The interaction between Southwestern dwarf mistletoe, Arceuthobtum vaginalum subspecies cryptopodum, infestation and defoliation by the pandora moth, Coloradia pandora pandora , on the Kaibab Plateau in Arizona was evaluated. Heavy defoliation of ponderosa pine, Pinus ponderosa, in 1979 and 1981 resulted in mortality of individual trees in areas of heavy dwarf mistletoe infestation. Postmortem evaluation of ponderosa pines indicated that dead trees had a significantly higher dwarf mistletoe rating than did nearby paired live trees. Of 25 tree pairs evaluated, only two live trees had higher dwarf mistletoe ratings than the paired dead tree. Mean dwarf mistletoe ratings were:live trees 2.9, dead trees 4.6 (6 class dwarf mistletoe rating system). Implications for management of the pandora moth are discussed

Mathiasen, Robert L.

Wagner, Michael R.

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DWARF MISTLETOE-PANDORA MOTH INTERACTION AND ITS CONTRIBUTION TO PONDEROSA PINE MORTALITY IN ARIZONA Michael R. Wagner' and Robert L. Mathiasen ' A BSTRACT.- The intera ction between Southwes te rn dwarf mistlet oe , Arceuth obtum vagina l um subspecies crup-topodum, infestat ion and defoliation by the pandora moth, Coloradia pandora pandora , on the Kaibab Plateau in  Arizona was evaluated. Heavy defoliation of ponderosa pine , fi,ms ponderosa, in 1979 and 1981 result ed in mortality of individu al trees in areas of heavy dwarf mistlet oe infestat ion . Postmortem eva luation of pond erosa pines indicated that dead trees had a significantly higher dwarf mistletoe rat ing than did nearb y pair ed live trees. Of25 tree pairs evaluated , only two live trees had higher dwarf mistlet oe rat ings than the paired dead tree. Mean dwarf mistlet oe ratings were: live trees 2.9 , dead tre es 4.6 (6 class dwarf mistlet oe ratin g syste m). Implications for managem ent of the pandora moth are discu ssed. An outbreak of the pandora moth , Color-adia pandora pandora Blake (Lepidopte ra: Saturniidae), began in 1979 on the Kaibab Plat eau in northern Arizona. Defoliation of ponderosa pine, Pinus ponderosa Doug!. ex Laws. , occurred overS,000 acres in 1979 and 19,000 acres in 1981 (Benne tt and Ragenovich 1982). Pandora moth defoliation resulted in radial growth loss between 17% (Mille r 1983) and 25% (Bennett and Andrews ' 1983). Tree mortality was not significantly greater in defo-liated plots than nondefoliated control plots (Benne tt and Andrews 1983). Though ther e was no significant effect of defoliation on mor-talit y on a stand basis, there were clearly small pocket s of mortality (Wagne r pel's. obs .). Field observations by th e authors indi cated that man y of the trees that died wer e infected with Southwestern dwarf mistl eto e , Arceu-thobium vaginatum subsp. cruptopodum (E n-ge lm.) Hawksw. & Wiens. Bennett and An-dr ews (1983) found that radial growth loss in trees with mistletoe and pandora moth was greater than for those with only pandora moth in this area. Man y insects and diseases do not cause di-rect serious impact on their host but rather function to predispose tre es to other damag-ing age nts. Num erous authors have reported that pandora moth defoliation increased the incidence of bark beetle mortality (Carolin and Knopf 1968, Keen 1952, Massey 1940, Patte rson 1929, Wygant 1941). Dwarf mistle-toes, which are se rious damaging agents in western forests (Hawksworth 1961, Hawks -worth and Wiens 1972), are a common agent predisposing trees to oth er agents . The nu-merous interactions between dwarf mistle-toes and forest insect s have been reviewed by Stevens and Hawksworth (1984). We report in .this paper that ponderosa pine mortality, fol-lowing the pandora moth outbreak in north-ern Arizona, occurred primarily on trees heavily infect ed with dwarf mistletoe. MATERIA LS AND METHODS The study site was approximately two miles north of Jacob Lake, Arizona, in an area heav -ily defoliated in 1979 and 1981 by the pandora moth. The sample area was approximately 100 acres in size and constituted the largest pocket