Bousfield, Wayne E.

Livingston, R. Ladd

Tunnock, Scott

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

Undetermined

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s p )IMPACT OF EGG VIABILITY, EGG PARASITISM, AND VIRUSON 1974 DOUGLAS-FIR TUSSOCK MOTH DEFOLIATION POTENTIALIN NORTHERN IDAHObyScott Tunnockli , R. L. Livingstonli , and W. E. Bousfield-1/INTRODUCTION Egg mass surveys designed to assess potential defoliation by Douglas-firtussock moth, Orgyia pseudotsugata McD., in northern Idaho were conductedduring the fall 1973 through the cooperative effort of a special taskforce of the Northern Rockies Forest Pest Action Council (Tunnock andLivingston 1974). As part of this survey, supplemental collections ofegg masses were made in order to assess effects of egg viability, eggparasitism, and virus on defoliation potential and readjust proposedtreatment boundaries accordingly.METHODS During the fall egg mass survey (Tunnock and Livingston 1974), fivenew egg masses were collected from plots sampled which contained newegg masses. These were stored in a cooler at 35° F. until February 1974.In February, half of each egg mass was placed in a Petri dish and incu-bated at 78° F. and 30 percent relative humidity. Eggs usually hatchedafter 14 days. All larvae and egg parasites were counted in each dish.From 20 to 30 larvae were retained in the Petri dish, and the egg masswas placed in another Petri dish to complete hatching. Larvae were fedon artificial media and kept in the incubator for 14 days. At the end of14 days each dish was examined for dead larvae. Dead larvae were smearedS  1/ Entomologist, USDA Forest Service, Division of State and PrivateForestry, Missoula, Montana.2/ Entomologist, State of Idaho, Department of Public Lands,Coeur d'Alene, Idaho.•••••••DIVISION OF STATE & PRIVATE FORESTRY	 MISSOULA, MONTANA••n••on a slide and examined under a compound microscope for presence of viruspolyhedra. Percentage of larvae killed by virus was computed for eachplot.Egg masses that were transferred to a second Petri dish were dissectedand all unhatched eggs counted per mass. Any additional emerged larvae• and parasites in each dish were counted. From these data, average num-ber of eggs per mass, percent nonviable eggs, and percent egg parasitismwere determined for each plot.A partial life table (Table 1) was prepared from the above data to deter-mine estimated larvae (viable eggs) per 1,000 square inches of foliage oneach plot. The virus level and estimated larval density per 1,000 squareinches of foliage were used in a key (Tunnock and Livingston 1974) whichestablished if an area qualified for treatment (high risk).RESULTS 0		 Percent nonviable eggs ranged from 0.3 to 68.9, and egg parasitism rangedfrom 0 to 14.9 percent (Table 1). Two species of egg parasites wererecovered, Telenomus californicus Ashm. 3/ (Hymenoptera: Scelionidae) andTrichogramma minutum RileyA/ (Hymenoptera: Trichogrammatidae). T. call-for-nicus was the more abundant of the two.Virus incidence was generally low throughout the infestation, averaging40	 1.1 percent on the Coeur d'Alene Unit, 3.3 percent on the St. Joe Unit,0.3 percent on the Craigmont Unit, 5.8 percent on the Salmon River portionof the Nezperce Unit, and 2.5 percent on the Selway River portion of theNezperce Unit. Virus incidence on the Coeur d'Alene and Selway Riverareas is sufficiently low to retain their status as test sites for pilotcontrol projects of two microbial agents--the natural virus and Bacillusthuringiensis.Acreage adjustments by unit are as follows:Coeur d'Alene Unit.