Mortality factors caused by pathogenic bacteria and fungi of the southern pine beetle in North Carolina

JOURKAL

OF

INVERTBBRATE

Mortality

P,lTHOLOGY

Factors the

17,

Caused

Southern

28-37

(1971)

by Pathogenic Pine

Beetle

Bacteria

in North

and

Fungi

of

Carolina

GORDON E. MOORE Southeastern

Forest

ExperinLentStation, 12264,

Research

Forest Triangle

Service, Park,

Received

April

U. S. Department of Agriculture, n’orth Carolina 27709

P. 0. Box

8, IQYO

Phytologic agents were isolated from 22.3y0 of the broods of southern pine beetles, Dendroctonus frontalis, collected in 1966-1968 from five geographic blocks in North Carolina. Bacteria isolated from dead beetles included Serratia marcescens, Pseudomonas aeruginosa, Bacillus thtringiensis var. thuringiensis, Flavobacterium spp., and several other pathogenic species. Fungi isolated included Fusariwn aolani, EealLveria bassiana, AspergillusjIavus, and four other pathogenic species. The associated fungal organisms were isolated from both the exterior and interior of the beetles.

several insect pathogens of I. typographus. In the west,ern United St,at’es,Farmer (1965) The southern pine bettle, Dendroctonus plated 10 genera of fungi from larvae and front& (Coleoptera: Scolytidae), is an adults of Dendroctonus ponderosaeand from important forest pest found from Pennits tunnels. Among t,hem was Cephalosylvania to Central America. Periodically, sporium sp., a genus which contains insect it becomes a serious killer of pines in the pathogens. Finally, Harrar and Mart,land southeastern United Stat’es. Epidemics of (1940) isolated Beauveria bassiana from D. Jiontalis that destroyed much timber D. frontalis larvae taken from pines in in the late 1800’s, 1920’s, and 1960’s have Virginia. been reported by Hopkins (1899), MacFronk (1947) listed several insects and Andrews (1926), and H. J. Green (personal mites associated with D. frontalis, but he did communication). Many attempts have been not attempt to measure their influence on made t’o control the southern pine beetle beetle populations. There are records sugby tree removal or chemical and mechanical gesting instances of natural and biological means. However, littIle research has been control. St. George (1931) found dead directed toward other avenues of control broods of D. frontalis during the spring in and the causes of population fluctuations. trees with moist and soggy bark. Also, Vaartaja (1967) studied the associates Hetrick (1940) found a pathogenic fungus of Ips grandicollis in Australia. He plated on D. jrontalis during the winter when the the fungi in three ways: (1) directly from bark was soaked and loosened. the bark, (2) from beetles placed on the There remains a great need t,o identify plates, and (3) from dissected beetle parts. and measure the scope of the many agents The fungi recovered included species of the influencing beetle populations. Seldom does genera Ceratocystis, Leptographium, and one pathogen, predator, or environment,al Macrophoma that were pathogenic to the stress alone reduce the population of a given trees but not to the beetles. Kot$nkov& species of prey. Lysenko (1959) pointed out SychoviL (1966) found similar fungi ns- that nat’ural populations are usually reduced sociated with Ips typographus in Czecho- by a complex of species. Steinhaus (1958) slovakia. In Poland, Balazy (1966) found indicated that crowding, injuries, moist’ure INTRODUCTION

28

l’L4THOGENS

OF

SOUTHEKS

in food, or excessive extremes in bemperature and humidity often provide enough stress to predispose insects to pathogens. A comprehensive study was begun in 1966 to help satisfy t’his need for information. This rep(Jrt, the first of t,wo, discusses the bacterial and fungal associates of the southern pine beetle. The second report covers the arthropod parasites and predat*ors and t.he nvian predators of the southern pine beet’le. X~TERIALS

AND

NETHODS

Thea North Carolina Division of Forestry supplied information and helped locate sites infestled by the sout,hern pine beetle. To provide an adequate &&stical base for collect8ing :md analyzing data, we selected five sampling blocks from widely separated infcsstations in representative areas of the State (Fig. 1). These blocks comprised 13 count,& located in the western and northern Yiedmontj and the esstern CoastSal Plain. Three species were sampled: loblolly pine, P~WUS fuedu; shortleaf pine, P. echi~nufa; and Virginia pine, P. virgimiana. Throughout the blocks containing shortleaf pine, t,rees with 1it.tlelea.f disease were common; in some areas, these were the trees most severely :\tt(:\ckctl by-the southern pine beetle.

