Journal of Chemical Ecology, Vol. 18, No. 4, 1992

THE RESPONSE OF MOUNTAIN PINE BEETLE (Dendroctonus ponderosae) TO LODGEPOLE PINE TREES BAITED WITH VERBENONE AND exo-BREVICOMIN

T.L. SHORE, 1"* L. SAFRANYIK, 1 and B.S. LINDGREN 2 IForestry Canada, Pacific Forestry Centre Victoria, British Columbia, Canada V8Z 1M5 ZPhero Tech Inc., Delta British Columbia, Canada V4G 1E9

(Received August 2, 1991; accepted November 19, 1991) Abstract--exo-brevicomin, a multifunctionalpheromoneof the mountainpine beetle, Dendroctonus ponderosae, was tested at release rates of 0.5 and 2.5

mg/day alone and in combinationwith the antiaggregationpheromone verbenone against unbaited controls. Significantlymore lodgepole pine Pinus contorta var. latifolia trees were attacked, and at higher densities, with both release rates of exo-brevicomin than with all other treatments. Verbenone significantlyreduced the response of mountainpine beetles to exo-brevicomin. Verbenone alone did not reduce the number of trees attacked by mountain pine beetle or the attack density when compared to the unbaitedcontrols. Key Words--Dendroctonus ponderosae, mountain pine beetle, Coleoptera, Scolytidae, pheromone, antiaggregation,verbenone, exo-brevicomin. INTRODUCTION The mountain pine beetle, D e n d r o c t o n u s p o n d e r o s a e Hopk., is currently the most destructive insect pest of mature forests in westem North America (Gibson, 1989; Van Sickle, 1989). Commercially available aggregation semiochemicals are used to attract and concentrate mountain pine beetle populations into trees that are scheduled for subsequent direct control treatment (Borden and Lacey, 1985; McMullen et al,, 1986). These aggregation semiochemicals include transverbenol, a pheromone produced by the female beetle that attracts mainly males (Pitman et al., 1968; Pitman, 1971; Conn et al., 1983; Borden et al., 1983), *To whom correspondenceshould be addressed. 533 0098-0331/92/0400-0533506.50/0 9 1992 Plenum Publishing Corporation

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exo-brevicomin, a pheromone produced by the male beetle that attracts mainly females (Rudinsky et al., 1974; Conn et al., 1983), and the monoterpene myrcene, a kairomone that synergizes the insects response to their aggregation pheromones (Billings et al., 1976; Conn et al., 1983; Borden et al., 1983). In recent years research on the mountain pine beetle has focused on antiaggregation pheromones. Verbenone (4,6,6-trimethylbicyclo[3.1.1]hept-3-en-2one) has been identified in a number of beetles in the family Scolytidae and found to have antiaggregative properties. These species include D. frontalis Zimm., D. brevicomis LeC. (Renwick, 1967; Renwick and Vit6, 1970; Hughes and Pitman, 1970; Payne et al., 1978; Bedard et al., 1980), D. adjunctus Bland. (Livingston et al., 1983), Ips typographus (L.) (Bakke, 1981; Schlyter et al., 1988), I. paraconconfusus Lanier (Byers and Wood, 1980), and Tomicus piniperda L. (Schlyter et al., 1988; Byers et al., 1989). In the mountain pine beetle, verbenone was identified in hindguts of emergent and feeding females (Pitman et al., 1969) and trapped in air passed over male-female pairs (Rudinsky et al., 1974). Verbenone inhibited the response of mountain pine beetle to traps baited with attractants in field tests (Ryker and Yandell, 1983; Borden et al., 1987; Schmitz and McGregor, 1990). Lodgepole pine stands baited with verbenone alone or with verbenone and attractant bait had lower percentages of massattacked trees than blocks baited with attractants alone or unbaited blocks, although differences were not always statistically significant (Amman et al., 1989; Lindgren et al., 1989). In ponderosa pine, P. ponderosae Lawson, no significant difference in number of attacked trees was found between 2.5-acre plots treated with four densities of verbenone capsules and untreated plots. It was noted that some of the pine trees to which the verbenone capsules were attached were attacked by the mountain pine beetle (Bentz et al., 1989). Although exo-brevicomin (exo-7-ethyl-5-methyl-6,8-dioxabiclyo[3.2.1]octane) (Silverstein et al., 1968) has been found to be an aggregation pheromone for the mountain pine beetle, there is evidence that it has a multifunctional role in the insect's chemical ecology; at low release rates it induces an aggregative response and at high release rates it induces an antiaggregative response (Rudinsky et al., 1974). Experiments testing various release rates of exo-brevicomin as a pheromone for the mountain pine beetle on traps and trees with and without other attractants can generally be summarized as follows: at release rates of 0.04 mg/day and lower, no response by mountain pine beetle was found (Libbey et al., 1985); at 0.05 mg/day an aggregative response was found (Conn et al., 1983; Borden et al., 1987); rates of 4.0, 5.0, 10.0, and 12.0 mg/day resulted in antiaggregative responses (Ryker and Rudinsky, 1982; Libbey et al., 1985; Borden et al., 1987). At release rates between 0.05 and 4.0, results have not been as consistent. Lodgepole pine trees baited with exo-brevicomin released at 0.2 rag/day were more frequently attacked than unbaited trees, but the attraction

