14 Chemoecology 3 (1992) 14-18

Orientation of grandis (Coleoptera: Rhizophagidae) to oxygenated monoterpenes in a species-specific predator-prey relationship

Jean-Claude Gr6goire 1, Daniel Couillien ~, Ralph Krebber 2, Winfried A. K6nig z, Holger Meyer 2, and Wittko Francke 2 1 Laboratoire de Biologie animale et cellulaire, CP 160, Section interfacultaire d'Agronomie, Universit6 Libre de Bruxelles, 50 av. F. D. Roosevelt, B-1050 Bruxelles, Belgium 2 Institut for Organische Chemie, Universit~it Hamburg, Martin-Luther-King-Platz 6, D-2000 Hamburg 13, Federal Republic of Germany

Received July 14, 1991 / Revision accepted September 28, 1991

Summary some of the components (fenchol, terpinene-4-ol and bor- neol) did not influence the predators' response. However, The predator, Rhizophagus grandis, is linked the addition of (-)-a-terpineol increased the attractivity of to its specific prey, , by semiochemical the synthetic blend to almost that of larval frass of the prey. signals regulating oviposition and long range orientation. A Ecological implications of the identified semiochemicals and mixture of simple oxygenated monoterpenes [(-)-fenchone, their use in pest management are discussed. (-)-pinocamphone, rac. camphor, terpinene-4-ol, borneol, fenchol and verbenone], identified from the frass of D: mi- cans has been found to be extremely active in a flight wind- Key words tunnel as a long-range attractant for the predator. The mix- ture elicited 84 07o of the response to larval frass of the prey. specificity, predation, long-range orientation, Excluding pinocamphone from the mixture did not influence windtunnel, Coleoptera, Rhizophagidae, Scolytidae, Rhizo- its activity. Also, changing the absolute configurations of phagus grandis, Dendroctonus micans

Introduction comparative analysis of the larval frass of D. micans and of a North American species, D. valens (normally out of R. gran- Rhizophagus grandis Gyll. has been described dis's geographic rang e but eliciting high oviposition of R. since the beginning of this century as a specific predator, at- grandis in laboratory tests), resulted in the identification of 7 tacking exclusively the Eurasian greater , Den- simple oxygenated monoterpenes generated by the larvae of droctonus micans (Kug.) (Bergmiller t903; Francke-Gros- both bark beetle species: (-)-fenchone, pinocamphone, cam- mann 1954; Kobakhidze 1965; Gr6goire 1988). phor, terpinene-4-ol, borneol, fenchol and verbenone (Gr6- goire et al. 1991). Bioassays showed that a mixture of these One striking feature of this specific associa- compounds strongly induced oviposition. tion is the particularly high capacity of R. grandis to discover its prey. For instance, in Belgium, about 90°7o of the prey's We have now completed our investigations on brood chambers contain predators, even though D. micans is the enantiOmeric compositions of the natural compounds and quite sparse, with usually less than 4 brood chambers/hectare we present our results obtained by testing the same blend as a (Gr6goire 1984). This spectacular capacity for prey location long-range attractant for R. grandis. has been attributed to the predator's perception of, and re- sponse to still unknown volatile components of the larval Materials and methods frass of D. micans (Tondeur & Gr6goire 1980). To our knowl- Chemical analyses and synthetic compounds edge, long-range attractants for Rhizophagidae have only been described for R. depressus (F.) and R. ferrugineus Enantiomeric separations of oxygenated mo- (Payk.) which respond to a 10:1 mixture of ethanol and a- noterpenes were carried out by gas chromatography using cy- pinene (Schroeder & Linde16w 1989). clodextrins as stationary phases. Determination of enantiom- eric purity of commercially available (+)-terpinen-4-ol and An important aspect of the specific link be- (-)-ceterpineol was achieved by transformation to the tri- tween R. grandis and D. micans is oviposition in response to fluoroacetates and separation on a 30 m, 0.25 mm i.d. fused specific chemical signals issued by the prey larvae. Recently, a silica capillary coated with octakis-(3-0-butyryl-2,6-di-0-pen- tyl)-y-cyelodextrin (LipodexE) (KOnig et al. 1989) at 100°C. Enantiomers of all other terpenes were separated without der- © Georg Thieme Verlag Stuttgart. New York ivatization under isothermal conditions using a 30 m, 0.25 Orientation of R. grandis in a windtunnel Chemoecology 3 (1992) 15

