Theoretical developments are helping us to comprehend the basic parameters governing the dynamics of the interactions between generalist predators and their many pest and nonpest prey. In practice, however, inter- and intraspecific interactions between generalist predators, and between the predators and their prey, within multispecies systems under the influence of rapidly changing biotic and abiotic variables are difficult to predict. We discuss trade-offs between the relative merits of specialists and generalists that allow both to be effective, and often complementary, under different circumstances. A review of manipulative field studies showed that in approximately 75% of cases, generalist predators, whether single species or species assemblages, reduced pest numbers significantly. Techniques for manipulating predator numbers to enhance pest control at different scales are discussed. We now need to find ways of disentangling the factors influencing positive and negative interactions within natural enemy communities in order to optimize beneficial synergies leading to pest control.

Can generalist predators be effective biocontrol agents

Invasions by non-native ants are an ecologically destructive phenomenon affecting both continental and island ecosystems throughout the world. Invasive ants often become highly abundant in their introduced range and can outnumber native ants. These numerical disparities underlie the competitive asymmetry between invasive ants and native ants and result from a complex interplay of behavioral, ecological, and genetic factors. Reductions in the diversity and abundance of native ants resulting from ant invasions give rise to a variety of direct and indirect effects on non-ant taxa. Invasive ants compete with and prey upon a diversity of other organisms, including some vertebrates, and may enter into or disrupt mutualistic interactions with numerous plants and other insects. Experimental studies and research focused on the native range ecology of invasive ants will be especially valuable contributions to this field of study.

The Causes and Consequences of Ant Invasions

In the last 15 years understanding of the higher systematics of Araneae has changed greatly. Large classical superfamilies and families have turned out to be polyor paraphyletic; posited relationships were often based on sym­ plesiomorphies. In this brief review we summarize current taxonomic and phylogenetic knowledge and suggest where future efforts might profitably be concentrated. We lack space to discuss fully all the clades mentioned, and the cited numbers of described taxa are only approximate. Other aspects of spider biology have been summarized by Barth (7), Eberhard (47), Jackson & Parks (72), Nentwig (l05), Nyffeler & Benz ( 1 06), Riechert & Lockley ( 134), Shear ( 1 49) and Turnbull ( 160).

Systematics and Evolution of Spiders (Araneae)

Spiders as Biological Control Agents

The BAWBILT bases in Europe.- The Bawbilt Context in Europe.- The Directory of European Experts.- The Bawbilt Database.- Damage and Control of Bawbilt Organisms an Overview.- Bark Beetles.- Taxonomy and Systematics of Bark and Ambrosia Beetles.- Genetic Tools in Scolytid Research.- General Biology of Bark Beetles.- Chemical Ecology of Bark Beetles in a Complex Olfactory Landscape.- Host Resistance to Bark Beetles and Its Variations.- Fungal Associates of European Bark Beetles With Special Emphasis on the Ophiostomatoid Fungi.- Research on Parasitoids and Predators of Scolytidae - A Review.- Pathogens in Bark Beetles.- Bark Weevils.- Taxonomy and Systematics of Bark Weevils.- General Biology and Life Cycles of Bark Weevils.- Semiochemicals in the Life of Bark Feeding Weevils.- Hylobius Abietis - Host Utilisation and Resistance.- Fungi Associated With Hylobius Abietis and Other Weevils.- Parasitoids, Predators, Nematodes and Pathogens Associated with Bark Weevil Pests.- Damage, Control and Management of Weevil Pests, Especially Hylobius Abietis.- Buprestids and Longhorns.- Biology, Ecology and Economic Importance of Buprestidae and Cerambycidae.- Natural Enemies of Cerambycidae and Buprestidae Infesting Living Trees.- "Non-Coleopteran" Bawbilt organisms.- "Non-Coleopteran Insects".- Research needs and priorities for Europe.- General Conclusions and Research Priorities for Bawbilt Organisms in Europe.

Bark and Wood Boring Insects in Living Trees in Europe, a Synthesis

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Composition, abundance and pest control potential of spider communities in agroecosystems: a comparison of European and US studies

In spite of the large number of studies about the ecology of spiders carried out in the last two decades in different types of ecosystems all over the world, the significance of these animals as natural control agents is still largely unknown. In this paper the literature about that subject is reviewed. Totally 300 scientific papers, published between 1920 and 1984, are cited here.

Several European and American studies have provided evidence, that in undisturbed grassland ecosystems and forest ecosystems spiders can play an important ecological role as predators of insects and other invertebrates. Also in orchards, not treated with pesticides, that are to a certain degree comparable with forest ecosystems, spiders can be abundant predators.

In contrast to that, the opinion about the predatory importance of spiders inhabiting cultivated fields is controversial. The results of some European studies indicate, that the foliage-dwelling spiders of cultivated fields, because of their low population densities, are of minor importance as predators of insects. Other European studies show, that the ground-dwelling spiders of cultivated fields are concerning their abundance a dominant predator group, those significance as control agents still is largely unknown up to the present. In rice fields (swamp ecosystems) in Asia, receiving little or no pesticides, as well as in European and American swamp ecosystems, spiders may be an important predator group.

In houses in South Africa spiders were used successfully as biological control agents against flies.