PINE

IiEETLES

29

Weather records were collected from the weather st,ations nearest each block. On-site readings \yere impractical because thci consecutive samples in each block I\-trt’ taken at different locations. San~plir~y. Trees were collected during each li-month period from January 1966 through December 1968. Stands current,JJ infested \vith the southern pine beetle ~vere sampled from similar sites in ruclt block. Three classes of host trees were sampled iI\ each stand: those recent,ly attacked, thostb \vi;itlt mature broods, and those rtAcent 1~ vacated. From 19tiG68, 172 trees \vertB sampled. Three bolts, one from the lowrcr, middle, and upper crown, were cut from each tree. These bolts ranged from 6 to 12 in ~II diameter and from 2 to 3 it in length. E:N:~I bolt was checked for beetle ussoci:lttAs h> removing two 6- by E-in sections of barI\. for which initial cuts \Irere made 1 in front each end of thr bolt. Thus 1 ft2 of bark n-:~> examined per bolt and 3 fY were twuninc~t1 per tree. Because the beetle generations overlapped during the year, even wit,hin a single trrts. the sample trees contained beetles in :1l1 stages of their life cycle. The beetles coultl therefore be checked during hatch, pup:\tiolI,

FIG. 1. The five sampling blocks in North Carolina: (1) Yadkin, Iredell, aud Rowan, Forsythe, and Davidson counties; (3) Person, Granville, and Vance roilut.ies; and (Greene counties; and (5) Cleveland Co\mtg.

I)avie cwllnt,ies; 12) (4) Wayne, I,ellc>ir,

30

MOORE

and emergence for disease, parasites, and adult stragglers. All insects, mites, bacteria, and fungi collected from each sample were identified, tallied, and recorded; and the live and dead adults of D. frontalis in the galleries were counted. Pupae in the outer portions of bark were tallied by breaking all bark over 3$-inch thick or removing the outer bark with a drawknife. The number of emerged beetles was determined by counting the emergence holes. These data were used to compute a ratio of live to dead beetles. Identification of pathogens. Moribund and dead beetles were checked for external evidence of sporulating fungi, and fungal spores were plated on Czapek-Dox, malt extract, and nutrient agars. After the plates were incubated 7-10 days, the fungi were identified. To isolate internal organisms, pathogenkilled larvae and adults from each sample were placed in small, thin-walled, plastic cups. The cups were sealed with Parafilm@ 1 and irradiated for 48 hr in a small aseptic chamber equipped with a 15-W, ultraviolet, germicidal light. The cups were shaken periodically to expose all surfaces of the beetles to this light. Some beetles were checked for surface sterility by streaking them across sterile culture media. Individual specimenswere macerated in crucibles under aseptic conditions and mixed with 1 ml of sterile water. Samples from each crucible were then streaked on malt extract, nutrient, brain heart, and Sabouraud dextrose agars. After the microorganisms grew out, the fungi were identified; selected samples of each morphological type of bacterial colony were then cultured for identification. Analysis of data. The data were subjected to a factorial analysis of variance by the method of unweighted means (Anderson 1 Mention necessarily Department

of a proprietary product imply its endorsement by of Agriculture.

does not the U.S.

and Bancroft, 1952). The factors used were two periods in each of 3 years, three tree classes,and three of the five blocks originally set up. (Because triennial data were available from only three blocks, the other two were omitted from the analysis of variance.) The analysis was made t,o determine whether there were significant differences in the number of dead beetles among the tree classes, between t’he two periods within a given year, and between years. In addition, t tests were made to determine population differences between areas with severe winter cold and those with milder winters, and between numbers killed by fungi and those killed by bacteria. A table of means was constructed to show the percentages of beetles killed in the lower, middle, and upper bolts of loblolly, short’leaf, and Virginia pines in each of Dhethree tree classes. RESULTS

