Bark Beetles

Biology and Ecology of Native and Invasive Species

Fernando E. Vega, Richard W. Hofstetter, Fernando E. Vega, Richard W. Hofstetter

• Publisher: Academic Press
• Year: 2014
• ISBN:
  9780124171732
• Topic: Sciences biologiques
• Subtopic: Entomologie

Bark Beetles: Biology and Ecology of Native and Invasive Species provides a thorough discussion of these economically important pests of coniferous and broadleaf trees and their importance in agriculture. It is the first book in the market solely dedicated to this important group of insects, and contains 15 chapters on natural history and ecology, morphology, taxonomy and phylogenetics, evolution and diversity, population dynamics, resistance, symbiotic associations, natural enemies, climate change, management strategies, economics, and politics, with some chapters exclusively devoted to some of the most economically important bark beetle genera, including Dendroctonus, Ips, Tomicus, Hypothenemus, and Scolytus.

This text is ideal for entomology and forestry courses, and is aimed at scientists, faculty members, forest managers, practitioners of biological control of insect pests, mycologists interested in bark beetle-fungal associations, and students in the disciplines of entomology, ecology, and forestry.

• Provides the only synthesis of the literature on bark beetles
• Features chapters exclusively devoted to some of the most economically important bark beetle genera, such as Dendroctonus, Ips, Tomicus, Hypothenemus, and Scolytus
• Includes copious color illustrations and photographs that further enhance the content

Chapter 1

Natural History and Ecology of Bark Beetles

Kenneth F. Raffa¹; Jean-Claude Grégoire²; B. Staffan Lindgren^{3 1} Department of Entomology, University of Wisconsin-Madison, Madison, WI, USA,
² Biological Control and Spatial Ecology Laboratory, Université Libre de Bruxelles, Bruxelles, Belgium,
³ Natural Resources and Environmental Studies Institute, University of Northern British Columbia, Prince George, BC, Canada

Abstract

Scolytine beetles show enormous diversity in their mating behaviors, host plant associations, chemical and acoustic signaling, symbiotic relationships, and other critical aspects of their life histories. They can be monogamous or polygamous, solitary or gregarious, and employ levels of parental care that range from gallery maintenance in many tribes to eusociality in some ambrosia beetles. Within this complexity, however, scolytines display some generalities that arise from reproducing within plants, such as sophisticated host location systems, morphological adaptations that facilitate tunneling, advanced communication systems that provide very specific information about plants, and close associations with microbial symbionts. Bark beetles produce pheromones that both attract mates and serve additional functions that vary with the beetles’ host–plant relationships. Some species use aggregation pheromones to coordinate cooperative resource procurement, a behavior needed to overcome the sophisticated defenses of live trees. A broad array of microbial symbionts is associated with bark beetles, and these fungi and bacteria vary in their degrees of association, impacts, mechanisms, and functional substitutabilities. Some symbionts contribute to acquisition, utilization, and defense of the host plant resource, and some provide a direct food base. A wide array of predators, competitors, and parasites exploit bark beetles. Many of these natural enemies utilize chemical signals emanating from the beetles or their symbionts in host location, depending on the stage they attack. The habitat in which bark beetles reside poses significant challenges to predators and parasites, so their effects on population dynamics are often limited. Some behavioral, reproductive, and landscape patterns emerge when bark beetle species are functionally categorized by the physiological condition of host plants they colonize. Bark beetles play important and varied roles in ecosystem processes, contributing to biodiversity, nutrient cycling, and heterogeneity. They also pose challenges to resource management in both native and commercial ecosystems. The scale at which beetles exert impacts varies markedly among functional groups, with most species having very localized effects. A few species exert landscape-scale effects, and these ecosystem engineers are among the most pronounced disturbance agents of the biomes they help shape. Their population dynamics are characterized by cross-scale interactions, density-dependent feedbacks, plasticity in host selection decisions, critical thresholds at multiple levels of interaction, and multi-equilibria. A variety of anthropogenic inputs, specifically transport into new regions, habitat manipulations that homogenize forest structure or impede predators, and climatic changes such as elevated temperature and increased drought, increase the socioeconomic losses caused by both eruptive and historically noneruptive species.

Keywords

bark beetles

biology

ecology

natural history

pheromones

plant defense

population dynamics

Scolytinae

symbioses

Acknowledgments

Helpful reviews of various portions of this manuscript were provided by Kier Klepzig, USDA Forest Service, and Patrick Tobin, USDA Forest Service.

1 Introduction

Bark beetles (Coleoptera: Curculionidae: Scolytinae) are a highly diverse subfamily of weevils that spend most of their life histories within plants. They occur in all regions of the world, and are associated with most major groups of terrestrial plants, almost all plant parts, and a broad array of invertebrate and microbial symbionts. Bark beetles have served as some of the most prominent model systems for studies of chemical ecology, symbiosis, sexual selection, population dynamics, disturbance ecology, and coevolution.

Bark beetles play key roles in the structure of natural plant communities and large-scale biomes. They contribute to nutrient cycling, canopy thinning, gap dynamics, biodiversity, soil structure, hydrology, disturbance regimes, and successional pathways. Several species in particular can genuinely be designated “landscape engineers,” in that they exert stand-replacing cross-scale interactions.

In addition to their ecological roles, some bark beetles compete with humans for valued plants and plant products, and so are significant forest and agricultural pests. These species cause substantial socioeconomic losses, and at times necessitate management responses. Bark beetles and humans are both in the business of converting trees into homes, so our overlapping economies make some conflict of interest inevitable.

Anthropogenic activities are altering the environmental and genetic background on which bark beetles, their host plants, and symbionts interact. Factors that have already been shown to alter these relationships include transport of bark beetles and/or microbial associates, habitat manipulations in ways that homogenize or fragment plant communities, and climate change that raises temperatures and increases drought. These factors often lead to higher plant mortality or injury.

This chapter is intended to introduce, summarize, and highlight the major elements of bark beetle life history and ecology, for subsequent in-depth development in the following chapters. The enormous diversity of Scolytinae makes it impossible to address each of these elements for all permutations of their life histories. Only relatively few species (1) exert documented selective pressures on their host species and have major roles in landscape-scale processes, (2) pose significant challenges to natural resource management, and (3) provide the majority of our basic biological knowledge. These are disproportionately concentrated within species that colonize the main stems of conifers. We therefore place particular emphasis on that guild.

2 Diversity of lifestyles and ecological relationships

The Scolytinae have a long evolutionary history (Cognato and Grimaldi, 2009). They are a subfamily within the Curculionidae, the weevils or snout beetles. They are distinct in having reduced snouts as an adaptation to spending much of their adult life within host plant tissues. These beetles are roughly cylindrical in shape, with short legs and antennae, suitable for a life of tunneling. The head is armed with stout mandibles and many scolytines have morphological adaptations to their elytral declivity (e.g., Ips spp.), head (e.g., male Trypodendron spp.), or legs for removing plant fragments from their breeding galleries, packing wood shavings in older parts of their gallery (e.g., some Dendroctonus spp.), or blocking unwanted conspecifics, competitors or natural enemies from galleries (S. L. Wood, 1982). Beyond those general traits, scolytine beetles are highly variable. While the common name “bark beetle” is sometimes applied to the entire subfamily, many are not associated with bark at all...