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did not extend to the other pines within a radius of 10 m of the baited tree (Borden et al., 1990). Lodgepole pine trees baited with other semiochemicals plus exo-brevicomin released at 0.37 or 1.26 mg/day initially experienced higher attack densities than trees baited with the other semiochemicals alone, but final attack densities were not significantly different (Borden et al., 1983). McKnight (1979) found an antiaggregative response to exo-brevicomin released at 0.53 mg/day on western white pine, P. monticola Dougl., but on lodgepole pine he found no significant response at release rates from 0.53 to 2.28 mg/day in one experiment, while in a second experiment, also on lodgepole pine, there was a significant increase in the percentage of trees killed by the mountain pine beetle for the treatment including exo-brevicomin released at 0.53 mg/day. Borden et al. (1987) found an intermediate response between aggregation and antiaggregation when exo-brevicomin released at 0.5 mg/day was added to baited funnel traps. endo- and exo-Brevicomin were tested in combination with verbenone as aggregation inhibitors for D. frontalis, and the brevicomin isomers and brevicomin-verbenone combination resulted in lower landing trap catches than verbenone alone (Richerson and Payne, 1979). Watterson et al. (1981) reduced D. frontalis emergent population density with a combination of exo- and endobrevicomin and verbenone. In 1989 we established an experiment with the following objectives: (1) to test the multifunctional role of exo-brevicomin and further refine the release rate that differentiates aggregative and antiaggregative responses; (2) to examine the response of the mountain pine beetle to combinations of the antiaggregative pheromone verbenone and the multifunctional pheromone exo-brevicomin; (3) to determine if individual trees can be protected from the mountain pine beetle by treatment with verbenone; and (4) to determine if trees in the immediate vicinity (5 m radius) of verbenone-baited trees can be protected from the mountain pine beetle.

METHODS AND MATERIALS

Lodgepole pine trees were baited with one of six treatments at each of 28 replications just east of Penticton, British Columbia, in late June 1989, prior to the main beetle flight period in late July-August. The six treatments were: (1) verbenone--released from a bubble cap at approximately 10 mg/day; (2) exobrevicomin (high)--released from a 250-/~1 polyethylene Eppendorf tube at approximately 2.5 mg/day; (3) exo-brevicomin (low)--released from a 6-cmlong solid PVC release device (Flex Lure) at approximately 0.5 rag/day; (4) verbenone plus exo-brevicomin (high); (5) verbenone plus exo-brevicomin (low); and (6) unbaited control. Verbenone had optical purity of 84% and chemical

