J. P. Vité

Dosage response to ethanol mediates host selection by “secondary” bark beetles

common one responded mainly to Z 9 14:OAc, a second type to Z7+ 14: OAc with a weak response also to Z 9 14:OAc, and a third type responded exclusively to Z11-14: OAc (Fig. 2). The medial shorter sensilla towards the antennal axis have two cells: Cell A with a high spike amplitude and cell B with a low spike amplitude. The A cell responds to totally different pheromone components than the cells in the marginal long sensilla: the majority (82%) responds to Z5-14: OAc, whereas a lower number (18%) is activated exclusively by Z7-12:OAc (Fig. 2). The function of the B cell is still unknown. It did not respond to any of the compounds tested. These results were corroborated by measuring the response of ten short sensilla to the same compounds with the penetration technique [81. The receptor types found by us are thus in agreement with what Priesner reported [6]. The proportion of sensillacontaining cells sensitive to compounds other than Z5and Z9-14:OAc is striking. Trapping experiments by Priesner [6] showed that these other compounds have an inhibitory effect on the attraction of male A. exctarnationis. Our own unpublished gas chromatographic analyses on capillary columns did not reveal traces of any of them in female extracts (<0 .5% of Z5 14:OAc). They are, thus, most probably pheromone compounds in some other competing species. More interestingly, however, we found a clearcut correlation between the morphology of individual sensilla, their spatial localization, and their sensitivity to different compounds. The receptors for the pheromone component z g 1 4 : O A c are exclusively arranged along the lateral margins of the antennal segments, and are each innervated by one neuron. The Z 5-14:OAc receptors are all placed medially in sensilla containing also a second cell. Such a spatial arrangement of receptors sensitive to different pheromone components has not been reported before. It is interesting to note that Z 9 14: OAc is perceived by a specific cell in the long distal sensilla placed on the edge of the male A. exclarnationis antennal segments. There is in the pheromone blend an optimal proportion of this component to Z5-14: OAc of less than 10% for male attraction. The proportion of molecules perceived by the sensilla from the air is by aerodynamic laws much higher for distal sensilla than for central ones [9]. This means that the localization of the Z 9 t 4 : OAc receptors on the male A. exclamationis antenna could be adaptive for sensitive detection of the m i n o r o n e of the two pheromone components. Received November 25, 1985 and January 10, 1986

Chirality of insect pheromones: Response interruption by inactive antipodes

(-)-disparlure, or both enantiomers [1] resulted in distinctly different response patterns by the nun moth and the gypsy moth (Fig. 1). With the nun moth, response to the traps increased with the concentration of(+)-disparlure regardless of the addition of(-)-disparlure (Table 1) which is known to drastically suppress gypsy-moth response at r~/cemic or higher concentrations [1]. Tests using traps baited with (-)-disparlure only ted to conflicting results. No moths were caught in two areas but large numbers in another [4]. Our findings are well in accordance with observations which indicate that nun moths respond to increasing concentrations of racemic disparlure while gypsy moths do so to a lesser degree [5]. One possible explanation of this phenomenon rests, indeed, with chiral differences in pheromone production between the two species [6]. Hypothetically, P. dispar would be expected to produce the (+)-enantiomer only, while P. monacha might produce both optical antipodes of the disparlure.

Semiochemicals from bark beetles: New results, remarks, and reflections

A brief survey is given about recent results in the identification of semiochemicals in bark beetles: Males ofIps sexdentatus (Boern.), stressed by the attack on resinous trees produce large amounts of 3(S)-1-methyl-5-(1-hydroxyl-1-methylethyl)-cyclohexa-1,3-diene. The compound appears to be derived from Δ3-carene and acts as a repellent. Males ofIps typographus (L.), stressed through the attack on unsuitable host material release 3-methyl-7-methylene-1,3(E), 8-nonatriene, which seems to act as a repellent. The odor bouquet of three species ofPityogenes is described. The occurrence of (+)-grandisol and other compounds related to weevil pheromones points to a close relation between Scolytidae and Curculionidae. Females ofDendroctonus simplex (Le Conte) use (−)-frontalin as the main pheromone. 6-Methyl-6-hepten-2-one, a minor component among the volatile compounds released by the females, is regarded as a possible precursor of frontalin. Similarly, (2R,5S)-2(1-hydroxyl-1-methylethyl)-5-methyltetrahydrofuran, pityol, a pheromone ofPityophthorus spp., is regarded to at least share a common biogenetic precursor with 6-methyl-5-hepten-2-ol, sulcatol. A new bicylic acetal, 2-ethyl-1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane, is described as an aggregation pheromone of the beech bark beetle,Taphrorychus bicolor (Herbst). Structural relationships between bark beetle pheromones and plant volatiles are discussed.