Zusammenfassung
Spinnen in der naturlichen und biologischen Schadlingsbekampfung: Ein Literaturuberblick

Weltweit wurden in den letzten 20 Jahren in verschiedenen Okosystem-Typen zahlreiche Studien uber die okologische Bedeutung der Spinnen als Pradatoren durchgefuhrt. Trotz der grosen Zahl durchgefuhrter spinnenokologischer Studien ist die Funktion der Spinnen als Pradatoren von Insekten und anderen Invertebraten heute noch weitgehend ungeklart. In vorliegender Arbeit wird die Literatur uber dieses Thema (insgesamt sind 300 wissenschaftliche Arbeiten, die zwischen 1920 und 1984 uber dieses Thema publiziert wurden, aufgefuhrt) analysiert.

Mehrere europaische und amerikanische Studien haben gezeigt, das Spinnen in unbewirtschafteten Grasland-Okosystemen und Forst-Okosystemen eine grose okologische Bedeutung als Pradatoren von Insekten haben konnen. Auch in ungespritzten Obstanlagen, die man bis zu einem gewissen Grad mit Forst-Okosystemen vergleichen kann, stellen Spinnen manchmal eine haufige Pradatorengruppe dar. Im Gegensatz dazu ist die okologische Bedeutung der in Kulturfeldern lebenden Spinnen als Insektenvertilger noch weitgehend umstritten. Einige europaische Studien deuten darauf hin, das den in der Vegetationsschicht von Kulturfeldern lebenden Spinnen ihrer niedrigen Populationsdichten wegen wahrscheinlich keine grose Bedeutung als Pradatoren von Insekten zukommt. Aus anderen europaischen Studien geht hervor, das die epigaischen Spinnen der Kulturfelder bezuglich ihrer Abundanz eine dominante Pradatorengruppe darstellen, deren Funktion als Kleinrauber allerdings noch weitgehend unbekannt ist. In asiatischen Reisfeldern, die nicht oder wenig mit Pestiziden behandelt wurden, konnen Spinnen eine wichtige Bedeutung als Pradatoren von Schadlingen haben. Reisfelder sind Sumpf Okosysteme; auch in europaischen und amerikanischen Sumpfokosystemen konnen Spinnen eine abundante Pradatorengruppe darstellen.

In Sudafrika wurden Spinnen erfolgreich bei der biologischen Bekampfung von Fliegen in Hausern eingesetzt.

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Spiders in natural pest control: A review

In this article, an overview of the general feeding patterns of common agroecosystem spiders is presented. Five groups of web-weavers (Tetragnathidae, Araneidae, Theridiidae, Linyphiidae, Dictynidae) and five groups of hunters (small-sized Oxyopidae, large-sized Oxyopidae, Thomisidae, Sal- ticidae, Lycosidae) are analyzed comparatively (based on 40 prey analyses previously published by various European and US authors). Fewer than 10 insect orders, as well as the order Araneae, make up the bulk of the prey of these spiders. Web-weavers and hunters both basically feed on the same prey orders, but in different proportions. The observed differences reflect in part the very diverse range of life styles and foraging modes exhibited by the various spider groups and, to some extent, differences in prey availability. Web-weavers are almost strictly insectivorous (insects constituting . 99% of total prey). Hunters, however, exhibit a mixed strategy of insectivorous and araneophagic foraging patterns (insects constituting 75- 90% of total prey). Diet breadth computed with the Inverted Simpson Index was, on average, significantly higher in the hunting spiders than the web spiders. There seems to be a consistent trend of greater diet breadth of the hunters compared to the web-weavers in agroecosystems. Overall, spider individuals of small size (including large percentages of immatures) numerically dominate the faunas of field crops, and these feed primarily on tiny prey ( , 4 mm in length).

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Prey selection of spiders in the field

Spiders have been suspected to be one of the most important groups of natural enemies of insects worldwide. To document the impact of the global spider community as insect predators, we present estimates of the biomass of annually killed insect prey. Our estimates assessed with two different methods suggest that the annual prey kill of the global spider community is in the range of 400–800 million metric tons (fresh weight), with insects and collembolans composing >90% of the captured prey. This equals approximately 1‰ of the global terrestrial net primary production. Spiders associated with forests and grasslands account for >95% of the annual prey kill of the global spider community, whereas spiders in other habitats are rather insignificant contributors over a full year. The spider communities associated with annual crops contribute less than 2% to the global annual prey kill. This, however, can be partly explained by the fact that annual crop fields are “disturbed habitats” with a low buildup of spider biomass and that agrobiont spiders often only kill prey over short time periods in a year. Our estimates are supported by the published results of exclusion experiments, showing that the number of herbivorous/detritivorous insects and collembolans increased significantly after spider removal from experimental plots. The presented estimates of the global annual prey kill and the relative contribution of spider predation in different biomes improve the general understanding of spider ecology and provide a first assessment of the global impact of this very important predator group.

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An estimated 400-800 million tons of prey are annually killed by the global spider community.

Although the beneficial status of the spiders as insectivores has been widely recognized for quite some time, biologists by and large seem to be rather unfamiliar with the specific feeding habits of this very diverse order. We present an overview of the feeding patterns of 10 groups of common agroecosystem spiders to inform entomologists and ecologists concerned with issues of natural biological control. The various spider groups discussed in this article exhibit a very diverse range of life styles and foraging modes, which is reflected in the diversity of their feeding patterns. Implications of the insectivorous activities of these predators for natural pest control are discussed.

Martin Nyffeler

Papers

Composition, abundance and pest control potential of spider communities in agroecosystems: a comparison of European and US studies

Spiders in natural pest control: A review

Prey selection of spiders in the field

An estimated 400-800 million tons of prey are annually killed by the global spider community.

How Spiders Make a Living