Mississippi State University Scholars Junction
Mississippi Agricultural and Forestry Bulletins Experiment Station (MAFES)
3-1-1983
Southern pine beetle : the host dimension
C. A. Blanche
J. D. Hodges
T. E. Nebeker
D. M. Moehring
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Recommended Citation Blanche, C. A.; Hodges, J. D.; Nebeker, T. E.; and Moehring, D. M., "Southern pine beetle : the host dimension" (1983). Bulletins. 764. https://scholarsjunction.msstate.edu/mafes-bulletins/764
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^OUfHERN PINE BEETLE: THE HOST DIHENSION ACKNOWLEDGEMENTS
This work was supported by the Integrated Pest Manage- ment Research, Development and AppHcation Program, Pineville, Louisiana, through USFS Grant #19-82-023, Mississippi State University and Mississippi Agricultural and Forestry Experiment Station. The findings, opinions, and conclusions are the responsibility of the authors. We gratefully appreciate the reviews by Drs. Alan A. Berryman, Gerard D. Hertel, Garland Mason, and Robert C. Thatcher. Their comments and suggestions greatly im- proved this manuscript. We thank Dr. Mark Brown for his input on the flow diagram of the attack process. SOUTHERN PINE BEETLE: THE HOST DIMENSION
C. A. Blanche, Research Associate, Mississippi State University, Department of Forestry J. D. Hodges, Professor and Forester, Mississippi State University, Department of Forestry T. E. Nebeker, Associate Professor, Mississippi State University, Department of Entomology D. M. Moehring (Deceased), Professor and Forester, Mississippi State University, Department of Forestry I
I
II
Ml i CONTENT
Introduction 1
Host and Host Characteristics 1
Hosts 1 Host Characteristics 3 Host Resistance/SusceptibiUty to SPB 3 What Constitutes Host Resistance 3 Criteria for Assessment 4 Host Physiology and Conditions under Stress 5 Under Deficient Moisture 5 Water Stress and Host Attractiveness 5
Oleoresin Exudation Pressure and Oleoresin Exudation Flow ... 6 Water Stress and Bark Moisture Content 7 Water Stress, Vigor and Growth 8 Water Stress and Host Chemistry 8
Water Stress in Relation to Stand Density and Thinning 9 Under Excessive Moisture 10 Effects of Excessive Moisture on SPB 10 Effect on the Host and Host Characteristics 10
Effects of Flooding on the Soil and Microorganisms 11 Lightning-struck Trees 11 Lightning and Extent of Damage 11
Attractiveness of Lightning-struck Trees to Bark Beetles 12 Chemical and Physiological Changes in Struck Trees 14 Role in Brood Development and Population Dynamics 14 Under Biotic Stress (Diseases and Other Pests) 15 Other Stress Forms (Harvesting, Wind, Fire, Etc) 15
(Continued) (Continued)
Host Physiology and Conditions in
Relation to Brood Development 16
Requirements for Brood Development 16 Host Conditions Affecting Brood Development and Mortality 16 Host-SPB-Microorganism Complex: The Role of Associated Microorganisms 17 The Beetle-Microorganism Association 17 Effects of the Associated Microorganisms on the Host 18
Host Response to Invasion by Associated Fungi 18 State of Knowledge Analysis and Research Needs 19 References 21 SOUTHERN PINE BEETLE: THE HOST DIMENSION
INTRODUCTION
Jhe southern pine beetle (SPB), dynamics (Coulson, 1980), sampl- The review was done in a com- [^ndroctonus frontalis Zimmer- ing and predicting population bined time sequence and topical iimn (Coleoptera: Scolytidae) is trends (Hain, 1980), impacts of the organization approach. In other iisidered one of the most serious SPB (Leuschner, 1980) rating of situations the approach was dic- )sts of southern pines. The first stands for susceptibility (Lorio, tated by developmental logic. )tbreak formally recorded in the 1980), silvicultural guidelines for In analyzing the literature we ;uthern United States occurred reducing losses (Belanger, 1980), used the following terms as defin- llring 1882 in southeast Texas direct control (BilHngs, 1980) and ed: lopkins, 1903). Since then, in- integrated management strategies 'ijitations have recurred extensive- (Coster, 1980). Intensive treatment Susceptibility = degree of spreading to areas roughly of the host as it influences the SPB resistance of the host to insect nnciding with the geographic is non-existent, except for the colonization. We visualize Istribution of loblolly pine (Pinus initial efforts of McAndrews (1926) resistance as a spectrum with one lleda L.). A historic account of and Caird (1935). Hanover (1975) extreme described as susceptible ibse outbreaks has been compiled reviewed the physiology of tree and the other extreme as immune. Price and Doggett (1978) for the resistance to insects with some Suitability = host quality in 3j 5utheastern United States. emphasis on the mechanisms of relation to brood development and Pomprehensive reviews on this resistance and host terpene resultant brood quality. cjetle were done by Thatcher physiology but with little reference Vigor = the overall state of the ;)60), Dixon and Osgood (1961) to the SPB. This review is therefore host as reflected in the different 3.d Coulson et al (1972). An in- aimed at consolidating scattered degrees of metabolic activities t^ated presentation edited by host-related information, par- (synthetic and degradative l^atcher et al (1980) covered the ticularly the physiological aspect, processes). Radial growth is one Le history and habits (Payne, analyzing and synthesizing such example of a manifestation of the 180), natural enemies and information and identifying degree of synthetic processes. ssociated organisms (Berisford, knowledge gaps with the ultimate Attractiveness - the quality of 180), climatic, site and stand objective of prioritizing research on the host that draws the beetles to fetors (Hicks, 1980), population the host-bark beetle relationship. attack or go near. HOSTS AND HOST CHARACTERISTICS bsts Che SPB can potentially attack loblolly pine is the other most the southern Appalachians, id kill all pine species within its susceptible species in the Coastal shortleaf and pitch (P. rigida Mill.) rage (St. George and Beal, 1929; Plain (Bfelanger and Malac, 1980). pines are the preferred hosts Cxon and Osgood, 1961). Payne In Arkansas, shortleaf pine is the (Belanger and Malac, 1980; !'i80) suggested that loblolly pine preferred host (Ku et al, 1980), Belanger and Hatchell, 1981) with
15 so highly preferred that the probably because of its abundance. pitch pine considered more suscep- ?3graphic distribution of the SPB In the (Borgia Piedmont, shortleaf tible (Belanger et al, 1979). In
LJ roughly approximated by the pine is again the preferred host another report, Kowal (1960) cited litribution of this pine species. despite the fact that it is not the shortleaf, loblolly and Virginia {P. Fliwever, in the three geographic most abundant pine species in the virginiana Mill.) pines as the n^ions of the South (Coastal Plain, area (Belanger et al, 1977). This preferred hosts, and slash (P. Fidmont and Southern Ap- latter preference for shortleaf pine elliotti Engel.), longleaf (P. plachians), shortleaf pine (P. has been attributed to the palustris Mill.) and spruce (P. e iinata MUl.) has been reported predisposing effect of littleleaf glabra Walt.) pines as the less t( be the most susceptible, while disease (Belanger et al, 1979). In desirable hosts. Earlier, St. George — — and Beal (1929) reported loblolly and shortleaf pine to be much more Table 1. Comparison of the four major southern pines. susceptible than longleaf and slash pine. The apparent preference for Longleaf Slash Shortleaf Lobloll;' specific host species appears to be Features Pine Pine Pine Pine related to variation in oleoresin 1/ properties. In comparing the four Turpentine...density— 0.8618 0.8533 0.8452 0.8525 major southern pines (loblolly, longleaf, slash and shortleaf). Turpentlne^^ index of refraction- 1 . 4657 1 .4631 1.4728 1,4700 Hodges et al (1977, 1979) identified total resin flow as the most dis- Optical rotation of criminating variable in classifying turpentine— +7.89° -30.78° +103.49° +46.2° the least desirable (most resistant) % turpentine from host. Belanger et al (1979) observed oleoresir>~ 22-23 22 16-20 14-19 that white pine (P. strobus L.) was 1/ . the least preferred host in the d, dl oe-pinene— (%) (based on turpentine) 64 75 85 71 southern Appalachians and this has been attributed to the ability of 1- 6-pinene^^(%) this species to "pitch out" the SPB. (based on turpentine) 31 21 11 22