--The number of acres qualifying for treatment in thisunit was decreased by 15,271 acres from 34,138 to 18,867 acres (Fig. 1).St. Joe Unit.--Acres to be treated in this unit were decreased from 64,779to 46,103 (Fig. 2).Clearwater Unit.--There was no reduction in the number of acres to betreated in this unit. It remained at 4,433 acres.Craigmont Unit.--There was no reduction in the number of acres to betreated in this unit, remaining at 4,762 acres.••S    3/ Determined byInsect IdentificationMaryland.4/ Determined byInsect IdentificationMaryland.Paul Marsh, USDA, Agricultural Research Service,and Parasite Introduction Research Branch, Beltsville,B. D. Burks, USDA, Agricultural Research Service,and Parasite Introduction Research Branch, Beltsville,-2-S1• 0Nezperce Unit.--There was a reduction in number of acres qualifying fortreatment only on the Selway River subunit. This was a decrease from33,501 to 29,713 acres. New proposed treatment boundaries of the Selway• subunit are shown in Figure 3.41		 Areas of 1973 defoliation within the 1974 proposed treatment area byownership and damage class are summarized in Table 3.DISCUSSIONThe 1973 fall egg mass survey was based on the best information available41		 on the biology, ecology, and population dynamics of the Douglas-firtussock moth. We recognize that it is very possible our sampling pro-cedures were not capable of detecting high concentrations of egg massesin upper crowns.Supplemental ground surveys are planned for early spring to verifyexisting survey data in areas designated as "spray option." Treeswill be felled to detect presence of new egg masses concentrated inupper crowns which might cause severe defoliation. If there are highconcentrations of new egg masses in upper crowns, these areas will beincluded in proposed treatment units.REFERENCE CITEDTunnock, S., and R. L. Livingston, 1974. Potential Douglas-fir tussockmoth damage in northern Idaho in 1974 based on a 1973 fall eggmass survey. USDA Forest Serv., N. Region, Div. State & Priv.Forestry, insect & disease report 74-4.•qi••••• -3-••Table 1.--Data from northern Idaho Dou glas-fir tussock moth egg masses hatched in the,laboratory during winter 1974.•(1)	2	3	4	5	6	7	8	(9	10)P lotlocationNew eggmasses/1000 sq.inchesfoliagerMeannumbereggs/mass(2x3)Eggs/1000 sqinches --Percentnon-viableegEpST. JOEPercenteggpars-sitismUNITEst.larvaldensity/1000 sq.inches ategg hatchPercentvirus1.3Estimatedlarvae/1000 sq.in. aftervirus--Risk*(highorlow)--T. R. Sec40N 3W 175 68.9 2.541N 2W 22 0.07 244 17.1 29.1 '	 12.2 10.7 2.4 10.5 Low41N 3W 5 .04 220 8.8 4.5 9.1 7.6 0 7.6 Low42N 3W 6 .18 226 40.7 13.1 .5 35.2 2.9 34.2 High42N 3W 18 .66 209 137.9 33.2 6.3 86.3 4.2 82.7 High42N 3W 32 .01 252 2.5 3.5 .3 2.4 0 2.4 Low42N 3W 8 .02 280 5.6 7.9 0 5.2 0 5.2 Low42N 3W 16 .02 134 2.7 10.4 10.4 2.2 0 2.2 Low42N 3W 19 .28 203 56.9 13.8 4.5 46.9 9.6 42.4 High42N 4W 3 .47 198 93.1 18.6 14.9 64.5 2.2 63.1 HighLow42N 4W 18 .03 180 5.4 8.4 0 5.0 5.3 4.7142N 4W 1 .07 164 11.5 16.8 .3 9.6 2.5 9.4 Low42N 4W 28 -- 222 -- 7.2 0 -- 2.0 --  --42N 4W 2 .91 192 174.7 24.4 13.1 114.8 0 114.8 High42N 4W 11 .21 200 42.0 6.0 1.3 39.0 0 39.0 High42N 4W 13 .10 110 11.0 12.1 6.1 9.1 7.3 8.4 Low43N 2W 20 .02 118 2.4 53.9 . 