Table 1 Source,chemical purity, enantiomeric excess (% ee) and rotation value of monoterpenesused in bioassays

3ompound Source Chemical Enantiomenc [a]d 2° Purity Excess (% ee)

[-)-Fenchone Fluka 97% 80 -54.70 (c=2.51; EtOH) ac. Camphor Ndrich 99% [-)-Verbenone Bedoukian 98% 70 -172.8 ° (c=2.52; EtOH) ',-)-Isopinocamphone a) 98% 98 -12.5 ° (c=1.43; EtOH) [-)-Pinocamphone a) 98% 98 -23.8 ° (c=0.47; EtOH) ',+)-Fenchol Aldrich 89% 85 +9.7 o (c=2.01; EtOH) [-)-Fenchol b) 98% 96 -12.9 ° (c=1.30; EtOH) ù-)-Borneol Fluka 80% 85 -18.20 (c=2.43; EtOH) ',+)-Terpinene-4-ol Merck 95% 35 +10.2 o (c=0.99; EtOH) ù-)-~-Terpineol Merck 98% 91 -93.80 (c=1.36; EtOH) a) Zweifel & Brown (1964) b) Beckmann & Metzger (1956)

Blend c. Identical to blend b, but racemic ter- pinene-4-ol, (-)-fenchol, racemic borneol, have been replaced ~o ~o .ao~O4~O by (+)-terpinene-4-ol, (+)-fenchol and (S)-(-)-borneol. Blend d. Identical to blend c plus an addition- 1 2 3 4 5 a], equal part of «-terpineol, a component also present in no- ticeable amounts in the natural frass of D. mieans (Grégoire et al. 1991). ~o~ ~où ~où ~où Bioassays The windtunnel used in our experiments is 6 7 8 9 2 m long, 1.2 m high and 0.6 m wide. The 'floor', 'ceiling' and lateral sides are made of 6 mm glass plates mounted on a Fig. 1 Structures of oxygenated monoterpenes identified from frass steel frame, with sliding plates on the lateral sides allowing of Dendroctonus micans larvae: 1 (-)-fenchone, 2 camphor, 3 verbe- easy access to every part of the arena. The two end panels none, 4 (-)-isopinocamphone, 5 (-)-pinocamphone, 6 (+)-fenchol, are made of Tergal gauze fixed on a removable frame. Air 7 (-)-borneol, 8 terpinen-4-ol, 9 G-terpineol is pushed into the windtunnel by an electric fan at a speed of 0.02-0.08 m/s as measured with a bot wire anemometer mm i.d. capillary with oktakis-(3-0-acetyl-2,6-di-0-pentyl)-7- (Testoven 4200). Before reaching the test arena, the airflow cyclodextrin as stationary phase: camphor, fenchone, isopino- passes through a 1.5 cm thick layer of activated carbon, then camphone and pinocamphone were separated at 100 °C, bor- through a 1.3 cm thick beehive structure (dimensions of the neol and fenchol at 110°C and verbenone at 140°C. Source, cells: 1.3 × 1.3 cm) Having passed this structure, the airflow is chemical purity, enantiomeric excess and rotation value of laminar, as checked during preliminary tests with ammonium compounds used in bioassays are shown in Table 1. The corre- chtoride 'smoke'. The windtunnel is lit from above by 5 fluo- sponding chemical structures are given in Figure 1. rescent tubes (Phillips, TLD 58W/33).

