The aggregation pheromone ofIps duplicatus and its role in competitive interactions withI. typographus (Coleoptera: Scolytidae)

Abstract

SummaryIps duplicatus with L typographus co-inhabiting Norway spruce (Picea abies (L.) Karst.) would benefit from a pheromone blend distinct from that of the larger competitor L typographus. GC-MS analysis showed that L duplicatus males feeding in the host produced ipsdienol (Id), cis-verbenol (cV), trans-verbenol (tV), myrtenol (Mt), and Emyrcenol (EM) and traces of 2-methyl-3-buten-2-ol (MB). L duplicatus produced Id in approximately racemic form (48.9-54.5% (+)-(S)-isomer). The amounts of Id and EM released over a 9 day period had a maximum of 250 and 5 ng/h/male, respectively, on day 2. Exposure of L duplieatus males to myrcene and «-pinene resulted in the production of small amounts of Id, cV, tV, Mt, and trans-pinocarveol, but not of EM. In laboratory bioassays with walking beetles, the pheromone component Id alone was weakly attractive while EM was inactive, but in binary combination with Id strongly synergized attraction. A combination of EM and Id at a release rate equivalent to 100-200 males was more attractive in the field than 70 unmated males in a spruce log. The addition of myrcene ( a suggested pheromone precursor of Id) to Id did not enhance trap caches, while addition of EM increased catches > 10-fold. Subtracting EM from a blend of Id, EM, cV and MB drastically reduced trap catches while subtraction of cV or MB or both had no significant effect. Addition of EM over a wide concentration range to the synthetic pheromone of L typographus did not reduce the attraction of females of this species in the laboratory. A twospecies pheromone interaction field test releasing L typographus pheromone components (MB + cV) at 10-1000 male equivalents (ME) and L duplicatus pheromone (Id + EM) at 0, 10-1000 ME in all possible combinations showed both positive intraspecific dose-response effects and an interspecific inhibition. Higher release rates of EM appeared to inhibit I.typographus, especially males. In a tree colonization model, the response of the two competing species to their respective pheromones show a good separation during the mass-attack with a small initial cross-attraction. It remains to be shown whether either of the two pheromone systems have in fact evolved in the present sympatry, or if they are an incidental effect of ancestry of these phylogenetically distant Ips.

Non-target Bark Beetles in <i>Ips duplicatus</i> (Sahlberg) Pheromone Traps Baited with Host Volatiles

“…Both substances are pheromone components of the European spruce bark beetle (Bakke, 1976;Bakke et al, 1977). On the other hand, the small captures of this species reflect not only the lower level of I. typographus populations comparing with I. duplicatus, but also the inhibitory effect of EM at high release rates of other pheromone components, as already noted Schlyter et al (1992).…”

“…Given our results and considering that the synthetic pheromone of I. typographus attracts many I. duplicatus beetles (Valkama et al, 1997), it would be possible to set in the same traps the pheromone dispensers of both species without affecting the captures of either species, thereby reducing the costs of control when these are the main pests. However, new tests should be conducted to clarify what happens with each species, because high release rates of EM inhibit the response of I. typographus males (Schlyter et al, 1992). Also, new studies are necessary to determine what happens if synthetic pheromone of I. duplicatus is used together with that of P. calcographus.…”

“…There are several studies on the pheromones of I. duplicatus (Bakke, 1975;Byers et al, 1990;Schlyter et al, 1992;Ivarsson et al, 1993;Ivarsson and Birgersson, 1995) and their use in forest protection (Schlyter et al, 2001), but none considering the non-target species attracted by synthetic pheromones of this species. This is the reason to present in this paper the data on non-target scolytine species caught during field tests concerning the response of I. duplicatus to different combinations of synthetic pheromone with (-)-alpha-pinene and (+)-limonene that was presented in a previous paper (Duduman, 2014).…”

Host-Tree Chemistry Affecting Colonization in Bark Beetles

“…Exposure of Ips duplicatus to myrcene vapor causes the beetle to produce small amounts of its pheromone component ipsdienol but not E-myrcenol, the other component (Schlyter et al, 1992). Both compounds are expected to be made from myrcene .…”

“…(+)-Ipsdienol inhibits response of both D. brevicomis and I. pini to their synthetic aggregation pheromones (Birch et al, 1980a;Lanier et al, 1980;Byers, 1982). In Europe, ipsdienol, a pheromone component of I. duplicatus could act as an allomone to inhibit response of I. typographus Schlyter et al, 1992). Mated males of I. typographus produce small amounts of ipsdienol and ipsenol during colonization that might function in avoiding competition (Birgersson et al, 1984;Birgersson and Leufvtn, 1988).…”