The southern pine beet,le population declined in North Carolina during 1966 and early 1967, but it increased during late 1967 and 1968. Trees were seldom attacked by D. frmtalis alone. Many Oreescontained Ips avulsus in the upper crown, D. frontalis at mid-bole, and D. valens in the lower bole. Populations of I. avulsus commonly merged with D. frontalis, sometimes throughout the tree. In several instances during 1966 and a few in 1967, att’acks of I. avulsus were primarily responsible for tree death but were later followed by infestations of the less vigorous D. frontalis in the middle and lower bole. This attack pattern has seldom been found during heavy infestations of D. frontalis in the past (Hopkins, 1909; H. J. Green, personal communication; E. W. Clark, personal communication). The D. frontalis adults found during the present study averaged 2.8 mm in length and did not exceed 3.1 mm, the range (2.24.2 mm) reported by Hopkins. The average number of beetles which emerged per ft2 of bark was 13.8 during 1966, 44.7

PATHOGENS

OF

SOUTHERN

in 1967, and 25.8 in 1968, or 28.1% of the total brood sampled for all years combined. hfost. newly emerged adults lacked the norma. vigor characterist.ic of the beetle, flying only occasionally and with difficulty. In about 22 ?:bof the trees sampled, woodpeckers had removed the outer bark. This removal :dlowecl the bark t,o dry faster than normally. Samples of inner bark from beetle-infested trees, with outer bark removed by woodpeckers, comained 19 % less moisture (dry-neight basis) t,han similarly infested t tees \vith bark intact. However, :I t test of brood morMit,y between trees wit II bark removed and those with bark int;ict was not, significant. Thus, bark removal may ltnve affected brood mort’alit,y due to disease, but the effect was not great. ( lold weather has been suspect in destroying bark beetle brood and in ending epidemics (Ifiller, 1931). The lowest temperature recorded during the 3-year study was -8”I“ in block 1 on January 29, 1967. Yet’, a f test showed t’hat there was no significwru difference between wint,er beetle popula,tions in blocks with extremely cold t.emper&ures and those in blocks with moderately cold t,emperatures, nor did the populations differ significantly by the following summer. Averages of all t.ree classes revealed that pathogens killed 20.8 % of the beetles collected (Table 1). From 1966 to 1968, mortality averaged 27.9% during period 1 (January-June) and 16.6 % during period 2 (July--December), or 22.3 % for all periods combined. The analysis of the data indicated a significant difference between the number of dead, diseased beet,les during the periods at the 5 ‘“0 level (F = 3.09, DF = 2, F = 3.07 at 5 % level). The interaction between years and periods was also significant (F = 3.09, df = 2, E‘ = 3.07 at 5 % level) (Table 2). Neither class nor any of the other interactions were significant atI the 5 % level. Several species of fungi were found in the tunnels surrounding living and dead

PIKE

BEETLES

31

beetles. The primary genera observed, Trichoderma, Pewicilliun~, Ceratocystis, and Aspergillus, grew in t,he pupal cavit’ies and sporulnted on the surfnce of the dead beetles and on frass in the tunnels. Fungi isolated are listed in Table :j. Some, especialI) invaded the dead beetles; Trichoclema, however, most) are believed to be sapro~ pbytic and innocuous. Fungi and baeteri:l were isolated from southern pine beet 1~ itI 148 of the 17:’ sample:: collect ccl f’ron~ 1966 to 11168. These microorganisms were isolat~ed from 50’; of the larvae, pup:lr. :u~tl adults in the 148 samples. Suspected pathogenic fungi were t’ount i in 49, or about 29C’;, of the samples, either on the outside or inside of the dead beetIt+ Occasionally, a saprophyt,ic fungus c)v(:rgrew t.he primary pathogen, and tile I:lt.tct WAS isolated and purified only ;Lft,er surface sterilization. Pathogenic fungi were founct on surface-sterilized b&les from all I:; counties in the five blocks surveyed: Al~l)~;?’ gillus flavus and Frcsarirm dam’ were fount l in all blocks; Pa.&/o~~~qces in blocks I, 2, and 3; Beauveria bassiana and Scopulnrio@s sp. in blocks 1 and 2; :Vetar~h:k&m M&V+ pliae in block L’; :mcl C’ephalospcwium sp. in blocks 2 and 3. Sonpathogenic fungi recovered included several species of A~3.~pe~/~gillus, Penicilliunf , Gliocladium, and Trichoderma.