Gross structures of naturally-occuring oxy- Experimental were produced in the genated monoterpenes have been assigned earlier (Grégoire et laboratory in "oviposition boxes" containing spruce bark al. 1991). Crude pentane extracts of larval frass of D. micans powder, fresh spruce bark, live D. micans larvae and pairs of feeding in the phloem of Picea abies, or of D. valens feeding adult predatôrs (Grégoire et al. 1984). As it was previously in Pinus lambertiana were used for analyses. Using synthetic established that flight ability in Rhizophagus grandis de- samples as references, absolute configurations of the natural creases with the time spent in cold storage at 4-5 °C (about products were determined under the conditions described 8 070 per month, D. Couillien, J.-C. Grégoire in prep.), only 1 above. to 3 months old were used. After sieving the insects under watet (to separate them from their bark powder storage Four blends of synthetic compounds were medium), they were sorted according to sex, and precondi- prepared for bioassays. tioned for 12 h in a Petri dish on moist paper at room temper- ature (20-23 °C) under the windtunnel light. 4 to 13 batches of Blend a. Equal mixtures of racemic terpinene- 50-80 insects were used for each test. Approximately equal 4-ol, (-)-c~-fenchol, (+)/(-)-borneol, (S)-(-)-verbenone, (-)- numbers of male and female batches were tun for each treat- fenchone, racemic camphor, (-)-pinocamphone and of 99 % ment. The same insects were allowed to fly only twice on the pure pentane (Merck). This blend was identical to the one same day in different tests. used in the oviposition tests (Grégoire et al. 1991). Bioassays were run according to the method Blend b. Identicai to blend a, minus (-)-pino- developed by T. Wyatt, A. Phillips, J.-C. Grégoire (in prep.). camphone. The stimuli were released from an artificial, black polyethy- 16 Chemoecology 3 (1992) Grégoire et al.

lene "tree" 9 cm in diameter an 118 cm high, standing 10 cm Table 2 Absolute configuration and enantiomeric excess (% ee) of in front of the air inlet of the test arena, equidistant from oxygenated monoterpenes identified from frass of Dendroctonus mi- both side pannels. The stimuli were deposited on 4 × 6 × 6 cm cans and D. va&ns triangular pieces of blotting paper fixed onto two 50 ml Ep- O. mi¢ans D. va&ns pendorff pipette tips affixed to the "tree" at an angle of 45 °C Compound abs. conf. (% ee) abs. conf. (% ee) and at heights of respectively 20 and 100 cm from the floor. The number and height of the dispensers (pipette tips) was Fenchone (-) 98 (-} 98 previously established in preliminary tests with ammonium Camphor rsc. (+) 50 chloride "smoke" in order to obtain the most homogeneous Verbenone rac. rsc. Isopinocamphone (-) 86 (-) 95 possible distribution of the stimuli over the vertical plane Pinocamphone (-) 91 (-) 96 which included the "tree". For the comparison with natural Fenchol (+) 98 (+) nd* frass, either 130 mg of D. micans larval frass, or 20 ml (14 Borneol (-) 72 (+) 25 mg) of synthetic stimuli (see dose-response results below) were + nd: not determined, due to an interferring compound deposited onto each micropipette tip. The insects were re- leased from a take-off platform situated 100 cm downwind from the "tree" and which consisted in a 10 × 10 cm piece of clearly separated. The absolute configuration of borneol was perspex, roughened with sandpaper and lying horizontally on found to be different in the frass extracts of the two species - top of a 2.6 cm high Petri dish, 9 cm in diameter. A 20 × 32 possibly due to differences in the composition of resins of the cm tray placed under this Petri dish collected all the host material, Picea abies and Pinus lambertiana. The enan- that did not take-off, so that biological respohses were calcu- tiomeric composition of natural terpinen-4-ol and a-terpineol lated only from the insects which did take-off. The insects hit- could not yet be determined. ting the "tree" in response to the attractants fell into a 26 × 40 x 1.5 cm tray, filled with water, where they could be Dose response to the synthetic mixture easily counted. Each tree was used for one single test, then was carefully washed with a detergent (Superdecontamin, In- Doses of blend a ranging from 2.5 ~tl (1.8 mg) tersciences, S. A., Bruxelles) followed by ethanol previous to to 50 ~tl (35 mg) were deposited onto each of the two micropi- any other use. All tests were performed at room temperature pettes on the "tree". A stable response of ca 60 °7o of the flying (20-23 °C). Results are expressed as percentages of flying in- insects was observed for doses above 15 ~tl (Fig. 2). sects hitting the 'tree' and collected in the tray underneath. Synthetic stimuli versus frass Results Chemical analyses Responses to stimuli (measured as a percent- ages of flying hitting the 'tree') are shown in Table 3. As may be seen from Table 2, the enantiomer- The responses to blends a, b, and c were found to be approxi- ic composition of terpene ketones in the frass of D. micans mately 84 %, 86 % and 80 % of the response to frass repsec- and D. valens is very similar, camphor in D. valens showing a tively. The addition of (-)-a-terpineol to blend c resulted in a 3:1 excess of the (+)-enantiomer. (-)-Fenchone shows a par- marked increase of the response (blend d: 97% of the re- ticularly high optical purity, which is also true for its reduc- sponse to frass). tion product, (+)-fenchol, at least in D. micans. Enantiomeric composition of (+)-fenchol in D. valens could not be @ter- Two-way analysis of variance after arcsine mined since another volatile component present in the frass transformation of the data indicated a significant effect of the extract interfered with the elution of the (-)-enantiomer. treatments on the orientation response of the beetles (F = However, the corresponding peak of the (+)-enantiomer was 131.568; p<0.000 with 5 d.f.), but no difference in response

