Differences in attraction to semiochemicals present in sympatric pine shoot beetles,Tomicus minor andT. piniperda

Abstract

Abstract--The chemical ecology of host-and mate-finding in the pine shoot beetles, Tomicus minor and T. piniperda, was studied in southern Sweden. Beetles were collected in the field from defined attack phases on Scots pine. Using gas chromatography-mass spectroscopy, a number of oxygen-containing monoterpenes, e.g., 3-carene-10-ol, myrtenol, trans-verbenol, and verbenone, were identified from hindgut extracts of both sexes of both species. Compared to T. minor, T. piniperda contained additional compounds and in larger amounts. The amounts were highest in both species at the time when the beetles had bored into contact with the resin-producing xylem-phloem tissue. The synthesis of (1S,6R)-3-carene-10-ol by photooxidation of (+)-(1S,6R)-3-carene is described. In comparative electroantennogram (EAG) measurements on males and females of both species, the most active of the tested compounds was trans-verbenol. Laboratory bioassays of walking beetles showed that T. piniperda was attracted to uninfested.Pine logs. T. minor was more strongly attracted to pine logs infested with females than to uninfested pine logs, indicating a female-produced aggregation pheromone. Field tests confirmed that 7". piniperda was strongly attracted to pine logs. The attraction of T. minor to logs was significant only when logs were combined with racemic trans-verbenol and (1S,6R)-3-carene-10-ol. T. minor was also Coleoptem: Scolytidae. ~This study was made within the project "Odour signals for control of pest insects." 5Present address: VDP Laboratories, P.O. Box 1547, 1200 BM, Hilversum, The Netherlands. attracted to a combination of these monoterpene alcohols alone. We suggest that host and mate location in T. piniperda is achieved by means of a kairomone composed of host monoterpenes, while T. minor utilizes a primitive pheromone synergized by host odors. Evolution of host colonization strategies of the two beetles are discussed.

Host-Tree Chemistry Affecting Colonization in Bark Beetles

“…Lanne et al (1987) showed compounds not found in T. piniperda (exo-brevicomin, ipsenol, and pheromone components of other bark beetle species) elicited an EAG response in the beetle. Some of these compounds are found in competing species of bark beetles, but other compounds are probably found only in species colonizing nonhost trees (e.g., Norway spruce).…”

“…Observations of I. paraconfisus, I . typographus, D. brevicomis, P. chalcographus, and T. piniperda in flight chambers under dim red light or in complete darkness using an electronic vibration detector indicate they will not fly after dark (Lanne et al, 1987;Byers and Lofqvist, 1989;Byers, unpublished). Bark beetles are attracted more so to traps baited with host odor or pheromone that are placed next to tree trunk silhouettes than to traps without such visual stimuli, indicating that beetles orient to the tree hunk during landing (Moser and Browne, 1978;Borden et al, 1982;Tilden et al, 1983;Lindgren et al, 1983;Bombosch et al, 1985;Ramisch, 1986; ChCnier and Philogbne, 1989).…”

“…Host volatiles are attractive to a number of forest scolytids including species in the genera Scolytus, Dendroctonus, Hylurgops, Trypodendron and Tomicus (Goeden and Noms, 1964;Rudinsky, 1966;Meyer and Noms, 1967a;Moeck, 1970;Byers et al, 1985;Lanne et al, 1987;Volz, 1988;Lindelow et al, 1992;Hobson et al, 1993). Species of bark beetle that regularly attack and kill living trees (termed aggressive) have been shown invariably to possess an aggregation pheromone, usually of two or more components, but are weakly, if at all, attracted by host volatiles alone (Vitt and Pitman, 1969;Byers, 1989b).…”

Optimal fractionation and bioassay plans for isolation of synergistic chemicals: The subtractive-combination method

“…Another disadvantage is that some insects such as locusts (Blaney and Simmonds, 1990) and bark beetles (Dickens et al, 1985;Lanne et al, 1987) contain either many generalist receptors or (more likely) many different kinds of more specialized receptors, since many chemicals elicit voltage potentials in the electroantennogram. This makes it more difficult to determine the importance of candidate chemicals to a specific behavior.…”

“…Ideally, the release rate should parallel the expected or measured rates of natural release (Byers et al, 1985). Usually, however, a range of rates that are expected to overlap the natural rate are used (Schlyter et al, 1987;Byers et al, 1988). As the release rate is increased, there is a point when activity begins (e.g., catch increases above the control), and this rate is assumed to be similar to the natural one.…”