Bark Beetles in the Genus Dendroctonus B 379 setae equipped with projections pointed backward Bark Beetles (to the base, or away from the point) that cause them to remain imbedded once contact with them is made. Some members of the subfamily Scolytinae (order Presumably they function in defense, especially Coleoptera, family Curculionidae). against vertebrate predators. Structures bearing such  Beetles projections are said to be barbed, and the occurrence  Bark Beetles in the Genus Dendroctonus of numerous setae is ­sometimes described as barbate. A small barb is called a barbule. Bark Beetles in the Genus Dendroctonus Barber, Herbert Spencer barbara j. bentz Herbert Barber was born in South Dakota on April U.S. Department of Agriculture Forest Service, 12, 1882. His father, an engineer, encouraged his Logan, UT, USA son’s interest in natural history. At the age of 16 he was given employment as an insect preparator at the The genus Dendroctonus (Coleoptera: Curculioni- U.S. National Museum. He worked at such tasks as dae, Scolytinae), originally described by Erichson in arranging the Hubbard and Schwarz ­collection of 1836, currently includes 19 species that are widely Coleoptera, but including a collecting trip with distributed. Seventeen species occur between Arctic Schwarz to Arizona and New Mexico. Although he North America and northwestern Nicaragua, and an was employed continuously at the museum until additional two species are in northern Europe and retirement, his pay was, after some years, and until Asia. Dendroctonus species attack and infest conifer his retirement, provided by the U.S. Department of hosts (Pinaceae) in the ­genera Larix, Picea, Pinus, Agriculture. In time, by association with entomo­ and Pseudotsuga. ­Species within the genus can be logists and through experience, he began to ­publish identified by the host­species they attack, egg gallery results of his own studies. His publications eventually patterns, population behavior, and morphological amounted to some 90 papers. One of the most distinctions. The smallest­species is D. frontalis (male intriguing was on his ­discovery of the strange life his- length 2.0–3.2 mm) and the largest is D. valens (male tory of Micromalthus (Coleoptera: Micromalthidae) length 5.3–8.3 mm). ­Members of the Dendroctonus in which there are several forms of larvae, and that genus, which means “tree killers,” are noted as the some larvae may produce eggs and larvae. He died most economically and ecologically significant spe- in Washington, DC, on June 1, 1950. cies affecting forest ecosystems in western North America. Tree ­mortality resulting from Dendrocto- Reference nus outbreaks can adversely affect timber manage- ment, forest planning, and recreational opportunities. Mallis A (1971) Herbert Spencer Barber, pp 281–283. In: In contrast, disturbance events caused by native bark American entomologists. Rutgers University Press, New beetle species are important drivers of forest succes- Brunswick, NJ, 549 pp sion, foster heterogeneity and biodiversity, promote­ ­biomass recycling, and play a critical role in the fire ecology and overall health of many ecosystems. Barberry Whitefly, Parabemisia Dendroctonus beetles are monogamous, and myricae (Kuwana) spend the majority of their lifecycle in a cryptic habitat beneath the bark of host trees where larvae A whitefly (Hemiptera: Aleyrodidae) pest of citrus. feed within the inner bark or phloem. Relative to  Citrus Pests and Their Management the length of their life cycle, only a short time is 380 B Bark Beetles in the Genus Dendroctonus spent as an adult moving from tree to tree. The commonly used, often with traps, for monitoring majority of the species in this genus is capable of and control of many economically important killing the host tree in one generation. In fact, death ­species in the genus. The complexity of the signal of the host is often a requirement for successful for interruption of aggregation has made it difficult brood production. Although most of the species to identify the chemical makeup of compounds, as are capable of attacking and killing standing, well as, the specific biological action of the ­vigorous trees, recently fallen trees are favored by ­compounds within the population ecology of some species. The female is the colonizing sex in many Dendroctonus species. Consequently, the the majority of Dendroctonus species. After attack current use of synthetic interruptive aggregation of a new host, mating typically occurs in a nuptial chemicals is limited. chamber beneath the bark and an egg gallery is As with most poikilothermic organisms, tem- ­initiated. Adults of a few species, however, mate perature is a strong driving force of Dendroctonus before emerging from the brood host. Eggs are laid population dynamics and an important controller either singly along the sides of the gallery, or in of seasonality. Diapause, which is often tempera- clumps. Egg galleries may be either vertical or ture related, is typically considered the universal ­sinuous, and larvae mine and feed horizontally in adaptation of insects for maintaining seasonality. the phloem, either singly or en mass, depending on However, with the exception of an adult reproduc- the species. Pupation takes place in individual tive diapause in D. rufipennis and D. pseudotsugae, niches within the phloem or in the outer bark of and a prepupal diapause in D. rufipennis, this the host tree. Upon adult emergence, which is usu- physiological timing mechanism appears to be ally ­temperature dependent, beetle dispersal to a absent in the Dendroctonus genus. Instead, new host occurs and the process begins again. ­Dendroctonus seasonality appears to be under Aggregation, which facilitates host selection direct temperature control. Life cycle duration in and mating, is an important life history