Fig, 2 Dose-response of flying beetles (me- (2) ans - s.e.) to a m]xture of synthetic compo- 70 (4) nents (blend a) in the windtunnel, BO to 80 (4) (4) l beetles were used in each test, Numbers in T • brackets indicate the numbers of repFcates ~+ 60 L for each dose ! I+~;~~- i o +, 1 < 5O o (2) • I-- © 4O Ld (~ Z 30

20 i 10 20 30 40 5O 60 DOSE (/~1 per pTpette tip) Orientation of R. grandis in a windtunnel Chemoecology 3 (1992) 17

Table 3 Response to frass, synthetlc stimuli or a blank polyethylene straints probably change, and the first threat facing the preda- 'tree' in the windtunnel (means:l:s, e.) tors becomes food shortage. This could explain why, once in a proper environment, adults and larvae of R. grandis start be- Treatment Replicates 1 Take-off Responding 2 having as real opportunists, feeding on whatever prey they 2ontrol 4 66.8%+-5.43 5.3%+0.7t (a) 3 meet in the brood chambers and making thus the best possible Synthetic blend a 6 73.2%+6.32 60.4%+1.16 (b) 3 use of every available resource in their restricted universe. Synthetic blend b 4 68.3%-+5.44 61.5%+1,66 (b) a This opportunistic attitude towards feeding has been observed Synthetic blend c 7 61.9%+5.15 57.4%+1,76 (b) 3 in the field where larvae sometimes feed on fungal mycelium 69.5%+1.69 (c) 3 Synthetic blend d 10 69.0%+3.98 (Francke-Grosmann 1954), and in the laboratory where both Frass 13 73.6%-+2.94 71.9%+1.82 (c) 3 adults and larvae accept to feed on a large range of prey, from 1 Average size of each batch tested (+s. e.):65.03-+1.95 insects D. micans to Calliphora maggots, cockroaches and catfood. 2 Calculated as a proportion of the beetles which took oft 3 Means followed by the same letter are not significantly different at Orientation of predators towards semiochem- the a = 0.05 level (Newman-Keuls multiple range test) icals released by their prey and corresponding host-plants is a widespread phenomenon which has also been observed in the relationships between bark beetles and their predators (Wood due to sex (F = 0.708; p = 0.406 with 1 d.f.). Three homoge- et al. 1968; Rice 1969; Vité & Williamson 1970; Pitman & Vité neous groups of stimuli eliciting significantly different average 1971; Dyer 1973; Bakke & Kvamme 1981; Heuer & Vité 1984; responses (~ = 0.05) were determined using a Newman-Keuls Schroeder & Lindelöw 1989). Bark beetle pheromones and range test: i) the control; ii) blends a, b, c, iii) blend d and constituents of their host trees such as monoterpene hydrocar- frass. bons seem to play a major role in prey location by clerid, tro- gositid and ostomid beetles. A similarly intriguing case is that Discussion of the dolichopodid fly, Medetera aldrichii, whose larvae are predators of bark beetle larvae. Host tree-produced c~-pinene Out windtunnel experiments show that the induces the female predators to oviposit under bark scales same small group of chemicals which elicits oviposition in (Fitzgerald & Nagel 1972). In the related M. bistriata, long- Rhizophagus grandis (Grégoire et al. 1991) is also largely re- range attraction proved to be due to a mixture of c~-pinene sponsible for its orientation in flight to its prey. Most of these and prey pheromones, frontalin and trans-verbenol (William- oxygenated monoterpenes are more or less common bark bee- son 1971), which would provide the searching flies with indi- tle volatiles (Francke & Vité 1983; Pierce et al. 1987; Francke cations as to prey location and the proper timing of attack. et al. 1988), however, (-)-fenchone is extremely rare in this Again, a combination of signals from the host-tree and the context and thus may give rise to a highly specific signal. prey may thus be necessary here. R. grandis