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Oxidation products of terpenes identified from Dendroctonus and Ips bark beetles
J. Insect Physiol., 1916, Vol. 22, pp. 125 to 127. Pergamon Press. Printed in Great Britain.
OXIDATION PRODUCTS OF TERPENES IDENTIFIED FROM DENDROCTONUS AND IPS BARK BEETLES J. A. A. RENWICK, P. R. HUGHES, G. B. PITMAN, and J. P. VITB* Boyce Thompson
Institute,
Yonkers,
N.Y. 10701, U.S.A.
(Received 29 October 1975) of adult males and females of Dendroctonus brevicomis and D. fvontalis to camphene vapor resulted in oxidation of the terpene to a prominent product, which was identified as 6-hydroxycamphene (camphenol). Exposure of D. breuicomis adults to myrcene vapor resulted in sex-specific oxidation of the hydrocarbon. A major product in both sexes was identified as 2-methyl-6-methylene-2,7-octadien-l-01 (myrcenol), whereas ipsdienol, a major product in males, was not detected in females. A compound detected in hindguts of feeding males of Ips pini and I. paraconjiisus was attributed to the presence of 3-carene in the host (Pinus spp.) and subsequently identified as 1-methyl-5-(a-hydroxyisopropyl)-cyclohexa-1,3-diene.
Abstract-Exposure
comis and I. paraconfusus), P. contorta Dougl. (I. pini), or P. taeda L. (0. fiontalis). Both sexes of D. brevicomis and D. j?ontalis were exposed to camphene vapor and D. brevicomis to myrcene as previously described (RENWICK et al., 1973). Males of the Ips species were exposed to individual terpenes in the same manner or were allowed to feed for a period of 48 hr in ponderosa pine billets. After the specified treatments, the beetles’ hindguts were removed, stored at -7o”C, and subsequently extracted with ethyl ether. Gas chromatography of the extracts was performed on a Varian 1200 with a loft x l/8 in. o.d. stainless steel column packed with 15% FFAP on 60/80 Chromosorb W. For preparative gas chromatography, a Varian Aerograph model 700 was used, and the column was 6 ft x 1/4in. o.d. stainless steel packed with loo/, Carbowax 20M on 70180 Varaport 30. Mass spectra were obtained with a Hitachi-PerkinElmer RMU-6E coupled to a Varian Aerograph model 204 gas chromatograph, and U.V. spectra were run in hexane solution using a Cary model 15. Infrared spectra were obtained in Ccl4 solution with a Perk&Elmer 221, and the NMR spectra were run in Ccl4 or CDC13 solution using a micro cell in a Jeol C-60 HL, with TMS as an internal standard.
INTRODUCITON THE MASS aggregation
of pine bark beetles on their host trees is known to be triggered and mediated by pheromones released by the attacking beetles. The biosynthesis of some of these pheromones can be directly related to contact with host oleoresin, and exposure of beetles to vapors of individual monoterpene components of the resin can result in the production of the pheromones and related compounds (HUGHES, 1973a, b; 1974). Analysis of hindgut volatiles from several Dendroctonus and Ips species collected during their mass attack on pines has revealed the presence of unknown compounds which were not detected before contact with host resin. One such compound detected in both D. brevicomis LeConte and D. frontalis Zimm. could be attributed to the presence of camphene in the resin. Exposure of emergent males of D. brevicomis to myrcene has been shown to result in the production of ipsdienol (I) (HUGHES, 1973b), but a major product in both sexes was not identified. Gas chromatographic studies on the hindgut contents of feeding males of Ips paracon&sus Lanier and I. pini Say revealed the presence of an unknown compound common to both species which could be related to resin exposure of the beetles. The purpose of this study was to identify the two major products associated with exposure of these bark beetles to camphene and myrcene, and the compound detected in Ips. MATERIALS
RESULTS Gas chromatography of the hindgut volatiles from camphene-exposed beetles indicated the presence of a major product in both D. brevicomis and D. jkontalis. The identity of this compound in male and female samples of both species was confirmed by mass spectrometry, so that the need for separation of the sexes was eliminated. Since greater supplies of emergent D.@ontalis were available at the time, this species was used for the characterization work. Preparative gas chromatography of an extract of 5000
AND METHODS
Beetles .were collected as they emerged from infested log sections of Pinus ponderosa Laws (D. brevi* Present address: sitlt,
Freiburg,
Forstzoologisches Institut 78 Freiburg i. Br., Germany.