of mortality that had occurred following defo-liation (Wagne r pel's. obs .). The study site was outside the area sprayed with Acephate" in 1981 (based on maps in Bennett and Ragen-ovich 1982). A system atic sample with a random start was used to survey the area of mortality. Sam-ple plots were two chains apart and one chain in radiu s. The nearest dead tree to the plot center was selected , and the nearest live tree of similar diameter (maximum acceptable dif-feren ce four inch es dbh) identified (Fig. I) . The diam et er breast height (d bh) and 6-class dwarf mistl etoe rating (D MR) (Hawksworth 'School or Fores try, Box.4098, Northern Arizona Univer sity. Flagstaff, Arizona 8601l. 423 424 GREAT B ASI N NATURALIST Vol. 45, No.3 rig. 1. Typ ical paired sample of a livin g and dead pon derosa pin e . Not e the heavier dwarf mistle toe infecti on on th e dead tree. 425 July 1985 W AG NER , MATHIASEN MISTLE TOE -M o TH I NT ERACTIO N TAB LE 1. Mean diameters and dwarf mistl e toe ra tings of pa ired live and dead ponde rosa pines, Live trees Dead trees dbh DMR db h D MR Mean (X) SO Range 16.4 8. L 5.9--35.9 284 1.75 0--6 16.5 8. 1 5.6-34.2 4.64 1.35 L-6 1977) were determined for each tree in the pair. If a suitable pair of tr ees could not be locat ed within a plot, th e plot was reject ed . A total of 38 plot s we re examined , of w hich 25 met th e cri te ria of having a suitab le pair o f tr ees . Data we re analyzed using a nonparametric s ign te st (C onove r 1980 ) (0. = 0 .005). T he sign test ind ica te s whe the r one ran dom varia b le in a pair tends to be larger than th e other ra ndom var iable in th e pa ir. The null h ypothesis was that th ere was no differe nce in th e d warf mis tle toe ratings between dead and live tr e es in the s ta nd . RE SULTS The mean d iamete rs and mean DMR's of th e paired trees are give n in Table 1. There was no s ta tistica lly s ign ifica nt difference in mean d bh between live and d ead trees, as sho uld be expecte d because of the pairs cho-se n . Howe ver, th ere was a h ighly siz rufican t d ifference in th e mean DMR of live an d dead trees. Dead tr ees sam pled ge nerally had signs of heavy dwarf m istle toe infec tio n (D M R 5 or 6). Dead trees had a higher mean DMR rati ng th an th ei r paired live tr e es in all but two sam-pled pa irs, where th e live tre e had a highe r DMR th an th e dead tre e. W e obs er ved th at th e mortality occ ur re d over a cons ide rable ra nge of tree d iamete rs. Non e of th e dead trees we examined we re free of dwarf mistle toe . DISC USSIO N Our data ind icate ponderosa pine mo rtality tended to occu r on tr ees th at were heavil y infec te d wit h dwarf mi stl etoe . We ca n co n-clude th at th e probability of mortality as a res u lt of pandora moth d efoli ati on is g reate r in sta nds heavily infes te d wi th dwarf mistl etoe . Our experimental design doe s not pe rmit th e es tab lishment of a ca use-effec t rel ati on ship, but it appears reason able th at d warf mistl etoe is p redisposing tree s to mortality following defol iation . W e d o not feel there is evidence to sugges t that the pandora moth p refers dwarf-mistl etoe-infested trees, s inc e d efolia-tion is oft e n uniform over large areas . Rather , we feel trees weakened by d warf mi stl etoe infection probably a re less tolerant of defolia-tion than a re healthier tr e es . W e did not at-te m pt to sys te ma tically de te rmi ne th e ca use of mo rtali ty of each sam p led tree in th e stud y a rea . H owe ver, th e few trees we did exa m ine did not ap pear to be killed by bark be etle s or othe r secondary agents. T he se findings have important im plica tio ns for ma nagemen t of the pandora moth . Since g rowth loss is moderate and probabl y doe s not Occ ur for more th an one or two years , co n tro l attempts d irected at reducing gr owth loss are not j us tified . Mortali ty is a more se rious im-p act and wo u ld jus tify con trol measures if ex-pe cted to occur over lar ge areas. We wo uld recommend co ntro lli ng th e agen t pr edispos -ing trees to mortalit y (dwarf m istl etoe) as th e preferred op tion . Silvic ultural co n trol strate -gies for d warf mistl etoes are well es tablished (Sc ha rpf an d Parmeter 1978). We would sp ecifically re com me nd se lec tively removing trees w ith a D M R of 3.0 Or grea te r in s ta nds likel y to be heavil y defoliat ed b y the pandora moth . Becau se th e importance dwarf mi stle-toes play in reducing growth is we ll known (H awksworth and Wiens 1972), th e added ef-  of expecte d d efoliat ion would certainly Ju sti fy co n tro l efforts in man aged fo re st stands. In forest a reas no t under intensive forest management, de foliation by th e pandora moth ma y ac tually hav e a beneficial e ffec t. Since mo rt ality prefe re n tially occ urs on th e more heavil y d warf-mistl etoe-infected tree s pand ora moth d efoli atio n may have th e affec t of reduci ng s ta nd mi stl etoe infest ati on level s. This may increase the des irab ility of th es e ar eas for future use as managed sta nds . C e r-tai nl y th e morta lity o f some trees wo uld provide con siderable wildlife habitat fo r a va-riety of cavi ty- nes ting birds. ACK NOWLED GMENT .We acknowledge E. A. Blake a nd J . M. DIMatteo for th e ir assi stance in d ata co l1ec-tio n. · .  426 GREAT BASI N N ATURALIST Vol. 45, No. 3 LITERAT URE CITED BEN NETI, D. D.. AND M. A. ANDREWS. 1983 . Biological eva lua tion of th e pandora moth-Kaibab Nationa l Forest. USDA Forest Service. Southwestern Re-gion. For e st Pest Man agement Rep ort R-3 83-7 . 15 pp . BENNETI, D . D , AND 1. R.   1982 . A pilot contro l project to evalua te Acephate" for control of th e pandor a moth , Coloradia pandora Blake (Lep-idopte ra: Sa turnii dae) , Jacob Lake , Arizona 1981. USDA Forest Service . Southwestern Region, For est Pest Man agem ent Rep ort R-3 82-1O. 36 pp. CAROUN, V. M , AND J A E. KNOPF. 1968 . The pando ra moth . USDA Forest Se rvice, Pacific Northwest Forest and Range Experime nt Sta tion. Fo res t Pest Leafl et 114. 7 pp. CONOVER, W. J 1980 . Pages 122-142 in Pr acti cal non-pa rametric stat istics, 2d ed. , John Wiley & Sons Inc. , New York. HAWKSWORTH , F. G. 1961. Dwarf mistl et oe of p onderosa pine in th e Southwest. USDA Forest Se rv ice Technical Bulle tin 1246. 112 pp . _ _ . 1977. Th e 6-class dwarf mistl etoe rating sys tem . USDA For est Se rvice . Genera l Techni cal Rep ort RM-4 8 . 7 pp. HAWKSWORTH, F. G.. AND D. WIENS. 1972. Biology an d classificat ion of dwa rf mistl et oes (Arce uthobium ). \ \.. US DA For est Se rvice Agri culture Handbook 401. 234 pp . KEEN. F. P. 1952. Pages  in Insect ene mies of west-e rn forests. US DA Miscell aneous Pub lica tion 273 . MASSEY. C. L. 1940. Th e pa ndora moth (Coloradia pan-dora Blake), a defolia tor oflodgepo le pin e in Colo-rado. Un published thesis. Du ke Uni versity . Durh am , North Carolina . 33 pp. MILLER. K. K. 1983. The ecology and impact of the pan -dor a moth , Coloradi a pando ra pandora Blake . in no rthe rn Arizona. Unpublished thesis. Northern Arizona Unive rs ity. Flagstaff. 62 pp . PATIERSON. J. E. 1929. T he pandor a moth , a peri odi c pest of western pin e fore sts. USDA Technical Bullet in 137.20 pp . SCHARPF. R. F , AND J R. PARAMETER, EDS. 1978. Proceed-ings of th e sym posium on dwarf mis tle toe control through for est man agemen t. US DA For est Se r-vice Gen eral Tec hnical Rep ort PSW-31. 190 pp. STEVENS, R. E., AND F. G HAWKSWORTII . 1984. In sect -dwarf mistl et oe associations: an update . Pages 94-100 in Proceedi ngs biology of dwarf mistl et oe. US DA For est Se rvice Gen eral Techn ical Rep ort RM:l 11. W YCAIIIT, N. D. 194 1. An infestati on of th e pandora moth, Colorad ia pandora Blake , in lod gepole pin e in Co lorado . J. Econ. Ent. 34(5):697-702. 

Dwarf mistletoe-pandora moth interaction and its contribution to ponderosa pine mortality in Arizona

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Dwarf mistletoe-pandora moth interaction and its contribution to ponderosa pine mortality in Arizona

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