is still in another situation: instead of responding to pheromones of adult prey, Further experiments will have to assess the it responds to volatiles produced by the larvae; instead of ovi- specific roles which single components play in oviposition positing on the outer bark, it has to enter the brood systems, and/or long-range orientation, and to evaluate possible com- packed with larval frass. A bouquet of the same oxygenated plementary actions of additional compounds. Preliminary re- monoterpenes produced by active prey larvae can thus be ad- sults indicate that (-)-verbenone at least is likely to be active vantageously used at two successive stages, first for locating a in both oviposition and orientation. It has been experimental- D. micans brood chamber in the forest, secondly for laying ly found to elicit some egg-laying (Baisier 1990), and also eggs in the most suitable places within this brood chamber, proved to trigger high electrophysiological activity in electro- presumably where the bouquet is the richest and most concen- antennograms and single cell recordings of antennal reactions trated due to recent prey activity. (Tommeräs et al. 1984). Since antennectomized females lay as many eggs as intact females (Baisier 1990), verbenone percep- From practical reasons concerning pest man- tion through the antennae might be related to orientation be- agement of D. micans, a better knowledge of the chemical sig- haviour. According to the very positive and similar responses nals governing the life history of R. grandis is also welcome. to blends a, b, and c, precise enantiomeric proportions of at R. grandis is mass-reared and released in outbreak areas for least some of the compounds do not seem to play an essential the biocontrol of D. micans (Grégoire et aL 1984; King & role. In blend d, (-)-c~-terpineol appears to act as a synergist. Evans 1984). Here, semiochemicals already provide an addi- Preliminary field tests using this blend showed extremely high tional and novel tool: on the basis of our results, oviposition recapture rates for released predators (J.-C. Grégoire et al. in stimuli are now used directly in the cultures, allowing a totally prep.). artificial, prey-free mass-production of the predator at low costs and reduced risks of diseases (J.-C. Grégoire, M. Bai- Further experiments will also have to take sier, A. Drumont, unpubl.). Other appealing prospects are of_ into account possible short fange orientation mechanisms (oc- fered by long range attractants for R. grandis. Their use in curring after the beetles have landed on an attacked tree), and traps might permit easy monitoring of natural or artificially- which may still rely upon other signals. Nevertheless, the pres- established populations of predators. Furthermore, the preda- ent results offer interesting insights into the mechanisms gov- tors could perhaps be used as 'markers' to monitor their prey. erning prey specificity in R. grandis which has never been As D. micans does not seem to use aggregation pheromones found in the galleries of any bark beetle other than D. micans. (Grégoire 1985) and therefore can not be directly monitored The simplest and most economic factor ensuring specificity is by trapping, and as R. grandis excels in locating its prey even likely to be long range attractants. A further step ensuring at low densities, releases and subsequent trapping of R. gran- prey specificity would then be the predators' response to spe- dis in areas previously uncolonised by the bark beetles would cific oviposition stimuli. From that point, the major con- indicate establishment of D. micans. Field experiments aimed 18 Chemoecology 3 (1992) Grégoire et al.

