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Are Bark Beetles Chewing Up Our Forests? What About Our Coffee?

By: , Posted on: February 24, 2015

bettlesBiologists, ecologists and entomologists have long been fascinated by bark and ambrosia beetles, which are believed to originate 90 to 120 million years ago. There are over 6,000 species in the subfamily Scolytinae, which contains the bark beetles and the ambrosia beetles, making this group more speciose than the entire mammal class, which is estimated to contain 5,416 species.  Both Charles Darwin and Alfred Russell Wallace collected and studied them, and there are currently more scientists focused on them than ever before. Such attention on them is a result of both their interesting biology and their economic importance

The damage caused by bark beetles can be staggering. For example, it has been estimated that from 2000-2020, bark beetle outbreaks in western North America and ensuing tree mortality will result in the release of more than 270 megatons of carbon and in the death of over 70,000 square miles of trees. Is this a result of climate change? Are these beetles invasive? Will this issue persist with continued changes in climate? These questions and more are addressed in a recent book published by Academic Press entitled “Bark Beetles: Biology and Ecology of Native and Invasive Species.” The overall prediction from scientists is that bark beetle populations in their native habitat will continue to rise and fall as resources (trees) become available. However, elevated temperature, drought, widespread environmental disturbance or immigration are all implicated as drivers in the recent large scale eruptions of some bark beetle species. As the book describes, there are many strategies available to reduce the severity and extent of bark beetle damage, when properly applied at appropriate scales. Forests are increasingly vulnerable to tree mortality as a result of the direct and indirect effects of climate change and the use of appropriate management plans and prioritization of their application to enhance resiliency is critical.

Interestingly, the majority of bark and ambrosia beetles live in tropical or subtropical habitats and we know very little about them. Not all bark beetles kill trees, but they can still cause significant problems.  For example, one tropical bark beetle, Hypothenemus hampei (commonly referred to as the coffee berry borer) is the most economically important insect pest of coffee worldwide.  The beetle enters the coffee berry and lays its eggs within galleries in the two coffee seeds, directly damaging the marketable product and reducing both quality and yields. Yearly losses in Brazil alone have been estimated at US$215-358 million, and with most of the approximately 80 coffee producing countries infested with this beetle, worldwide economic losses are colossal. Though there is less information on the biology and ecology of the many other Hypothenemus species, one chapter in the book summarizes what we do know, and provides color images to help readers better understand their ecology, taxonomy, and economic impact.

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Why are bark beetles so diverse and why are they so successful? The answer likely lies in their selection of habitat (i.e., trees or tree tissues). Bark beetles are highly adapted to this unusual lifestyle and come with a wide diversity of symbionts. Most bark beetle species are associated with fungi, bacteria or other microbes that can serve as sources of nutrition or that ameliorate tree defenses.  It’s not widely known that bark and ambrosia beetles exhibit an intriguing variety of reproductive behavior. For instance, some bark beetles species have harems and numerous instances of bigyny, i.e., males mating with two females. There are several forms of parthenogenesis (clonal reproduction) such as thelyotoky in which females only produce daughters, or pseudoarrhenotoky, in which daughters are formed sexually and are diploid and males arise from fertilized eggs but express and pass on only genes from their mothers.

bark beetlesEndlessly fascinating, the study of bark beetles is sure to remain at the forefront of ecological and taxonomical research for many years to come, and it is our hope that this book will sustain the interest in this topic and stimulate further research.

Bark Beetles: Biology and Ecology of Native and Invasive Species is available on the Elsevier Store at a 25% discount. Just use discount code “STC215” at checkout and save!

About the Authors

Richard W. Hofstetter and Fernando E. Vega are co-editors of the book Bark Beetles: Biology and Ecology of Native and Invasive Species. Richard is an Associate Professor in the School of Forestry at Northern Arizona University in Flagstaff, Arizona (USA), and Fernando is a Research Entomologist with the Agricultural Research Service of the United States Department of Agriculture in Beltsville, Maryland (USA).

RichHofstetterRichard W. Hofstetter is Associate Professor of Forest Entomology in the School of Forestry, Northern Arizona University. He has a BS degree (1992) in Population Biology, and a MS degree (1996) in Entomology from University of Wisconsin-Madison, and a PhD (2004) in Ecology and Evolution from Dartmouth College. In 2005, he was hired as a Research Faculty in the School of Forestry at Northern Arizona University.  In 2008, he started his tenure-track faculty position in the School of Forestry at Northern Arizona University.  He teaches undergraduate and graduate courses in Forest Entomology, Tropical Forest Ecology, Symbioses, and Forest Health.

Richard’s research focuses on bark beetle ecology related to plant-insect interactions, predator-prey dynamics, biological control, bioacoustics, and interactions among fungi and mites associated with bark beetles.  He has contributed over 150 presentations and 60 peer-reviewed articles. He has offered a short course on bark beetle ecology and management open to both students and professionals in the fields of ecology, entomology and forestry. He is past-President of the Western Forest Insect Work Conference and the Symbiosis subject editor for the journal of Environmental Entomology.

Fernando VegaFernando E. Vega received an undergraduate degree from the University of Puerto Rico, and a Master’s and doctorate degree from the University of Maryland. He is a scientist with the United States Department of Agriculture – Agricultural Research Service, where he conducts research on the coffee berry borer, the most important insect pest of coffee worldwide.

Fernando co-organized a scientific conference held at the Rockefeller Foundation Bellagio Center in Italy and received, together with Dr. Soroush Parsa in Colombia, a Gates Foundation “Grand Explorations Challenges” grant to develop a technique to introduce fungal entomopathogens into cassava and beans. Fernando is a Fellow of the Linnean Society of London and of the Royal Entomological Society. He has international experience in 20 countries, and has been a member of the U.S. government delegation to several International Coffee Organization meetings in London.

In addition to “Bark Beetles: Biology and Ecology of Native and Invasive Species”, Fernando has co-edited “Insect-Fungal Associations: Ecology and Evolution” (Oxford University Press), “The Ecology of Fungal Entomopathogens” (Springer), and “Insect Pathology, Second Edition” (Academic Press).

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