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purity of 98 %, exo-brevicomin was racemic with a chemical purity of 97 % and 2 % endo-brevicomin. All chemicals and release devices were supplied by Phero Tech Inc., Delta, British Columbia, Canada. Baited trees were selected as larger diameter lodgepole pine with a mean diameter at breast height of 23.3 cm (_+0.3 SE) and were spaced approximately 20 m apart. Baits were assigned randomly within each replication and stapled on the north side at a height o f approximately 2 m on each tree. The replications ranged from 50 m to several kilometers apart and were in an area o f active mountain pine beetle infestation. The locations of each replication were selected where the majority of trees were still alive but were of sufficient age and diameter to be susceptible to beetle attack (Safranyik et al., 1974). To verify that randomization had resulted in a similar number of unattacked lodgepole pine trees o f suitable diameter for the mountain pine beetle to attack (Safranyik et al., 1974) in each treatment, an analysis of variance was conducted. The mean number of unattacked lodgepole pine 10 cm and larger was not significantly different among treatments (F = 0.18, P = 0.97). In late September, following the beetle flight, baited trees and all trees within a radius o f 5 m of each baited tree were checked for mountain pine beetle attacks. Tree species, diameter at breast height, and total number of attacks were recorded. If the number of attacks was too high to count, it was estimated using the method of Safranyik (1988) based on tree diameter, the attack height, and attack density in two 15-cm • 15-cm bark samples taken on opposite sides of the tree at breast height. The experiment was analyzed as a randomized block using the general linear models procedure in SAS (SAS Institute, Inc., 1985). Differences among means were tested using Duncan's multiple-range test. Data on number o f attacks per baited tree and total attacks within a 5-m radius of the baited tree were transformed to l o g l 0 ( x + 1) prior to analysis. A separate analysis was conducted on "mass-attacked" trees. Trees were classified as attacked (having one or more mountain pine beetle attacks on them) or mass attacked (having more than 31.3 attacks/m 2 at breast height); the attacked category included mass-attacked trees. Mass-attacked trees have been defined as those having more than five attacks in a 0.16-m 2 sample area at breast height (31.3/m2), which is a beetle density sufficient to be lethal to the host tree (Lindgren et al., 1989).

RESULTS Trees baited with both high and low release rates o f exo-brevicomin were attacked more frequently than all other treatments (Table 1). There was no significant difference in the number of attacked trees between the two release rates of exo-brevicomin. The addition of verbenone significantly reduced the

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TABLE 1. MEANNUMBERS(SE) OF ATTACKEDOR MAsS-ATTACKEDBAITEDTREES FOR SIX SEMIOCHEMICALTREATMENTSREPLICATED28 TIMES Treatment ~

A t t a c k e d trees b

M a s s - a t t a c k e d trees"

exo-B, high exo-B, low Verb. + exo-B, high Verb. + exo-B, low

0.89a (0.06) 0.86a (0.07) 0.39b (0.09) 0.29bc (0.09) 0.18be (0.07) 0.10c (0.06)

0.82a (0.07) 0.68a (0.09) 0.11bc (0.06) 0.21b (0.08) 0.14be (0.07) 0.00c (0.00)

Unbaited Verbenone

aexo-B. = exo-brevicomin, high = 2.5 mg/day, low = 0.5 mg/day, Verb. = verbenone 10

mg/day. hMeans withina columnfollowedby the same letter are not significantlydifferent, ANOVAattacked F5,~35 = 21.0, P < 0.0001; mass attacked Fs.t35 = 25.5, P < 0.0001; Duncan's test on means, P = 0.05. "Trees having an attack density of more than 31.3/m 2.