To test if there was any 2/ Oleoresin viscosity— preference for loblolly over (stokes) 60 306 24 18 shortleaf pine, Thomas et al (1981) 9 / assayed for biting responses of Total flow (ml)- 18 11 9 12 SPB to bark extracts of different Rate of flow (ml/hr)-^ 1 . 55 0.56 0. 78 1. 12 polarities. Judging from the bioassay responses, there seems to Flow at 8 hrs. (%)-^ 66 38 67 77 be no preference for loblolly over Time to initial shortleaf. However, when inner crystallization (hrs) HO/ft 0.98 bark and outer bark extracts were separated, extracts from the outer a-pinene (mg/lOOmg bark of shortleaf pine eUcited the oleoresin)- 21. 18 16.44 14.30 16.56 greatest number of biting Camphene (mg/lOOmg responses. In loblolly pine. White oleoresin)— 0. 18 0.22 0. 18 0.20 (1981) demonstrated, through a bioassay, that diethyl ether and Myrcene (m|/100mg oleoresin)— 0. 70 U. 48 U. OU 1.56 methanol extracts of inner and outer bark influenced beetle tunnel- 6-pinene f mg / 1 OOmg ing. The positive and negative oleoresin)— 5.23 4.22 12.06 8.58 responses of SPB to the bark Limonene (mg/lOOmg extractives were attributed to tree- oleoresin) 0.49 0. 25 0.93 1.68 to-tree variation in extractive con-
centrations. White viewed these 0.22 2.86 0. 90 1.04 positive and negative responses as
indicative of responses to Total monoterpene . gustatory stimulants and (mg/lOOmg oleoresin)— 28.00 24.47 28.96 29.63 deterrents. Pimaric acid (mg/lOOmg Other coniferous species reported oleoresin)— 3. 79 3.76 3. 77 5. 11 to be occasional hosts of SPB in the S.C. Pimaric acid United States are table ^ mountain (mg/lOOmg oleoresin)— 1.11 1.09 1.19 1.22 pine (P. pungens Lamb.) (Knull, 1934), red spruce (Picea rubens Palustric acid (mg/1 OOmg)— 12.21 15. 10 8.40 12.18 Sarg.) (Payne, 1980), pond pine (P. 3/ Levopimaric acid (mg/lOOmg)— 16.83 8.62 18.74 19.44 serotina Michx.) (Payne, 1980) and 3/ ponderosa pine (P. ponderosa Isopimaric acid (mg/lOOmg)— 10.98 17.40 10.05 7. 15 Dougl. ex Laws.) (Wood, 1963). (continued)
2
I " There are no reports to indicate that outbreaks have occurred in these occasional hosts. SPB outbreaks in Central
. America have occurred in the Table 1. (continued) following pine species as hosts: P. Schiede (Coyne and Longleaf Slash Shortleaf Loblolly , oocarpa Features Pine Pine Pine Pine Critchfield, 1974), P. carihaea Morelet (Coyne and Critchfield, 1974), P. pringlei Shaw (Hendricks, Abietlc acid (mg/ lOOmg)-'' 8.08 8.57 7.95 8.63 1977 as cited by Payne, 1980) and P. 3/ Dehydroabletic (mg/lOOmg)— 3. 76 2.67 4.20 3.82 ^^pseudostrobus teocate Lindl. (Hen- 3/ dricks, 1977 as cited by Payne, Neoabietic acid (mg/lOOmg)— 11.61 13.75 10.85 9 .49 1980). The broad range of host Total resin .acids (mg/lOOmg species attests to the aggressive oleoresin)— 68. 37 70.96 65. 15 67. 04 behavior of this species. Radial resin duct width Host Characteristics: Com- (u)i^ 57.6 54.8 49.0 54.6 parison of the Four Major 4/ No. of resin ducts— 32.6 43.9 35.5 35.3
i Southern Pines Motivated by our desire to ex- Oleoresin .viscosity 4/ plore the possibilities ofidentifying (stokes)— 55.7 241.0 20.9 16.2 relevant host characteristics for 4 / Resin flow rate (ml/hr)— 1.1 0.6 0.8 1.5 breeding and rating resistance of individual trees and stands to SPB Most critical disease^^ brown fusiform llttleleaf fusiform attack, we have tabulated species spot rust disease rust characteristics of the four major -'^Mirov, 1961. southern pines (Table 1). We I 2/ premised our characterization on —Hodges et al . , 1977. the recognition that slash and 3/ -Hodges et al. , 1979.
I longleaf pine are more resistant, 4/ and shortleaf and loblolly pine are - Hodges et al. , 1981. more susceptible to SPB attack. A -^Dorman, 1976. cursory look at the table provides no significantly consistent feature
I for the four species, except for oleoresin viscosity, which stands
I out as a possible distinguishing characteristic for resistance. HOST RESISTANCE/ SUSCEPTIBILITY TO SPB
What Constitutes Host Any effective investigation of slash pine and the result of the Resistance to SPB? host resistance to insect pests must biting response bioassay of al to support I The preference for a particular recognize the components of Thomas et (1981) tend host is a valid manifestation of resistance. The resistance com- this general cause of host I resistance. to Painter (1951) resistance to SPB. Although tree- ; When a particular host ponents according species is preferred at one location are preference or non-preference, killing bark beetles apparently use and not in another it indicates that tolerance and antibiosis. In- both random and directed host induced resistance or dications from the Hterature show selection (Wood, 1982), decisive j pseudoresistance exists. Our dis- tolerance to play no important role studies leading to the identification I cussion to SPB. The of the basis for host selection are j of resistance of southern in host resistance pines to SPB does not distinguish preference or non-preference com- lacking (Cates and Alexander, j between induced resistance and ponent appears likely. Field obser- 1982). For as long as the question of I inherited resistance. Suffice it to vations of host preferences, the host selection remains unresolved, say that host resistance to SPB attractiveness of loblolly and our understanding of host exists. shortleaf pine over longleaf and resistEince to SPB will continue to
3 '
s between trees. Rates of soil dicated that almost all roborating Craighead's obseri! moisture depletion are con- photosynthetic variations on the vations, found heavy brood mon siderably reduced in thinned bottom one third of the crown were tality of SPB in 1926-27 iri shortleaf pine stands. This slow- accounted for by radiation. Asheville, NC to be due to excessive down in water use prolongs However, other microclimatic fac- rain in the fall of 1926 and higbij
available soil moisture for extend- tors, such as ambient air temperatures in January. On the ' ed seasonal growth (McClurkin, temperatures, vapor pressures and other hand, r^ression analysis
1961). The same pattern has been ambientC02 concentrations, play revealed that excessive moisture j
observed in thinned pine plan- more significant roles in the upper appeared to favor the reproduction ij tations in other places. For in- crown. The paper further asserted and rapid development of SPB^M stance, a thinned 39-year-old red that the secondary effect of thin- broods as expressed by the regres^ij^ pine (P. resinosa Ait.) plantation in ning is to increase transpiration si on coefficients of the twa j lower Michigan exhibited in- rates and nutrient uptake. This moisture variables used (Kalks-s||
creased diameter growth, and the increase in transpiration rate is on tein, 1976). Integrating excessive.'i! , initial supply of moisture was an individual tree basis and should rainfall with season, Kroll and
available for a longer period of time be compensated for by fewer Reeves (1978) showed that periods i ^ (Della-Bianca and Dils, 1960). In numbers of trees utilizing the water of high summer rainfall wereii| the West, Helvey (1975) reported supply. correlated with increased numbersn!
