Host resistance elicited by methyl jasmonate reduces emission of aggregation pheromones by the spruce bark beetle, Ips typographus

Abstract

We treated Norway spruce (Picea abies) stems with methyl jasmonate (MeJA) to determine possible quantitative and qualitative effects of induced tree defenses on pheromone emission by the spruce bark beetle Ips typographus. We measured the amounts of 2-methyl-3-buten-2-ol and (S)-cis-verbenol, the two main components of the beetle's aggregation pheromone, released from beetle entrance holes, along with phloem terpene content and beetle performance in MeJA-treated and untreated Norway spruce logs. As expected, phloem terpene levels were higher and beetle tunnel length was shorter (an indication of poor performance) in MeJA-treated logs relative to untreated logs. Parallel to the higher phloem terpene content and poorer beetle performance, beetles in MeJA-treated logs released significantly less 2-methyl-3-buten-2-ol and (S)-cis-verbenol, and the ratio between the two pheromone components was significantly altered. These results suggest that host resistance elicited by MeJA application reduces pheromone emission by I. typographus and alters the critical ratio between the two main pheromone components needed to elicit aggregation. The results also provide a mechanistic explanation for the reduced performance and attractivity observed in earlier studies when bark beetles colonize trees with elicited host defenses, and extend our understanding of the ecological functions of conifer resistance against bark beetles.

Chemical similarity between historical and novel host plants promotes range and host expansion of the mountain pine beetle in a naïve host ecosystem

“…Furthermore, we suspect that differences in secondary compounds remaining in the cut bolts can still affect pheromone production by beetles (i.e. Zhao et al ., ).…”

Pheromone Production by an Invasive Bark Beetle Varies with Monoterpene Composition of its Naïve Host

“…It is likely that the profile of volatiles from cut bolts differs to some extent from those emitted from standing live trees. Nevertheless, we suspect that differences in secondary compounds remaining in the cut bolts still can affect pheromone productions by beetles (i.e., Zhao et al 2011) Second, compared to the wide natural range of jack pine forests throughout North America, we sampled trees from relatively few locations. Our most recent work using needles from 610 jack pine trees (or 61 populations) across Canada and the USA demonstrate that jack pine trees show various chemotypes, suggesting that this will likely affect the amount of pheromones, particularly trans-verbenol produced by D. ponderosae (Taft et al 2015).…”

Successful reproduction and pheromone production by the spruce bark beetle in evolutionary naïve spruce hosts with familiar terpenoid defences

“…Previous studies of the spruce bark beetle and other tree-killing bark beetles have shown that the beetles tend to avoid trees with very strong or rapid terpene accumulation (Boone et al 2011;Schiebe et al 2012;Zhao et al 2011a). Norway spruce had higher total induced terpene concentrations than Sitka and Lutz spruce (55% and 102% higher, respectively), suggesting that the novel hosts should be a more favorable substrate for the spruce bark beetle than Norway spruce.…”

“…In fact, thunbergol and thunbergene were not detected at all in Sitka spruce (Figure 3). The effect of thunbergene and α-longipinene on the spruce bark beetle is unknown, but thunbergol has been suggested to inhibit growth of the beetle's fungal associate E. polonica (Zhao et al 2011a;Zhao et al 2010). Considering the negative effects of thunbergol we were surprised to find a positive relationship between constitutive levels of thunbergol and offspring production.…”