at evaluating the potentials of this promising method are cur- Grégoire J-C (1985) Host colonization strategies in Dendroctonus: larval rently being developed in France in the Départements of Hér- gregariousness vs. mass-attack by adults? Pp 147-154 in Safranyik LS (ed.) Proc Symp IUFRO Working Parties $2.07-05 and $2.07-06, ault and Aude which are still beyond the limits of the rapidly Banff, Canada, September 1983 moving range of D. micans but are surrounded by Départe- Grégoire J-C (1988) The Greater European spruce beetle, Dendroctonus ments already colonised by the pest (Gard and Aveyron on the micans (Kug.). Pp 455-478 in Berryman AA (ed.) Population Dyna- East, Ariège on the West), and are thus likely to be invaded in mics of Forest Insects. New York: Plenum Grégoire J-C, Baisier M, Drumont A, Dahlsten DL, Meyer H, Francke W the near future. (1991) Volatile compounds in the larval frass of and Dendroctonus micans (Coleoptera: Scolytidae) in relation to ovi- Acknowledgements position by the predator, Rhizophagus grandis (Coleoptera: Rhizopha- gidae). J Chem Ecol 17:2003-2019 Sincere thanks are due to J. M. Pasteels and A. Heuer HG, Vité JP (1984) Chalcogran: unique kairomone-governed pre- Foggo for critical reading of the manuscript. A. Foggo also corrected dator-prey relations among ostomid and scolytid beetles. Naturwissen- schaften 71:214-215 the English. Our gratitude goes also to Leticia Chrétien, Alain Dru- mont and Joëlle Van Bambeke, who helped with the rearings. Part of King CJ, Evans HF (1984) The rearing of Rhizophagus grandis and its release against Dendroctonus micans in the United Kingdom. Pp 87- this work was financed by a grant to J.-C. G. from Region Langue- 97 in Grégoire J-C, Pasteels JM (eds) Proceedings of the EEC Seminar doc-Roussillon/FEOGA Special Programme F.2.89, Project on the Biological Control of Bark Beetles (Dendroctonus micans), 5.6.1.1.d.W.F. thanks the Deutsche Forschungsgemeinschaft~and Brussels, 3-4/10/1984 the Fonds der Chemischen Industrien for financial support. Kobakhidze DN (1965) Some results and prospects of the utilization of beneficial entomophagous insects in the control of insect pests in Ge- References orgian SSR (USSR). Entomophaga 10:323-330 König, WA, Krebber R, Mischnick P (1989) Cyclodextrines as chiral sta- Baisier M (1990) Biologie des stades immatures du prédateur Rhizophagus tionary phases in capillary gas chromatography. J HRC 12:732-738 grandis Gyll. (Coleoptera: Rhizophagidae). Doctoral dissertation, Pierce HD, Conn JE, Oehlschlager AC, Borden JH (1987) Monoterpene Université Libre de Bruxelles metabolism in female mountain pine beetles, Dendroctonus pondero- Bakke A, Kvamme T (1981) Kairomone response in Thanasimus predators sae Hopkins, attacking Ponderosa pine. J. Chem Ecol 13:1455-1480 to pheromone components of 1ps typographus. J Chem Ecol 7:305- Pitman GB, Vité JP (1971) Predator-prey response to western pine beetle 312 attractants. J Econ Entomol 64:402-404 