,vironmental Factors Affecting

'RUCE BUDWORM GROWTHJ. W. Bruce Wagg

Senior Research Associate, Forest Lands Research Center

Lands Research Center . . . Corvallis, Oregon . . . Dick Berry, Director

inch Bulletin No. 11 August 1958

Forest Lands Research Center

. Its PurposeDevelop the full potential of Oregon's timber resource by:

increasing productiveness of forest lands with improved forest

practices.

improving timber quality through intensified management and superiortree selection.

reducing losses from fire, insects, and diseases-thus saving timberfor products and jobs.

Keep development of the forest resource in harmony with development ofother Oregon resources.

. .. Its Current ProgramSeed production, collection, extraction, cleaning, storage, and germination.

Seedling production, establishment, and survival for new forests.

Growth and development of trees, quality of growth, and methods ofthinning and harvesting to grow improved trees.

Study of forest fire behavior and fire weather to prevent fires.

Insect pests and their control, to save trees.

Disease control and prevention in Oregon forests.

Mammal damage and the controls to help regrowth.

Soils and their relationship to growth.

Development of improved forests through selection and breeding.

EW-ironmental Factors Affecting

SPRUCE BUDWORM GROWTH

J. W. Bruce WaggSenior Research Associate, Forest Lands Research Center

ContentsPage

Abstract ---------------------------------------------------------------------------------------- 2

Introduction -------------------------------------------------------------------------------- 3

History of Present Study ---------------------------------------------------------- 4

Procedures ---------------------------------------------------------------------------------- 5

A Major Principle of Ecological Study -------------------------- 6

Method of Field Study ------------------------------------------------------ 6

Environment and Spruce Budworm Development ---------- 9

Time and Spruce Budworm Development ---------------------- 15

Some Problems Pertaining to the Use of Weather Datain Predicting Budworm Development ------ --------------- 19

Summary --------------------------------------------24-----------------------------------------

Literature Cited and General References -----------_-------------_---- 26

OREGON FOREST LANDS RESEARCH CENTER

Corvallis, Oregon

AbstractThe spruce budworm is an important enemy of

the Douglas fir-true fir forests in Oregon. It can besuccessfully controlled by aerial spraying with DDT.

The influence of air temperature on spruce bud-worm growth, the growth of the host, and interrela-tionships between insect and host were studied on 15areas in northeast Oregon. The principle of heat ac-cumulation as advanced by Merriam was used.

Growth of the spruce budworm was found to de-pend upon the growth of the host-grand fir. Thegrowth of grand fir is related to accumulated degreedays. Spruce budworm development on an area wasbest estimated from a consideration of the growth ofgrand fir in combination with the accumulation of de-gree days. Growth of the insect is also related todegree days.

Insect development from the third to succeedinginstars showed an ineffective relationship with timeand an improved relationship with increase in accu-mulated degree days.

The relationship of insect development to eleva-tion was determined for the La Grande data of 1953.

Temperature data, gathered either by the UnitedStates Weather Bureau or by special stations usinghygrothermographs set up in the forest, can be usedfor prediction of spruce budworm development. .

For any one year, the development of the insectfrom a given date can he estimated for a future date,subject to all the year to year irregularities of temp-erature for the area.

2

Environmental Factors Affecting

SPRUCE BUDWORM GROWTH

The spruce budworm, Choristoneuraf umi f erana (Clem.), was epidemicover nearly 3 million acres of Douglasfir, Pseudotsuga menziesii (Mirb.)Franco, and true firs, Abies spp., inOregon and Washington by 1950 (1)with most of the affected area east ofthe crest of the Cascade Mountains.Before the end of 1954 over 2,900,000acres of Oregon forest land had beentreated for control of the pest at a costof over $3,000,000, or about $1.05 peracre.

Damage by the spruce budworm oc-curs as the larvae eat developing fo-liage, with three successive years ofsevere defoliation sufficient to kill atree. Effective control of the insectcan be realized when a maximum num-ber are in the fourth larval stage.

A spruce budworm overwinters as asecond instar larva under the protec-tion of scales on the twigs, branches,and trunk of the host tree. In thespring the larva begins movementwhen average air temperatures reach42°F. (8). During the spring it feedson the developing foliage of the hostand passes through four moults to thesixth instar. It pupates on the foliageand eventually transforms to the adultduring summer. Eggs laid in masseson the needles by the adult hatch intofirst instar larvae and then moult onceto form second instar larvae by fall.The second instar hibernates.

Instars before the fourth remain ina silken sheath on the foliage and are

not exposed to any spray controls.After the fourth instar the larvae for-age from the silken sheath and are ex-posed on the growing foliage. It seemsto take about ten days for the insectto develop from the fourth to fifth in-star. Because of this pattern of insectdevelopment, precise timing of sprayapplications is essential.

Effective control is realized by ap-plying a spray of one pound of DDTper gallon of petroleum carrier at arate of one gallon per acre (2). Theapplication must occur while the insectis in its later larval stages but beforepupation. On the Meacham area in1951 the average instar prior to con-trol was 4.4 instars.

Contracts for equipment and mater-ials must be let far in advance of theprogram. This situation is unavoidablealthough arriv4l of lanes and men inthe field too early results in excessivecosts, whereas delayed preparednessresults in inadequate control.

To aid in administration of an aer-ial spray program, an estimate isneeded of the approximate time ofthe insect's development to the fourthinstar. The most logical approach togaining the necessary information ap-peared to be a study of insect develop-ment as related to air temperature.

In the field, relationships betweeninsect development and air tempera-ture could be used to determine thetime at which the budworms were de-veloped enough to spray.

3

History of Present StudyVariations in the required time for

insect development to a given instarwere observed between large areas. Asin 1950, the average fourth instar wasreached at Roseburg about May 17,whereas at an average elevation of4,000 feet at Kinzua, it was reached

000

m

WV

W

3

0 2

on June 22, as illustrated in figure 1.Since these areas are extreme, and lieon opposite sides of the CascadeMountains, they illustrate that calen-dar time is of no value in determiningrelative insect development on diverseareas.

