Historic, Archive Document

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September 1970

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INSECTS and MITES ASSOCIATED WITH DWARF MISTLETOES

By Robert E. Stevens Frank G. Hawksworth

Abstract

Three main ecological relationships are recognized between arthropods and dwarf mistletoes(Arceuthobium spp.); the arthropods pollinate and feed on the dwarf mistletoes, and mistletoe infec- tion may predispose trees or parts of trees to attack by insects, especially bark beetles (Scolytidae). Diptera, Hymenoptera, and Thysanoptera are the main pollinators. Larvae of Lepidoptera are the most important group of insects that feed on dwarf mistle- toes, at times causing severe damage to external portions of plants. Several species of mites (Acarina) are common associates; their relationship with the host is unknown. Biological control may be possible through manipulating populations of insects that feed on or pollinate mistletoe.

Key words: Arceuthobium, biological control, pollination

ABOUT THE COVER:

Larvae of the thicket hairstreak butterfly , Mitouva spinetonan Hewitson, in typical feeding position on dwarf mistletoe shoots. Drawing by Anne Steely.

USDA Forest Service Research Paper RM-59

September 1970

Insects and Mites Associated with Dwarf Mistletoes

Robert E. Stevens, Principal Entomologist

and

Frank G. Hawksworth, Principal Plant Pathologist Rocky Mountain Forest and Range Experiment Station1

Central headquarters maintained at Fort Collins, in cooperation with Colorado State University.

CONTENTS

Page

Arthropod-Dwarf Mistletoe Relationships 1

Pollination of Dwarf Mistletoes 1

Insect Feeding on Dwarf Mistletoes 3

Mites . 7

Increased Tree Susceptibility to Insects

Induced by Dwarf Mistletoes 8

Possibilities for Dwarf Mistletoe Control

Through Manipulation of Insect Associates 9

Field Identification of Arthropods

Found on Dwarf Mistletoes 9

Field Key to Insects and Mites Known

to Occur on Dwarf Mistletoes 10

Conclusions 11

Literature Cited 11

Insects and Mites Associated with Dwarf Mistletoes

Robert E. Stevens and Frank G. Hawksworth

Dwarf mistletoes, Arceuthobium spp., parasitize conifers in North and Central America, Africa, and Eurasia, but most species are confined to the New World. In many parts of the western United States they are serious economic pests (Gill and Hawks- worth 1961).

The literature on insects associated with other mistletoes is extensive (Schumacher 1918, Gill and Hawksworth 1961). Some of the more detailed accounts have been on Viscum album in Europe (Tubeuf 1 923), Phoradendron flavescens in the United States (Tucker 1922), and Loranthus longif lorus in West Pakistan (Baloch and Mohyuddin 1969). The insects associated with the dwarf mistletoes have not been comparably reviewed, however. Hawks- worth (1961) listed several species of insects found on Arceuthobium vaginatum subsp. cryptopodum, a parasite of Pinus ponderosa Laws, in the south- western United States, and several other insects have been reported on Arceuthobium. It is our purpose in this Paper to summarize all of this liter- ature, and to present previously unpublished infor- mation on arthropods (insects and mites) associated with the dwarf mistletoes of the western United State and Mexico.

Arthropod-Dwarf Mistletoe Relationships

Several kinds of insects and mites are associated with dwarf mistletoes, and these associations involve three main ecological relationships. Of these, two are direct relationships that involve insects as con- sumers and pollinators of dwarf mistletoe plants. A third, indirect, relationship concerns dwarf mistle- toe infection predisposing trees or parts of trees to attack by insects. The relationship between dwarf mistletoes and insects has been somewhat of a "no-man's land" between forest entomology and forest pathology that has scarcely been investigated.

Most of the direct arthropod-dwarf mistletoe associations we report involve insects feeding on or pollinating dwarf mistletoe plants. However, in some instances— especially with mites— the rela- tionship is unclear, and we do not know for- certain what the arthropod is doing in or on the host plant.

Several of the arthropod species recorded in the literature are represented by a single or only a few collections. Again this is especially true for the mites, and probably reflects lack of attention rather than rarity of occurrence.