der Univer725
126
J. A. A. RENWICK,P. R. HUGHES,G. B. PITMAN,AND
J. P. VIT&
hindguts yielded about 2mg of the material, which crystallized in the collection tube. The mass spectrum of the unknown indicated a mol. wt of 152, and fragments at m/e 137 (P-CH,) and 134 (P-H20) suggested a terpene alcohol structure. The base peak was at m/e 108 with major fragments at m/e 93 (77%), 91 (44%) 41 (31%) 77 (27%), 67 (23%) 39 (23%) 109 (23%), 107 (22%) and 79 (21%). A small parent ion peak (3%) was present. The i.r. spectrum showed diagnostic peaks at 36OOcm- ’ (OH), 2960cm-’ (C-H), 3070 and 1656cm-’ (C=C), with other prominent peaks at 1050, 977, and 886cm-I. The presence of an exocyclic methylene group was suspected from the i.r. spectrum and confirmed by the NMR spectrum, which exhibited sharp peaks at 7 = 4.85 and 4.65. The NMR spectrum further suggested the presence of the basic camphene structure. with neaks at z = 2.62 and 1.72 (bridgehead protons),’ 1.04 and 0.97 (CH,), and a complex peak centered at z = 3.70 (H-C-O).
15 Time,
IO
min
of hindgut volatiles from Ips 48 hr feeding and (b) after hr exposure to 3-carene. The unknown compound is indicated by an arrow.
Fig. 1. Gas chromatograms
paruconfisusmales (a) after 20 I
II
m
lx
The spectral data were in close agreement with those of RICHEY et al. (1964) for camphenol. This compound was previously synthesized by TISHCHENKO (1953) but the original structure assignment was challenged by RICHEY et al. (1964) who determined the most likely structure to be that of 6-hydroxy-camphene (II). Synthesis of camphenol according to the method of TISHCHENKO (1953) yielded a product which had spectral and gas chromatographic properties identical to those of the natural material. Comparative gas chromatographic analyses of D. breuicornis male and female kindgut samples after exposure of the beetles to myrcene vapor indicated that ipsdienol was produced by the males only. However, a major compound with a much longer retention time than ipsdienol was present in both sexes. The mass spectra of this component from male and female samples were identical, so samples collected by preparative gas chromatography of separate male and female extracts could be combined. Hindguts from 3000 males and 2000 females yielded approximately 2mg of the compound. The mass spectrum of the purified material showed the following diagnostic peaks: m/e 152 (P), 134 (P-H,O), and 119 (P-33). The base peak was at m/e 43, with other prominent fragments at m/e 41 (81%) 93 (72%), 39 (58%) and 79 (51%). The i.r. spectrum had significant peaks at 3590 (OH), 1591 (conjugated C=C), 1373, 991, and 894 cm- ‘. The U.V. spectrum in hexane solution had an absorption maximum at 224 nm.
The spectral data, along with the gas chromatographic retention time, suggested a primary terpene alcohol with conjugated double bonds. The most likely structure was considered to be that of 2-methyl-6-methylene-2,7-octadien-l-01 (III), which is presumably the ‘myrcenol’ described, but not identified by DELABV and DUPIN (1938). This alcohol was synthesized by selenium dioxide oxidation of myrcene according to the method of B&HI and WUEST (1967) and the chromatographic, as well as the spectral characteristics, matched those of the natural material. Combined gas chromatography-mass spectrometry of hindgut extracts from feeding male 1. puruconfkus and I. pini confirmed the identity of the unknown compound produced by both of these species. Gas chromatograms of hindgut volatiles from beetles exposed to a-pinene, myrcene, 3-carene, and limonene showed that a prominent product with the retention time of the unknown was obtained with the 3carene treatment (Fig. 1). The mass spectrum of this product also matched that of the compound detected in feeding beetles. For further analysis, 8000 I. pini males were exposed to 3-carene to obtain about 2 mg of the product. The mass spectrum of the compound indicated a mol. wt of 152, with fragments at m/e 134 and 137 suggesting a terpene alcohol structure. The base peak in the mass spectrum was at m/e 59, with other major fragments at m/e 94 (99%) 79 (73x), 91 (59%) 93 (54%) 43 (43%) 77 (42%) 39 (23%), 41 (23%) 31 (20%), and 119 (20%). The i.r. spectrum had character-