O

\tiO'5000 4000

ff.\' fVO.

P0J

Oy

-

20

MAY

30 I0

JUNE

2020 30 10

JULY

Figure 1. Instar development of the spruce budworm for Roseburg and Kinzua in 1950.

Also, variations in insect develop-ment due to mountainous terrain wereobserved. Assuming that insect devel-opment is delayed one day for each100 foot increase in elevation (10),then a correlation is observed betweenthe areas at Kinzua. Actual develop-

ment to the fourth instar was retardednine days in the climb from 3,000 to4,000 feet. The theoretical differencewould be ten days. The relationshipbetween Roseburg and Kinzua is muchless exact, with an estimated develop-ment lag of 18 to 28 days for Kinzua's

3,000 to 4,000 foot elevations and anactual development retardation of 26to 35 days.

This relationship will not hold overwidely separated areas, since it is im-probable that the' same air mass willcover both areas. Within areas cov-ered by the same air mass, the rela-tion of insect development to elevationwill be useful.

What is the length of time before-each area reaches an average instar of5.0? Again there was no adequate an-swer in number of days. Indicationswere that the younger instars devel-oped faster, or with less total heatthan the older. Due to the elevationdifferences, however, older instars atlower elevations could develop as rap-idly as younger instars at higher ele-vations in the same number of days.Although more heat was required toproduce an instar of growth in thelater instars, with more heat availableat the lower elevations changes frominstar to instar seemed to require thesame number of days at all elevations.The need was obvious for additionalstudy of the development of the insectunder field conditions.

In 1951 an exploratory study wasstarted concerning the influence of

temperature on spruce budworm de-velopment under field conditions. Fromthis beginning the study was expandedthe following season and terminatedin 1954. The study occupied fourteenseparate locations in the Blue Moun-tain area of northeast Oregon (3), agenerally mountainous area with char-acteristic timber types. Grand fir,Abies grandis; Douglas fir, and pon-derosa pine, Pinus ponderosa; occurbelow 5,500 feet, yielding to alpine fir,Abies lasiocarpa ; Engelmann spruce,Picea engelmanni ; and lodgepole pine,Pinus contorta in the higher eleva-tions. Ponderosa pine occupies thesouthern exposures and the firs thenorthern exposures. On the plateausor scab rock flats, the distribution ofspecies was probably influenced bysoil, with the firs being replaced byponderosa pine, juniper, Juniperus oc-cidentalis and mountain mahogany,Cercocarpus ledifolius. Lower distri-butions of timber are various, depend-ing on soil and aspect. The timber ex-tends like fingers downward into thevalleys to an elevation of about 3,500feet.

In varying degrees the spruce bud-worm infested the major part of thisarea.

ProceduresThe study was designed to disclose

some of the environmental factors in-fluencing the development of the in-sect. Air temperature and soil temper-ature were studied in relation to insectdevelopment under field conditions.These are considered the two most im-portant physical factors since air tem-perature influences the movement ofthe insect and soil temperature the de-

velopment of the host. The influenceof the growth of the host on thegrowth of the spruce budworm is alsostudied. It is hoped that, with this in-creased knowledge, a better forecast ofdevelopment can be made that will beof assistance in control operations.

The principle on which the study isbased is outlined. Study areas and thedata collected are described.

5

A Major Principle of Ecological Study

A major principle applied in thestudy is one of the temperature lawsof Merriam (4) which states : "Ani-mals and plants are restricted in north-ward distribution by the total quantityof heat during the period of growthand reproduction."

This theory of temperature summa-tion utilizes the accumulation of heatabove the threshold of development asan index for the distribution of plantsand animals. The threshold of develop-ment is that temperature, on the as-cending scale, initiating growth in

plants, and growth and activity in ani-mals. One degree of the mean dailytemperature above the threshold ofdevelopment is known as a degree day.Accumulated degree days are the ex-pression of accumulated heat.

Pearls (5) and Cook (6) have uti-lized this principle in the study of in-sect activity. Ripening of peas (7)also has been gauged by this method.The application of the method tomountainous forest conditions is notknown to have been employed pre-viously.

Method of Field Study

The selection of the study areas isimportant in order to fulfill the re-quirements for data on temperature,insect, and host.

Areas of studyStudy areas for each year were lo-

cated within working limits of eachother but did not overlap from year toyear. Each area needed sufficient bud-worm population for inventory. Theexact location for an area was dictatedby topography and distribution of thehost species.

A study area consisted of five -acre plots. The center, or number 1plot, was selected to represent the area.It was never chosen in a very densestand, in an area without timber, in acreek bottom, or on a ridge, but wasalways selected in an area of free airmovement. Usually it was located onan upper sidehill or saddle and inmixed timber. From the center plot,number 2 was located five chainsnorth ; 3, five chains east ; 4, five chainssouth ; and 5, five chains west. Since

the remaining four plots were locatedsystematically, they sometimes fell inconditions that were avoided in the lo-cation of plot 1. Figure 2, for MarksCreek Summit area, is an example ofthe arrangement used.

The number of trees from 1.1 to2.0 inches D. B. H. were recorded,and the D. B. H. of all trees above 2.0inches were listed for each plot.

A hygrothermograph was located4.5 feet above ground in a standardweather shelter in the center of plot 1.No use has, as yet, been made of thehumidity data, but this instrument wasused because it was readily availablefor measuring air temperature.

Study plot descriptionEach plot was circular with a radius

of 58.9 feet and an area equivalent toone-quarter of an acre. The legal de-scription, aspect, slope, and elevationwere recorded.

Data collected on each areaData were collected on each area

from the time the number 1 plot had

6

H^1 Contour interval 10 eel

Figure 2. Plot layout for Marks Creek Summit area.

at least 50% ground cover of snowuntil the spruce budworm had pupated,and in some cases further. A 50%snow cover would usually mean thatthere was no herbaceous growth onthe area. Plots that fell on the south-ern aspects with rocky soils sometimeswere exceptions.