Pollination of Dwarf Mistletoes

lThe scientific names for Arceuthobium used in this paper are from "Biology and class- ification of the dwarf mistletoes ," by Frank G. Hawksworth and Delbert Wiens , U. S. Dep. Agr . , Agr. Handb. (in press) . In the Arceuthobium ectmpylopodum group, the specific names are usually the same as the form names used by Gill (1935). Exceptions are A. " ' oocidentale" — a Cal- ifornia species on Pinus sabiniana, P. radiata, and P. murioatcL; A. " calif ornicum" — a species principally on Pinus lombertiana in California and southern Oregon; and A. "apachecum" — on Pinus strobiformis in southwestern United States and northern Mexico.

3 The authors express their thanks to the many taxonomists who identified the insects.

Arthropods— especially insects— appear to play the major role in dwarf mistletoe pollination (Hawks- worth 1961, Kuijt 1955, Weir 1915). Evidence for this centers on characters of insect pollinated plants demonstrated by Arceuthobium: spined pollen shed in clusters, relatively limited amount of pollen, nectar production, and odor emission by both male and female flowers, along with the presenceof numerous insects in and on the flowers during the flowering period. Some wind pollination may occur, but probably only within a meter or so.

The most consistent association we have ob- served (table 1) is pollination of A. vaginatum subsp. cryptopodum by thrips. Thrips, including a species of Frankliniella and possibly others, occur essentially throughout the range of this mistletoe in the Southwest and in Colorado (Hawksworth 1961).

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During the flowering period, these normally dark insects appear yellow due to the masses of pollen transported on their bodies. Coleman ( 1 92 1 ) records Arceuthobium campylopodum as a honey plant in California, so honeybees may also be involved in pollination of the species. W. V. Showalter (per- sonal communication 1968) has observed bumble- bees, other bees, and thrips apparently involved in pollination of A. campylopodum on ponderosa ipine in California.

Our observations of Arceuthobium americanum in Colorado suggest that ants and flies are its pri- mary pollinators. Early in the flowering period, small flies, particularly Bradysia sp.- (Sciaridae), are most common, but toward the end of the flowering period the flies are succeeded by ants. Formica sanguinea subnuda Emery, Lasius niger neoniger Emery, and Tapinoma sessile (Say) have all been observed to frequent flowering plants and to trans- port pollen.

Some phytophagous insects (table 2) may be i passively involved in pollination if their season of activity coincides with the flowering period of their host.

Cooperative University of Utah-Rocky Mountain Station studies on the pollinators of Arceuthobium americanum are currently being conducted by Dr. Delbert Wiens.

Insect Feeding on Dwarf Mistletoes

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Several kinds of insects— especially larvae of Lepidoptera— feed on dwarf mistletoe plants (table 2). In some cases they are highly destructive. With a few exceptions the insects that feed on dwarf mistletoe have not been commonly collected, and little is known of their life histories and other characteristics. Three species of Lepidoptera, Fila- tima natalis (Heinrich), Dasypyga alternosquamella Heinrich, and Mitoura spinetorum (Hewitson), appear to be specific to Arceuthobium, and are broadly distributed throughout its range in western North America. Neoborella tumida Knight, a mirid bug, is also widely distributed in the West and appears to be restricted to Arceuthobium. The Lepidoptera larvae can all be highly destructive to individual plants, but the impact of their feeding on a broad scale has not been evaluated. N. tumida, while widely recognized as a dwarf mistletoe associate, has only this past season been conclusively found feeding on the host; the effect of its feeding has not been studied.

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Mites

Several species of mites (table 3) have been collected from dwarf mistletoes. Brevipalpus porca Pritchard and Baker, a red tenuipalpid, is common throughout the southwestern United States. Typhlo- dromus arceuthobius Kennett is often associated with B. porca, and is probably a predator of it (Kennett 1963). Paraphytoptus arceuthobii Keifer is

reported from staminate flowers (Keifer 1952). While B. porca and P. arceuthobii are members of phyto- phagous groups and could be expected to feed on the dwarf mistletoe plants, we have not seen this. B. porca, while not difficult to find, occurs in such low densities that visible damage would not be expected. The life history, habits, and ecological relationships of dwarf mistletoe-inhabit- ing mites remain to be learned.