1.1 0 1.1 Low43N 2W 28 .18 178 32.0 37.5 0 20.0 2.8 19.4 Low43N 2W 19 .64 200 128.0 25.2 0 95.8 3.0 92.9 High43N 3W 4 .44 148 65.1 23.3 9.5 45.2 1.7 44.4 High43N 3W 26 .22 168 37.0 21.5 0 29.1 1.4 28.7 High43N 3W 22 .44 236 104.0 7.9 0 95.8 0 95.8 High_43N 3W 35 .04 210 8.4 46.7  1.4 4.4 3.7 4.2 Low43N 4W 18 .09 172 15.5 38.2 4.2 9.2 14.5 7.9 Low43N 4W1 17 .34 232 78.9 56.2 4.2 33.2 5.3 31.4 High43N 4W 26 .42 180 75.6 17.9 6.3 58.2 10.0 52.4 High43N 4W 35 .68 172 117.0 11.6 2.3 101.0 0 101.0 High43N 4W 5 .52 194 100.9 27.0 3.5  71.1 1.7 69.9 High43N 4W 6 .02 185 3.7 21.3 .8 2.9 2.3 2.8 Low43N 4W 64.0 High43N 4W 20 -- 23.5 2.3 -- 1.9 -- --43N 4W 32 14.0 3.4 0 13.5 0 13.5 Low43N 5W 121 6.0 17.0_0 5.0 5.0 4.8 Low*Risk of defoliation is "high" on plot if estimated larval density exceeds 20larval per 1000 sq. in. of foliage or if virus levels are less than 30 percentin class III or IV areas or less than 50 percent in class I or II areas.•••••••••• -4-n••Table 1.--Data from northern Idaho Douglas-fir tussock moth egg masses hatched in the laboratory during winter 1974, con.•1	2	3	4	5	6	7	8	(9)	(1 0),.41AMINPlotlocationNew eggmasses/1000 sq.inchesfoliageMeannumbereggs/mass(2x3)Eggs/1000 sqinchesPercentnon-viableeggsPercenteggpara-sitismEst.larvaldensity/1000 sq.inches ate:: hatchPercentvirusEstimatedlarvae/1000 sq.in. aftervirusRisk*(highorlow)T. R. Sec43N 5W 22 0.28 201 56.3ST. JOE UNIT11111111High26.6 043N 5W 24 .35 196 68.6 28.0 8.4 High43N 5W 27 .11 222 24.4 19.7 11.7 Low44N 2W '11 .04 220 8.8 18.7 0 Low44N 3W 17 .76 208 158.1 3.8 7.7 I High44N 3W 8 .03 208 6.2 3.5 .311111111Low44N 3W 18	 .07 150 10.5 33.1 1. Low44N 4W 11	 .07 208	 14.6	 10.0	 .4 Low45N Low45NIIILow45N1111111111.11Low45N45N Low45 Low45N Low45N • High45N Low45N Low46N.--48N HighHigh49N49N High49N49NIEMI 20 137 MIEMIKEIMIKINI 2.4 1.1 2.3 LowLow.02 0 2.6 Low49N IIIIIIIIIIIIIIIIIIIIIIIIII 1.2 3.3 Low49N Hie,h49 Low49N2WMllaBliMilialL111111Low49 N•	 k n 1Low49N49N 2W 1.11 Hi:h49N 2W 22	 .14 206	 28.8 .3 28.7 28.7 High••••••••-5-n.411Table 1.--Data from northern Idaho Douglas-fir tussock moth egg masses hatched in the laboratory during winter 1974, con.•1	2	3	4	5	5	7)	(8)	(9)	(10)PlotlocationNew eggmasses/1000 sq.inchesfoliageMeannumbereggs/mass(2x3)Eggs/1000 sqinchesPercentnon-viableeggsPercenteggpars-sitismEst.larvaldensity/1000 sq.inches ategg hatchPercentvirusEstimatedlarvae/1000 sq.in. aftervirusRisk*(highorlow)T. R. Sec49N 3W 33 0.04 184COEUR D'ALENE UNIT3.3 7.0 Low7.4 3.3 0 7.249N 3W 24'	 .65 198 128.7 2.7 0 125.2 2.4 122.2 HighHigh49N 3W 25	 .73 144 105.1 5.5 0 99.3 .9 98.449N 3W 14	 .49 136 66.6 7.1 1.1 61.2 10.7 54.7 High49N 3W 36	 .03 180 5.4 7.7 0 5.0 0 5.0 Low50N 2W 361	 .01 178 1.8 6.0 0 1.7 0 1.7 Low123N 1W 291	 .51 154NEZPERCE (SALMON) UNIT30.0 20.5 High78.5 