Seldom was more than one pathogenic fungus found in a diseased beetle, although several times a pat,hogenic fungus and bacteria were found together. More beetles were killed by pathogenic fungi than by pathogenic bacteria during the survey (Table 4). Holvever, a t test showed that the difference was nonsignificant,. llte grentest mortality and number of dead beetles per ft” of bark occurred in the t.rees recently vacated (Table 5). Alert alit y averaged 20 % in the trees recently vacated, 18 % in those recently ntt,acked, and 10 % in those with mature brood. Differences in mortality between bolts, howevc~r, wt’re

is

G mo

mean

No. % No. % No.

No. % No. %

No. % No. %

period

Tree

% class No. mean y0 Period mean 1st 6 mo No. % 2nd 6 mo No. %

Block

2nd B mo

1968 1st 6 mo

2nd

1967 1st 6 mo

2nd 6 mo

1966 1st G mo

Sampling

NUMBER

1.3 25.8 3.7 5.3 7.0 21.4

12.6 39.5 2.8 7.G

20.0 42.5 1.8 8.0

1

AND

2.4 4.6 6.6 8.4 10.0 17.0

0.3 0.9 8.9 12.1

13.3 30.7 28.6 46.2

2

Trees

-

4.3 48.2 7.4 6.4 6.8 23.7 7.4 17.4

9.3 19.7 0.3 1.4

lG.7 46.5 3.3 20.4

3

2.8 5.3

-

-

14.2 20.6 2.5 4.0 6.5 9.9

_-

4

2.3 1.8 4.3 3.4 4.6 4.7

7.4 9.1

-

-

5

-

-

4.9 20.1 4.9 5.5

7.4 20.0 4.4 7.1

16.6 39.9 11.2 24.8

I Mean

OF SOUTHERN

recently attacked Blocks

PERCENTAGE

-

_-

-

1

6.a

14.6 16.6 30.8 19.4 14.7 28.9

15.3 16.7

-

66.7

-

20.3 27.1 31.3 31.1 14.2 21.0

7.1 9.5 11.8

7.0

8.0 26.3 9.2 22.8

2

45.5 59.3 12.B 11.3 15.5 28.5 15.2 23.6

0.5 0.5 5.5 5.6

13.3 40.0 15.7 54.F

3

24.8 19.1 7.6 4.G 12.5 9.9

5.2 6.0

-

-

4

24.8 41.0 14.8 13.4 19.8 24.0

19.9 17.8

5

brood

-

2G.O 32.6 19.3 15.9

G.0 3.8 11.0 11.5

-

--

L

-

21.5 43.6 22.9 10.7 15.9 30.7

26.0 31.9 10.0 13.4

11.0 51.4 3.B 33.3

1

1960-1968

9.4 30.5 10.3 48.0

Mear

PER FT~ FHOM

1

mature Blocks

KILLED

TABLE

Trees with

BEETLES

7.0 25.3

PINE

-

THE

35.2 27.0 12.7 19.0 11.9 17.5

53.0 53.0 LO.6 7.2 10.8 22.8 15.5 21.F

22.2 16.3 7.7 4.4

3

7.1 5.1 34.1 36.9 15.0 9.3 18.7 17.1

__

4

-

-

5

12.8 16.3 10.3 7.6 l-1.5 12.-I

20.4 13.5

vacated

Frv~s SAMPLING

Trees recently Blocks

3.6 2.3

IN

6.3 28.3 4.1 18.3

Mea1

BLOCKS

20.7 30.0 12.8 10.7 12.6 22.3

11.1 20.8 8.4 8.8

10.8 32.9 8.5 30.4

’ erioc I

-

Mean

22 .3

12.6 20.8

16.8 20.4

9.2 12.0

9.6 31.6

Annual

Source

df

* Significant

at the

5yC level.