Air temperature data were collectedfrom the hygrothermograph on thecenter of number 1 plot only, as shownin figure 3. Soil temperature wasmeasured by the use of thermometers

at a 6-inch depth under the duff onall plots. Four measurements weretaken once a week for each plot about30 feet from the center on each ofthe cardinal directions. These valueswere averaged for each plot. The soiltemperature measurements were takenbetween 10 a.m. and 2 p.m.

Insects were collected from two ofthe plots from the time they enteredthe buds until pupation. Collectionsof about 25 larvae were made at week-ly intervals until there was about 0.75

7

inch of growth on the host, or 80%of the bud scales had fallen. Afterthis time collections were made everyfour days and consisted of 50 larvae.Since the larvae then were distributedover a greater number of instars,larger collections were necessary toobtain an estimate of development.For statistical purposes in this study

s q a

t

.,

CtkL try" .

ash `u .1 _aL y;

Figure 3.Marks Creek Summit, Plot 1.

the instars were numbered from 1 to6, the pupae indicated as number 7and the adults as number 8.

The stage of larval instars can bedetermined by the width of the headcapsule as outlined by Freeman (9).Spruce budworm development on anarea is expressed as the average instar.

DEVELOPING BUD

NEW TWIG GROWTHFigure 4.

Method of measuring lateral growth of grand fir.

Table 1. RELATIONSHIP OF WIDTH OF HEAD CAPSULE TO SPRUCE LUDWORMINSTAR (9)

Width of head capsule

Millimeters< - 0.41 ............................. ------........... ............................. .....................

0.41-0.62 ..................................................................................................0.63-1.01 ............ .......................................................................1.02-1.64 .................... .._...r..........._...._ .-. ..._.. M._»_.....,..1.65 - ................ ............... ....... ...............:... .......

lnstar

Hosts

Observations of lateral growth weremade on grand fir, Douglas fir, andalpine fir. Grand fir was the mostabundant host on the study areas.Early observations on foliage develop-ment were visual selections of the av-erage development in the area. Aver-age typical growth was selected by oc-ular estimate and measured. No at-tempt was made to measure the sametwig each time since early develop-ment is erratic both between and with-in trees.

When the new foliage of the host

had developed to a length of 0.75 inch,three twigs were tagged, each on adifferent tree. These were measuredat each time of observation thereafter.Figure 4 is a diagrammatic presenta-tion of the growth of grand fir andthe method for measuring the growth.

Plant developmentObservations on the stage of herba-

ceous plant growth were also made.A standard form was used for thispurpose. The more common plantswere observed as to the stage of bud-ding, flowering, and fruiting.

Environment and Spruce Budworm Development

Growth of the host, air tempera-ture, and soil temperature are factorsof varying importance in the develop-ment of the spruce budworm.

Growth of spruce budworm relatedto the growth of grand fir

The relation of instar development(Y) to the average growth of the lat-erals of grand fir (X) was explored.The equation Y = a + bX was fittedto the data. Although differences inthe regression coefficient (b) were ob-served in the analysis, these were notconsidered of great enough magnitudeto prevent the use of a common co-efficient for all plots. The a value wassignificantly different for all plots. Theequation resolved to Y = a + 1.856Xwith an error of estimate (s$) equal to0.144. Figure 5 indicates the extremerange of the data by plots.

At the third instar, growth of grandfir varied from 0.39 to 1.21 inches.From observation, trees in dense

stands began growth later than thosein adjacent, sparse stands due to dif-

ferences in retention of snow which

maintained soil temperatures below42°F., the growth threshold for grandfir. In the dense stands, the insect de-velops before the foliage while in thesparse stands insect and foliage de-velop at about the same time. Uniform-ity in insect movement in adjacentstands is due to the temperature simi-larity of the air mass about each stand.

Although growth of trees on theseplots varied as to beginning date, allplots terminated growth, as nearly ascould be measured, at the same time.Hence, some trees would producelonger laterals than others. A varianceof growth from 1.47 to 2.28 inches ap-peared at the fifth instar of the insect.

Taking into account the expectedvariation in amount of growth betweentrees in open and in dense situations,it is possible to estimate the develop-ment of the spruce budworm from theamount of lateral growth on the host.With 1.25 inches of lateral growth ofgrand fir, the spruce budworm wouldrange in development from 3.08 instarsin less favorable locations to 4.60 in-stars in the more favorable places.

9

8

2rc03 70

4

3

2

teO1

6\06O15g6

U s

ed

2'

o+ 1.856 X

.144

0 .25 .50 .75 1.00 1.25 1.50 1.75 2.00 2.25 2.50

AVERAGE GROWTH IN INCHES OF LATERALS OF GRAND FIR

2.75

Figure 5. Instar development of the spruce budworm related to the growth in inches of laterals ofgrand fir.

Growth of grand fir asinfluenced by air temperature

Since it was observed that sprucebudworm development is related to thegrowth of grand fir, an analysis wasmade of the influence of air tempera-ture on the growth of the tree. Thethreshold of development for grandfir was considered as 42°F. The prin-ciple of temperature summation wasused. From the mean temperature foreach day, 42°F. was subtracted; eachdegree above 42°F. was termed a de-gree day. Degree days were added to-gether successively to give accumulateddegree days. If, in calculation, degreedays had a negative value, this resultwas considered as a zero, since it isonly possible to arrest growth and notreverse it.

An analysis was made of accumu-lated degree days (Y) and the growthof the laterals of grand fir (X). Theequation Y = a + bX was fitted. Ana-lysis was terminated at 2j inches ofgrowth for grand fir. The terminationwas influenced by two factors : themaximum growth that may occur ongrand fir in the area, and the beginningof the insect's pupal stage. Out of 39plots tested, 31 had a correlation co-efficient of 0.91 or greater. A commonslope is used for all plots (b-0.00349), but individual a' values are

necessary. The error of estimate (s2)equals 0.052. Figure 6 indicates theextremes of the data.