121
Oxidation products of terpenes
istic peaks at 1655 and 1597 cm- 1 conjugated c--C), 3610 and 342Ocm-’ (OH), and 724 and 687cn-’ (C=C, cis). The U.V.spectrum had an absorption maximum at 265 nm, confirming the presence of conjugated double bonds. The NMR spectrum showed a singlet at z = 8.86 (6 protons = 2 CH,), also at z = 8.24 (3 protons = 1 CH, on a double bond), and a multiplet centered at z = 4.40 (3 vinyl protons). The spectral data were consistent with a menthadienol structure. Comparison with an authentic sample of 1-methyl-4-(a-hydroxyisopropyl)-cyclohexa2,6-diene led to the conclusion that the beetleproduced compound was likely to be l-methyl-5-(clhydroxyisopropyl)-cyclohexa-1,3-diene (IV). The compound was synthesized by photochemical oxidation of 3-carene to 2caren-puns-4-01 (&LLNICK et al., 1965) followed by an acid-catalyzed rearrangement (GOLLNICKet al., 1966). The spectral and gas chromatographic properties of the synthetic material proved to be identical to those of the natural substance. DISCUSSION The metabolism of camphene by D. frontalis and D. brevicomis appears to involve oxidation to the same major product by both sexes. The oxidation of myrcene by D. brevicomis, however, further demonstrates the existence of sex-specific systems for the metabolism of terpenes by bark beetles. Both sexes are capable of producing myrcenol (III) and other oxygenated derivatives, but ipsedienol (I) has been found in males only. Previous studies have revealed similar sex related differences in terpene metabolism by species of Dendroctonus and Ips. The oxidation of 3-carene by Ips paraconfusus and I. pini represents the first confirmed case of ring cleavage during the oxidation of terpenes by bark beetles, although several examples of rearrangements have been observed (RENWICKand HUGHES,1975). To our knowledge, none of the alcohols identified has previously been found in nature, and their possibIe biological significance in bark beetles is presently under study.
Ackrlowfedgements-We are indebted to Dr. HERMAN G. RICHEY,Jr., Department of Chemistry, Pennsylvania State
University, for providing spectral data on camphenol; and to Dr. E. KLEIN, Dragoco, Holzminden, Germany, for supplying a sample of 1-methyl-4-(cc-hydroxyisopropyl)~cyclohexa-2,6-diene. The work was supported in part by NSF Grant BMS 73-01599.
REFERENCES BYJCHIG. und WRIESTJ. (1967) Eine Synthese des betaSinensals. Helv. chim. Acta 50, 2440-2445. DELABYR. and DUPIN E. (1938) Myrcenal and myrcenols. ButI. Sue. chim. Fr. 5, 931-938. GOLLNICKK., SCHADE G., und SCHROETER S. (1966) Studien in der Carenreihe-IV iiber die Umlagerung Von (5S)-l(-) (IR:4S:6S)-A*-caren-trans-4-01 in (-) methyl-S-(cc-hydroxyisopropyl)-cyclohexa-1,3-dien. Tetrahedron 22, 139-144. GOLLNICKK., SCHROETER S., OHLOFFG., SCHADEG., und SC~~NCK G. 0. (1965) Zur photosensibilisierten 0,Ubertragung auf I+)-Caren-(3). J. Liebias Ann. Chem. ” 687, 14-25- ’ HUGHESP. R. (1973a) Effect of alpha-pinene exposure on trans-verbenol synthesis in Dendroctonus ponderosae Hopk. Naturwissenshaften 60, 261-262. HUGHESP. R. (1973b) Dendroctonus: Production of pheromones and related compounds in response to host monoterpenes. Z. angew. Ent. 73, 294312. HUGHESP. R. (1974) Myrcene: A precursor of pheromones in lps beetles. J. Insect Physiol. 20, 1271-1275. RENWICKJ. A. A. and HUGHESP. R. (1975) Oxidation of unsaturated cyclic hydrocarbons by Dendroctonusfrontalis. Insect Biochem. 5, 459-463. RENWICKJ. A. A., HUGHESP. R., and TY T. DEJ. (1973) Oxidation products of pinene in the bark beetle, Dendroctonus frontalis. J. Insect Physiol. 19, 173% 1740. RICHEYH. G., Jr., GARBACIKT. J., DULL D. I,., and GRANT J. E. (1964). Monochloro products from camphene. Identification of camphenol as 6-hydroxycamphene. J. org. them. 29, 3095-3097. TISHCHENKO D. (1953) New type of transformations of terpenes. XIV. Reaction of chlorine with camphene. J. gen. Chem. USSR 23, 1051-1060.