Table 3. --Mites known to occur on dwarf mistletoes

Mite

Host

Tree

Locality

Reference 1

MESOSTIGMATA Phytoseiidae

Typhlodromus arceuthobius Kennett

Do Do Do Do

T. bakeri (Garman) Do Do

T. validus Chant Do

T. pusillus Kennett Do

Typhlodromus sp. nr. rosellus

TROMBIDIFORMES Eriophiidae

Paraphytoptus arceuthobii Keifer

Tenui pal pidae

Brevipalpus porca Pritchard & Baker

Unidentified mites

A. "ocoidentale " do do

A. campy lopodum do

A. pusillum do do

A. "ocoidentale" do

A. pusillum do

A. campy lopodum A. "ocoidentale"

A. vaginatum subsp. cryptopodum

Arceuthobium sp. A. douglasii

A. divaricatum A . campy lopodum

Pinus sabiniana do do

P. jeffreyi do

Picea mariana do do

Pinus sabiniana do

Picea mariana do

Pinus jeffreyi P. sabiniana

P. ponderosa do do

do do

Pseudotsuga menziesii

Pinus edulis P. ponderosa

Mt. Diablo, Calif.

Lake County, Calif.

Fiddletown, Amador County, Calif.

Snow Lake, Plumas County, Calif.

Pinecrest, Tuolomne County, Calif.

Stokes Bay, Ontario, Canada

Pine Tree Harbor, Ontario, Canada

Howdenvale, Bruce County, Ontario Canada

Outlet Park, Prince Edward County, Ontario, Canada

Lake County, Calif.

Fiddletown, Amador County, Calif.

Stokes Bay, Ontario, Canada

Howdenvale, Bruce County, Ontario, Canada

Troy, Cape Breton Island, Nova Scotia, Canada

Red Bay, Ontario, Canada

Lake Tahoe, Calif. Mt. Diablo, Calif.

Flagstaff, Ariz. Fort Valley, Ariz. Mescal ero Indian Reserv. Bryce Canyon, Utah Calif.

Bryce Canyon, Utah

Jacob Lake, Ariz. Charleston Mts . , Nev.

N. Mex.

Kennett 1963

Do Do Do Do Do Do Do

Do Do

Keifer 1952 Do

Pritchard & Baker 1958

Kennett 1963

Pritchard & Baker 1958

(Hawksworth)

References in parentheses are original; insects were identified by individual named.

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Increased Tree Susceptibility to Insects Induced by Dwarf Mistletoe

The question is often asked "Since both dwarf mistletoes and bark beetles (Scolytidae) kill trees,

is there a relationship between the activity of the two pests?" Although an indirect relationship does exist (the few pertinent reports are summarized in table 4), none of the published reports seems to indicate that these are important in pines. Dwarf

Table 4. --Reports of dwarf mistletoes predisposing trees to attack by bark beetles1

Tree and

dwarf mistletoe

Pseudotsuga menziesii

Araeuthobium douglasii Do Do

Insect

Local ity

Dendrootonus pseudotsugae Pacific Northwest do Utah do Southwest

Pinus lambertiana

Araeuthobium " calif ornioum" Dendrootonus montiaolae California

Pinus ponderosa

Araeuthobium campy lopodum

Araeuthobium vaginatum subs p. cryptopodum

Dendrootonus brevioomis

Dendrootonus sp.

Pinus edulis

Araeuthobium divarioatvtm Ips oonfusus

Oregon Southwest

Ari zona

Refe rence2

Weir 1916 Chick 1936 3 (Hawksworth)

Struble 1965 Scharpf &

Hawksworth 1968

Miller & Keen 1960

Korstian & Long 1922 Hawksworth 1961

(Hawksworth )

*Dwarf mistletoe may also affect bark beetle brood production; this is apart from predisposi- tion. In a recent study of Dendrootonus ponderosae , it was found that lodgepole pines moderately to heavily infected by Araeuthobium americanum were less suitable as brood trees because they have thinner bark than uninfected trees (Roe and Amman 1970).

References in parentheses are original; insects were identified by individual named.

Unpublished National Park Service report, on file at Rocky Mountain Forest and Range Experi- ment Station, Fort Collins, Colorado.