From this analysis it is observedthat a relationship does exist betweengrowth of grand fir and air tempera-

10

% 2.50U.

aa 225

U.21

O1.2

03W

vz )Ai

z

0rc

z17

V04'

Y- 0+.00349Xhro 31=.0.2

.7

5

0 too 200 300 400 500 600 700 800ACCUMULATED DEGREE DAYS ABOVE 42°F

900 1000

Figure 6. Average growth in inches of laterals of grand fir related to accumulated degree daysabove 42°F.

ture. This relationship is not the samefor all areas. One densely forestedplot located in a creek bottom producedonly 0.39 inch of growth for 400 de-gree days of air temperature. Thegrand fir on another plot, located inopen forest on an upper sidehill, grew1.24 inches during an accumulation of400 degree days.

Initial observations relating degreeday and grand fir growth to sprucebudworm development

An attempt to improve the estima-tion of spruce budworm developmentwas made by including growth ofgrand fir along with accumulated de-gree days in the analysis. The equationY = bo + b1X1 + b2X2 was fitted. The

Table 2. REGRESSION STATISTICS OF SPRUCE BUDWORMGROWTH RELATED TO GRAND FIR GROWTH AND DEGREE DAYS

Name Symbols ValueStandard

error

Regression coefficientIntercept ---------------------------------------------- bo 0.2705 0.0031Regression on growth ------------------------------ bl 0.871 0.0109Regression on degree days ---------------------- b2 0.00318 0.0001

Error of estimate ------------------------------------------- S2 0.00136Coefficient of determination ---------------------------- R2 0.91

11

instar growth (Y) was related togrowth of the laterals of grand fir(X1) in inches and the accumulationof degree days(X2)-all from the firstobservation.

These statistics would indicate thatif a single observation for spruce bud-

worm growth, growth of grand fir,and accumulated degree days were tobe made early on an area, excellentfuture predictions could be made of in-star growth, using the increase ingrand fir growth and accumulated de-gree days.

Table 3. ESTIMATED SPRUCE BUDWORM GROWTH BASED ON GROWTHOF GRAND FIR AND INCREASE IN DAY DEGREES

Growthof

grand fir(X,)

0.25------------------------------------

0.50------------------------------------0.75................. -------------------1.00------------------------------------

1.25........... ............------------1.50------------------------------------1.75----------- -------------------------2.00........... -------------------------2.25--------- ---------------------------2.50------------------------------------

1000.791.001.201.411.611.82

Accumulated degree days from first observation (X2)

2001.111.321.521.731.932.142.34

3001.431.641.842.052.252.462.662.86

The data are illustrated in figure 7.

4001.751.962.162.372.572.782.983.183.39

5002.072.282.482.692.893.103.303.503.713.91

ACCUMULATED DEGREE DAYS FROM FIRST OBSERVATION (X.)

25

ITS

2

0

5

100 200 300 400 500 600 700 800 900

21 3

1000

Y .2705 + .8172X, +.0032X,

5'.00136RYA 91

41 5

INCREASE IN SPRUCE BUOWORM DEVELOPMENT FROM FIRST OBSERVATION (;I

Figure 7. Initial observations of instar development related to growth of grand fir and accumulateddegree days.

600

2.602.803.013.213.423.623.824.034.23

700

3.123.333.533.743.944.144.354.55

800

3.653.854.064.264.464.674.87

1000

4.704.905.105.315.51

1100 1200

12

From table 3, with an increase of300 degree days and a growth of 1.00inch by grand fir from the first ob-servation, the spruce budworm devel-oped 2.05 instars from the first ob-servation. If at the first observationthe average budworm instar was 2.50,the estimated average instar would be4.55 instars.

Growth of spruce budworm asinfluenced by air temperature

By plotting the data, growth of thespruce budworm was observed to be

Dto

0

related to the logarithm of accumulatedair temperature above 42°F. Withspruce budworm development (Y), ininstars, related to the logarithm of ac-cumulated air temperatures (X), theequation Y = a + b log X was fittedfor each plot. The development wassignificantly related to the logarithmof air temperature on all plots, but theregression coefficients were differentfor some plots. Figure 8 represents thetwo extreme plots studied.

This variation could be the result ofa number of interacting factors. It is

75. 3000 X - 8.7561

s2 .184

S

4

Y 10.7239 X - 25.6272st .048

150 200 300 400 500 600 700 800 900 1000ACCUMULATED DEGREE DAYS ABOVE 42F

1500

Figure 8. lnstar development of spruce budworm related to logarithm of accumulated degree daysabove 42°F. for two areas.

not possible to measure temperature ture is measured within the stand andunder uniform conditions between is not wholly representative of the en-areas, for there are the inevitable vari- vironment activating either growth ofations of slope, exposure, and forest the host or of the insect. The insect,composition. Then, too, air tempera- for growth and movement, is depend-

13

ent upon a suitable microenvironmentcombined with a synchronized responseof growth in the tree.

As no particular factors could beisolated from the data, and their con-tribution to the variation evaluated, acommon equation was fitted to the data.The equation Y = 6.8559 log X -14.0323 resulted from the analysis.The error of estimate of instar growth(s`) equals 0.3331.

The 95% confidence limits of thepredicted instar growth are repre-sented in figure 9. For 9591c of all sta-tions showing an accumulation of 600degree days, the budworm instar de-velopment will range between 3.85 and6.15 instars. If the station should re-cord the average of all stations reportedin this data, the average of instarswould be 5.00.

0 4

3

2

200 300 400 500 600 700 800 900 1000ACCUMULATED DEGREE DAYS ABOVE 42' F.

