A survey is given of the wide range of different materials and organisms that can be classified as biopesticides. Details are given of those currently of commercial importance, and future developments in this area are discussed. It is considered that, while in the immediate future biopesticides may continue to be limited mainly to niche and speciality markets, there is great potential for long-term development and growth, both in their own right and in providing leads in other areas of pest management science.

Biopesticides: a review of their action, applications and efficacy

Nonanomeric spiroketals in natural products: structures, sources, and synthetic strategies.

The purview of chemical ecology and the recent criticisms of improper application of theory to bark beetle phenomena is briefly discussed. Seven levels of research in chemical ecology are presented as well as their relationship to research on bark beetles. The biology and chemical ecology of several pest bark beetles from North America and Europe are discussed in regard to host tree selection theories of random landing on trees or attraction to semiochemicals. The diversity and similarities of pheromone components among species are presented in relation to their biosynthesis from host tree precursors and in relation to the ecological implications of de novo or precursor syntheses. Individual variation in biosynthesis of, response to, and release of pheromones is discussed. Olfactory perception of semiochemicals at both the electrophysiological and behavioral levels is presented. Orientation to semiochemicals during walking and flying is discussed with reference to the significance of dose-response curves for determining a compound's functionality in short- or long-range communication. The regulation of attack density, termination of the aggregation, mechanisms of attack spacing, and recognition of host suitability are presented in the context of an individual's avoidance of intra- and interspecific competition. Finally, a brief summary of topics where our understanding of the chemical ecology of bark beetles and their associates is poorly known is presented.

Chemical ecology of bark beetles

The Scolytidae (bark and ambrosia beetles) comprise a taxonomic group of at least 6000 species that, although appearing similar, may differ widely in their ecology and biochemical adaptations to host trees. Bark beetle species that feed on phloem (a relatively thin layer just under the corky bark) are usually restricted to one or a few host species, whereas ambrosia beetle species that are xylomycetophagous (woodfeeding) and introduce symbiotic fungi for "cultivation" in their galleries generally colonize a larger range of hosts (S.L. Wood 1982). Most biological knowledge on bark and ambrosia beetles derives from studies on relatively few pest species in the genera Dendroctonus, Ips, Scolytus, Xyleborus, Trypodendron, Tomicus=Blastophagus (Fig. 1), Pityogenes, Hypothenemus, Pityophthorus, Hylastes, and Gnathotrichus. Many of these species are obligate and facultative tree-killing bark beetles that comprise only about 10% of scolytid species in the United States and Canada (Raffa et al. 1993). However, these pests that kill trees are the most likely to significantly influence the evolution of the host tree and its chemistry. The diversity of bark beetle biology, in which each species is adapted to only one or a few host tree species, probably has resulted due to natural selection from the great variety of plant biochemicals. It is also theorized that each species of tree has coevolved various chemicals to defend against the herbivorous selection pressures of the tree-killing bark beetles (Erlich and Raven 1965; Feeny 1975; Cates 1981; Berryman et al. 1985; Byers 1995). Semiochemicals (behavior modifying chemicals) from both the tree and the beetle have many functions during the life cycle of a bark beetle (for reviews see D.L. Wood 1982; Borden 1982, 1997; Lanier 1983; Birch 1984; Borden et al. 1986; Byers 1989a, b, 1995; Raffa et al. 1993; Schlyter and

Chemical Ecology of Bark Beetles in a Complex Olfactory Landscape

557 chelys aprix from the Early Jurassic of North America [11], also possesses four pairs of pores on inframarginal scales (Fig. 2). These pores in K. aprix establish Rathke’s gland as the oldest amniote skin gland. We are unable to document Rathke’s gland pores in several extinct taxa, including the oldest pleurodire, Proterochersis robusta from the Late Triassic of Germany [12], and a variety of cryptodire groups (Fig. 1). Neither do we observe gland pores in the most primitive turtle, Proganochelys quenstedti from the Late Triassic of Germany [13]. Aside from the obscurity of gland pores, determining the presence of Rathke’s gland in some extinct taxa is problematic because the developed skeletal components through which gland ducts would otherwise pass en route to the shell bridge or skin are lacking.

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B. Gerken

Papers

2-Ethyl-1,6-dioxaspiro[4.4]nonane, principal aggregation pheromone of Pityogenes chalcographus (L.)

Response of european populations of Scolytus multistriatus to isomers of multistriatin