response of mountain pine beetle to e x o - b r e v i c o m i n so that it was not statistically different from the response to the unbaited (control) trees. The verbenone-baited trees were attacked less often than the unbaited trees but the difference was not statistically significant (Table 1). The treatment effect for mean number of massattacked trees was very similar to that for mean number of attacked trees except the position of the two verbenone plus e x o - b r e v i c o m i n treatments was reversed. None of the trees baited with verbenone was mass attacked (Table 1). The mean numbers of trees attacked within a 5-m radius of the trees baited with e x o - b r e v i c o m i n were significantly higher than those of the other treatments (Table 2). There was no significant difference between the means of the two e x o - b r e v i c o m i n treatments. There also was no significant difference between the verbenone plus high e x o - b r e v i c o m i n treatment and the verbenone treatment, as was found for baited trees alone (Table 2). The numbers of trees that were mass attacked within 5 m of the baited trees showed the same treatment effects as for trees receiving any attack (Table 2). The treatments had a similar effect on the number of mountain pine beetle attacks on baited trees as they did on the number of trees attacked. Trees baited with either high or low e x o - b r e v i c o m i n had significantly higher attack densities than trees in any of the other treatments (Table 3). Verbenone significantly reduced the attack density on trees baited with e x o - b r e v i c o m i n so that they were not statistically different from the unbaited trees. The attack density on the trees baited with verbenone was slightly lower but not significantly different from the control (Table 3). The total number of attacks within a 5-m radius of baited trees reflected the same treatment preferences by the beetles as for the baited trees except that

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TABLE 2. MEAN NUMBERS (SE) OF ATTACKED OR MAsS-ATTACKED TREES WITHIN A 5 - m RADIUS OF BAITED TREE FOR SIX SEMIOCHEMICAL TREATMENTS REPLICATED 28 TIMES

Treatment~

Attacked treesb

exo-B, high exo-B, low Verb. + exo-B, high Verb. + exo-B, low

Unbaited Verbenone

3.75a 3.75a 1.21b 1.18b 0.89b 0.71b

(0.56) (0.55) (0.39) (0.38) (0.32) (0.30)

Mass-attacked trees" 2.50a 2.46a 0.61b 0.61b 0.50b 0.46b

(0.43) (0.42) (0.29) (0.22) (0.23) (0.23)

~exo-B. = exo-brevicomin, high = 2.5 m g / d a y , low = 0.5 m g / d a y , Verb. = verbenone 10

mg/day. b Means within a column followed by the same letter are not significantly different, ANOVA attacked F5.~35 = 15.5, P < 0.0001; mass-attacked F5.~35 = 15.6, P < 0.0001, Duncan's test on means, P = 0.05. CTrees having an attack density of more than 3 1 . 3 / m 2. TABLE 3. MEAN NUMBERS (SE) OF ATTACKS PER BAITED TREE AND TOTAL ATTACKS WITHIN A 5 - m RADIUS OF BAITED TREE FOR SIX SEMIOCHEMICAL TREATMENTS REPLICATED 28 TIMES

Treatmenta

Baited trees only b

exo-B, high exo-B, low Verb. + exo-B, high Verb. + exo-B, low

Unbaited Verbenone

291.0a 178.9a 90.6b 61.0b 40.2b 29.5b

(35.2) (33.6) (45.9) (29.7) (20.7) (29.5)

Trees in 5-m plot 587.2a 524.7a 194.8b 182.4b 88.6b 158.1b

(110.7) (92.5) (87.6) (76.7) (37.9) (73.2)

aexo-B. = exo-brevicomin, high = 2.5 m g / d a y , low = 0.5 m g / d a y , Verb. = verbenone 10

mg/day. . ~'Means within a column followed by the same letter are not significantly different, ANOVA baited tree F~.~35 = 27.2, P < 0.0001; 5-m plot F5.~35 = 17.9, P < 0.0001; Duncan's test on means, P = 0.05. Data transformed to logl0(x + 1) for analysis. t r e e s in t h e u n b a i t e d t r e a t m e n t h a d f e w e r a t t a c k s t h a n t h o s e n e a r t h e v e r b e n o n e t r e a t m e n t , b u t t h e d i f f e r e n c e w a s n o t s t a t i s t i c a l l y s i g n i f i c a n t ( T a b l e 3), DISCUSSION exo-Brevicomin

w a s a t t r a c t i v e to m o u n t a i n p i n e b e e t l e at b o t h r e l e a s e r a t e s .