150

From these data it was observedthat, although the relationship of insectdevelopment to accumulated air temp-erature was a logarithmic growth curvefor each plot, the variation betweenplots would make a common curve apoor estimate of spruce budworm de-velopment for an individual plot. Con-versely, once the relationship is es-tablished between insect developmentand temperature measurements at anindividual station, that station couldprovide a good estimate of budwormdevelopment for the following years.

Air temperature and soiltemperature related to sprucebudworm development

From a multiple regression analysisof accumulated degree days on soiltemperature measurements and insect

ii6.8559 log X - 14.0323

i .333

i

LIFigure 9. Instar development of spruce budworm related to accumulated degree days above 42° F.

for all plots.

14

development, the effect of soil temper-ature was shown to be nonsignificant.It is as effective to use air temperaturealone to determine insect growth.

When the increase in the numberof degree days for an initial observa-tion and the change in soil temperaturefor the same time were related tothe growth of the insect from thefirst observation, little contributionwas found from soil temperature.

Soil temperatures are deemed, inade-quate. They are subject to diurnal

fluctuation, the magnitude of whichvaries with the type of forest areabeing sampled. The fluctuation indense stands is less than in open standsbecause of shading of the soil surfacefrom direct sunlight and retention ofprecipitation by the tree crowns.

The use of increase in the growth ofthe host, as earlier described, is to bepreferred over the soil temperaturechange for estimating the budworm de-velopment.

Time and Spruce Budworm DevelopmentSpruce budworm development fromthird to succeeding instars

At first, an analysis was made ofthe relation of spruce budworm de-velopment (Y) to the number of days(X) required for development fromthe third instar to the adult. This analy--sis is expressed by the equation Y0.1403 + 0.0872X. By observation ofthe data presented in figure 9, it isconcluded that only a very poor esti-mate of instar development is possibleon an individual plot. Considering aperiod of 27 days from the third instaras an example, the budworm developedanywhere from 1.54 to 3.74 instars asindicated in figure 10.

In an attempt to improve this re-lationship a second analysis was made.

This was a multiple regression analy-sis relating development of the sprucebudworm from the third instar, to thenumber of days and accumulated de-gree days from the third to the sixthinstar. It was shown that the numberof days was not significant and thataccumulated degree days alone wouldproduce as good relationship.

A third analysis was based on therelationship of the spruce budwormdevelopment (Y) to the increase inaccumulated degree days (X) fromthe third to the sixth instars. The formof the analysis is expressed by theequation Y = bo + bl X-}- b2 X2. Thesolution of the equation provided thestatistics in table 4.

Table 4. REGRESSION STATISTICS FOR SPRUCE BUDWORMGROWTH FROM THE THIRD INSTAR TO DEGREE DAYS

Name Symbols ValueStandard

error

Regression coefficientIntercept -------------------------------------------------- ba 0.0205 0.0042Regression on degree days ---------------- bl 0.009797 0.000117Regression on degree days squared -- b2 -0.00000785 0.00000018

Error of estimate ------------------------------------------ s2 0.001114 --_.-_---..-__..

Coefficient of determination ------------------------ R2 0.85 ---.-------.--.-

15

8

Z

O

0

h2W2CL

4

0 10

.1403+.087 X

20 30 40NUMBER OF DAYS FROM 3RD INSTAR

50

WU

aN

6

5

Q

3

Figure 10. Instar development of the spruce budworm from the third instar as related to numberof days for development from the, third instar.

The use of accumulated air temp-erature gives the best estimate ofspruce budworm development at anystage from the third to the sixth in-stars. Figure 11 illustrates the data.

Elevation and sprucebudworm development

The following analysis was basedon data gathered in the La Grandearea in 1953. This is a part of thedata used to develop the earlier rela-tionships.

In order to compare insect develop-ment at different elevations, each areawas related to the others in terms ofphenological time. Phenological time isthe successive numbering of the daysof the year beginning with January 1as 1 and ending with December 31 as365 or 366.

Fron} Hopkins (10), each 100 footincrease in elevation results in a one-day retardation of insect development.

The development of the spruce bud-worm at La Grande in 1953 was an-alyzed according to Hopkins' state-ment. Since the average elevation fortimber in the area is 5,000 feet, devel-opment of the spruce budworm on allplots was corrected to this elevation.This means that since development islater at high elevations, one day was

,subtracted from the development forevery 100 feet over the 5,000 foot ele-vation. Also, one day was added tothe time of development for each 100feet under 5,000 feet.

The equation Y = a + bX was fittedto the data with the instar develop-ment (Y) of the spruce budworm andphenological time (X) corrected for

16

7

Y 3.0519

.001114

+ .009797 At -.0000078X=

0 100 200 300 400 500INCREASE IN ACCUMULATED DEGREE DAYS ABOVE 42°F FROM 3RD INSTAR

Figure 11. Instar development of the spruce budworm from the third instar as related to the increasein accumulated degree days above 42°F. from the third instar.

elevation. This resulted in a solutionof Y = 0.0906 X -13.30 and a stand-ard error of estimate (s2) equal to0.401. These data are presented infigure 12.

The La Grande data were furtheranalyzed to determine if a better rela-tionship than that of Hopkins' couldbe found between elevation (Y) andinstar development (X). The regres-sion coefficient (b) of instar develop-ment for 100 feet of elevation was cal-culated in order to determine the bestcorrection for spruce budworm de-velopment at different elevations.

The adjustment of time for eleva-tion would be the regression coeffi-cient (b = 0.0746) of development for

100 feet of elevation divided by theregression coefficient (b = 0.09178)of instar development for one day.This resulted in 0.81 day of differencein time of development with each 100foot change in elevation. Figure 13illustrates the time of development offourth and sixth instar larvae andadults for different elevations in theLa Grande area for 1953.

The 0.81 day of change for each100 feet of elevation is not consideredimportant when compared to the 1.00day as advanced by Hopkins.