strategy of the genus is variable depending on the species, most, although not all, Dendroctonus species. latitude, elevation, and microclimate of the popu- Aggregation is often a response to chemicals lation. Species in the south can have as many as ­produced by the host tree, adults from the same or seven ­generations per year, whereas in the north, a different species attacking the host tree, microbes, or at high elevation some species require up to 3 or a combination of these factors. Aggregation on years to ­complete a single generation. Intraspecific a single host tree allows for a mass attack by lati­tudinal differences in many temperature-­ ­conspecific beetles, thereby overcoming the resin associated life history traits exist as well. Global defensives of the conifer hosts. To overcome the climate warming will undoubtedly have significant defenses of healthy, vigorous hosts, many beetles impacts on the distribution and seasonality of the must attack within a short time (1–3 days). Con- Dendroctonus species. versely, trees of poor health may be overcome by Many Dendroctonus species carry spores of fewer beetles (e.g., endemic population levels). symbiotic fungi either passively on the exoskele- Because a single tree is a limited resource, some ton or in specialized structures of the integument Dendroctonus species have evolved a response to a called mycangia. The fungi are disseminated series of chemicals that interrupt aggregation. among host trees via adult Dendroctonus beetles. These chemicals act to space beetle attacks along a Although little research has been conducted on single tree and signal incoming beetles to begin fungal associations of the majority of Dendrocto- attack on another, nearby tree. Synthetic forms of nus species, the work that has been done shows both attractive and interruptive aggregation chem- both a benefit and a detriment to the beetle, icals have been developed for many Dendroctonus depending on the particular fungal associate. species. The attractive aggregant chemical(s) are ­Benefits gained include protecting the beetle brood Bark-Lice, Book-Lice or Psocids (Psocoptera) B 381 from other antagonistic associates, aiding beetles Office, Forest Service, U.S. Department of Agriculture. in overcoming host tree defenses through patho- USDA Forest Service, Rocky Mountain Research ­Station, General Technical Report RMRS-GTR-62 genic action of the fungi, altering the moisture Seybold SJ, Bohlmann J, Raffa KF (2000) Biosynthesis of composition of the phloem, and providing or coniferophagous bark beetle pheromones and conifer ­concentrating nutrients essential for reproduction isoprenoids: evolutionary perspective and synthesis. or development. Can Entomol 132:697–753 Wood SL (1982) The bark and ambrosia beetles of North and Native Dendroctonus bark beetles play signifi- Central America (Coleoptera: Scolytidae), a taxonomic cant roles in long term forest ecosystem function monograph. Great Basin Naturalist Memoirs, Number 6 and structure. However, forest conditions in many Brigham Young University Provo, UT, 1359 pp parts of the Dendroctunus range in North America have changed from conditions that existed prior to pre-European colonization. The result is large Bark-Gnawing Beetles ­landscapes vulnerable to Dendroctonus outbreaks which are often in conflict with current land use Members of the family Togossitidae (order objectives. The formulation of effective manage- Coleoptera). ment strategies for Dendroctonus populations  Beetles requires careful consideration of all aspects of land use including timber production, the urban/wild- land interface, wilderness, watershed, recreation Bark-Lice, Book-Lice or Psocids and wildlife. Synthetic attractive and interruptive (Psocoptera) ­aggregation chemicals and silvicultural options are available for some species to aid in the preven- arturo baz tion and suppression of large scale outbreaks. Any Universidad de Alcalá, MadridSpain action, including no action, should be tightly tied to the management objectives for the landscape The insects of the order Psocoptera (=Copeog- under ­consideration. Restoration of the landscape natha, Corrodentia) are commonly called psocids, to reestablish ecological integrity after an outbreak although outdoor species living on tree trunks and is also important for maintaining long-term branches have been called bark-lice, whereas ­ecosystem health. indoor species, sometimes found in old books,  Mountain Pine Beetle have been called book-lice. The Psocoptera are a  Douglas-Fir Beetle small order of paraneopteran insects (near 4,000  Roundheaded Pine Beetle species have been described around the world) which are found in a wide range of terrestrial eco- systems throughout the world. Most psocids References inhabit trees and shrubs, some others occur in ground litter, others are found on rocks and in the Coulson RN, Witter JA (1984) Forest entomology, ecology nests of birds and mammals. Some live on herbs and management. Wiley, New York, NY, 669 pp and grasses, and a few in moss, whereas others are Mitton JB, Sturgeon KB (1982) Bark beetles in North ­American conifers, a system for the study of evolution- found in caves. Lastly, several species are found in ary biology. University of Texas Press, Austin, TX domestic habitats. The Psocoptera share certain Schowalter TD, Filip GM (1993) Beetle-pathogen interac- morphological features with the lice (orders Mal- tions in conifer forests. Academic Press, London, UK. lophaga and Siphunculata; Phthiraptera of some 252 pp Samman S, Logan J (2000) Assessment and response to bark authors), and these taxa are grouped together in beetle outbreaks in the rocky mountain area. Report to the superorder Psocodea by some authors. Fossil Congress from Forest Health Protection Washington insects identified as psocids have been reported