that heavy thinning of a 50-year Mason (1971) reported that the of spots, while high spring and falll*' old ponderosa pine stand resulted average OEF was 40% greater in rainfall were correlated withreduc-( in a radical reduction in soil loblolly pines in thinned plots than ed beetle activity. (More on thisn
moisture depletion, but growth was in trees in unthinned plantations. under host conditions in relation toii greatest in stands thinned to a 15- This should not be construed as a brood development.) foot spacing (moderate thinning). direct effect of thinning in enhan- In New Zealand, dense stands of cing OEF but rather the effect of Effect on the Host and Hosth\ Monterey pine (P. radiata D. Don) eliminating individuals with low Characteristics exhausted available soil moisture OEF. Overstocking in the stand The overall effect of excessive as early as November, and was found to reduce OEF rates moisture on SPB hosts was ex-* diameter growth stopped. Moisture more than temporary moisture pressed by Hetrick (1949) when he was available in heavily thinned stress did (Mason, 1971). This is not wrote "the most susceptible hosts stands, and diameter growth con- surprising since flow rate is more a are pines weakened by excessive
tinued until the following March or function of oleoresin reservoir precipitation." The key point in ' April (Butcher and Havel, 1976). In (Hodges et al, 1977). And thi-s statement is that tree vigor is the same investigation. Butcher Schopmeyer and Larson (1955) influenced by surplus moisture, ^
and Havel (1976) claimed that have shown that oleoresin produc- and not tree growth since drought ' moisture limitations manifest tion is influenced by dbh, crown is more effective than flooding in themselves first in depression of size, and position of trees in slash reducing cross-sectional growth of diameter growth, second in pine stands. loblolly pines (Lorio and Hodges,
predisposition to attack by I. gran- 1968). Despite the slower radial i dicollis, and third in direct drought Under Excessive Moisture growth of pines in dry or droughty deaths. Effects of Excessive Moisture on conditions, trees growing in wet or It has been claimed that the the SPB waterlogged soils are more suscep- immediate effect of thinning is to Too much moisture could be tible to beetle attack (Hicks et al, increase light levels in the bottom beneficial or detrimental to the 1979). Reduced vigor of trees grow-
one third of the crown, providing a SPB depending on its stage of ing along Kerr Reservoir in North I
wider zone of high photos ynthetic development. Craighead (1925) Carolina was believed to be due to i surface and increased production observed that heavy precipitation, periodic flooding (Hicks, 1980; ' by older needles (Woodman, 1976). while the young broods were Maki et al, 1981). Lorio (1968) < His light measurements at developing under the bark, caused reported that pines growing on < different heights along the crown high mortality. He also noted that poorly drained sites are particular- showed that only 2% of full heavy precipitation effectively ly susceptible to SPB attack. Kalks- sunlight reached the needles on the killed the beetles during periods of tein (1976, 1981), in his attempt to bottom branches of 37-year old attack. He then concluded that identify significant climatic unthinned Douglas fir {Pseudot- excessive precipitation is one of the variables associated with SPB suga menziesii (Mirb. Franco) causes of rapid decline of SPB outbreaks, suggested that the vigor trees. A correlation analysis in- epidemics. Beal (1927), cor- of loblolly pine is adversely in-
10 luenced by moisture surplus since transpiration activity when retardation. Waterlogged soils 16 areas under study are often their root systems are not have been known to produce harm- aterlogged. completely flooded (Vereten- ful substances such as sulphides Why are loblolly pines that are nikov, 1964); (Culbert and Ford, 1972), high abjected to flooding more j) under temporary cessation of CO 2 concentration (Hook et al, iilnerable to SPB attack than respiration (due to 1971) and soluble iron and lose under droughty conditions? anaerobiosis) plant cells lose a manganese (Jones, 1972). The ^e do not fully understand this significant portion of their production of hydrogen sulphide denomenon, but we do know that water, and the water retaining (H 2 S) brought about by the reduc- a) flooding significantly reduces ability of the leaves drops (as ing conditions in soils may not only the bark-water potential of reviewed by Samuilov, 1965); affect the host trees but may attract loblolly pine just as drought k) flooding increases the the beetles. AH and Anderson does (Hodges and Lorio, 1969); glycolytic rate of intolerant (1974) have shown that pioneer
b) continuous flooding adversely trees (Crawford and McMan- beetles of /. grandicollis are at- affects both OEP and relative non, 1968); tracted to such odors as carbon
water content of loblolly pine 1) glycerol accumulates in the disiilfide (foul odor). (Lorio and Hodges, 1968); roots under flooded conditions Mycorrhizal fungi do not grow c) flooding noticeably reduces (Crawford, 1976) and anaerobically (Coutts and the rate of growth of conifer m)OEP is high in the early Armstrong 1976). Under flooded terminals (Ahlgren and morning in all control and conditions, the mycorrhizal Hansen, 1957); drought-stressed trees, but association maybe entirely absent. d) flooding increases the mor- flooded trees exhibit low Mycorrhizal surface area appears tality of secondary roots pressures as well as the to be related to water regime. When (Hosner, 1959); drastic and prolonged reduc- the soil becomes drier, mycorrhizal e) loblolly pine growing on flat tion in OEP all day (Lorio and surface area is reduced on mounds or concave sites (periodically Hodges, 1968). and increases on flats. The surface waterlogged) have fewer fine This last observation (m) is in- area is greatly reduced on flat sites roots than those on com- teresting in that it appears to during most of the wetter period parable trees on mounds implicate OEP in the greater (Lorio et al, 1972). The forms of (Lorio, Howe and Martin, susceptibility of flooded trees than mycorrhizae also appear to change 1972); drought-stressed trees. with soil moisture conditions. The ,
1 f) loblolly pine subjected to con- nodular types become common flooding exhibits Effects Flooding on the Soil and there is soil ; tinuous a of when excessive remarkable increase in Microorganisms moisture, and the bifurcate and sugars, but the increase occurs A knowledge of the effects of branched types predominate under later relative to sugar increase flooding on soil provides us better moisture stress (Lorio et al, 1972). in drought stressed trees insight into the SPB/host interac- j (Hodges and Lorio, 1969); tion since these effects are even- Lightning-struck Trees g) under anaerobic conditions, tually translated into host and Lightning and Extent of Damage the roots of many species finally into beetle response (sur- Lightning is a very powerful vival). know that flooding change agent in a forest ecosystem. j produce compounds such as We ethanol and acetaldehyde causes oxygen deficiency. Very It starts forest fires, acts as a (Fulton and Erikson, 1964), often anaerobiosis may develop nitrogen fixer and predisposes
^ ethylene (Kawasi, 1972) and within a few hours after flooding trees to other agents of deteriora- j cyanogenic compounds (Rowe due to displacement of gas from the tion (Taylor, 1969, 1971, 1974). A and CatHn, 1972); soil pore space (Coutts and lightning bolt can produce as many h) summer flooding is more in- Armstrong, 1976). Under such as 345,000 amperes of electricity jurious to woody plants reduced conditions, phosphorus (Anonymous, 1966) and can because oxygen is less soluble availability usually increases but develop peak color temperatures of at higher temperatures nitrogen availability is diminished the channel in air from 21,000°to (Verentennikov, 1964); (Patrick, 1978). Ahlgren and 31,000°K (Prueitt, 1963; Uman, little is i) under flooded conditions, Hansen (1957) pointed out that the 1964). Although very transpiration is much lower soil carbon dioxide-oxygen ratio known about the peak temperature (McColl, 1973; Veretennikov, and nitrate availability are altered developed by a lightning discharge 1964), but trees on moist soils by flooding and that such at the ground level, it is believed to are capable of increased alterations may cause growth develop energy sufficient to melt