Herbaceous plant development at thefourth spruce budworm instar

Observations were made on develop-ment of the herbaceous plants. The

17

B

6

3

JUNE 9

160 170

JULY I11

AUG. III

Y.0906X-I3.30as .40I 1

SEPT. I

190 200 210 220 230 240

NUMBER OF DAYS FROM DECEMBER 31

250

.SEPT. 27

260 270

Figure 12. Instar development of the spruce budworm on all areas adjusted to a 5,000 foot elevationand related to the number of days for development from December 31.

definitions of the symbols used are asfollows :

1. First growth refers to the leafbud elongation up to the time ofunfolding of the leaves.

2. Leaves unfolded includes thatperiod from the first unfoldingof the leaves to their appearanceas normal leaves except in size.

3. First flower buds indicates theperiod from first observation ofthe flower buds to the next stage.

4. First flowers open includes theperiod from first flower buds upto one-third of the flowers beingopen. No seed has formed norhave flowers withered.

5. Flowering indicates the period ofgreatest number of flowers. In

this stage some buds are notopen while others have begun toform seed.

6. Last flowers indicates the periodwhen more flowers are witheredthan remain in flower.

Table 5 lists stage of developmentof the predominant herbaceous spe-cies of interest at the time of thefourth spruce budworm instar.

It was observed that many of theplants were flowering (stage 5) at thetime the spruce budworm was in thefourth instar. These included themore showy species of Achillea, Bro-diaea, Geum, Potentilla, Scorzonella,and Vicia. Fragaria was also in flowerbut this species blooms over a verylong period and is of little value as anindicator.

18

Table 5. STAGES IN DEVELOPMENT OF PLANTS AT THE FOURTH SPRUCEBUDWORM INSTAR

SpeciesStage of

development

Totalplots

observed

Achillea lanulosa (Western Yarrow) .............................................. 3.92 25Antennaria spp. (Everlasting) .......................................................-. 4.70 10

Arnica cordifolia (Heart-leaved Arnica) ._..._..---_..----...._..-........ 5.67 12

Brodiaca spp. (Brodiaea)----------------------------------- ------------------------------ 5.14 7Castille ja spp. (Paint-brush) --------------- ------------------------------------------- 4.33 3Chinaaphila umbellata (Western Prince's Pine) --.--.-__._ ............. 3.00 2

Erythronium grandiflorum (Yellow Adder's-tongue) ................ 6.00 2Fragaria spp. (Strawberry) ----------- --------------- ---------------------------------- 5.00 29Geum cileatum (Long-plumed Avens) ........................._.--.......---..-- 4.70 10

Geum spp. (Avens) -------------------------------- ------ ------------------------------------ 5.00 2Hieracium spp. (Hawkweed) ----------- ---------- ----------------------------------- 2.80 10

Linnaea borealis (American Twin-flower) ------------------------------------ 2.60 5Lithophragma parviflorum (Small-flowered Fringe-cup)-------.-. 5.60 5Lupinus leucophyllus (Woolly-leaved Lupine) .............................. 3.67 12

Lupinus polyphyllus (Large-leaved Lupine) ................................. 4.71 17Lupinus sulphureus (Sulphur-flowered Lupine) ----------------------- ... 4.00 2Potcntilla spp. (Cinquefoil)-------------------------- ------------------------------------ 5.00 3Scorzonella spp. (Scorzonella) ------------------------------- -..-....-.......-..-.... 5.00 11

Sedum spp. (Stonecrop) ------------------- -------------------------------------------------- 3.40 10

Trifolium eriocephalum (Woolly-headed Clover) ...................-_. 5.67 3hicia spp. (Vetch)--------------- --------------------------------------------------------- ------- 4.71 7

Some Problems Pertaining to the Use of Weather DataIn Predicting Budworm Development

The relationship of accumulated de-gree days and spruce budworm devel-opment can be useful in estimating in-sect development over large areas orfor estimating future development onan area.

Air temperature data expressed indegree days above 42°F. from UnitedStates Weather Bureau stations maybe used in at least two ways to esti-mate budworm development. The datafrom these stations, situated in orabout the forest area, can be relatedto spruce budworm development with-in the forest. In the following yearsthe relationship may be used as aguide to insect development.

For any station the rate of degreeday accumulation, expressed in days,

may be estimated from an initial ac-cumulation to a desired total accumu-lation. In this manner the number ofdays required for the spruce bud-worm to develop from one instar toanother can be estimated.

Both of these uses assume the re-lationship of budworm developmentto degree days as developed in fig-ure 9.

Relationship of accumulated degreedays, as determined by weatherstations, to spruce budwormdevelopment near and withinthe forest area

The 1953 development of the sprucebudworm for five areas west of LaGrande was related to accumulated de-gree days for weather stations within

19

'" tH -7 E ELJ ii/-6TH INSTAR -ADULT4TH INSTAR

58

56

54

52

50

48

46

44

42LA GRANDE 1953

40 ----AFTER HOPKINS

35

-Aa

W0a00W0OZ

Z0

W

W

160 170 ISO 190 200 210 220 230 240NUMBER OF DAYS FROM DECEMBER 31

250

Figure 13. The influence of elevation on time required for spruce budworm to develop to fourth,sixth, and adult stages.

and near the forest area. The distribu-tion of the study areas and weatherstations can be observed from figure14. For all stations, Granite, Ukiah,Meacham, La Grande, Union, and PilotRock, accumulated degree days wererelated to spruce budworm instar de-velopment at 5,000 feet. Instar devel-opment for all study plots was cor-rected to the 5,000 foot elevation byusing the coefficient (0.0746) of instarchange for each 100 feet of elevationfrom the La Grande data of 1953.The relationship of degree days toinstar development was significant forall stations, and all are equally reliablefor predicting insect development with-in the forest area. Once this relation-ship has been established the accumu-

260

lation of degree days could be usedin succeeding years for determininginsect development within the forestarea. From figure 15 the accumula-tion of degree days to the fourth in-star is greater at Pilot Rock than atGranite, being 1,476 and 385 degreedays respectively. This is the result ofa change in elevation from 1,640 feetat Pilot Rock to 4,939 feet at Granite.In mountainous country, weather sta-tions are seldom situated within theforest area but are usually at lowerelevations about the forest. The rela-tionship between the degree day re-corded at the weather station and in-sect development in the forest mustbe known to predict development ofthe insect in future years.