B a s e d o n p r e v i o u s w o r k b y B o r d e n et al. ( 1 9 8 7 ) w e e x p e c t e d s o m e a n t i a g g r e g a t i v e r e s p o n s e at 2 . 5 m g / d a y .

However,

with the exception of one experiment

PHEROMONE RESPONSES OF MOUNTAIN PINE BEETLE

539

in which e x o - b r e v i c o m i n was released on western white pine (McKnight, 1979), the antiaggregative effects of e x o - b r e v i c o m i n have been demonstrated on traps, not live trees. In trees, any successful attacks by the beetles bring the complication of additional semiochemicals being released. If our release rates of exobrevicomin were sufficient to induce an antiaggregative response from the mountain pine beetle, we would have expected a reduction in the number of attacks on the baited trees and an increase in attacks on the surrounding trees. It appears, however, that a release rate of 2.5 mg/day is too low to induce an antiaggregative response on live trees because even the baited trees were heavily attacked. Our results clearly show that verbenone reduced the response of mountain pine beetle to trees baited with e x o - b r e v i c o m i n . Verbenone influenced not only the attack on the baited trees but on the trees within a 5-m radius of the baited tree. This supports results of previous studies using traps in which the response of mountain pine beetle to aggregation pheromones was reduced with the addition of verbenone (Ryker and Yandell, 1983; Borden et al., 1987; Schmitz and McGregor, 1990). Our results provide some insight regarding the potential for protecting individual trees or small groups of trees with verbenone. The effect of verbenone on the mountain pine beetle cannot be described as repellent because the verbenone treatment did not result in significantly fewer attacked trees or lower attack densities on either the baited trees or trees within a 5-m radius of the baited trees when compared to the unbaited treatment. The effect was more that of neutralizing or masking the attractiveness of the aggregation pheromone exobrevicomin to the mountain pine beetle. Treating trees with verbenone would not appear to make the trees any less attractive to the beetle than an unbaited tree. It may, however, make them (and the trees within a 5-m radius) less attractive than a recently attacked tree and thereby reduce mass attack, hence tree mortality, in a treated stand. These results support previous findings that verbenone reduces the number of mass-attacked trees in stands (Amman et al., 1989; Lindgren et al., 1989). In our study no trees baited with verbenone were mass attacked. Acknowledgments--We appreciate the technical assistance of R.E. Betts and D.A. Linton in establishing and assessing this experiment. Research supported in part by Science Council of British Columbia grant 28 to B.S.L.

REFERENCES AMMAN, G.D., THIER, R.W., MCGREGOR, M.D., and SCHMITZ, R.F. 1989. Efficacy of verbenone in reducing lodgepole pine infestation by mountain pine beetles in Idaho. Can. J. For. Res. 19:60-64. BAKKE, A. 1981. Inhibition of the response in lps typographus to the aggregation pheromone; field evaluation of verbenone and ipsenol. Z. Angew. Entomol. 92:172-177.