11 Taylor, j^" some metals and to ignite forest a nearby tree (Schmitz and August alone of those years ha ij
ranges i^'s fuels (Taylor, 1969). Coupled with 1969). Structural damage lightning-struck trees (Hodges an li these energy characteristics is its from the removal of the cambium Pickard, 1971). [w frequency; it is estimated that or sapwood (Fuquay et al, 1967; Studying the spatial-temporaij about 8 million lightning dis- Taylor, 1969; Hodges and Pickard, distribution of SPB infestationnj charges strike the earth each day, 1971) to splitting and ejection of near Oakdale, Louisiana, Lori(rijl and if these were evenly dis- slabs from the most severely and Bennett (1974) found thaiji (Fuquay et al 1967; 299i tributed, roughly half a million damaged trees lightning was associated with ; i
would be striking the world's Taylor, 1969). Loosening of bark of of the infestations tallied froni ' forests (Taylor, 1969). struck trees has been observed in April, 1965 to March, 1969. And ir J Lightning damage has been loblolly pine (Howe et al, 1971). August 1965 alone, 77% of th Southeast Asia (Anderson, 1964; 1966; Schmitz and Taylor, 1969), struck trees. Available informatiomj I Brunig, 1964), the rubber plan- exposure of main roots (St. George, indicates that lightning plays all' tations of Sumatra (LaRue, 1922), 1930) and excavation of the soil at very important role in the SPE the banana plantations of Hon- the base of the Hghtning scar population dynamics. In lateij duras (Reinking, 1930), the Valdi- (Schmitz and Taylor, 1969) have summer and early fall, when beetki! vian rain forest of Chile (Wilhelm, likewise been reported. Crown populations are normally low ; 1968), the Trans-Saharan regions injuries, in the form of ruptured (Thatcher and Pickard, 1964)j: of Africa (PhilHps, 1965), the branchlets and needles, by flying lightning-associated infestationsn: radiata pine stands in Australia bark and wood debris (Taylor, peaik (Lorio and Bennett, 1974f j (Minko, 1966), the forests of 1969) and ignition of crown foliage Lorio and Yandle, 1978). a\ Scotland (Murray, 1958) and the and upper stem (Fuquay etal, 1967) southwide survey of SPB-infested^ coniferous forests of the U. S., are common in lightning-struck plots showed that 39.0%, 31.6% and:; particularly the western states ponderosa pine. Sometimes, a 23.0% of the attacked plots in ^ (Taylor, 1969). Forest wildfires struck tree literally explodes (John- Arkansas, Texas and Georgia,ij|l could be the most destructive direct son, 1966b) causing its virtual respectively, contained lightning r effect of lightning on the temperate disappearance. It appears that all struck trees as opposed to 0.4%, coniferous forests of North parts of a tree are vulnerable to 0.9%, and l.(Fo of the corresponding America. Each year, lightning lightning injury. non-attacked plots (Hicks, 1980). causes some 10,000 forest and Also, trees around a struck tree , range fires in the U. S. alone Attractiveness of Lightning-struck often become vulnerable. For in-i| (Fuquay et al, 1967). Timber mor- Trees to Bark Beetles stance, a study by Schmitz andi" tality caused by lightning probably Conifers that are structurally Taylor (1969) revealed that 76% of ranks second in severity. FfoUiott damaged by lightning are very the ponderosa pine trees within an and Barger (1967) examined 634 attractive to bark beetles (Hopkins, 80-foot radius of the struck tree sawtimber trees in northern 1909; St. George, 1930; Knull, 1934; were infested by the pine engraver Arizona and foimd 10% of these to Beal and Massey, 1945; Hetrick (7. pini Say) in the upper two-thirds have been damaged by lightning. 1949; Thatcher, 1960; Anderson of the stem, with some mountain Johnson (1966a) claimed that light- 1960; McMullen and Atkins, 1962; pine beetle at 50 feet and western ning was responsible for 4% of the Rudinsky, 1962; Thatcher and pine beetle in the lower 20 feet. mortality of old-growth ponderosa Pickard, 1964; Johnson, 1966b; Whether such increased suscep- pines in western Montana. Repor- Anderson and Anderson, 1968; tibility of neighboring trees is ting from the northeastern U.S., Schmitz and Taylor, 1969; Hodges directly attributable to lightning is Nelson (1958) found that lightning and Pickard, 1971; Howe, et al, uncertain. However, reports of caused 25% mortahty of 1,300 1971; Lorio and Bennett, 1974; declining trees around struck i mature eastern hemlock trees. Lorio and Yandle, 1978). Johnson stems have been published From the South, Trousdell (1955) (1966b) reported that about 80% of (Jackson, 1940; Murray, 1958; indicated that lightning was one of all mature ponderosa pine struck Anderson 1964; Komarek, 1964; the most important single causes of by lightning were attacked and Minko, 1966b). Schmitz and Taylor , mortality ofloblolly pine seed trees. killed by the western pine beetle. Of (1969) suggested that lightning »| Lightning that strikes the forest the 2,100 SPB infestations over a causes unobserved physiological does not necessarily cause a wild- three-year period in south-central injury to trees surrounding a struck fire, but often causes structural Louisiana, 31% were associated tree, making them susceptible to damage to the struck tree. Oc- with lightning-struck trees, and beetle attack. casionally, such damage extends to 75% of the beetle spots found in What makes a struck tree highly 12 I attractive to bark beetles is not al (1971) stressed that the arrestant property of pine trees |fully understood, but hypotheses microorganisms may play a major that holds the SPB from getting have been stated as follows: role in modifying the condition of outside its host range. At the a) Fermentation of the phloem, trees and enhancing their suitabili- individual tree level, it is the whether by anaerobic respira- ty for brood development. distribution, duration, and concen- tion or from external Hypothesis b appears promising. tration of potential host attrac- microorganisms, could be a For instance, Werner (1972) tant(s) that provides a sphere of product of the wounding of demonstrated that /. grandicollis is influence that directs the SPB to its ponderosa pine trees by light- attracted to volatile terpenes susceptible host. After a successful ning. Volatile odors from this released from host tree phloem. All initial attack, a stronger secondary fermented phloem attract and Anderson (1974), working on attraction (pheromone effect) leads newly emerged beetle adults the same species of bark beetle, to mass attack. Therefore, the host (Johnson, 1966b); provided further support for the selection catena for SPB may be b) When lightning strikes a pine hypothesis that /. grandicollis composed of orthokinesis (host tree and ruptures the bark, initially selects and attacks host finding movement with an arres- certain host volatiles are trees as a chemotactic response to tant), olfactory, biting and released from the exposed olfactory stimuli. The initial attack gustatory responses. Hypothesis c wood and phloem. Some of by SPB was hypothesized to be in at first appears attractive (Howe et these volatiles are attractive response to volatiles emitted by al, 1971), but observations in north to Ips spp. flying through the dead pines (Heikkenen, 1977). Florida, strongly suggest that forest (Anderson and Ander- Heikkenen's data were collected in ozone produced by lightning son, 1968); an area of endemic beetle pop- strikes is at best insignificant, and c) The sudden release of ozone ulations. The problem with even declines regardless of intensi- following a lightning strike hypothesis b is the difficulty of ty and severity of the lightning attracts beetles (Howe et al, designing a decisive experiment to activity (Davis, 1974). Hypothesis e 1971); test it. To date no experiment has proposes that the black turpentine d) Microorganisms invading a ever attempted to collect volatilized beetle responds to a primary (host) lightning wound produce bee- compounds from a lightning struck attractant, produced as a result of tle attractants (Howe et al, tree. The other complication is the the strike, and in turn produces a 1971); pheromone produced by the first secondary attractant responsible e) The black turpentine beetle beetles attacking a struck tree. At for the attack by the SPB (Hodges may respond to an attrac- this point, the issue of host selec- and Pickard, 1971). This tant(s), produced as a result of tion as being random or directed hypothesis is based on the observa- the strike, and in turn produce inevitably causes argument tion, by the same authors, that the a secondary attractant between individuals. Whether black turpentine beetle usually responsible for attack by the pioneer beetles attack a host tree in attacks first, /. grandicollis and SPB (Hodges and Pickard, a random manner (Vite, 1961; Vite SPB at about the same time and /. 