20

aa as

STUDY AREA LOCATION 4.

UNDER 3000' C 3000 to 5000'

CONTOUR INTERVAL 2000'

5000' to 7000' = 7000' OVER -

Figure 14. Topographic map of the headwaters of the Grand Ronde River showing study areas andU. S. Weather Bureau stations.

Existing accumulated degree daysas an index of the number of daysrequired to accumulate 300, 400,and 500 degree days

A relationship has been found toexist between spruce budwOrnl (level-opmcnt and temperature, expressed indegree (lays, as recorded by a weather

station for the forest area. The long-term temperature data of the weatherstation can he used to develop an an-ticipated temperature pattern for thestation and that information can berelated to the insect development.

Figure 16 illustrates 20 years oftemperature data for Meacham from1936 to 1955. The degree day accumu-

21

45

lation above 42°F. from March 1

through April 30 was related to thenumber of days required to accumu-late a total of 300, 400, and 500 de-gree days. The actual data is plottedfor an accumulation of 400 degreedays.

If Meacham on April 30 has an ac-cumulation of 100 degree days, thenit will require 30, 41, and 50 daysfrom April 30 to accumulate 300, 400,and 500 degree days. From figure 7,

e

5

4

at 300, 400, and 500 degree days thespruce budworm is in the 2.9, 3.8, and4.5 instars respectively. It is obviousthat the accuracy of this method ofprediction is dependent upon uniformweather conditions. Extreme numbersof either hot or cold days can shortenor lengthen the period of time for adesired accumulation. However, sincethe estimate can be made daily fromApril 30, extremes of weather areconsidered.

o9 a a9'9 e0 ry4

_

{f.(vV O v'

P rP

`4r

UQ, O4r pGam! aP ., J? Q

06,0r'~

her1ryZ+ya _

r b b

+

6{

`eC eq+ }o

}0

Zo , o.

6{ r e-

'a1 y0 tiDjO^

9b

300 400 500 600 700 BOO 900 IDOO 1900

ACCUMULATED DEGREE DAYS ABOVE 42' F.

Figure 15. Relationship of spruce budworm instar development at 5,000 feet to the accumulated

degree days above 42°F. based on 1953 data for five U. S. Weather Bureau stations.

22

.2000, 3000

0I-4

0M

Ja 304

500 DEGREE DAYSY 64.2182 -.1475 Xr -.601

= 400 DEGREE DAYSAY 56.6899-.1536X

608r -.300 DEGREE DAYS

Y 46.4544-.16136Xr -.669

Soo ofRffD, YS

ofQgfO4 YS

00fcRff

oil's

0 25 50 75 100 125 150 175 200 225 250 275TOTAL ACCUMULATED DEGREE DAYS FROM MARCH I THROUGH APRIL 30

Figure 16. Degree day accumulations above 42°F. for Meacham; 1936 to 1955 inclusive.

23

SummaryThe spruce budworm, Choristone-

ura f umi f erana (Clem.), is an im-portant enemy of the Douglas fir-truefir forests of Oregon. At the end of1954 about 3 million acres of foresthad been aerially sprayed with DDTto control the insect.

The influence of air temperature onspruce budworm growth, the growthof the host, and interrelationships be-tween insect and host were studied on15 areas from 1951 to 1954.

The principle of heat accumulationas advanced by Merriam (4) wasused. Degree days are calculated bysubtracting the threshold of develop-ment (42°F.) for the spruce bud-

worm from the average daily temper-ature. The degree days are added to-

gether in sequence to give the value of

accumulated degree days. Air temper-ature was measured at 4.5 feet above

the ground by the use of hygrotherm-

ographs on each area.The following data were collected

for the plots : the instar value for eachplot was the average for all insectsfound on the plot, the average lateralgrowth on grand fir was determined,spot soil temperatures at a 6-inchdepth were recorded weekly, and ob-servations were made on herbaceousplant development. Relationships werefound from the observed data.

Growth of the spruce budworm wasfound to depend upon the growth ofthe host-grand fir-but varied withthe forest density. At the fifth sprucebudworm instar, laterals of grand firin dense situations grew 1.47 inchesas compared to 2.28 inches of growthin open areas.

The growth of grand fir is relatedto accumulated degree days but is also

related to stand density. For an accu-mulation of 400 degree days the grandfir of a densely forested area. grewonly 0.39 inch, whereas in a moreopen area, growth was 1.24 inches.

Spruce budworm development on anarea was best estimated from a con-sideration of the growth of grand firin combination with the accumulationof degree days. From an initial ob-servation of insect and grand fir de-velopment the growth of the insect,in instars, can be predicted from theincrease in the growth of grand fir andthe number of accumulated degreedays from the first observation. With1.00 inch increase in growth of thelaterals of grand fir during a periodwith an increase of 300 degree days,the spruce budworm would develop2.05 instars.

Growth of the insect, in instars, isrelated to accumulated degree days. Atan average accumulation, for all areas,of 300, 400, and 500 degree days, thespruce budworm developed to 2.9, 3.8,and 4.5 instars.

A poor relationship exists betweeninsect development, accumulated de-gree days, and spot soil temperaturemeasurements at the 6-inch depth,Spot soil temperature measurementsare particularly subject to the vari-ables of diurnal fluctuation and pre-cipitation and cannot be considered areliable basis for analysis.

Insect development from the thirdto succeeding instars showed an in-effective relationship with time but animproved relationship with increase inaccumulated degree days. When a per-iod of 27 days was considered startingwith the third instar, the spruce bud-worm developed from 1.54 to 3.74 in-

24

stars with respective increased accu-

mulations of 252 and 553 degree days.

