An attempt was made to predict western spruce budworm defoliation using
egg counts from plots in the Douglas-fir type east of the Continental
Divide in Montana, the Douglas-fir type west of the Continental Divide
in Montana, and the mixed grand fir Douglas-fir type of northern Idaho.
The parameters used in a linear regression model for the three
ecotypes were eggs per 100 buds in 1972 as the independent variable and
percent defoliation in 1973 as the dependent variable. Correlation
coefficients (0 were: 0.39, 0.54, and 0.66 for the data from grand
fir in northern Idaho and Douglas-fir in eastern and western Montana
respectively. A covariance analysis of the three regression lines
showed there were differences between the three ecotypes

Tunnock, Scott

United States. Forest Service. Northern Region. State & Private Forestry

Undetermined

ScholarsArchive@OSU

USDA FOREST SERVICE/NORTHERN REGION5t)/(/-4411,1	 Report No. 74-27 5200December 1974• "S'irA/044WESTERN SPRUCE BUDWORM EGG MASSESFOR PREDICTING DEFOLIATION POTENTIAL INTHE NORTHERN REGION--PROGRESS REPORTbyScott Tunnock, EntomologistForest Environmental ProtectionABSTRACT An attempt was made to predict western spruce budworm defoliation usingegg counts from plots in the Douglas-fir type east of the ContinentalDivide in Montana, the Douglas-fir type west of the Continental Dividein Montana, and the mixed grand fir Douglas-fir type of northern Idaho.The parameters used in a linear regression model for the threeecotypes were eggs per 100 buds in 1972 as the independent variable andpercent defoliation in 1973 as the dependent variable. Correlationcoefficients (0 were: 0.39, 0.54, and 0.66 for the data from grandfir in northern Idaho and Douglas-fir in eastern and western Montanarespectively. A covariance analysis of the three regression linesshowed there were differences between the three ecotypes.INTRODUCTION The western spruce budworm, Choristoneura occidentalis Freeman, is oneof the most destructive insect enemies of the mixed conifer type in theNorthern Region. In recent years, more than 4 million acres have beendamaged in Montana, northern Idaho, and Yellowstone National Park,Wyoming.•At present, there is no reliable method of predicting budworm infestationtrends west of the Continental Divide in the Northern Region. Terrell(1961) (1966) had some success with egg mass counts in the pure Douglas-firstands of eastern Montana. Other Regions (McKnight, et al. 1970; Orr44110-		 1960) are still using egg mass counts to predict defoliation. Carolinand Coulter (1959) were the pioneers who first suggested usingle egg mass counts to predict damage and still advocate their use today(Carolin and Coulter 1972).STATE & PRIVATE FORESTRY	 MISSOULA, MONTANA•••••••••••••wThe advantages of using egg masses to estimate next season's damage are:they can be easily collected, are obvious, and are available when roadsare open. Also, an early prediction helps land managers decide for oragainst control with ample time to organize a project if control isneeded. One disadvantage is that new egg masses are hard to separatefrom old ones.The objective of this study was to improve existing methods of predictingdefoliation based on egg mass counts in the three major forest typessusceptible to spruce budworm in the Northern Region:1. Douglas-fir type east of the Continental Divide in Montana.2. Douglas-fir type west of the Continental Divide in Montana.3. Mixed grand fir/Douglas-fir type of northern Idaho.METHODS Egg mass sampling was initiated during late August 1972 in areas infestedwith western spruce budworm in the three ecotypes mentioned. The fol-lowing number of plots were established in each ecotype:1. Eastern Montana - 33 Douglas-fir plots.2. Western Montana - 32 Douglas-fir plots.3. Northern Idaho - 32 grand fir plots.Five trees, open grown, from 30 to 50 feet in height, were sampled perplot. From each of the five sample trees, two 30-inch branches were cutfrom opposite sides at midcrown. Both branches from a sample tree wereplaced in a nylon bag, identified, and stored in a cooler.In the laboratory, the total number of the following year's buds werecounted on each branch and all egg masses on the needles were removedand put into plastic cups. The new from old egg masses were separatedunder a microscope and the length in millimeters of each new egg masswas measured. The number of rows of eggs in each new egg mass wasdetermined by a staining technique (Jennings and Addy, 1968).The total number of eggs per new mass could not be determined by countingindividual eggs even after staining. Hatching and weathering had dis-figured the egg masses too much. The length and number of rows of eggswere used to calculate total eggs per new mass by using tables developedby Washburn and Brickell (1973) and McKnight (1969). Washburn andBrickell's tables were used to determine eggs per mass for Douglas-firin western Montana and grand fir in northern Idaho, and McKnight's tableswere used for Douglas-fir from eastern Montana.