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mistletoes and bark beetles more often than not occur practically in the absence of each other. An important relationship may exist, however, between Douglas-fir dwarf mistletoe, A. douglasij, and the Douglas-fir beetle, Dendroctonus pseudotsugae Hopk., in interior Douglas-fir,Pseudotsuga menziesii var. glauca (Beissn.) Franco. Beetle outbreaks have been observed to develop in mistletoe-infected stands and spread out into uninfected timber. Further work is needed to clarify this relationship.

Miller and Keen (1960) discussed dwarf mistle- toe-bark beetle relationships from the standpoint of the western pine beetle, Dendroctonus brevi- comis Lee, and concluded that heavily infected ponderosa pines were three to five times more susceptible to beetle attack than uninfected trees. They further pointed out, however, that the mistle- toe-infected trees are probably the older and more decadent trees in a stand, a factor in old-growth ponderosa pine that often contributes to beetle attack. Korstian and Long (1922) reported that, in an area near Flagstaff, Arizona, about 69 percent of the mortality in "black jack" ponderosa pines (trees under 125 to 150 years old) was attributable to mistletoe. About half of this mortality was due directly to mistletoe and half to the parasite in association with bark beetles. Struble (1965) indi- cated that dwarf mistletoe is common in old-growth sugar pine, Pinus lambertiana Dougl., attacked by the mountain pine beetle, Dendroctonus ponderosae Hopkins. The association appears to be similar to that reported by Miller and Keen (1960).

Other records of dwarf mistletoe-insect relation- ships include (1) the tendency of twig beetles, Pi tyopthorus and Pityogenes, to attack dwarf mistle- toe-infected ponderosa pine branches in the South- west (Hawksworth 1961), (2) the preference of an engraver beetle, Scolytus subscaber Leconte for branches of true firs, Abies spp., infected by dwarf mistletoe (Struble 1957), and (3) the attack by wood bo rers in dwarf mistletoe infections on the boles of western larch, Larix occidentalis Nutt., and pon- perosa pine (Weir 1916).

Edmunds and Allen (1958) found no significant difference in population density of black pine leaf scales, Nuculaspis californicus (Coleman), infesting ponderosa pines near Spokane, Washington, with and without Arceuthobium campy lopodum.

Possibilities for Dwarf Mistletoe Control through Manipulation of Insect Associates

The direct dwarf mistletoe-insect relationships (pollination and predation) suggest possibilities for biological control.

Two biological approaches might be considered. The first is the standard technique of introducing or augmenting populations of phytophagous insects. The potential for this seems theoretically favorable. A second, less conventional, approach would involve limiting pollination and subsequent mistletoe repro- ductive capacity by controlling or repelling the pol- linators. In this way, dwarf mistletoes on seed trees might be rendered harmless so the trees could be safely left to regenerate new, mistletoe-free stands.

Either of these approaches could be combined with existing silvicultural control methods or new methods yet undeveloped to provide an integrated program.

A limited amount of effort has already been put into a search for predators. During the early 1960's, C. B. Huffaker and associates at the Division of Biological Control, University of California, Albany, made preliminary studies on arthropods affecting Arceuthobium. The description of new species of mites by Kennett (1963) is a result of this activity. Hawksworth has observed arthropods on various Arceuthobium species for a number of years, with biological control in mind. The possibilities do appear intriguing, but they can be realized only if economic and other benefits justify the work neces- sary to develop techniques.

Field Identification of Arthropods Found on Dwarf Mistletoes

The following preliminary field key is presented to enable nonspecialists to make tentative deter- minations of insects and mites found in or on dwarf mistletoes. We recognize that the key is not com- plete and generally does not permit identification to species. We expect that a more comprehensive key can be constructed as we get more information on some of the species involved.

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Field Key to Insects and Mites Known to Occur on Dwarf Mistletoes4

1. Mites living in or on plants

Typhlodromus spp. Brevipalpus poraa Paraphytoptus araeuthobii

Bradysia sp. , and other flies

2. Adult or nymphal insects living freely in or on plants

A. With a single pair of wings, found mostly on flowers; flies

AA. With two pairs of wings or wingless--B

B. Wings fringed, small insects generally less than

2 mm. long, mostly on flowers; thrips Frankliniella oocidentalis

Frankliniella sp.