1971); and Wood, 1961; Gara, Vite and avulsus last. Merkel (1981) also f) The ejection and deposition of Cramer, 1965; Franklin, 1970; noted that pines attacked by the the debris shower from the Berrjmian and Ashraf, 1970; Howe black turpentine beetle are subse- struck tree on neighboring et al, 1971; Hynum and Berryman, quently attacked by other bark trees provide a means for 1980; Moeck et al, 1981) or initial beetles. Fvirthermore, the black short-term oleoresin release attacks result from attraction to turpentine beetle exhibits a strong that enhances the probability odors emanating from susceptible preference for wounded trees, of discovery and attack by host trees (Person, 1931; Anderson, which provide strong initial attrac- pioneer beetles in an 1948; Chapman, 1963; Rudinsky, tancy for the pioneer beetles (Gold- otherwise marginal olfactory 1966; Heikkenen and Hrutfiord, man, Cleveland and Parker, 1979). search situation (Taylor, 1965; All and Anderson, 1974; The attraction of black turpentine 1974). Heikkenen, 1977) remains un- beetles to oleoresin liberated by Vite'and Gara (1962) and Howe, et resolved. There is no doubt that lightning strikes was observed al (1971) presented convincing host selection by the SPB is ex- earlier (Hopkins, 1909). Vite' et al evidence against hypotheses a and tremely complicated and very like- (1964) demonstrated that black d. Both studies concluded that ly species specific. However, it is turpentine beetles respond to un- microorganisms do not have a role possible that host selection is a infested log sections and to various in the initial attraction of the SPB catenary process (Kennedy, 1965). resinous compounds. Also, the to struck trees. However, Howe, et At the ecosystem level, it is the possibility of beetles of one species 13 1 8S aggregation attacks or brood development, The effect of lightning is subse- j iti being attracted by the | reflected in io pheromone of another species (Vite' except in cases of extreme water quently the growth of ; lei is worth considering. loss. the tree as loss in increment and I et al, 1964) j Hypothesis / is the same as The chemistry of lightning- volume (Wadsworth, 1943). Allij ii hypothesis b except that a means of struck trees and subsequent things being equal, most of theitj a oleoresin release and distribution changes with time have not been lightning-struck trees die sooner i K investigated. non-struck trees (Baker, k is specified. This hypothesis also adequately Some than 1 in It attempts to explain the "group kill" changes reducing and non- 1974). I associated with lightning strikes. reducing sugars, starch (Hodges Role in Brood Development and 1 j and Pickard, 1971), amino N and Population Dynamics j | Chemical and Physiological total N (Smith, 1968; Hodges and Apparently, lightning renders a ik it in Struck Trees Pickard, 1971) have been reported. tree favorable for brood develop- 1 I tl Changes j Reports on the chemical and Amino N and total N were little ment and survival. To wit, the c i physiological changes in influenced by lightning strikes breeding potential of D. brevicomis s J lightning-struck trees are scarce. (Hodges and Pickard, 1971), but was estimated to be greater in i I The suggestion by Johnson (1966b) with time, total N increased while lightning struck ponderosa pines i amino decreased (Smith, 1968). in living that fermentation of the phloem by N than ponderosa pines that 1 anaerobic respiration or by exter- Smith (1968) attributed this in- were normally attacked (Johnson, i i nal microorganisms occurring as a crease in total N to 1966b). For example, the mean ij i result of wounding by lightning microorganisms colonizing the number of emergence holes in i jI has never been validated. lightning wounds. Howe et al struck trees was estimated to be el The water relations of lightning- (1971) isolated and identified from 150 to 200/ ft^ of bark as Jj struck trees have been shown to be microorganisms from lightning against a mean of 63 holes/ft^ in i! wounds. In addition, Bridges (1978) markedly altered (Anderson and normal host trees. With D. fron- \ isolated nitrogen-fixing Anderson, 1968; Hodges and bacteria talis, a record emergence of 950 '\ Pickard, 1971). The relative water from D. frontalis, D. terebrans, I. beetles/ft^ was estimated in a ly content of the inner bark of struck avulsus and /. calligraphus. After struck tree against an as average 'P loblolly pines is much lower than in these beetles attacked struck trees, emergence of 250/ ft^ in unstruck i|i green trees, and the difference total N increased while amino N infested trees (Hodges and Pickard, increases with time (Hodges and decreased (Hodges and Pickard, 1971). This increased suitability of n Pickard, 1971). Anderson and 1971). Whether the increase in total struck trees may be attributed to 'H Anderson found the and decrease in amino were lower resinosis (Berryman, (1968) that N N 1976), I hydrostatic condition of the struck due to attack or would have greater amounts of available trees deteriorated first in the crown happened anyway is uncertain. energy substrates and other essen- and progressed gradually down the However, a closer look at Smith's tials for insect growth and develop- stem. Since the turgor of the data (Smith, 1968, Tables 3 and 4, ment, since lightning-struck trees epithelial cells regulates the OEP pp. 18 and 19) indicates some are often the largest and most (Vite and Rudinsky, 1962), a reduc- increase in total N and decrease in vigorous individuals in a tion in hydrostatic pressure is amino N even before attack took stand. Also, the reduction of the accompanied by a decrease in OEP. place. relative water content of the inner Hodges and Pickard (1971) Lightning strikes apparently bark improves the brood environ- reported that the average OEP for cause marked reduction in non- ment of the beetles. Although control trees was 7.7 atm. as reducing sugar, which is further Anderson and Anderson (1968) I against 2.3 atm. and 0.4 atm. on the reduced after beetle attack. The claimed that the moisture content j undamaged and damaged sides of reducing sugar is increased by the of the inner bark did not have a struck loblolly pines, respectively. strike slightly over the control direct effect on brood development , Concommittant with the reduction (Hodges and Pickard, 1971). The of Ips spp., the moisture content of in OEP was the reduction in OER. starch level is unaffected by the their experimental tree did not go Anderson and Anderson (1968) strike but declines slightly after the below 100%. Earlier, Anderson obtained OER values ranging from beetles have attacked. Other (1948) pointed out that heavy brood 0 to 0.9 ml/hr for a struck loblolly chemical changes (e.g., volatiliza- mortality of Ips occurred when pine, with the lowest values oc- tion of terpenoids, oxidation of bark moisture content was below curring nearest to the Hghtning- monoterpene compounds, elec- 100%. Anderson and Anderson . caused fissure. Their data on the trolysis of water) which may play (1968) attributed the successful water content of the inner bark did some role in host