1 The presence and abundance of arthropods were compared in three olive orchards under organic, integrated and conventional management regimes. In each olive orchard, trees were sampled in the canopy by beating branches and soil arthropods by placing pitfall traps. Contrary to expectations, the highest abundance of arthropods occurred in the integrated management orchard. The most abundant groups were Formicidae and the species Euphyllura olivinae (Homoptera: Psyllidae). 2 Canopies and the soil under the tree canopy (interior soil) were selected as the most informative sites for sampling. The months with the strongest differences were May, June and July, especially June. In the canopy, Araneae, Coleoptera, Diptera, Heteroptera, Hymenoptera, Homoptera, Lepidoptera, Neuroptera and Thysanoptera were the most abundant, and showed significant differences in abundance among orchards with different management regimes. Moreover, in the canopies, Coleoptera and Lepidoptera showed a seasonal pattern of abundance and consistent significant differences between the organic orchard vs. the integrated and conventional ones in both years of study. In the soil, 12 orders showed significant differences in abundance among management regimes at some point of the sampling season. 3 In a search for biological indicators that could help to distinguish between management regimes, a discriminant analysis applied to the data indicated that only the samples from the canopy were classified according to their management regime in a consistent way over time. The groups selected by the analysis to establish differences among management regimes were Coleoptera, Diptera, Heteroptera, Lepidoptera and Thysanoptera. The analysis applied to compare organic vs. non-organic olive orchards, again identified Coleoptera and Lepidoptera as suitable groups. The results suggest that these two orders are potential bioindicators to distinguish, in a simple way, organic olive orchards from non-organic ones.

Within‐generation mortality of the bark beetle L. varius was studied in a Spanish olive orchard by placing cut logs in the field for adult females to breed. Mortality was greatest at the larval stage with only 10% of the original egg number surviving to adulthood. There was no evidence that the density of eggs laid per maternal gallery affects subsequent mortality at the egg, larval or pupal stages. The density of maternal galleries on a log, however, was found to have a positive influence on the mortality of larvae, but not of eggs or pupae. Part of this density‐dependent mortality could be attributed to insect parasitoids, but the effects of intraspecific competition between larvae was also important. However, the relative contribution of each of these components to the density‐dependent relationship was unclear. A simple model showed that the population is regulated by density‐dependent larval mortality at an equilibrium of 11 newly‐emerged females/dm2. Overwintering adult mortality is unlikely to affect this equilibrium significantly. However, year‐to‐year variations in density‐independent egg mortality (or oviposition success) was shown by the model to have a major potential effect on both the equilibrium level and population stability. Zusammenfassung Zur Populationsdynamik von Leperisinus varius (Fabr.) (Col., Scolytidae) in Olivenbäumen (Olea europaea) Die Mortalität des Borkenkäfers Leperisinus varius im Laufe einer Generation wurde in einer spanischen Olivenplantage mit Hilfe ausgelegter Baumabschnitte als Brutplätze untersucht. Die Mortalität war im Larvenstadium am größten mit etwa 10 %. Es gab keine Hinweise darauf, daß die Eidichte pro Muttergang die nachfolgende Mortalität der Eier, Larven und Puppen beeinflußte. Die Dichte der Muttergänge in einem Stammabschnitt jedoch zeigte eine positive Korrelation zur Mortalität der Larven, nicht aber zu jener der Eier und Puppen. Anteil an dieser dichteabhängigen Mortalität hatten zweifellos die Parasitoiden, doch war auch die intraspezifische Konkurrenz zwischen den Larven von Bedeutung. Allerdings blieb der relative Anteil jedes einzelnen der genannten Faktoren unklar. Ein einfaches Modell zeigt, daß die Populationsdichte durch die dichteabhängige Larven‐Mortalität mit einem Gleichgewicht bei elf frischgeschlüpften Weibchen/dm2 reguliert wird. Die Mortalität der überwinternden Adulten nimmt auf dieses Gleichgewicht keinen bedeutenden Einfluß. Jedoch zeigt das Modell, daß Jahr‐zu‐Jahr‐Variationen der dichteunabhängigen Ei‐Mortalität von wesentlicher Bedeutung sowohl für den Gleichgewichtslevel, als auch für die Populationsstabilität sind.