3 11 24 7 5 3 3 1

sp.

Aspergillus JIat~ts” Aspergillua spp. Beauveria bassianaa L’ephalosporittm ~p.~ C’eralocyslis spp. (‘lado.sporium q. E’picoccum sp. e Fluigi

supposedly

Status

Lo. of saml)les containing fungi

X0. of samples containing fungi

Fungus Alternaria

Variance

ms

SS

pathogenic

Xumher/ft”

-

of beetles

-I_

to D. frontalis.

Block

.~__ 19% Live and exited” Killed with fungi Killed with bacteria 1967 Live and exit.ed” Killed with fungi Killed with bacteria l!lti8 Live and exited’ Killed wit,h fungi Killed with bact,eria

1

Block

2

__-~--

Block

3

Block 4 -.-__~~-.~~-----._~

Block

11.5 7.7 G .3

13.5 6.3 2.9

LG.5 8.X 1.7

37.1 5.5 5.7

40.0 3 .9 3 -5

2G.X 3 .3 :< .5

53. 1 1.3 3 8

ti5.0 8.1 s.2

51.1 3.9 13.0

38 .3 15.7 6.2

5G.0 9.5 7.3

48.9 8.2 11.7

Ii4 .:: s .o 4.4

.i

-a Iticlitdes

live

beetles

in tunnels

and

those

that

had 33

varated

tree.

_

34

MOORE

TABLE

5

MEAN IMORTALITY AND NUMBICR/FT~ OF SOUTHERN PINE BEETLES KILLED WITH B.ICTERI.Z .ULI FUNGI ACCORDING TO POSITION OF BOLT, CLASS OF TREK, AND TRICE SPECIES Position of bolt

Trees recently EG

attacked

T*

V”

Trees with Ea Mortality

Base Mid TOP

5.5 12.1 11.2

9.2 7.7 10.2

40.5 29.2 38.2

17.9 22.7 20.3

mature

brood

Trees recently

vacated

VC

E”

T*

VC

7.7 12.7 5.3

6.1 0.0 0.0

15.G 16.8 14.7

13.8 16.6 17.7

28.5 31.2 26.7

8.5 19.6 5.4

4.0 0.0 0.0

18.4 17.5 13.4

19.6 22.0 22.1

19.7 14.8 14.2

Tb (Yo)

Nwnber/ft2 Base Mid Top 0 E = Pinus 5 T = Pinus c \’ = Pinus

4.1 8.8 6.2

5.3 6.8 8.2

10.1 6.6 5.9

15.2 20.2 17.2

echinata. taeda. virginiana.

in the lower bolts and least in the upper bolts. However, the greatest number of dead beetles per ft2 of bark occurred in the THE~S IN 1966-1968 middle bolts and the least number occurred No. Percent in the lower bolts. samples of total Pathogenic bacteria were isolated from Bacteria conbacteria taining ’ the intestinal tracts of both living and dead bacteria0 saA;lesa beetles. Nine genera of bacteria were identified in 103, or 60%, of t,he 172 sample trees Aerobacte~ aerogenes 17 9 Alcaligenes faecalis 18 9 (Table 6). Some of them, especially PseuBacillm cere& 6 11 domonasaeruginosa, are potential pathogens, Bacillus megateriwx 2 1 depending upon the degree of host st’ress. Bacillus thuringiensis var. Nevertheless, the bacteria must be tested 1 thuringiensisb 2 to determine their pathogenicity on healthy 1 Enlerobactersp.
6

BA~T~RIARECOVER~D FROM SURFACE-Q~~ERILIZED SOUTHERN PINE BEETLES FROM 172 SAMPLE

PATHOGENS

OF

SOUTHERN

pwvdery or sticky spores, similar to t,hose of Cemtocystis, that easily cling t’o the hairs of the southern pine beetle. Two species of yeast, genus Can&da were also found during the survey in 18 samples. They were associates of the beetle and only contributed to its diet. Ihxx~ssros

