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Quinney Natural Resources Research Library, The Bark , Fuels, and Fire Bibliography S.J. and Jessie E.

1989

Mountain Pine : Biology Overview

Lee Safrenyik

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Recommended Citation Safrenyik, L. (1989). Mountain pine beetle : biology overview. In: Proceedings: Symposium on the Management of Lodgepole Pine to Minimize Losses to the Mountain Pine Beetle, pp. 9-12. USDA Forest Service, Intermountian Forest and Range Experiment Station, General Technical Report INT-262.

This Contribution to Book is brought to you for free and open access by the Quinney Natural Resources Research Library, S.J. and Jessie E. at DigitalCommons@USU. It has been accepted for inclusion in The Bark Beetles, Fuels, and Fire Bibliography by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. MOUNTAIN PINE BEETLE: BIOLOGY OVERVIEW

Les Safranyik

ABSTRACT: The general biology and ecology of the others 1985). In infested stands managed for mountain pine beetle in lodgepole pine forests was commercial production, the value of losses during reviewed with emphasis on -host interaction epidemics is usually considerably greater than and causes of outbreaks. During endemic periods that indicated by the volume loss because most the beetles normally infest trees of low vigor mortality is among the larger diameter trees. such as injured, diseased or otherwise weakened Outbreaks usually affect management plans and may trees and windfalls, usually in association with create marketing problems. Outbreaks change stand secondary bark beetles. Attack success in such density, age and species composition of stands, trees tends to be high even at low attack the size distribution of pine, and aesthetic densities but brood production is usually low. values. Outbreaks also increase fuel loading, and When the beetle populations switch from endemic to hasten succession to the climax forest type. epidemic, the beetles infest proportionately more of the larger diameter trees in the stand. Many The objectives of this overview are to provide a of these trees have thick phloem. Normally, such brief account of the population biology of the stands are more than 60 years old and the average beetle in lodgepole pine forests, to highlight key diameter for trees 10 cm and larger is about 20 features, and to identify gaps in the knowledge as cm. Precisely which factors are responsible for a background to the main theme of the symposium. triggering outbreaks is uncertain; however, all For more detailed descriptions of the population factors that would significantly reduce host biology of the mountain pine beetle the reader is resistance or increase the size of the beetle referred to Amman and Cole (1983) and other population above a threshold necessary for publications cited in this paper. colonizing at least some of the large diameter trees with thick phloem could trigger outbreaks. BIONOMICS

INTRODUCTION Geographic Distribution and Host Trees

The mountain pine beetle, ponderosae The mountain pine beetle occurs in forests from Hopk., (Coleoptera: Scolytidae), a native insect northern (latitude 31 0 N) to northwestern in the pine forests of western , has (latitude 56°N) and from the been referred to as the most destructive bark Pacific Ocean east to the Black Hills of South beetle (Wood 1963). In areas where the beetle is Dakota. It occurs up to about 750 m near the common, it is the most important pest of mature northern limits and up to about 3650 m near the lodgepole pine, var. latifolia southern limits of the beetles' range (Safranyik Engelm. During endemic periods, populations are 1978). innocuous, and only a few scattered infested trees are to be found. However, during outbreaks, which The main hosts are lodgepole pine, ponderosa pine occur at irregular intervals and may persist for (P. ponderosa Laws.), western white pine (P. periods of 5 to 20 years, more than 80% of the monticola D. Don), and sugar pine (P. lambertiana host trees with a DBH of 10 cm or more may be Douglas) (Amman 1978). This list oY-principal killed over large areas. hosts is based on the commercial impact and intensity of epidemics. -Other species of pine, In recent years, the losses caused by the mountain including several exotic species within the range pine beetle, particularly in lodgepole pine, have of the beetle, are infested and killed. Some been devastating. In British Columbia, for non-host trees (e.g., Picea) are occasionally example, losses resulting from the 1983 attacks attacked and killed, but populations are usually alone were estimated at 41 million trees killed in not maintained in such trees. infested areas totaling 482 000 ha (Wood and

Life Cycle Paper presented at the Symposium on the Management of Lodgepole Pine to Minimize Losses to the In the optimal portion of its range, the mountain Mountain Pine Beetle, Kalispell, MT, July 12-14, pine beetle normally completes one generation per 1988. year. Brood adults typically mature in July. Young beetles are dark brown to black, and range Les Safranyik is a Research Scientist, Pacific in length from 3.5 to 7.5 rom. In order to complete Forestry Centre, Canadian Forestry Service, 506 maturation, they feed on the inner bark and on West Burnside Road, Victoria, British Columbia, spores of blue stain fungi and yeasts which line Canada, V8Z IM5 the walls of the pupal chambers. During