Southern pine beetle: Olfactory receptor and behavior discrimination of enantiomers of the attractant pheromone frontalin

In laboratory and field bioassays, the response ofDendroctonus frontalis was significantly greater to the mixture of (1S, 5R)-(−)-frontalin andalpha-pinene than to (1R,5S)-(+)-frontalin andalpfa-pinene. Electro-physiological studies revealed that antennal olfactory receptor cells were significantly more responsive to (1S, 5R)-(−)-frontalin than to (1R, 5S)-(+)-frontalin. Both enantiomers stimulated the same olfactory cells which suggests that each cell possesses at least two types of enantiomer-specific acceptors.

Semiochemicals in host selection and colonization of pine trees by the pine shoot beetleTomicus piniperda

amt Materialien 1/84, 169 (1984); Battarbee, R.W.: Philos. Trans. R. Soc. Lond. B 305, 451 (1984); Renberg, I., Hellberg, T. : Ambio 11, 30 (1982) 2. Smol, J.P., et al. : Nature 307, 628 (1984); Can. J. Bot. 62, 911 (1984) 3. Stool, J.P. : ibid. 58,458 (1980); Battarbee, R.W., et al. : Hydrobiologia 71,225 (1980) 4. Steinberg, C., et al. : Naturwissenschaften 71, 631 (1984) 5. Cronberg, G., Kristiansen, J. : Bot. Not. 133, 595 (1980) 6. Steinberg, C., et al.: Umweltbundesamt Materialien 1/84, 304 (1984) 7. Renberg, I., Hellberg, T. : see [1]

Disparlure: Differences in pheromone perception between gypsy moth and nun moth

nothing fashion with carefully controlled stimulus intensities (Fig. I c). Small changes in snprathreshold intensities can be accompanied by abrupt changes in the shape of the short-latency potential (Fig, 1 d). They are understood as combined action potentials of two large axons. Separation between the spikes of two large axons was found in some preparations where stimulus and recording site were far apart from each other indicating slightly different conduction velocities of the fibres (Fig. l c). These short-latency spikes are the largest electrical events recorded after electrical stimulation ipsior contralateral to the recording site. Spikes run equally well in both directions along the cord as expected for a through-running axon system. It is reasonable to attribute the described action potentials to the two giant fibres shown by morphology. The conduction velocity of the giant fibres was determined as 1.14 m/s (n=19) and fell in the range of 0.7 1.7 m/s. Giant-fibre responses can be produced by mechanical stimulation of the antennae, the dorsal parts of the head, the tail, the feet and dorsolateral body walls. The strongest phasic discharges of the giant fibres were obtained from touching the head or tail. The response shows rapid habituation. Contralateral response is prevented by cutting the commissures of the ladder-like-type nerve cord near the stimulus site. The animal displays different fast reactions when touched or pinched. One of them is a quick shortening of the body including several segments when the head or tail is stimulated. The contraction shortens the soft-body animal up to 65% of its former length in 200-500 ms. It is assumed that the activity of the giant fibres is associated with rapid overall body movements. The acquisition of a fast-conducting through-running giant-fibre system is a typical feature of many polysegmental invertebrates. The giant fibre system of Per# patoides shows considerable similarities to those of annelids with respect to morphology and function in relation to behavior (for comparison see [2]).