38.5 2.9 29.323N 1W 27	 .48 166 79.7 44.6 5.3 42.0 6.1 39.4 HighHighdli6N 1E 61	 .33 176 58.1 9.0 3.4 51.2 0 51.2Ilt6N 1E 16 1	-- 98 -- 47.0 2.0 -- 0 -- --26N 1E 31[	 .46 112 51.5 7.5 8.5 43.6 2.3 42.6 High27N 1E 33	 1.80 216 388.8 7.8 5.5 338.8 2.4 330.7 High27N 2E 35	 -- 122 -- 35.9 6.0 -- 2.7 -- --27N 2E --	 -- 214 -- 19.4 7.9 -- 3.1 -- --31N 5E 35	 .09 200NEZPERCE (SELWAY) UNIT0 16.2 Low18.0 I	 5.6 5.0 16.231N 5E 24	 .10 110 11.0 8.6 1.4 10.0 12.6 8.7 Low31N 7E 6	 .41 176 72.2 12.4 7.9 58.3 0 58.3 High32N 6E 16	 -- 134 -- 6.7 .7 -- .8 -- --32N 6E 28	 -- 164 -- 31.1 14.6 -- 2.0 -- --32N 6E 25	 .10 156 15.6 14.6 0 13.3 0 13.3 Low32N 6E 34	 .22 166 36.5 9.2 0 33.2 5.0 31.5 High32N 7E 30 -- 316 -- 3.8 13.9 -- 0 -- --33N 3W 29	 .31 205 63.5CRAIGMONT UNIT56.5 .6 56.2 High10.0 1.2_.. 33N 3W 201	 .08 198 15.8 8.21	 6.3 13.6 0 13.6 Low-6-••••n•••••••••410••••••Table 2.--Acres of proposed treatment, and treatment option in northern Idaho during 1974.UnitProposedtreatmentTreatmentoptionCoeur d'AleneState and private 998 4,096Forest Service 17,869 24,678Subtotal 18,867 28,774St. JoeCoeur d'AleneIndian Reservation 988 3,512State and private 30,268 80,317Forest Service 14,847 13,670Subtotal 46,103 97,499ClearwaterState and private 2,686 861Forest Service 1,747 547Subtotal 4,433 1,408CraigmontState and private 4,762 7,162Forest Service 0 0Subtotal 4,762 7,162NezperceState and private 1,312 1,045Forest Service 28,401 17,668Subtotal 29,713 18,713Northern Idaho total 103,878 153,556-7-•••	•Table 3.--Areas of 1973 defoliation within the 1974 proposed treatment area (byownership and damage classes).by damage class*••AreaAcres of defoliationOverlap acres	 New acresTotalDead Class I Class II Class III Class IVNorthern IdahoNezperce unitNezperce NF 0 468 0 10,423 17,510 28,401State and private 0 312 0 0 1,000 1,312Subtotal 780 10,423 18,510 29,713Craigmont unitState and private 0 0 250 799 3,713 4,762Clearwater unitClearwater NF 0 0 0 0 1,747 1,747State and private 0 0 120 0 2,566 2,686•	 Subtotal 120 4,313 4,433III St. Joe unitSt. Joe NF 0 425 1,573 8,274 4,575 14,847Coeur d'Alene IR 0 505 48 300 135 988State and Private 0 2,437 870 16,766 10,195 30,268Subtotal 3,367 2,491 25,340 14,905 46,103Coeur d'Alene UnitCoeur d'Alene NF 0 200 700 490 16,479 17,869State and private 0 0 30 50 918 998nSubtotal 200 730 540 17,397 18,867Northern Idahosubtotal 4,347 3,591 37,102 58,838 103,878• *Class I - 50 percent or more of the host type has been completely defoliated.Class II - 50 percent or more of the host type has at least the top quarterof the crown completely defoliated.Class III - Host type has defoliation visible from survey aircraft. The cur-rent year's foliage has been removed on most trees, but less than a quarterVP	 of the crown has been completely defoliated.VI	 Class IV - Defoliation is not readily visible.•-8-•

Impact of egg viability, egg parasitism, and virus on 1974 Douglas-fir tussock moth defoliation potential in northern Idaho

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Impact of egg viability, egg parasitism, and virus on 1974 Douglas-fir tussock moth defoliation potential in northern Idaho

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