9 maturation feeding the flight muscles increase in distribution of attacks on the bole. On size (Reid 1958) and the mycangium (a special individual trees, mass attacks are normally structure on the head) becomes charged with fungal completed within 1-2 days. spores, which ensures transport of the fungi to new trees (Safranyik and others 1975). During gallery establishment, the beetles carry spores of the blue stain fungi, yeasts, and Ambient temperatures are instrumental in bacteria. These spores slough off along the walls determining the onset of emergence, the length of of the galleries and grow in the living tissues. the emergence period, diurnal rates of emergence, Although the roles of these organisms are not and flight activity. Emergence normally begins completely known, the blue stain fungi quickly after several days of warm, dry weather, but there invade and kill live cells, thereby preventing is no apparent relationship between the duration them from producing resin, which is the main of such warm periods and the onset of emergence defense of the tree against invasion by the (Safranyik 1978). Emergence and flight start at beetle-microorganism complex. Blue stain fungi about 16oC, and rates of emergence are reduced at also effect a rapid reduction of moisture in the temperatures greater than 30oC. Peak daily sapwood. emergence normally occurs during a period of 2-3 hrs in mid-afternoon when the temperature exceeds The female beetle bores through the bark and 20oC. The median dates of annual emergence can constructs an gallery averaging 25-30 cm in vary by as much as 1 month, but normally vary by length in the phloem parallel to the grain. 10 days or less. The period of peak emergence Mating takes place in the lower end of the egg normally lasts a week to 10 days, but can vary gallery. The male often leaves after mating. The from a few days to 3 weeks. female plugs the gallery entrance and packs the lower end with boring dust. Usually 60-80 , Beetles that do not disperse from the stand in about 2 per cm, are laid singly in niches cut into which they develop usually locate suitable host the sides of the gallery. The eggs usually hatch trees within 2 days of emergence, but are capable in 1-2 weeks and the larvae feed in the phloem, of searching for several days. In release­ roughly at right angles to the gallery. The recapture experiments using marked beetles in larvae normally become dormant in late October or central British Columbia, one beetle was trapped November and begin feeding again in April. at a baited tree 11 days after release more than 1 Pupation takes place during mid to late spring and km from the release site. In the absence of development is completed during late June to mid pheromones, beetles tend to disperse downwind, July. mainly below the canopy in the clear bole zone, and search upwind only after an attractive There are exceptions to the l-year cycle described pheromone plume is encountered. Very l.it tIe is above, and they depend primarily upon climate and known about beetle flight above the canopy (other weather (Safranyik 1985). The most common than that it occurs), or about long-range exceptions occur when many parent beetles dispersal. Collection of mountain pine beetles in establish two broods in a single warm, dry year, high-elevation snowfields in eastern British or in very cool years or at high elevations and Columbia, Alberta, Washington (Furniss and Furniss latitudes where a proportion of the brood may 1972), and circumstantial evidence from elsewhere require more than 1 year to complete development. in the United States (Evenden and others 1943), indicates that long-range dispersals occur during outbreaks and may be significant factors in the Brood Survival spread of epidemics. Systematic studies of the nature and effect of Searching adult beetles usually select and attack factors affecting brood survival within and among living trees during late July or early August. trees have only been done on high endemic, Fresh felled trees or windfall may also be epidemic, and postepidemic populations of the attacked. Searching beetles land at random on mountain pine beetle. Consequently, we have a host and non-host trees, hence one of the dominant poor understanding of brood survival and mortality theories of host selection states that initial factors in endemic populations. attack by the pioneer beetles occurs at random, as opposed to being directed by some stress-induced It is generally believed that the same factors of "primary attraction." There is evidence, however, mortality operate in both endemic and epidemic that dispersing adults land preferentially on populations; however, the relative impact of some lodgepole pines suffering from injury or disease of these factors on brood survival, alone or in (Gara and others 1984). As the pioneer female interaction with other factors, is considerably beetles bore into the bark, they release different at the two population states. For semiochemicals which attract both sexes and result example, during endemic periods, often due to the in the aggregation of beetles on the focus tree, low rates of attack, low attack densities, and and eventually to close-range redirection of perhaps also because of higher tree resistance, responding beetles to nearby trees (Borden and much higher proportions of unsuccessful attacks others 1986). In lodgepole pine, the beetles are and higher brood mortality can occur than during strongly oriented to large-diameter trees. Vision epidemic periods. is believed to play a key role in locating the host (Shepherd 1966). In addition to Several life table studies from the United States semiochemicals, physical and physiological host (Amman and Cole 1981) suggest that during factors and beetle population size are thought to epidemics none of the natural, within-tree be important determinants of the density and mortality factors investigated (competition,