-2-•6vz$0 10CO4.1afaCUtoa)14W44rn"c1Oa ger10.•AT CM nT 01 CA ri	 ul ul Ul rA VD AT 01 03 CD 04 PA 03 PA ri ul 01 VD At ul OD AT PA NO r, I• • • • . . • • • •	 •	 • • .	 • • •	 •	 •	 •	 •	 •	 •	 • •	 .	 •	 • •	 • • •VD rA NO OD At Ch ul NO 03 01 rA rA V) ch Cl WI VI At VD 03 --T rA 01 C) r, ma un on on r, N-04 rA 01 CV 04 rA	 H	 r4 04	 rA C4 H 01 rA u1 At	 011+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1÷1+1+1+1+1+1÷1+1+1+1+1+1U1 u1 CAI rs C) AT CAI TAA u1 on NI	 r, un on	 .f co on rA Ch Ul CV ul C) VD Ch CA 03 VD CO• •	 • •	 •	 • •	 •	 •	 •	 •	 • •	 •	 • •	 •	 •	 •	 •	 •	 •	 •	 •	 • •	 •	 • •	• • •H un co r, on in co ch 04 rA 01 01 04 rA 01 ri r, ch ri or, Hoar. N. op r, ri r,C4 r-1 Ul Ul At CD aD ul H	 At H N 0, rA rA 01 VD At 04 01 01 04 VD H HH	 H r-I r-I	 HCAI HA 04 01 At VI VD N. 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U1 AT At 0+100 OD	 0 H on OD 01• •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	•	 •	 •.D .O 01 CI -4 4. cl un 04 01 CA 0, 0100 cp r4 c4 on .4- .4 co r, co CD CD VD CD r, ol cm maOH .tI ul •0 0 VD Cn 0 ON -41- cm P.	 ul r, on H ul	 ul H cm CA1 ul 4) C) 0'101 H H nT rA	 CV1-1 ,A	 ,4	 H	 r4	 H	CT At PA 04	 ul• •	 •	 •	 •	 •VD cn H H CD AT+1+1+1+1+1+1u1 vD en .4t 04• •	 •	 •	 •	 •00 CO CT .7 01 03eA,14-4finCdHOC0COaaaaalrr) W M40ffi Oat 0,CO r4W7 alR;-44.3 a)fpH ga a•	r-1  on un r H 1-A At ,4 r- VD C	 0M ,1 Ch VD C) Ch CA 00 rA PA r, un 01 Ch OD VD 0 4 01.t VD • I• •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 •	 IC up on 04 01 rA rA rA CD CD CS CD CD CD rA CD CD r-1 C) CD rA rA rA 01 AT 01 01 st VD CD 01 At1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1÷1+1+1	u)	 ol uI OD CI ,T cy cn N.7	 ten At At r, .7 CD VDUI u1001 CA Lrl CD rs p, 01 At Ul CA V1 I• .	 •	 •	 •	 .	 •	 •	 •	 .	 •	 •	 .	 •	 •	 •	 •	 •	 •	 •	 •	 •	 .	 •	 •	 •	 •	 •	 •	 •	 •	 Iel H 01 PA At Ch CA N. 0A cl ir1 r 4 in 0'4 • .1. VD CO 04 Ul CD Ch 00 H H C) 4) H oa H N. AT	C4	 c4	 CI	 H	 CA 01 01	 CO V)	 rA rAN. 04• •Ch VDH Hulla014S40H13 C414 0b a001 CV 0• •	 coon CA .1-1 0Ch ul W 003co+10•--1 00 HINIa 144-10E-1••••From the above data, the average number of eggs per 100 new buds wascomputed for each plot.Percent defoliation on each sample plot was rated during July andAugust 1973. This consisted of cutting an 18-inch midcrown branchfrom each cardinal side of the five plot trees. The first 25 shootson each branch were rated for percent defoliation as follows:Percent defoliationof each shoot	 Rating 	0 - 25	 1	25 - 50	 2	51 - 75	 3	76 - 100	 4For instance, if a shoot was 51 to 75 percent defoliated, a tally counterwas punched three times. The total on the tally counter after 25 shootswere rated was the percent defoliation for that branch. Adding percentdefoliation on all branches and dividing by 20 gave average defoliationper plot.To determine if percent defoliation the following year could be predictedby counting eggs per 100 buds, a regression analysis was used where:1. The independent variable X = eggs per 100 buds in 1972.2. The dependent variable Y = percent defoliation in 1973.Linear and curvilinear regressions were computed from the data. Linearregression gave r values of 0.39, 0.54, and 0.66 for data from northernIdaho, eastern Montana, and western Montana respectively. The R valuesfrom curvilinear regression for these areas were 0.37, 0.62 and 0.68.This showed data from eastern Montana tended to fit curvilinear regres-sion slightly better. However, linear regression was chosen to representthe data from the three areas because there were only very slight dif-ferences between the two types of regressions, and because linearregression lines had already been plotted and their F-values and 95percent confidence limits computed.Arc sine transformations were made on the dependent variable Y but theresulting regression lines did not fit as well as when true percentageswere used.RESULTS Table 1 lists average number of eggs per 100 buds in 1972 and averagepercent defoliation in 1973 on all plots in Montana and Idaho. Eggs 	 4per 100 buds ranged from 1.1 to 228.9 and defoliation ranged from 1.4 to81.3 percent on Douglas-fir plots in western Montana. Eggs per 100 buds 410.