Beckmann S, Metzger R (1956) Über sterisch selektive Reduktion von Ke- Rice R (1969) Response of some predators and parasites of 1ps confusus torten der Campherreihe mit Lithiumaluminiumhydrid. Chem Ber (Coleoptera: Scolytidae) to olfactory attractants. Contrib Boyce 89:2738-2742 Thompson Inst 24:189-t94 Bergmiller F (1903) Dendroctonus micans und Rhizophagus grandis. Zen- Schroeder LM, Lindelöw Ä (1989) Attraction of Scolytids and associated tralbl ges Forstw 29:527-534 beetles by different absolute amounts and proportions of c~-pineneand Dyer EDA (1973) Spruce beetle aggregated by the synthetic pheromone ethanol. J Chem Ecol 15:807-817 frontalin. Can J Forest Res 3:486-494 Tommeräs BÄ, Mustaparta H, Grégoire J-C (1984) Electrophysiological Fitzgerald TD, Nagel WP (1972) Oviposition and larval bark surface recordings from olfactory receptor cells in Dendroctonus micans and orientation of Medetera aldrichii (Diptera: Dolichopodidae). Ann Ent Rhizophagus grandis. Pp 98-106 in Grégoire J-C, Pasteels JM (cds) Soc Am 63 (3):913-914 Proceedings of the EEC Seminar on the Biological Control of Bark Francke W, Vité JP (1983) Oxygenated monoterpenes in pheromone sy- Beetles (Dendroctonus micans), Brussels, 3-4/10/1984 stems of bark beetles. Z angew Entomol 96:146-156 Tondeur A, Grégoire J-C (1980) Chemical orientation of Rhizophagus Francke W, Bartels J, Schmutzenhofer H, Kohnle U, Vité JP (1988) The grandis towards mates and towards prey: Dendroctonus micans. Pp odour-bouquet of Ips schmutzenhoferi Holzschuh (Coleoptera: Scoly- 93-94 in Gilles R (ed.) Animals and Environmental Fitness. Oxford: tidae). Z Naturforschung 43:958-960 Pergamon Press Francke-Grosmann H (1954) Populations-dynamische Faktoren bei der Vité JP, Williamson DL (1970) Thanasimus dubius: prey perception. J In- Massenvermehrung des Dendroctonus micans Kug. an der Sitkafichte sect Physiol 15:233-239 in Schleswig-Holstein. Verh Dtsch Ges angew Entomol: 108-117 Grégoire J-C (1984) Dendroctonus micans in Belgium: the situation today. Williamson DL (1971) Olfactory discernment of prey by Medetera bistri- Pp 48-62 in Grégoire J-C, Pasteels JM (cds) Proceedings of the EEC ata (Diptera: Dolichopodidae). Ann Ent Soc Am 64:586-589 Seminar on the Biological Control of Bark Beetles (Dendroctonus mi- Wood DL, Browne LE, Bedard WD, Tilden PE, Silverstein RM, Rodin cans), Brussels, 3-4/10/1984 JO (1968) Response of Ips confusus to synthetic sex pheromones in Grégoire J-C, Merlin J, Pasteels JM, Jaffuel R, Vouland G, Schvester D nature. Science 159:1373-1374 (1984) Mass-rearings and releases of Rhizophagus grandis. Pp 122- Zweifel G, Brown HC (1964) Hydroboration of terpenes. II. The hydrobo- 128 in Grégoire J-C, Pasteels JM (cds) Proceedings of the EEC Semi- ration of c~- and 13-pinene. The absolute configuration of the dialkyI- nar on the Biological Control of Bark Beetles (Dendroctonus micans), borane from the hydroboration of ~-pinene. J Am Chem Soc 86: 393- Brussels, 3-4/10/1984 397