Thrips tabaai

Neoborella tumida N. tumida nymphs Clastoptera obtusa

Chionaspis striata Diaspis visai Niveaspis spp. Hemiberlesia spp. Pseudoparlatoria serrulata Orgyia antiqua

Mitoura spinetorum M. johnsoni

Dasypyga aternosquamella Filatima natalis Tortricid nr. peronea

**If identification to species is critical, specimens should be referred to specialists . Adult forms are needed for determination of species. Unidentified grasshoppers , thrips, scales, spittlebugs , geometrid moths, weevils, and ants, not included in the key, are also reported from dwarf mistletoes (see tables on individual species) .

BB. Wings not fringed, larger insects generally between 2 and 4 mm. long; true bugs

BBB. Wingless, smaller but as BB

3. Insects living within a white, frothy mass; spittlebugs

4. Hard shelled, sessile insects; scales A. On A. oxyoedri, Europe

AA. On New World species

5. Caterpillars feeding in or on shoots; moth larvae A. Larvae hairy; tussock moths

AA. Larvae not hairy- -------- -B

B. Larvae slug-shaped, segments in folds and ridges; hairstreaks

BB. Larvae not slug-shaped, segments smooth

-10-

Conclusions

Dwarf mistletoes harbor a considerable arthropod fauna, but we know little about the details of the ecological relationships involved. Insects do play a major role in pollination, and insect feeding can severely damage dwarf mistletoe plants, at least locally. In some instances, mistletoe appears to be related to increased tree susceptibility to insects.

There are many opportunities for further study of insect-dwarf mistletoe relationships. Practical as well as scientific benefits may be obtained, since dwarf mistletoe is an economic pest, and additional control techniques are needed. Manipulation of arthropod populations would provide another approach. Utilization of phytophagous insects is an obvious possibility. Another intriguing approach, since pollination by arthropods seems to be prac- tically obligatory, is to limit the pollinators and thus reduce reproductive capacity of dwarf mistletoe. It may also be possible to combine biological control with other control methods to provide an effective integrated control program.

Literature Cited

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1964. The false spider mites of Arizona (Aca- rina: Tenuipalpidae). Ariz. Agr. Exp. Sta. Tech. Bull. 163, 80 p. Baloch, G. M., and Mohyuddin, A. I.

1969. The phytophagous fauna of a mistletoe (Loranthus longif lorus Desr.: Loranthaceae) in West Pakistan. Weed. Res. 9(1): 62-64. Coleman, G. A.

1921. Beekeeping in our California national forests. II. Honey flora. West. Honey Bee 9: 376-377. Comstock, John A., and Dammers, Charles M.

1938. Notes on the metamorphosis of Mitoura spinetorum Hew. ( Lepidoptera, Theclinae). S. Calif. Acad. Sci. Bull. 37: 30-32. Edmunds, G. F., Jr., and Allen, R. K.

1958. Comparison of black pine leaf scale popu- lation-density on normal ponderosa pine and those weakened by other agents. X Int. Congr. Entomol. [Montreal, August 1956] Proc. v. IV, p. 391-392. Essig, E. O.

1958. Insects and mites of western North America. 1055 p. N.Y.: The Macmillan Co.

Garth, J. S.

1950. The butterflies of Grand Canyon National Park. Grand Canyon Nat. Hist. Ass. Bull. 11, 52 p. Gill, L. S.

1935. Arceuthobium in the United States. Conn. Acad. Arts and Sci. Trans. 32: 1 1 1- 245, illus.

and Hawksworth, Frank G.

1961. The mistletoes; a literature review. U. S. Dep. Agr. Tech. Bull. 1242, 87 p. Hawksworth, Frank G.

1961. Dwarfmistletoe of ponderosa pine in the southwest. U. S. Dep. Agr. Tech. Bull. 1246, 1 12 p. Heinrich, C.

1921. On some forest lepidoptera with descrip- tion of new species, larvae, and pupae. U.S. Nat. Mus. Proc. 57: 53-96.

Heinricher, E.

1915. Beitrage zur Biologie der Zwergmistel, Arceuthobium oxycedri, besonders zur Kenntnis des anatomischen Baues und der Mechanik ihrer explosiven Beeren. Akad. Wiss. Wien, Math.-natur. Kl. Sitzungsber. Abt. I. 124: 181-230.

Keifer, H. H.