selection, have brood development of Ips in a not show any direct effect upon Ips not been examined. lightning-struck tree to a markedly 14 reduced OER. Despite limited data, namomi and other organisms may hazard annosus root rot sites, but Hodges and Pickard (1971) predispose trees to insect attack. not in low-hazard sites such as the demonstrated a positive correla- Prolonged wet conditions on flat Piedmont (Belanger, 1981). Skelly tion between SPB emergence and sites (common in the lower Gulf (1976) found that about 30% of the carbohydrate content of struck Coastal Plain) are believed to favor roots of SPB-attacked trees had trees. Earlier, it was indicated that the distribution and development annosus root rot infection com- hexose sugars were more readily of rootlet pathogens (Lorio and pared with 20% for un attacked utilized by the SPB (Barras and Hodges, 1971). Pines on inter- trees. In an extensive survey of the Hodges, 1969). mound areas have been observed to Coastal Plain, Skelly et al (1981) The attractiveness of lightning- form rough bark on roots, and this and Alexander et al (1981) noted struck trees to beetle attack and has been associated with phloem that annosus root rot is significant- their suitability for brood develop- starvation due to impeded syn- ly associated with trees infested by ment may play a major role in the thesis or translocation of food by the SPB. The same studies dynamics of SPB populations. root diseases (Jackson and Hep- suggested that the disease stressed Struck trees have not only served ting, 1964). The dynamics of the SPB-attacked trees as indicated as centers for spot infestations mycorrhizal associations (abun- by reduced mean annual radial (Lorio and Bennett, 1974) but have dance and types) in these flat sites growth in the last 5-10 years. sustained beetle populations dur- and mounds (Lorio, et ad, 1972) may Kuhlman (1970) identified isolates ing periods of low seasonal activity find some value in the of annosus root rot with varying (Hodges and Pickard, 1971). It is maintenance of tree vigor. degrees of virulence, hence causing apparent that the effect of light- Mycorrhizal roots have been different degrees of infection of ning is more pronounced during shown to be resistant to certain living pine roots and, in turn, endemic periods and generally pathogens (Marx, 1967; Marx and varying effects on tree growth masked diuing epidemics. Davey, 1969; Zak, 1964). Very (Bradford and Skelly, 1976). recently, the vesicular-arbuscular Aside from these pathogenic Under Biotic Stress (Diseases mycorrhizal fungi have been organisms, other pests may initiate and Other Pests) pointed out to affect plant parasitic the decline of the host. Lorio (1973) The association of root injury due nematodes by physiologically suggested that black turpentine to microorganisms and other altering or reducing root exudates beetle may contribute indirectly to agents with increased attrac- responsible for chemotactic attrac- SPB epidemics by weakening trees tiveness to SPB attack was first tion of nematodes or directly retar- and rendering them more attrac- pointed out by Hetrick (1949). He ding nematode development or tive to other beetles. Lorio and asserted that any disturbances reproduction within the root tissue Hodges (1977) observed black that interfere with the normal (Hussey and Roncadori, 1982). turpentine beetles attacking their functioning of the root systems of In the Georgia Piedmont, flooded and drought-stressed trees pines may induce bark beetle littleleaf disease has been im- before they could induce SPB at- attack. His observation of the plicated as an agent predisposing tacks. mushroom root rot {Armillaria shortleaf pine to beetle attack In most instances, these biotic mellea) on SPB-infested trees clear- (Belanger et al, 1977). A study of factors act in concert with en- ly indicated that the fungus preced- this disease by Copeland (1952) vironmental factors so that their ed the bark beetle attack. The indicated that mortality of roots true effects are hard to isolate. attractiveness of flooded and less than one-fourth inch in Regardless of how they affect the lightning-struck pines, as describ- diameter contributes to the rapid trees, the obvious consequence is ed earlier in this paper, lends decline of shortleaf pine. Also, the alteration of normal host support to this claim. when 18 to 34% of the roots are metabolism resulting in reduced Root pathogens play some role in infected, normal growth stops and growth and vigor. predisposing southern pines to the tree declines very rapidly. SPB attack. Lorio (1966) reported Under certain conditions, par- Other Stress Forms that Phytophthora cinnamomi ticularly on the Coastal Plain, (Harvesting, Wind, Fire, Etc.) Rands, and Pythium spp. were annosus root rot {Heterobasidion Any stress that causes elastic or associated with declining 40-year annosum (Fr.) Bret.) is an impor- plastic strain is bound to alter the old loblolly pines in the lower Gulf tant pre(Msposer of pines to SPB normal physiology of the host. Coastal Plain of Louisiana. Obser- attack in thinned loblolly pine Unfortunately, we know very little vations on Monterey pine by Har- stands (Alexander, 1977; Alex- about host physiology under stress tigan (1964) indicated that root ander et al, 1978; Alexander et al, due to harvesting, thinning, wind, destruction by Phytophthora cin- 1980). This is very true on high- ice, etc. However, we do know that 15 above- and below-ground injuries windthrow (St. George, 1930; wounded ones tend to be attacked } from harvesting and thinning KnuU, 1934), recent fire (KnuU, more frequently by the SPB (Bro wn , operations serve as infection courts 1934) and logging disturbance (Ku and Michael, 1978). for organisms causing decay and et al, 1976; Porterfield and Rowell, We need more thorough in- discoloration. In fact, thinning 1981), have been associated with vestigations of these stress- j increases the incidence of annosus SPB outbreaks. In some areas, causing influences as they affect!! root rot on deep sandy sites un- however, fire has never been SPB population dynamics. Studies "^j derlain with clay (Powers and associated with SPB infestation geared towards cause-and-effect Ij Verrall, 1962; FroeHch et al, 1977). (Ku et al, 1980). Between water- relationships should have high j Other stress forms, such as stressed and wounded trees, the priority. HOST PHYSIOLOGY AND CONDITIONS IN RELATION TO BROOD DEVELOPMENT Requirements for Brood 3. 10 essential amino acids obtained the best brood survival Development 4. 7 to 10 water soluble vitamins with pine engraver when the inner- The food and microenvironmen- 5. vitamin C bark moisture content did not tal requirements for SPB brood 6. a sterol deviate much from that found in development have received little 7. carbohydrate. vigorous trees. He also found that attention. We do not yet have a The water, amino acid and car- heavy brood mortality occurred good handle on its nutritional bohydrate components of the bark when the inner-bark moisture needs. Initial attempts at mass have been investigated (Gaumer dropped below 100%. Gaumer and rearing, providing a number of and Gara, 1967; Hodges et al, 1968; Gara (1967) identified an optimum nutritional compounds, met with a Lorio and Hodges, 1968; Barras rearing environment for SPB from limited success (Clark and Osgood, and Hodges, 1969; Hodges and infested bolts to be from 20 to 22°C 1964). Mott et al (1978) aseptically Lorio, 1969; Hodges and Pickard, and RH of 50 to 60%— conditions reared SPB from egg to advilt on 3% 1971; Lorio and Hodges, 1977; that approximate the natural nutrient agar with lobloDy pine Webb and Franklin, 1978; Wagner, events occuring in infested trees. In callus initiated on Brown and et al, 1979). The other nutritional general, high phloem moisture is Lawrence nutrient medium. When components have not received any associated with the formation of they added /3 -sitosterol to the research attention. elongate larval mines and reduced medium, adult production increased survival (Thatcher, 1960; Clark from 14 to 26% of hatched larvae. It Host Conditions Affecting and Osgood, 