OXIDATION PRODUCTS OF TERPENES IDENTIFIED FROM DENDROCTONUS AND IPS BARK BEETLES J. A. A. RENWICK, P. R. HUGHES, G. B. PITMAN, and J. P. VITB* Boyce Thompson
Institute,
Yonkers,
N.Y. 10701, U.S.A.
(Received 29 October 1975) of adult males and females of Dendroctonus brevicomis and D. fvontalis to camphene vapor resulted in oxidation of the terpene to a prominent product, which was identified as 6-hydroxycamphene (camphenol). Exposure of D. breuicomis adults to myrcene vapor resulted in sex-specific oxidation of the hydrocarbon. A major product in both sexes was identified as 2-methyl-6-methylene-2,7-octadien-l-01 (myrcenol), whereas ipsdienol, a major product in males, was not detected in females. A compound detected in hindguts of feeding males of Ips pini and I. paraconjiisus was attributed to the presence of 3-carene in the host (Pinus spp.) and subsequently identified as 1-methyl-5-(a-hydroxyisopropyl)-cyclohexa-1,3-diene.
Abstract-Exposure
comis and I. paraconfusus), P. contorta Dougl. (I. pini), or P. taeda L. (0. fiontalis). Both sexes of D. brevicomis and D. j?ontalis were exposed to camphene vapor and D. brevicomis to myrcene as previously described (RENWICK et al., 1973). Males of the Ips species were exposed to individual terpenes in the same manner or were allowed to feed for a period of 48 hr in ponderosa pine billets. After the specified treatments, the beetles’ hindguts were removed, stored at -7o”C, and subsequently extracted with ethyl ether. Gas chromatography of the extracts was performed on a Varian 1200 with a loft x l/8 in. o.d. stainless steel column packed with 15% FFAP on 60/80 Chromosorb W. For preparative gas chromatography, a Varian Aerograph model 700 was used, and the column was 6 ft x 1/4in. o.d. stainless steel packed with loo/, Carbowax 20M on 70180 Varaport 30. Mass spectra were obtained with a Hitachi-PerkinElmer RMU-6E coupled to a Varian Aerograph model 204 gas chromatograph, and U.V. spectra were run in hexane solution using a Cary model 15. Infrared spectra were obtained in Ccl4 solution with a Perk&Elmer 221, and the NMR spectra were run in Ccl4 or CDC13 solution using a micro cell in a Jeol C-60 HL, with TMS as an internal standard.
INTRODUCITON THE MASS aggregation
of pine bark beetles on their host trees is known to be triggered and mediated by pheromones released by the attacking beetles. The biosynthesis of some of these pheromones can be directly related to contact with host oleoresin, and exposure of beetles to vapors of individual monoterpene components of the resin can result in the production of the pheromones and related compounds (HUGHES, 1973a, b; 1974). Analysis of hindgut volatiles from several Dendroctonus and Ips species collected during their mass attack on pines has revealed the presence of unknown compounds which were not detected before contact with host resin. One such compound detected in both D. brevicomis LeConte and D. frontalis Zimm. could be attributed to the presence of camphene in the resin. Exposure of emergent males of D. brevicomis to myrcene has been shown to result in the production of ipsdienol (I) (HUGHES, 1973b), but a major product in both sexes was not identified. Gas chromatographic studies on the hindgut contents of feeding males of Ips paracon&sus Lanier and I. pini Say revealed the presence of an unknown compound common to both species which could be related to resin exposure of the beetles. The purpose of this study was to identify the two major products associated with exposure of these bark beetles to camphene and myrcene, and the compound detected in Ips. MATERIALS
RESULTS Gas chromatography of the hindgut volatiles from camphene-exposed beetles indicated the presence of a major product in both D. brevicomis and D. jkontalis. The identity of this compound in male and female samples of both species was confirmed by mass spectrometry, so that the need for separation of the sexes was eliminated. Since greater supplies of emergent D.@ontalis were available at the time, this species was used for the characterization work. Preparative gas chromatography of an extract of 5000
AND METHODS
Beetles .were collected as they emerged from infested log sections of Pinus ponderosa Laws (D. brevi* Present address: sitlt,
Freiburg,
Forstzoologisches Institut 78 Freiburg i. Br., Germany.