ASD

CONCLUSIONS

The quantit,y of southern pine beetle brood was very low, averaging 57.8 per ft2 of bark, as compared to the vigorous populat.ions reported by Hopkins (1909) and MacAndrcws (1926). For example, MacAndrews found that in a heavy infestation as many :LS300 beetles emerged per fte. Although he gave t\le average IS 131, he included no dat,a on the percentage of emergence. The xignific:mce of the factors “year” and “period” in the analysis implies several differences in diswse levels. There was a diffcrencc between diseaselevels during the t’wo periods as sllown in Table 1: the first Ci-montlt period averaged 27.9 % mortality and the srcond (i-mont,h period averaged l(i.(i

‘.‘;,.

‘Flit’

Xdysis

dS0

SLggtds

hit,

dewing late lY(;i, ~vhcn t,he beetle population:: were higher than at any other time in the study, the discasc Ievctl was lower. The significant diffcrencc\ in the interact#ion btbtween tile factors “years” and “periods” xts 1‘robably due t.o the low morta1it.y of only 12.6 SEin 1967. Fewer pathogeuic fungi ww found during 1!1)67t,han during either 01’ t lw ot~ller 2 years. P’urthermore, the :m:Ilysis indicates there was no significant difwwx bet wen the disease levels in freslrly attjacketl trees and in trees Cth mat urc brood :wd those recently vacated. This uniformity indicates t,hat beetles died at :rpprtJximatcly tlw same rate throughout their lift cycle. Cold, w-et~xe:lther was reported to halt infestations in t,he past. Miller (1931) reported t.hat :t D. frontalis epidemic was halted in West Virginia after a severe freeze in 1892-1893. Temperat.ures of -4°F or

PINE

BEETLES

.36

MOORE

bacteria, and that all agents combined caused a mortality of 80 %. The fungi found during the present study, therefore, should be tested against’ healthy beetles to determine the extent of their pathogenicity. Ot’hers have also found the same bacteria as those recovered in the present study. Lysenko (1963) listed several species of Pseudon1on.a.s as pathogenic to insects, and he recovered P. aeruyinosa from Saperda .caroharia.s. He also Iist.ed Bacillus and Flavobacterium as pathogenic genera. Wilkinson and Jouvenez (unpubl.) found S. marcescens on Ips calligraphus. Vago (1963) statfed that fungi such as Fusarium and Aspeygillus may parasitize insects, producing a toxic effect and promoting bacterial proliferation and septicemia by S. mar.cescens. He indicat,ed that diseases may have this type of synergistic effect or may be partially or entirely independent proc‘esses,acting at different sites within the insect. During the present study, Fusariwm and Aspergillus killed healthy D. frontalis adults in t’ests, frequent’ly without the presence of X. marcescens. Erroneous conclusions about the ability ,of an agent to reduce beetle populations may be avoided if a study is made of several agents from the microenvironment of the insect. No single biological agent caused D. frontalis populations to fluctuate in North Carolina in 19661968. Since pathogenic organisms destroyed nearly one-third of the brood each year, they must be considered an important factor in the environment of the beetle. Diseasefavors no particular st,ageof the beetle, but it is significantly more prevalent, during winter and spring than in summer and fall, in the middle of trees than at the base or at the top, in trees recently vacated than in t’rees recently attacked or those with mature brood, and among beetles in P. virginiana than among those in P. echinata or P. taeda.

The writ.er gratefulIy acknowledges the assistance of several individuals during the course of this study: Dr. C. S. Hodges of this laboratory for help in identifying the fungi; Mr. G. M. Thomas, Department oi Entomology, University of California, Berkeley, and Dr. Benjamin Cosenza, Kulp Private Laboratory, Storrs, Connecticut, for identifying the bacteria. The many hours spent by the staff of the North Carolina Division of Forestry in locating and collecting the study material from all five blocks are also gratefully acknowledged.