Synergistic effect of a pheromone and a kairomone on host selection and colonisation by Ips avulsus

WE report for the first time a synergistic effect on the pheromone response of a bark beetle species (Coleoptera: Scolytidae) by the pheromone of a sympatric species. Ips avulsus Eichh. and I. grandicollis Eichh. are two sympatric Ips species often found colonising the same host tree in the southern USA. Male I. avulsus produce the pheromone ipsdienol (2-methyl-6-methylene-2,7-octadiene-4-ol)1,2 and both sexes are attracted to this compound in the field3. Male I. grandicollis produce the pheromone ipsenol (2-methyl-6-methylene-7-octene-4-ol)1,2,4 and both sexes respond to the S-(–)-isomer5. I. avulsus is known to respond in low numbers to both the crude attractant6 and infested host material7 of I. grandicollis. To investigate this relationship, a series of tests was carried out in east Texas. Two to four tree trunk-simulating olfactometers8 set 10 m apart adjacent to a loblolly pine stand at Lufkin, Texas, were baited with test material during the afternoon, when flight of I. avulsus occurred. Test materials included the optically pure enantiomers of ipsenol9, racemic mixtures of ipsenol and ipsdienol, and billets infested with male I. avulsus and I. grandicollis. All test materials used in a test series were offered simultaneously.

Present and future use of semiochemicals in pest management of bark beetles.

Attractive compounds affecting the mass aggregation of bark beetle populations on host trees suitable for colonization usually consist of two obligatory components that act synergistically and species-specifically. Semiochemicals inhibiting response act on their own and seem less specific. From nearly 100 species investigated so far, mass aggregation can be simulated with commercial synthetics in about nine species of economic importance. Aspects leading to the application of attractants in monitoring and mass trapping pest populations affecting European spruce forests result from intensive coordinated research at the university, industry, and forestry level. Technology transfer was facilitated by, and adapted to, the infrastructure of European forestry; traps economically replace the trap tree methods conventionally used for centuries. Expected applications in the near future are refined monitoring methods to measure population levels and predict damages. Also, mass trapping should remain a worthwhile tool in preventing beetle damage in forests under management intensive enough to remove excessive breeding material. In the long run, response-inhibiting semiochemicals resulting in the dispersal of pest populations (Ablenkstoffe) may gain wider application. The spruce engraverIps typographus L. and its associatePityogenes chalcographus L. are used as examples to describe the feasibility of developing and applying inhibitors as new tools in the management of bark beetle pests: Applying a slow-release verbenone formulation (verbenone strip) wrapped around the trunk of spruce trees at breast height appears to protect spruces from destructive attack byIps typographus, while small polyethylene ampullae containing terpinene-4-ol counteract aggregation of P. chalcographus. Inhibitors appear applicable in both strategies, damage prevention as well as damage restriction, and consequently may accommodate also pest control in less intensively managed forests. Future application of semiochemicals in the management of bark beetle pests will rest with the availability of effective means and methods and their acceptance by the forestry interest. This acceptance is presently somewhat hampered by misconceptions about mass trapping, and by (1) “missing links” in the knowledge of the beetles′ dispersal and aggregation behavior, (2) the chemosynthesis of chiral pheromone components at the industrial level, and (3) legal barriers.

The odour bouquet of three pine engraver beetles (Ips spp.)

Nearly 50 volatile compounds are identified from hindguts of the pine engraver Ips acuminatus, I. sexdentatus and I. lecontei. Among these, α‐phellandren‐8‐ol, ipsdienon, ipsenon and others are described from bark beetles for the first time. The quantitative composition of the odour bouquet of both sexes largely depends on the phase of colonization; after the initial phase of attack, they are particularly rich in oxidized monoterpenes. I. acuminatus and I. lecontei contain the male specific terpene alcohols (+)‐ipsdienol and (—)‐ipsenol in high optical purity while I. sexdentatus produces racemates. Racemic ipsdienol proves attractive to I. sexdentatus under field conditions, but does not seem to promote the subsequent steps in colonization such as landing or penetrating the bark.

Chiral building units from carbohydrates-XIII. : Identification of the absolute configuration of endo-brevicomin from dendroctonus frontalis and synthesis of both enantiomers from d-ribose

Abstract The synthesis of both enantiomers of endo -7-ethyl-5-methyl-6,8-dioxabicyclo[3.2.l]octana ( endo -brevicomin, 12 and 12a ) starting froni D-ri-bose is described. Key interinediate is the open chain derivative 7 , a chiral building unit easily available from carbohydrates. Complexation gas chromatography showed the natural pheromone of males of the southern pine beetle, Dendroctonus frontalis Zimm. , to be (1R,5S,7S)- endo -brevicomin.