10 predators and parasites, pathogens, drying of the develop into outbreaks in a few years or may bark, and resinosis) regulate beetle populations; continue, especially in lodgepole pine stands of survival of beetles at these times is more closely poor site quality, until most of the related to tree diameter and phloem thickness than large-diameter pine component are killed. A major any other factor. Reid (1963), based on exception to this pattern of outbreak development population studies of a small infestation in occurs when local populations are augmented by the southeastern British Columbia, found that tree influx of large numbers of beetles from nearby diameter was the most important factor determining infested stands, especially those at lower beetle survival. elevations. In this case, low populations and damage levels in a given year in some areas could The life table studies corroborated previous work be followed by epidemic infestations in the (Cole 1974, 1975) showing that in areas where following years. mountain pine beetle has mainly a I-year life cycle, winter temperatures and drying of the Outbreaks in lodgepole pine last from 3 to 20 phloem are the two most important causes of years, range in size from a few hectares to within-tree mortality and their effects are hundreds of square kilometers, and invariably inversely related to tree diameter. With the deplete the large-diameter component of stands exception of the predaceous fly, Medetera, beetle (Safranyik and others 1974). In areas with cooler mortality resulting from predators, parasites, climates, such as areas at high elevations and disease and resinosis was considerably less than northern latitudes, the intensification and spread that recorded for temperature and bark drying; of outbreaks tend to be less but outbreaks may Medetera showed a density dependent response over persist longer than in areas within the beetle's time. Reid (1963) too showed the importance of optimum range. low temperature and subcortical moisture for affecting brood survival within trees, but he also During mountain pine beetle epidemics, large found competition (in terms of egg gallery populations of secondary bark beetles usually density) and resinosis to be important factors. build up in the tops and other sections of the bole and large branches of trees killed by In general, mortality factors that are most mountain pine beetle. Following the decline of important during the I-year life cycle cause mountain pine beetle epidemics, these secondary similar levels of mortality when more than 1 year bark beetles, especially Ips and Pityogenes, is required to complete a generation (Schmitz attack and kill some of the remaining pines, 1985). However, at higher elevations and northern mostly in the smaller diameter classes. latitudes, cool temperatures that delay Occasionally, tree killing can be extensive, but development and increase winter mortality replace it rarely lasts longer than 1-2 years. food (phloem thickness) as the main factor limiting population survival. CAUSES OF OUTBREAKS In the life table studies referred to above, about one-half of total mortality was caused by unknown Although a great deal is known about the factors. This is a rather typical result for bark population ecology of the mountain pine beetle in beetle population studies in general and lodgepole pine, our knowledge of how the emphasizes the need for better knowledge of transition from endemic to epidemic populations mortality factors and improved experimental occurs is uncertain. procedures. In natural lodgepole pine stands, outbreaks Mortality within trees is just one component of usually occur when the average age of the pine total mortality in each generation. component is about 80 years or more and the We have inadequate knowledge of mortality among average diameter of the pine greater than 10 cm is emerged beetles during the dispersal-host finding about 20 cm. Outbreaks usually develop in areas phase. This mortality may be 60% or higher, that are climatically most suited for beetle depending on population levels in relation to host development and survival. Proportionately more of availability, weather, and other factors, and may the large diameter trees are killed (Hopping and be one of the key factors limiting population Beall 1948; Cole and Amman 1969). Brood growth at endemic and postepidemic levels. production from infested trees is directly proportional to the thickness of the inner bark (Amman 1972; Berryman 1976). Epidemiology Resin production in response to invasion of the Under endemic conditions the mountain pine beetle beetle-blue stain fungi complex is a measure of often infests trees of poor vigor which were first host resistance to attack (Reid and others 1967), infested by secondary bark beetles such as Ips and and is normally greatest in the largest diameter, Pityophthorus spp. (Amman 1978), or attack --­ fastest growing trees at a given age and site injured, diseased, defoliated or otherwise quality (Shrimpton 1973). At the stand level, stressed trees, and windfalls. High endemic or resistance tends to be the greatest near the incipient infestations, which characteristically culmination of current annual increment (between kill small groups of trees, are often found in 40 to 60 years, depending on site quality) and draws, gullies, along edges of stand openings, or declines rapidly with increasing age (Safranyik in areas subjected to soil compaction or wide and others 1975). The culmination of stand fluctuations in the water table (Safranyik and resistance corresponds to the attainment of the others 1974). These incipient infestations may greatest basal area, biomass, and nitrogen

11 accumulation in lodgepole pine ecosystems lodgepole pine forests: Symposium Proceedings: following a stand-replacing fire (Fahey and Knight 1978 April 25-27: Pullman, WA.: Washington 1986). State University: 39-53.