der Univer725
126
J. A. A. RENWICK,P. R. HUGHES,G. B. PITMAN,AND
J. P. VIT&
hindguts yielded about 2mg of the material, which crystallized in the collection tube. The mass spectrum of the unknown indicated a mol. wt of 152, and fragments at m/e 137 (P-CH,) and 134 (P-H20) suggested a terpene alcohol structure. The base peak was at m/e 108 with major fragments at m/e 93 (77%), 91 (44%) 41 (31%) 77 (27%), 67 (23%) 39 (23%) 109 (23%), 107 (22%) and 79 (21%). A small parent ion peak (3%) was present. The i.r. spectrum showed diagnostic peaks at 36OOcm- ’ (OH), 2960cm-’ (C-H), 3070 and 1656cm-’ (C=C), with other prominent peaks at 1050, 977, and 886cm-I. The presence of an exocyclic methylene group was suspected from the i.r. spectrum and confirmed by the NMR spectrum, which exhibited sharp peaks at 7 = 4.85 and 4.65. The NMR spectrum further suggested the presence of the basic camphene structure. with neaks at z = 2.62 and 1.72 (bridgehead protons),’ 1.04 and 0.97 (CH,), and a complex peak centered at z = 3.70 (H-C-O).
15 Time,
IO
min
of hindgut volatiles from Ips 48 hr feeding and (b) after hr exposure to 3-carene. The unknown compound is indicated by an arrow.
Fig. 1. Gas chromatograms
paruconfisusmales (a) after 20 I
II
m
lx
The spectral data were in close agreement with those of RICHEY et al. (1964) for camphenol. This compound was previously synthesized by TISHCHENKO (1953) but the original structure assignment was challenged by RICHEY et al. (1964) who determined the most likely structure to be that of 6-hydroxy-camphene (II). Synthesis of camphenol according to the method of TISHCHENKO (1953) yielded a product which had spectral and gas chromatographic properties identical to those of the natural material. Comparative gas chromatographic analyses of D. breuicornis male and female kindgut samples after exposure of the beetles to myrcene vapor indicated that ipsdienol was produced by the males only. However, a major compound with a much longer retention time than ipsdienol was present in both sexes. The mass spectra of this component from male and female samples were identical, so samples collected by preparative gas chromatography of separate male and female extracts could be combined. Hindguts from 3000 males and 2000 females yielded approximately 2mg of the compound. The mass spectrum of the purified material showed the following diagnostic peaks: m/e 152 (P), 134 (P-H,O), and 119 (P-33). The base peak was at m/e 43, with other prominent fragments at m/e 41 (81%) 93 (72%), 39 (58%) and 79 (51%). The i.r. spectrum had significant peaks at 3590 (OH), 1591 (conjugated C=C), 1373, 991, and 894 cm- ‘. The U.V. spectrum in hexane solution had an absorption maximum at 224 nm.
The spectral data, along with the gas chromatographic retention time, suggested a primary terpene alcohol with conjugated double bonds. The most likely structure was considered to be that of 2-methyl-6-methylene-2,7-octadien-l-01 (III), which is presumably the ‘myrcenol’ described, but not identified by DELABV and DUPIN (1938). This alcohol was synthesized by selenium dioxide oxidation of myrcene according to the method of B&HI and WUEST (1967) and the chromatographic, as well as the spectral characteristics, matched those of the natural material. Combined gas chromatography-mass spectrometry of hindgut extracts from feeding male 1. puruconfkus and I. pini confirmed the identity of the unknown compound produced by both of these species. Gas chromatograms of hindgut volatiles from beetles exposed to a-pinene, myrcene, 3-carene, and limonene showed that a prominent product with the retention time of the unknown was obtained with the 3carene treatment (Fig. 1). The mass spectrum of this product also matched that of the compound detected in feeding beetles. For further analysis, 8000 I. pini males were exposed to 3-carene to obtain about 2 mg of the product. The mass spectrum of the compound indicated a mol. wt of 152, with fragments at m/e 134 and 137 suggesting a terpene alcohol structure. The base peak in the mass spectrum was at m/e 59, with other major fragments at m/e 94 (99%) 79 (73x), 91 (59%) 93 (54%) 43 (43%) 77 (42%) 39 (23%), 41 (23%) 31 (20%), and 119 (20%). The i.r. spectrum had character-