-4-•ranged from 1.8 to 161.1 and defoliation ranged from 3.2 to 88.1 percent• on Douglas-fir plots in eastern Montana. Eggs per 100 buds ranged from0 to 55.1 and defoliation ranged from 0 to 90.6 percent on grand firplots in northern Idaho. On the average, eggs per 100 buds were more•		numerous (66.4) in eastern Montana but percent defoliation (41.5) washighest in northern Idaho which had the least eggs (16.3).•Linear regression lines showing the correlation between eggs per 100 budsand percent defoliation in the three ecotypes are featured in Figs. 1, 2,and 3. Correlation coefficients (r) were: 0.39, 0.54, and 0.66 for•		data from northern Idaho, eastern Montana, and western Montana respectively.These r values are low and indicate poor correlation between eggs per100 buds and percent defoliation. This is also obvious because the plotteddata does not fit any of the three regression lines.• The F-ratio for slope was 13.93 for eastern Montana and 25.65 for westernMontana, and both F-ratios were highly significant at the 99 percent level.For northern Idaho, F=6.17 and this was significant at the 95 percentlevel.Figure 4 compares the three regression lines. A covariance analysis was• used to test for common regressions between northern Idaho and eastern andwestern Montana. The test showed no significant difference at the 95 per-cent level for common slopes. However, there was a significant differencebetween levels. Therefore, the regressions were considered different.The slopes of the regressions were not significantly different because ofthe low r values obtained from the regressions.410These regressions illustrate there are differences between the three eco-types. A regression line based on western Montana data could not be usedto predict what would occur in eastern Montana.DISCUSSION •The parameter, eggs per 100 buds, does not seem to reflect degree ofdefoliation the following season. This was very apparent in northernIdaho where the average number of eggs per 100 buds was the lowest ofthe three regions but percent defoliation was the highest (Table 1).An explanation for this might be that grand fir chosen for sampling• were mostly understory trees and not many were over 30 feet high. Thewestern spruce budworm may prefer to lay its eggs in the crowns of over-story grand fir trees which are too high to sample. This should bedetermined because in past egg mass surveys in the grand fir type ofnorthern Idaho, egg mass counts have been consistently low.• In the future, we should express new egg masses per 1,000 square inchesof foliage on at least 50 plots in eastern and western Montana to seeif this parameter would give us a better correlation. In north Idaho,grand fir studies should be initiated to determine distribution of sprucebudworm egg masses by crown level and tree crown class.•-5-•LITERATURE CITED •I•Carolin, V. M. Jr., and W. K. Coulter, 1959. Research findings relatedto the biological evaluation of spruce budworm infestations inOregon. U.S. Forest Serv., Pac. NW Forest and Range Expt. Sta.,Portland, Ore., 39 pp.Carolin, V. M. Jr., and W. K. Coulter, 1972. Sampling western sprucebudworm on Douglas-fir in eastern Oregon. USDA Forest Serv., Pac.NW Forest and Range Expt. Sta., Portland, Ore., 55 pp.Jennings, D. T., and N. D. Addy, 1968. A staining technique for Jack-pine budworm egg masses. Jour. Ec. Ent. 61(6): 1766.McKnight, M. E., 1969. Estimating numbers of eggs in western budwormegg masses. USDA Forest Serv., Rocky Mtn. Forest and Range Expt.Sta., Ft. Collins, Colo., Res. Note RM-146.McKnight, M. E., J. Chansler, D. B. Cahill, and H. W. Flake, Jr., 1970.Sequential plan for western spruce budworm egg mass surveys in theCentral and Southern Rocky Mountains. USDA Forest Serv., Rocky Mtn.Forest and Range Expt. Sta., Ft. Collins, Colo., Res. Note RM-174.Orr, P. W., 1960. Evaluation of 1960-61 spruce budworm populations inOregon and Washington. USDA Forest Serv., Pac. NW Forest and RangeExpt. Sta., Portland, Ore., unpub. report.Terrell, T. T., 1961. Techniques of spruce budworm surveys in theNorthern Rocky Mountain Region. 1960 progress report. USDA ForestServ., Intermountain Forest and Range Expt. Sta., Ogden, Utah.Terrell, T. T., 1966. Spruce budworm survey methods in the NorthernRegion. USDA, Co-op. Econ. Insect Rpt. 16(46): 1071-1072.Washburn, R. I., and James E. Brickell, 1973. Western spruce budwormegg mass dimensions--an influence on population estimates. USDAForest Serv., Intermountain Forest and Range Expt. Sta., Ogden, Utah,Res. paper INT-138.•II•••4•-10-•

Western spruce budworm egg masses for predicting defoliation potential in the northern region : progress report

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Western spruce budworm egg masses for predicting defoliation potential in the northern region : progress report

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