As average phloem thickness is related to basal Amman, Gene D.; Cole, Walter E. 1983. Mountain area growth during the preceding 6- to 10-year beetle dynamics in lodgepole pine forests. Part period (Shrimpton and Thomson 1985), both phloem II: Population dynamics. General Technical thickness and resinosis are directly related to Report INT-145. Ogden, UT: U.S. Department of tree or stand vigor. Consequently, there is an Agriculture, Forest Service, Intermountain apparent paradox in our information: if epidemic Research Station. 59 p. infestations can only be maintained in large diameter trees with thick phloem and if these are Borden, J.H.; Ryker, L.C.; Chong, L.C.; Pierce, also the trees that tend to be the most resistant, H.D.; Johnston, B.D.; Oehlschlager, A.C. 1986. how then can the switch from endemic to epidemic Response of the mountain pine beetle, occur at all? We do not have definite answers, Dendroctonus ponderosae Hopkins (Coleoptera: but a plausible explanation is as follows: It is Scolytidae), to five semiochemicals in British generally acknowledged that the degree of host Columbia lodgepole pine forests. Canadian response to attack and host suitability for Journal of Forest Research. 17: 118-128. mountain pine beetle reproduction is dependent on beetle numbers, at least at low population levels Berryman, A.A. 1976. Theoretical explanation of (Raffa and Berryman 1983). Consequently, as the mountain pine beetle dynamics in lodgepole pine beetle population increases, trees of higher forests. Enviromental Entomology. 5: 1225-1233. resistance become available for colonization and outbreaks are triggered when a threshold of beetle Berryman, A.A. 1978. A synoptic model of lodgepole numbers is attained that can successfully colonize pine/mountain pine beetle interaction and its large diameter trees with thick phloem (Berryman potential application in forest management. In: 1978). This beetle population threshold may be Berryman, A.A.; Amman, Gene D.; Stark, R.W., exceeded in stands suffering from temporary eds. Theory and practice of mountain pine beetle weakening such as that caused by drought or management in lodgepole pine forests: Symposium defoliation, or from decline of tree vigor Proceedings; 1978 April 25-27; Pullman, WA.: following attainment of physiological maturity Washington State University: 98-105. (reduction of phloem thickness follows growth reduction with considerable time lag). The Cole, Walter E. 1974. Competing risks analysis in threshold may also be exceeded when endemic mountain pine beetle dynamics. Researches in subpopulations within scattered weakened trees are Population Ecology. 15: 183-192. close enough to concentrate attacks on one tree or a small group of trees of medium to large diameter Cole, Walter E. 1975. Interpreting some mortality and moderate to thick phloem (Amman 1978), or when factor interactions within mountain pine beetle large numbers of beetles disperse into a stand broods. Enviromental Entomology. 4: 97-102. from other infestations. If weather conditions are unfavorable for the beetle, these incipient Cole, Walter E.; Amman, Gene D. 1969. Mountain pine infestations will decline and several years may beetle infestations in relation to lodgepole elapse before conditions for the development of an pine diameters. Research Note INT-195. Ogden, epidemic occur again. UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 7 p. Better understanding of outbreak development is of great practical importance for development of Evenden, J.C.; Bedard, W.D.; Struble, G.R. 1943. better systems for predicting outbreak hazard, and The mountain pine beetle, an important enemy of for development of more effective methods of western pines. Circular No. 664. Washington, management to reduce losses. More knowledge is D.C.: U.S. Department of Agriculture: 25 p. urgently needed on population dynamics in the endemic state, qualitative differences between Fahey, Timothy J.; Knight, Dennis H. 1986. endemic and epidemic beetle populations, primary Lodgepole pine ecosystems. Bioscience. 36: attraction and chemical communication, the role of 610-617. host tree injury and stress factors in triggering outbreaks, and the role of dispersal in the spread Furniss, M.M.; Furniss, R.L. 1972. Scolytids of epidemics. (Coleoptera) on snowfields above timberline in Oregon and Washington. The Canadian Entomologist. 104: 1471-1477. REFERENCES Gara, I.R.; Geiszler, D.R.; Littke, W.R. 1984. Amman, Gene D. 1972. Mountain pine beetle brood Primary attraction of the mountain pine beetle production in relation to thickness of lodgepole to lodgepole pine in Oregon. Annals of the pine phloem. Journal of Economic Entomology. Entomological Society of America 77:333-334. 65: 138-140. Hopping, G.R.; Beall, G. 1948. The relation of Ammanf' Gene D. 1978. Biology, ecology and causes diameter of lodgepole pine to incidence of o outbreaks of the mountain pine beetle in attack by the bark beetle (Dendroctonus lOdgepole pine forests. In: Berryman, A.A.; monticolae Hopkins) Forestry Chronicle. 24: ~an, Gene D.; Stark, R.W., eds. Theory and 141-145. praCtice of mountain pine beetle management in

