contents of field-caught ground-active predators, no difference in predation rates was found on these two pests. Spiders were the most efficient predators of emergent adult moths in spring, whereas the carabid beetles, feeding on diapausing larvae, were important in the autumn. 5 The temporal complementarity between spiders and carabid beetles, attacking different stages of the pests at different times of year, highlights the need for diverse predator assemblages to optimize biological control.

Immunofluorescence and cytohistochemical studies have been performed to understand the host-parasite relationships in the pathosystem: peach-Xanthomonas arboricola pv. pruni (Xap). Using a commercial immunodetection kit, Xap cells were specifically identified in tissues from infected leaves and fruits. Sections from infected leaves showed that the pathogen penetrates the mesophyll via stomata and develops in the intercellular spaces where it degrades the cell wall components. This leads to cell collapse and consequently to the formation of necrotic lesions. The same events have been noted in sections from infected fruits. However, the contaminated zones of mesocarp parenchyma exhibited cell dedifferentiation and generated somatic embryo-like structures. Sections from midrib samples collected at different distances from infected lamina revealed the presence of Xap cells in the sieve tubes and xylem suggesting a systemic trafficking of the pathogen. The results are discussed in terms of cytological effects and epidemiology of Xap.

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