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Mortality from parasitism and intraspecific larval competition was measured on a spatial scale for the olive bark beetle, Phloeotribus scarabaeoides, in cut logs within a Spanish olive orchard. Mortality due to parasitism was inversely density‐dependent, whilst that due to competition was directly density‐dependent. The consequences of these mortality effects of parasitoid and host population dynamics were investigated using a simple population model. In the absence of parasitism, the beetle population stabilized at around three reproducing females per 10 cm2 of olive log surface. Using Roger's random parasite equation to model the parasitoid‐host interaction, the effects of parasitism were to destabilize an otherwise stable interaction. The limitations of the model in its current from are discussed in detail. Suggestions are also made for future improvements to the model including the incorporation of spatial heterogeneity in parasitism.

Effects of parasitoid spatial heterogeneity, sex ratio and mutual interference on the interaction between the olive bark beetlePhloeofribus scarabaeoides (Col., Scolytidae) and the pteromalid parasitoid Cheirupachus quadrum (Hym., Pteromalidae) Abstract: Information on parasitoid sex ratio, mutual interference and spatial heterogeneity, obtained from both field and laboratory experiments, was integrated into a model of the interaction between the solitary pteromalid, Chriropachus quadrum, and the olive bark beetle pest, Phloeotribus scarabaeoides. Parasitism was predominately aggregated in its distribution within the beetle breeding logs, while percentage parasitism ranged from spatially random to spatially density dependent between logs. The effects of spatial density dependence in the model was, however, overshadowed by the effects of both parasitoid mutual interference and competition between female beetles for oviposition 'space'. Searching efficiency (area of discovery) declined with increasing adult parasitoid density as a result of mutual interference. This density dependent change in searching efficiency had a strong stabilizing influence on the parasitoid-host interaction. Crowding of adult parasitoids also led to a decline in the proportion of female progeny emerging. Such density-dependent changes in the secondary sex ratio had very little effect on either stability or equilibrium levels. The model predicts that whilst C. quadrum has the potential to strongly regulate beetle populations, its contribution in practice is only to suppress P. scarabaeoides populations by a mere 20%, which is insufficient to reduce the beetle numbers to non-damaging levels. A major constraint on the effectiveness of the parasitoid appears to be mutual interference, without which the emerging beetle population could be reduced by about 70%.

Mortality from parasitism and intraspecific larval competition was measured for the olive bark beetle, Leperisinus varius, in cut logs within a Spanish olive orchard. Mortality due to parasitism was inversely density-dependent, whilst that due to competition was directly density-dependent. The consequences of these mortality effects of parasitoid and host population dynamics were investigated using a simple population model. In the absence of parasitism, beetle populations stabilized at around 12 adult females per dm' of olive log surface. Using Roger's Random Parasite Equation to model the parasitoid-host interaction, the effects of parasitism were to destabilize an otherwise stable interaction.The limitations of the model in its current form are discussed in detail. Suggestions are also made for future improvements to the model including the incorporation of spatial heterogeneity in parasitism and the effects of interspecific competition between parasitoids. MethodsThe present analysis is based on the results of a field study described by LOZANO et al. (1993). Briefly, five logs were placed in the centre of an olive orchard near Granada from March until July, in order to U.S.

Over 900 predators were collected during two years from a Portuguese organic olive orchard, and tested in a serological bioassay for Prays oleae predation.The highest number of predators tested positive during the phyllophagous and antophagous generations of P. oleae. Ants were the most commonly found predators, followed by Coleoptera, Hemiptera and spiders. INTRODUCTIONOlive is an important crop in Portugal, grown over a surface of 360 000 ha. Among its pests, Prays oleae (Lepidoptera: Plutellidae), is the most important. This moth has three generations a year, phyllophagous, antophagous and carpophagous, the last one, which presents infestation levels of up to 60% being responsible for the highest damage (Bento, 1999). Control methods are chemical applications and the use of Bacillus thuringiensis. Concerning the auxiliary fauna the most important agents of biological control are parasitoids, with predators having a minor role.A recent study of P. oleae predators in southern Spanish olive orchards was carried out using immunological techniques such as ELISA (Morris et al., 1999). This test is based on the identification of the remains of specific preys (antigen) in the stomach of predators using prey-specific antibodies (Hagler and Naranjo, 1994;Symondson et al., 1996). According this study, the main P. oleae predators detected were ants, followed by Heteroptera and Coleoptera. The aim of the present work is the detection by ELISA of predators of P. oleae in a Portuguese olive orchard.