12 Raffa, K.F.; Berryman, A.A. 1983. The role of host Safranyik, 1.; Shrimp ton , D.M.; Whitney, H.S. 1975. plant resistance in the colonization behavior An interpretation of the interaction between and ecology of bark beetles (Coleoptera: lodgepole pine, the mountain pine beetle and its Scolytidae). Ecological Monographs. 53: 27-49. associated blue stain fungi in Western Canada. In: Baumgartner, David M., ed. Management of Reid, R.W. 1958. Internal changes in female lodgepole pine ecosystems symposium: mountain pine beetle, Dendroctonus monticolae Proceedings; 1973 October 9-13, Pullman, WA.: Hopk., associated with egg laying and flight. Washington State University, Coop. Ext. Serv.: The Canadian Entomologist. 90:464-468. 406-428.

Reid, R.W. 1963. Biology of the mountain pine Schmitz, Richard F. 1985. Effect of the life cycle beetle, Dendroctonus monticolae Hopkins, in the duration on factors limiting survival of the East Kootenay Region of British Columbia. III. mountain pine beetle. In: Hall, P.M.; Maher, Interaction between the beetle and its host, T.E., eds. Pest Management Report No.7: with emphasis on brood mortality and survival. Mountain pine beetle symposium proceedings; 1985 The Canadian Entomologist. 95:225-238. April 16-18; Smithers, B.C.: Ministry of Forests: 25-36. Reid, R.W.; Whitney, H.S. Watson, J.A. 1967. Reaction of lodgepole pine to attack by Shepherd, R.F. 1966. Factors influencing the Dendroctonus ponderosae Hopkins and blue stain orientation and rates of activity of fungi. Canadian Journal of Botany. 45: Dendroctonus ponderosae Hopkins 1115-1126. (Coleoptera:Scolytidae). The Canadian Entomologist. 98: 507-518. Safranyik, 1. 1978. Effect of climate and weather on mountain pine beetle populations. In: Shrimpton, D.M. 1973. Age-and size-related Berryman, A.A.; Amman, Gene D.; Stark, R.W., ed. response of lodgepole pine to inoculation with Theory and practice of mountain pine beetle Europhium clavigerum. Canadian Journal of management in lodgepole pine forests: Symposium Botany. 51: 1155-1160. Proceedings; 1978 April 25-27; Pullman, WA.: Washington State University: 77-84. Shrimpton, D.M.; Thomson, A.J. 1985. Relationship between phloem thickness and lodgepole pine Safranyik, 1. 1985. Effect of climate factors on growth characteristics. Canadian Journal of development, survival, and life cycle of the Forest Research. IS: 1004-1008. mountain pine beetle. In: Hall, P.M.; Maher, T.F., eds. Pest Management Report No.7: Wood, S.1. 1963. Revision of the bark beetle genus Mountain pine beetle symposium preceedings; 1985 Dendroctonus Erichson (Coleoptera: Scolytidae). April 16-18; Smithers B.C.: B.C. Ministry of Great Basin Naturalist. 23: 1-117. Forests: 14-24. Wood, C.S.; Van Sickle, G.A.; Shore, T.1. 1985. Safranyik, 1.; Shrimpton, D.M.; Whitney, H.S. 1974. Forest insect and disease conditions. British Management of lodgepole pine to reduce losses Columbia and the Yukon, 1984. Information from the mountain pine beetle. Forestry Report BC-X-259. Victoria, B.C. Canadian Technical Report 1. Victoria, B.C.: Canadian Forestry Service, Pacific Forest Research Forestry Service, Pacific Forest Research Centre. 20 p. Centre. 24 p.

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