REFERENCES ANDEHSON, Ii. L., .ZND BANCROFT, T. A. 1952. “Statistical Theory in Research,” 399 pp. McGraw-Hill, New York. ANDREWARTHA, H. G., AND BIRCH, L. C. 1954. “The Distribution and Abundance of Animals,” 772 pp. Univ. of Chicago Press, Chicago. ARKHIPOV.~, V. 1). 1965. Fungus diseases of the codling moth, Carpocapsa pomonella L. (Lepidoptera: Tortricidae). Entomol. Rev.,

1, 48-54. BALAZY, S. 1966. Living organisms as regulators of population density of bark beetles in spruce forest, with special reference to entomogenous fungi. I. Poznbn. Tow. Przyj. Nauk Wydz. Nauk Roln. Les. Pr. Kom. Nauk Roln. Kom. Nauk Les. 21, 3-50. (In Polish.) BEAL, J. A. 1933. Temperature extremes as a factor in the ecology of the southern pine beetle. J. Forest., 31, 329-335. BERRYM.~N, A. A. 1968. Development of sampling techniques and life tables for the fir engraver Sc01ytus ventralis (Coleoptera: Scolytidae). Can. Entomol., 100, 1138-1147. CRAIGHEAD, F. C. 1925. Bark-beetle epidemics and rainfall deficiency. J. Econ. Entomol., 18, 577-586. F.4RMER, L. J. 1965. “The Phloem-Yeast Complex during Infestations of the Mountain Pine Beetle in Lodgepole Pine,” 124 pp. Ph.D. Thesis, Univ. of Utah, Salt Lake City. FRONK, W. I). 1947. The southern pine beetle. Its life history. Vu. Agr. Exp. Sta. Tech. Bull., 109,12 pp. GARNER, J. H. B. 1967. Some notes on the study of bark fungi. Can. J. Bot., 45, 554-556. HARRAR, J. G., AND MaRTLAND, J. G. 1940. A fungous parasite of the pink hark beetle. Phytopathology, 30, 8. HETRICK, L. A. 1940. Some factors in the natural control of the southern pine beetle

I’.\THOGENS

OF

SOUTHERX

I’ISE

ii7

BEETLES

S, A. H. 19%. “The Biology of the Southern PilIe Beetle,” 103 pp. ?\i.S. Thesis. K;. ‘I’. State Coil. Forest ., Syracuse. MILLIE. J. 31. 1931. High and low lelhal ten-perattrres for the western pilIe beetle. ./. .-1cqr Kes., -13, 303-321.

~~.ICANDIIIC\\

A. I). 1899. I:eport on investigations to dctrrmiue t,he callse of unhealthy condit iotw of spruce arld piue from 1800-1893. II-. \‘a. dgr. Exp. Sta. Hull., 56, pp. 297-331. Ho~~xs, A. I). lYC9. Practical information of t heScolyt id beetles of North American forests. I’. S. Dep. Agr. Hull.. 83, Part 1, pp. l-169. E;(l’riStcc,\-6-~YcHuvd. I*:. 19iXi. Mpkoflora chodeb krwovcu v C”rskoslovellskrl. Ceska dl!/kd., 20, 15-53. JAYsI-:Nlio, 0. 1959. IScologg of microorganisms in biological cant rol of insects. ‘I’runs. Znt. (‘on,f’. In.secl Pa/ho/. Hiol. (‘onlrd, I., Prague, ,‘p. 1011-113. LYsicstio, 0. 19Ki. “Cidture Collection of I’:iltornogenous Bacteria,” 30 pp. Dept. Insrct Pathol.. 111st. Entomol.. Pragrle. IfOl~IiINS,

1~:. A. illsect disease. l/M, -4, 725-730.

STPEIXH.\I-5,

1958. I’,oc,.

Stress as a factor Inl. C”onqr. E~/wol

it1 .

0. 196:. The cornmolt f1111ga1 associates of the bark beetle Ips grauclicd/j,\, 3-j A usl. Forest. li’es., 2, JO-*2. VAGO. C‘. 19tiS. Predispositions and interrelationships it1 insert disease. In “insect Pathology” (I<. -4. Steinhaus, ed.), Vol. \‘I I, pp. 339-379. i2c:tdemic Press, New York. \rA.~tLT.\J.~,