With the difference in the degree day

accumulation, a dissimilarity of insectdevelopment would be expected.

The relationship of insect develop-ment to elevation was determined forthe La Grande data of 1953. The de-velopment was found to be retarded0.81 day for each increase of 100 feetin elevation. For practical purposes,this approximates the one day retard-ment of development for each 100 footincrease in elevation advanced by Hop-kins. The amount of instar change forthe La Grande data was 0.0'46 instarsfor each 100 foot change in elevation.

At the fourth spruce budworm in-star the following herbaceous specieswere found to be in flower: Achillea,Brodiaea, Geum, Potentilla, Scorzon-ella, and Vicia.

Temperature data, gathered eitherby the United States Weather Bureauor by special stations using hygro-thennographs set up in the forest, canbe used for the prediction of spruce

budworm development. Such data, con-verted to degree days, from forest andnonforest stations can be related tospruce budworm development within.the forest area. The degree day-instardevelopment relationship is calculatedfor the average elevation of the forest ;then other elevations can be adjustedto the average. Once the insect devel-opment is related to the degree daysof a given weather station, it ,vouldbe possible in the following years topredict the development by using thatsame weather station.

For any one year, development ofthe insect from a given date can be es-timated for a future date, subject toall the year to year irregularities oftemperature for the area. If the in-sect's rate of development for addi-tional degree days, and the numberof days required for a station to ac-cumulate a specified number of degreedays are estimated, then an estimatecan be made of the number of days re-quired for the insect to develop fromone instar to another.

25

Literature Cited1. Spruce Budworm Control Plan for 1951 in Oregon and Washington. Spruce Budworm

Action Committee. Portland, Oregon. l7pp. 1950.

2. Brockman, C. F. and D. Berry. The Chesnimnus Experimental Spruce Budworm Con-trol Project. Oregon State Board of Forestry. Research Bulletin 5. 22pp. 1950.

3. Peck, M. E. A Manual of the Higher Plants of Oregon. Portland, Oregon: Binfordsand Mort. 866pp. 1941.

4. Kendeigh, S. C. A Study of Merriam's Temperature Laws. Wilson Bulletin 44 (3) :129-143. 1932.

--5. Pearis, L. M. Some Phases of the Relation of Temperature to the Development ofInsects. West Virginia University Agricultural Experiment Station Bulletin 208. 62pp.1927.

6. Cook, W. C. The Relation of Spring Movements of the Beet Leafhopper (Eutettixtenellus Baker) in Central California to Temperature Accumulations (Homoptera).Annals of the Entomological Society of America 38 (2) :149-162. 1945.

7. Daily Weather Map. U.S. Dept. Commerce. Weather Bureau. Washington 25, D. C.April 9, 1951.

8. Henson, W. R. Influence of Meteorological Factors on Behaviour of the Spruce Bud-worm. Canada. Science Service. Division of Entomology. Bimonthly Progress ReportForest Insect Investigations. 4 (6) :2. 1948.

9. Freeman, T. N. External Anatomy of the Spruce Budworm Choristoneura fumiferana(Clem.) (Lepidoptera: Tortricidae) Canadian Entomologist 79:21-31. 1947.

10. Hopkins, A. D. The Bioclimatic Law. Journal of the Washington Academy of Science10 (2) :34-40. 1920.

General References1. Snedecor, G. W. Statistical Methods. The Iowa State College Press. Ames, Iowa. 485

pp. 1946.

2. Uvarov, B. P. Insects and Climate. Transactions of the Entomological Society of London79 (1) :247pp. 1931.

26

AcknowledgmentsThis project was made possible by

the Oregon Forest Lands ResearchCenter while under the supervision ofthe Oregon State Board of Forestry.

Much of the field work and com-pilation of data were accomplished byFedor Kudrjavcev of the Oregon For-est Lands Research Center.

For his patient and understandingassistance in the statistical analysis,the author is warmly indebted to Dr.Lyle D. Calvin of the Oregon StateAgricultural Experiment Station.

The hygrothermographs used in thestudy were provided by the Office of

the Meteorologist in Charge, U.S.Weather Bureau, Portland, Oregon.

Background data of spruce bud-worm development were from theForest Insect Laboratory of the U.S.Forest Service, Portland, Oregon, andthe Insect Control Division of the Ore-gon State Board of Forestry.

Illustrations were prepared by Wil-liam Eastman, Jr.

The assistance of members of theOregon Forest Lands Research Cen-ter for their constructive review ofthe manuscript is appreciated.

27

THE OREGON FOREST LANDS RESEARCH CENTER program is guided byrepresentatives of public and private land owners who are interested in the bestuse of Oregon's forest land resources.

The following men constitute current membership:

NAT GIUSTINA, Principal . .

DAVE BURWELL, Alternate

GENE KNUDSON, Principal . .

WILLIAM D. HAGENSTEIN, Alternate

T. J. ORR, Principal . . . .

A. W. MOLTKE, Alternate

B. SAM TAYLOR, Principal . .

ROBERT KLINE, Alternate

JOSEPH W. MCCRACKEN, Principal

SAM R. KONNIE, Alternate

R. W. COwLIN

RUSSEL GETTY

GEORGE H. BARNES

D. L. PHIPPS

Willamette Valley Lumbermen'sAssociation

Industrial Forestry Association

Western Pine Association

Southern Oregon Conservation andTree Farm Association

Western Forest IndustriesAssociation

Pacific Northwest Forest andRange Experiment Station

Bureau of Land Management

School of Forestry

State Forester

The Forest Protection and Conservation Committee, established in 1953,administers research funds and approves research projects. Present members are:

SIDNEY LEIKEN

A. C. ROLL . .

WALTER F. MCCULLOCH

ELIOT JENKINS .

FREEMAN SCHULTZ

R. M. KALLANDER

Western Forest Industries Association

. Member at Large

. School of Forestry

West Coast Lumbermen's Association

. Western Pine Association

. Administrator