121
Oxidation products of terpenes
istic peaks at 1655 and 1597 cm- 1 conjugated c--C), 3610 and 342Ocm-’ (OH), and 724 and 687cn-’ (C=C, cis). The U.V.spectrum had an absorption maximum at 265 nm, confirming the presence of conjugated double bonds. The NMR spectrum showed a singlet at z = 8.86 (6 protons = 2 CH,), also at z = 8.24 (3 protons = 1 CH, on a double bond), and a multiplet centered at z = 4.40 (3 vinyl protons). The spectral data were consistent with a menthadienol structure. Comparison with an authentic sample of 1-methyl-4-(a-hydroxyisopropyl)-cyclohexa2,6-diene led to the conclusion that the beetleproduced compound was likely to be l-methyl-5-(clhydroxyisopropyl)-cyclohexa-1,3-diene (IV). The compound was synthesized by photochemical oxidation of 3-carene to 2caren-puns-4-01 (&LLNICK et al., 1965) followed by an acid-catalyzed rearrangement (GOLLNICKet al., 1966). The spectral and gas chromatographic properties of the synthetic material proved to be identical to those of the natural substance. DISCUSSION The metabolism of camphene by D. frontalis and D. brevicomis appears to involve oxidation to the same major product by both sexes. The oxidation of myrcene by D. brevicomis, however, further demonstrates the existence of sex-specific systems for the metabolism of terpenes by bark beetles. Both sexes are capable of producing myrcenol (III) and other oxygenated derivatives, but ipsedienol (I) has been found in males only. Previous studies have revealed similar sex related differences in terpene metabolism by species of Dendroctonus and Ips. The oxidation of 3-carene by Ips paraconfusus and I. pini represents the first confirmed case of ring cleavage during the oxidation of terpenes by bark beetles, although several examples of rearrangements have been observed (RENWICKand HUGHES,1975). To our knowledge, none of the alcohols identified has previously been found in nature, and their possibIe biological significance in bark beetles is presently under study.
Ackrlowfedgements-We are indebted to Dr. HERMAN G. RICHEY,Jr., Department of Chemistry, Pennsylvania State
University, for providing spectral data on camphenol; and to Dr. E. KLEIN, Dragoco, Holzminden, Germany, for supplying a sample of 1-methyl-4-(cc-hydroxyisopropyl)~cyclohexa-2,6-diene. The work was supported in part by NSF Grant BMS 73-01599.
REFERENCES BYJCHIG. und WRIESTJ. (1967) Eine Synthese des betaSinensals. Helv. chim. Acta 50, 2440-2445. DELABYR. and DUPIN E. (1938) Myrcenal and myrcenols. ButI. Sue. chim. Fr. 5, 931-938. GOLLNICKK., SCHADE G., und SCHROETER S. (1966) Studien in der Carenreihe-IV iiber die Umlagerung Von (5S)-l(-) (IR:4S:6S)-A*-caren-trans-4-01 in (-) methyl-S-(cc-hydroxyisopropyl)-cyclohexa-1,3-dien. Tetrahedron 22, 139-144. GOLLNICKK., SCHROETER S., OHLOFFG., SCHADEG., und SC~~NCK G. 0. (1965) Zur photosensibilisierten 0,Ubertragung auf I+)-Caren-(3). J. Liebias Ann. Chem. ” 687, 14-25- ’ HUGHESP. R. (1973a) Effect of alpha-pinene exposure on trans-verbenol synthesis in Dendroctonus ponderosae Hopk. Naturwissenshaften 60, 261-262. HUGHESP. R. (1973b) Dendroctonus: Production of pheromones and related compounds in response to host monoterpenes. Z. angew. Ent. 73, 294312. HUGHESP. R. (1974) Myrcene: A precursor of pheromones in lps beetles. J. Insect Physiol. 20, 1271-1275. RENWICKJ. A. A. and HUGHESP. R. (1975) Oxidation of unsaturated cyclic hydrocarbons by Dendroctonusfrontalis. Insect Biochem. 5, 459-463. RENWICKJ. A. A., HUGHESP. R., and TY T. DEJ. (1973) Oxidation products of pinene in the bark beetle, Dendroctonus frontalis. J. Insect Physiol. 19, 173% 1740. RICHEYH. G., Jr., GARBACIKT. J., DULL D. I,., and GRANT J. E. (1964). Monochloro products from camphene. Identification of camphenol as 6-hydroxycamphene. J. org. them. 29, 3095-3097. TISHCHENKO D. (1953) New type of transformations of terpenes. XIV. Reaction of chlorine with camphene. J. gen. Chem. USSR 23, 1051-1060.