1964; Webb and is intuitively obvious, though, that Brood Development and Mor- FrankHn, 1978). The rapid in nature, the two basic brood re- tality dehydration of the phloem to a quirements of the beetle are a bark The larval stage is a critical moisture content below 200% which serves as a habitat and period in the life of the SPB. In fact, appears essential to brood survival substrate and a favorable environ- larval mortality is greater than (Gaumer and Gara, 1967). The ment. The environment can have a mortality in any of the other life importance of this initial decline in direct effect on brood development stages (Coulson et al, 1976; Gold- moisture content to brood survival and survival of the beetle or an man and Franklin, 1977; Wagner et has been corroborated by Wagner al, 1979). Since the larval stages are indirect one through its effect on etal (1979). Anderson (1967) on the the host. The bark offers the best primarily spent in the inner bark other hand, employing techniques and with short time in the outer medium for establishing the nutri- a of girdling gind bark isolation to for pupation, conditions tional requirement (qualitatively) bark host produce a variety of physiological in through chemical characterization. the inner bark must have a conditions, observed that the strong influence the Such bark chemical characteriza- on develop- moisture content of the inner bark ment and survival of the brood. For tion must be guided by established was not critical to either the instance, the high mortality success of Ips attacks or brood knowledge of nutritional require- from to the first and development under his experimen- ments necessary for insect growth (70.7%) egg second larval instars could be tal conditions. Anderson and such as that given by Dadd (1970, attributed to host-tree conditions, Anderson (1968) concluded that the 1973) and Hagen (1974) as follows: since there are so few predators and inner bark moisture content parasites associated with these limited Ips brood development only 1. water first two instars (Goldman and where severe dessication occurred. 2. minerals (salts) Franklin, 1977). Anderson (1948) Investigations on the changes in 16 noisture status of the tree through moisture above 170%. High bark- is disturbed and its OEP reduced to time revealed that xylem water moisture content also slows the 60 psi, the bark beetles cannot Dotential, xylem moisture and development of 4th instar larvae breed successfully (Grossman, )hloem moisture influenced SPB and pupae. 1967). levelopment (Webb and Franklin, Environmental stresses are It is apparent that host suitabili- L978; Wagner et al, 1979; Coulson, believed to cause chemical changes ty for brood development is one of 980). Egg and early larval in the irmer bark, which in turn the final determinants of the subse- jlevelopment proceed with xylem influence the nutritional quality of quent population status of SPB md phloem dehydration. As soon the tissue. Water stress causes an with respect to quality and quanti- IS the phloem and xylem moisture increase in reducing sugars, which ty. Unfortunately, host suitability iipproaches the minimum, the are readily used by the SPB and is not a constant property of the arvae migrate to the outer bark, associated microorganisms host but is related to a number of md the rehydration of the phloem (Barras and Hodges, 1969). Using factors, such as the levels of readily akes place at about the time brood cellular and extra-cellular liquid of assimilated compounds (C)hararas idults emerge (Wagner et al, 1979; bark samples from sound and et al, 1960; Hodges et al, 1968; Coulson, 1980). Webb and Franklin xmhealthy trees of Picea abies and Barras and Hodges 1969; Hodges 1978) on the other hand reported Pinus sylvestris, Chararas et al, and Lorio, 1969), rate of tissue in earlier time of phloem rehydra- (1960) observed that the rate of dessication (Gaumer and Gara, ion, which occurred about the time development of Scolytidae is close- 1967; Webb and FrankHn, 1978; he larvae reached the outer bark. ly related to the amount of soluble Wagner et al, 1979), initial host Phis phenomenon of phloem sugars. Adequate hydration of tree vigor (Lorio and Hodges, 1977), ehydration has not been tissues maintains a high level of iimer bark temperature (Gaumer ;lucidated. Changes in phloem oleoresin flow which prevents and Gara, 1967; Powell, 1967), host noisture content elicit varjdng effective egg and larval develop- tree species and age (Coulson, •esponses from the different beetle ment (Lorio and Hodges, 1977). 1980), diameter of the host tree ife stages. Wagner et al (1979) Anderson (1967) showed that high (Fargo et al, 1979), presence of demonstrated that eggs and first- OEP, a variable highly correlated microsymbionts (Howe et al, 1971; stage larvae of SPB are unaffected with tissue hydration, reduces the Barras, 1973) and an array of ' y changes in phloem moisture, suitability of the host tree for Ips environmental factors. hile development of 2nd and 3rd attack and brood development. nstar larvae is slowed by phloem Unless the water balance of the tree HOST-SPB- MICROORGANISMS COMPLEX: THE ROLE OF THE ASSOCIATED MICROORGANISMS j^he Beetle-Microorganism 1^.88001311011 The relationship between the number of egg niches, but the (Barras, 1969). The reduction of i jPB and the blue-stain fungi is number of progeny decreases, and progeny in SPB in the absence of •onsidered symbiotic, but the the emergence is delayed 13 to 24 blue-stain fungi can have greater ;emonstration that the beetle can days (Barras, 1973). Also, implications for beetle population omplete its Kfe cycle without the laboratory observations show that status. This reduction can perhaps lue-stain fungi (Barras and the blue-stain fungi are detrimen- spell the difference between an ridges, 1976) indicates that the tal to SPB development (Barras, endemic population and a popula- plationship is protocooperative. 1970; Franklin, 1970). The fungi are tion outbreak. Unfortunately, the Grossman and Hamburg (1965) thought to reduce the nutritive above studies were conducted on jelieve that the relationship value of the inner bark and may bolts or bark tissues; therefore, the letween bark beetles and the blue- even be toxic or repellent to larvae relationships observed between the ig fxmgi in general is optional. In and adults (Franklin, 1970). fungus and the beetle do not jact, the absence of the fungi has no However, the presence of other necessarily reflect the relationship ffect on the number of attacks, microorganisms prevents the ex- between them in standing trees. vipositional gallery length and pression of this detrimental effect The blue-stain fungi and some 17 : 1 associated bacteria have some 1978). Earlier investigations, tests also revealed no dye in stain-^ beneficial effects on the beetle. The however, impUcated the blue-stain ed sapwood. The possibility ol presence of the mycangial fungi fungus in accelerating the death of toxin production by these can increase the level of nitrogen the beetle-infested host (Caird, associated fungi exists. For in- St. stance, the isolation identifica- compounds for beetle nutrition 1935; Craighead and George, and ; (Becker, 1971). Bridges (1978) 1938; Bramble and Hoist, 1940). tion of phenolic metabolites, es^j demonstrated the presence of How the associated fungi kill the pecially 6, 8-dihydroxy- S-j nitrogen-fixing bacteria in the host tree has remained a subject for hydroxymethyl isocoumarin, fromM SPB-microorganism association. further investigation. Caird (1935) Ceratocystis minor (McGraw and Comparison of the levels of lipids noted that, after attacks by the Hemingway, 1977) appear to sup-i: in the phloem without mycangial bark beetles, the outer rings of port this hypothesis. fungi with phloem colonized by the shortleaf pine trees lose their fungi shows that lipids increase capacity to translocate water in the over time in the fungi-colonized sapwood. He attributed this to the phloem (Berisford, 1980). Kok et al, invasion of the vascular elements Host Response to Invasion by ^i (1970) suggested sterol metabolism by the fungi. This was later cor- Associated Fungi 1 