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infestations in lodgepole pine forests. Canadian Forest Service, Pacific Forest Research Centre, Information Report BC-X-276. PAYNE, T.L., COSTER, J.E., RICHERSON, J.V., EDSON, L.J., and HART, E.R. 1978. Field response of the southern pine beetle to behavioral chemicals. Environ. Entomol. 7:578-582. PITMAN, G.B. 1971. trans-Verbenol and alpha-pinene: Their utility in manipulation of the mountain pine beetle. J. Econ. Entomol. 64:426-430. PITMAN,G.B., VIT~, J.P., KINZER, G.W., and FENTIMAN,A.F., JR. 1968. Bark beetle attractants: trans-V erbenol isolated from Dendroctonus. Nature 218:168-169. PITMAN, G.B., VIT~, J.P., KINZER, G.W., and FENTIMAN,A.F., JR. 1969. Specificity of populationaggregating pheromones in Dendroctonus. J. Insect. Physiol. 15:363-366. RENWICK, J.A.A. 1967. Identification of two oxygenated terpenes from the bark beetles Dendroctonus frontalis and Dendroctonus brevicomis. Boyce Thompson Inst. 23:355-360. RENWICK, J.A.A., and VIT~, J.P. 1970. Systems of chemical communication in Dendroctonus. Boyce Thompson Inst. 24:283-292. R1CHERSON, J.V., and PAYNE, T.L. 1979. Effects of bark beetle inhibitors on landing and attack behavior of the southern pine beetle and beetle associates. Environ. Entomol. 8:360-364. RUDINSKY, J.A., MORGAN, M.E., LIBBY, L.M., and PUTNAM, T.B. 1974. Antiaggregative rivalry pheromone of the mountain pine beetle, and a new arrestant of the southern pine beetle. Environ. Entomol. 3:90-98. RYKER, L.C., and RUDINSKY, J.A. 1982. Field bioassay of exo-and endo-brevicomin with Dendroctonus ponderosae in lodgepole pine. J. Chem. Ecol. 8:701-707. RYKER, L.C., and YANDELL, K.L. 1983. Effects of verbenone on aggregation of Dendroctonus ponderosae Hopkins (Coleoptera, Scolytidae) to synthetic attractant. Z. Angew. Entomol. 96:452-459. SAFRANYIK,L. 1988. Estimating attack and brood totals and densities of the mountain pine beetle in individual lodgepole pine trees. Can. Entomol. 120:323-331. SAFRANYIK,L., SHRIMPTON,D.M., and WHITNEY,H.S. 1974. Management of lodgepole pine to reduce losses from the mountain pine beetle. Environment Canada, Canadian Forest Service, Forest Technical Report 1. SAS Institute, Inc. 1985. SAS Users Guide: Statistics, Version 5 Edition. SAS Institute, Inc., Cary, North Carolina. SCrfLYTER, R., BYERS, J.A., LOFQVlST, J., LEUFVEN, A., and BIRGERSSON,G. 1988. Reduction of attack density of the bark beetles Ips typographus and Tomicus on host bark by verbenone inhibition of attraction to pheromone and host kairomone, pp. 53-63 in T.L. Payne and H. Saarenmaa (eds.). Proceedings of the IUFRO Working Party and XVIII International Congress of Entomological Symposium, "Integrated Control of Scolytid Bark Beetles." Vancouver, British Columbia, Canada. SCHMITZ,R.F., and MCGREGOR, M.D. 1990. Antiaggregative effects of verbenone on response of the mountain pine beetle to baited traps. U.S.D.A. Forest Service, International Research Station, Research Paper INT423. SILVERSTEIN, R.M., BROWNLEE,R.G., BELLAS, T.E., WOOD, D.L., and BROWN, L.E. 1968. Brevicomin: principal sex attractant in the frass of the female western pine beetle. Science 159:889891. VAN SICKLE,G.A. 1989. Status of mountain pine beetle in western Canada, 1988, pp. 6-8, in G.D. Amman (ed.). Proceedings--Symposium on the Management of Lodgepole Pine to Minimize Losses to the Mountain Pine Beetle. U.S.D.A. Forest Service, International Research Station, General Technical Report INT-262. WATTERSON,G.P., PAYNE, T.L., and RICHERSON, J.V. 1981. The effects of verbenone and brevicomin on the within-tree populations ofDendroctonusfrontalis. J. Ga. Entomol. Soc. 17:119126.

The response of mountain pine beetle (Dendroctonus ponderosae) to lodgepole pine trees baited with verbenone and exo-brevicomin.

exo-brevicomin, a multifunctional pheromone of the mountain pine beetle,Dendroctonus ponderosae, was tested at release rates of 0.5 and 2.5 mg/day alo...
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