1952. Eriophyid studies XIX. Calif. Dep. Agr. Bull. 41(2): 65-74. Kennett, C. E.

1 963. Some species of Typhlodromus from dwarf mistletoes in North America (Acarine: Phyto- seiidae). Pan-Pac. Entomol. 39(4): 247-252. Knight, Harry H.

1 925. Description of thirty new species and two new genera of North American Miridae (Hemiptera). Brooklyn Entomol. Soc. Bull. 20: 33-58. Korstian, Clarence F., and Long, W. H.

1922. The western yellow pine mistletoe. U.S. Dep. Agr. Bull. 1 1 12, 35 p.

Kuijt, Job.

1955. Dwarf mistletoes. Bot. Rev. 21: 569-627. Lindinger, L.

1912. Die Schildlause(Coccidae) Europas, Norda- frikas, und Vorderasiens einschliesslich der Azoren, der Kanaren und Madeiras. 388 p. Stuttgart: E. Ulmer. Miller, J. M., and Keen, F. P.

1960. Biology and control of the western pine beetle. U.S. Dep. Agr. Misc. Publ. 800, 381 p.

-11-

Pritchard, A. E., and Baker, E. W.

1958. The false spider mites (Acarina: Tenuipal- pidae). Univ. Calif. Entomol. Publ. 14(3): 175-274. Remington, Charles L.

1958. New records of larval host plants of Mitoura spinetorum (Lycaenidae). Lepidop- terists News 12: 14. Roe, Arthur L, and Amman, Gene D.

1970. The mountain pine beetle in lodgepole pine forests. USDA Forest Serv. Res. Pap. INT-71, 23 p. (Ogden, Utah) Scharpf, Robert F., and Hawksworth, Frank G.

1968. Dwarf mistletoe on sugar pine. U.S. Dep. Agr. Forest Pest Leafl. 1 1 3, 4 p. Schumacher, F.

1918. Die Insekten der Mistel und verwandten Loranthaceen. Naturwiss. Z. Forst-u. Land- wirt. 16: 195-238. Shields, Oakley.

1965. Callophrys (Mitoura) spinetorum and C (M.) johnsoni: their known range, habits, variation, and history. J. Res. on the Lepid. 4(4): 233-250. Struble, George R.

1957. The fir engraver, a serious enemy of

western true firs. U.S. Dep. Agr. Prod. Res. Rep. 11, 18 p.

1965. Attack pattern of mountain pine beetle in sugar pine stands. U.S. Forest Serv. Res. Note PSW-60, 7 p. Pacific Southwest Forest and Range Exp. Sta., Berkeley, Calif. Tilden, J. W.

1960. An additional note on the life history of Mitoura spinetorum (Hewitson) (Lepidop- tera: Lycaenidae). Pan-Pac. Entomol. 36(1 ): 40.

Tubeuf, C. von.

1923. Monographie der Mistel. 832 p. Munich: R. Oldenburg. Tucker, E. S.

1922. Studies on insects associated with the American mistletoe. Kansas Acad. Sci. Trans. 30: 143-170. Weir, James R.

1915. Wallrothiella arceuthobii. J. Agr. Res. 4: 369-378.

1916. Mistletoe injury to conifers in the north- west. U.S. Dep. Agr. Bull. 360, 39 p.

Agriculture — CSU, Ft. Collins

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About The Fotest Sen ice.

As our Nation grows, people expect and need more from their forests— more wood, more water, fish and wildlife; more recreation and natural beauty; more special forest products and forage. The Forest Service of the U. S. Department of Agricul- ture helps to fulfill these expectations and needs through three major activities:

• Conducting forest and range research at over 75 loca- tions ranging from Puerto Rico to Alaska to Hawaii.

• Participating with all State forestry agencies in co- operative programs to protect, improve, and wisely use our Country' s 395 million acres of State, local, and private forest lands .

• Managing and protecting the 187 -million acre National Forest System.

The Forest Service does this by encouraging use of the new knowledge that research scientists develop; by setting an example in managing, under sustained yield, the National Forests and Grasslands for multiple use purpos es ; and by cooperating with all States and with private citizens in their efforts to achieve better management, protection, and use of forest resources .

Traditionally, Forest Service people have been active members of the communities and towns in which they live and work. They strive to secure for all, continuous benefits from the Country' s forest resources .

For more than 60 years, the Forest Service has been serv- ing the Nation as a leading natural resource conservation agency .