for mutualistic sym- by Bramble and Hoist Observations of failures as a basis roborated of bark III biosis. (1940). Mathre (1964), using dye beetle colonization are common. From the standpoint of beetle indicators, showed that water is These are often attributed to pitch i behavior, the mycangial fungi conducted around but not through flow. However, the possibility ex-< appear to play some regulatory fungal infected areas of the ists that this is due to the failure of )l' role. Brand et al (1976) showed sapwood. He suggested that the fungi to establish themselves, s, that mycangial fungi are capable pathogenecity may involve entry Kulman (1964), for instance, i\ of transforming trans-verbenol to of air into the sapwood. Anderson observed that unsuccessful Ips "! verbenone. Some yeast metabolites (1960) suggested several colonization of red pine did not i: have also been shown to enhance mechanisms by which the have blue-stain in the wounds. ^ the attractiveness of the attractant associated fungi cause rapid host Basham (1970) noted a zone of mixture of frontalin, trans- death. These include phenols and resins in the region of verbenol and host odor (Brand et a) toxin production, fungal invasion of resistant loblol- al, 1977). A bacterium, Baccillus b) mycellial plugging of the ly pine trees but not in trees killed il cereus, isolated from southern pine tracheids, by the fungi. Berryman (1972) : bark beetles is capable of produc- c) release of gas bubbles into the reported that resistant trees i- ing verbenol (Brand et al 1975). tracheids and produce a hypersensitive reaction, i , A mycangial basidiomycete has been d) production of particles that causing a wound periderm to form i reported to produce isoamyl- block the pit openings by around the necrotic lesion caused alcohol, 6-methyl-5-hepten-2-one causing tori aspiration. by fungal infection. When there is and 6-methyl-5-hepten-2-ol (Brand The study of blue-stain fungi no hypersensitive reaction, the tree and Barras, 1977). associated with the mountain pine may die. The production of beetle by Shepard and Watson polyphenols and other toxic com- Effects of the Associated (1959) indicated that the fungi pounds may also serve as a host t Microorganisms on the Host probably reduce stored food in the defense system to Ceratocystis The blue-stain fungus parenchyma cells and restrict infection (Shrimpton, 1973). {Ceratocystis minor (Hedge.) Hunt) water conduction by destroying the However, some known toxic com- is considered the principal tree- ray parenchyma cells, which part- pounds such as flavonoids and killing agent (Coulson, 1980). This ly control water movement. stilbenes have been shown to be claim has not been fully elucidated Pathogenecity tests of some blue- degraded by Ceratocystis minor in SPB infested southern pines. stain fungi revealed that stain (Hemingway et al, 1977). Attempts to verify the role of the penetrates into the sapwood and Therefore, such compounds could fungus have been unsuccessful can kill loblolly pine seedlings not be considered a host resistance (Hare, 1969; Brown and Michael, (Basham, 1968). Dye conduction factor against Ceratocystis. 18 STATE OF KNOWLEDGE ANALYSIS AND RESEARCH NEEDS The SPB attacks all pine species HOST within its natural range. The SELECTION (; physical properties of the oleoresin PITCHED OUT 71^ system appear to be the primary NO idefense mechanism against attack jby this beetle. However, other [factors influence this resistance LOW mechanism either directly or in- DISPERSAL I DENSITY — directly. Hence, the host resistance 7^ (R) to SPB may be briefly described as YES HIGH DENSITY GR, Of, PEP, PER, HR \ Age, stress, stand BA, beetle density / EGG GALLERY RE-ATTACK CONSTRUCTION where, ^ REEMERGENCE ^ Gr = radial growth rate O = oleoresin quantity OEP = oleoresin exudation NO BROOD / NO DEVELOPMENT pressure OER = oleoresin exudation rate HR = hypersensitive response. Although some of these variables YES are expected to be autocorrelated, the above representation is BROOD DEVELOPMENT presented as a form of synthesis of the qualitative information we now have on host resistance to SPB. Host physiology and conditions are inextricably intertwined with EMERGENCE all these variables. Integrating these variables simplifies the host resistance (R) equation into 1 Figure . Flow diagram of the southern pine beetle attack process. vigor R = beetle density Based on current knowledge, the The susceptibility /resistance The suitability component of the ^ttack process of the SPB is sum- components of the host have been host has not been adequately marized in a flow diagram (Figure fairly well researched, and a investigated. We feel this ranks 1). The flow diagram emphasizes number of relationships have been second in research priority since the importance of the host (suscep- uncovered. Unfortunately, we do this may finally determine the jtibility and suitability) in the not have the critical values of the consequent beetle population. attack process. The level of the variables associated with these The beetle-inoculated blue stain beetle population is also emphasiz- relationships to make full use of fungus, Ceratocystis minor, is jsd, and its interaction with the host them. Hence, the establishment of recognized as the principal tree- lis shown in Figure 2. Combining the threshold levels of these killing agent. How the fungus kills these host variables and the beetle- variables, such as oleoresin flow, the tree is not fully understood. attack density in a host-by-beetle OEP, OER, rate of crystallization, Investigation along this line will Imatrix, the beetle population con- bark or tree water potential, etc., for not only lead us to a better un- sequences can be conceptualized as successful colonization of host to derstanding of the host-SPB- shown in Table 2. occur, is a high priority need. microorganism complex but will 19 , provide us with alternative Table 2. Conceptualization of relationship between host conditions and methods of control. beetle attack density. Other aspects of the host that demand investigative attention in- clude: chemistry and Degree of Host Beetle Attack a) host Resistance Suitability Low Density High Density physiology as affected by different forms of stress (ex- cess water, deficient water, Susceptible Low endemic population population may col lapse logging damage, wind, fire, lightning, disease, etc.); High may lead to explosive b) the synchronization of epidemic seasonal host physiology with seasonal beetle activity; and Resistant Low endemic endemic, dispersal dispersal c) the development of host vigor indices. High endemic but may explosive build-up upon host predisposition -Attack Period Lasts 3-4 Days Relatively -First Attacking Beetles Usually Die Resistant -Gallery Construction & Ovipbsition Lasts 5-20 Days Tree -Tree Dead At This Time -Brood Production-4 To 6 Weeks Highest Quality Brood (# & Vigor) Mass Attac -Attack Period Lasts 3-4 Days Relatively -Even First Attacking Beetles Survive Susceptible -Gallery Construction & Ovlposltion Lasts 5-20 Days Tree -Tree Dead At This Time -Brood Production-4 To 6 Weeks Quality & Number Lower Than Before SPB' Relatively -Attacking Beetles Die Within 2-3 Days Resistant -Tree Survives Tree -Very Little Gallery Construction and No Brood Production Low Level. Attack -Attack Period May Be Extended Relatively -Even First Attacking Beetles Survive Susceptible -Gallery Construction & Ovlposltion Lasts 5-20 Days Tree -Tree Dead At This Time -Brood Production-4 To 6 Weeks Low Quality & Numbers Figure 2. 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Frankhn. 29 Mississippi State University does not discriminate on the basis of race, color, religion, national origin, sex, age, or handicap. In conformity with Title IX ofthe Education Amendments of 1972 and Section 504 of the Rehabilitation Act of 1973, Dr. T. K. Martin, Vice President, 610 Allen Hall, P. O. Drawer J, Mississippi State, Mississippi 39762, office telephone number 325-3221, has been designated as the responsible employee to coordinate efforts to carry out responsibilities and make investigation of complaints relating to nondiscrimination.