Attraction to monoterpenes and beetle‐produced compounds by syntopic Ips and Dendroctonus bark beetles and their predators

Abstract

1 Bark beetles are significant mortality agents of conifers. Four beetle species, the pine engraver Ips pini, the six-spined pine engraver Ips calligraphus sub. ponderosae, the southern pine beetle Dendroctonus frontalis, and the western pine beetle Dendroctonus brevicomis, cohabitate pines in Arizona. 2 A pheromone trapping study in ponderosa forests of Arizona determined the attraction of beetles to conspecific and heterospecific pheromone components in the presence and absence of host volatiles, and tested whether predators differ in their attraction to combinations of pheromone components and tree monoterpenes. 3 All four bark beetle species differed in their responses to heterospecific lures and monoterpenes. Ips calligraphus was the only species that increased in trap catches when heterospecific lures were added. Heterospecific lures did not inhibit the attraction of either Dendroctonus or Ips species. The replacement of myrcene with α-pinene increased the attraction of Dendroctonus, whereas the addition of α-pinene had mixed results for Ips. The prominent predators Temnochila chlorodia and Enoclerus lecontei were more attracted to the I. pini lure than the D. brevicomis lure, and the combination of the two lures with α-pinene was most attractive to both predator species. 4 Cross attraction and limited inhibition of bark beetles to heterospecific pheromones suggest that some of these species might use heterospecific compounds to increase successful location and colonization of trees. Predator responses to treatments suggest that tree volatiles are used to locate potential prey and predators are more responsive to Ips than to Dendroctonus pheromone components in Arizona.

Semiochemicals in the Natural History of Southern Pine Beetle Dendroctonus frontalis Zimmermann and Their Role in Pest Management

“…As with endo-brevicomin, reported behavioural responses by D. frontalis to exo-brevicomin have varied. It has alternately been shown to reduce (Vit e and Renwick, 1971), enhance (Hofstetter et al, 2008(Hofstetter et al, , 2012Pureswaran et al, 2008a), or not significantly alter (Payne et al, 1978a) responses of D. frontalis to traps baited with frontalin and host odours. As with the endo-isomer, it has not demonstrated attractive properties when presented alone or with host odours.…”

“…Little research has been done on the role of D. frontalis pheromones in mediating reproductive isolation from closely related species, although several such species may occupy the same portions of hosts (ie, exist in syntopy), utilize the same aggregation pheromone components, and be capable of pairing in the laboratory (Armendáriz-Toledano et al, 2014Davis and Hofstetter, 2009;Hofstetter et al, 2008Hofstetter et al, , 2012Lanier et al, 1988;Moser et al, 2005;Niño-Domínguez et al, 2015a;Sullivan et al, 2012). In olfactometer studies of D. frontalis and its sibling D. mesoamericanus which jointly colonize the same hosts in the Central American region, it was found that males could readily distinguish odours of conspecific and heterospecific female gallery entrances, and ipsdienol and endo-brevicomin (compounds produced by D. mesoamericanus but not D. frontalis females) were identified as the species-specific cues that mediated this discrimination (Niño-Domínguez et al, 2015a).…”

“…A significant degree of cross-attraction between D. frontalis and syntopic species of Dendroctonus to their respective aggregation pheromones (Armendáriz-Toledano et al, 2014;Hofstetter et al, 2008Hofstetter et al, , 2012Niño-Domínguez et al, 2015a) would seem to be at odds with pressures to maintain reproductive isolation between such species. However, it is likely that mass attacks by multiple-species may be more successful than single-species attacks if a single species is at insufficient numbers to mass attack a tree (Økland et al, 2009, 2011).…”

“…One might expect pheromones produced by each member of such a guild to mediate at least one of three potential interspecific responses: (1) synchronized, multispecies mass attack in which species are simultaneously engaged in overcoming host defence, (2) sequential species attack due to species that "easvesdrop" on pheromones of the earlierarriving, mass-attacking species and then colonize only after host defences are rendered sufficiently neutralized, (3) cross-inhibition to reduce competitive interactions through host partitioning. Given the seeming fitness benefits of any or all of the three responses above, it is surprising both that (1) Dendroctonus frontalis shows no attraction to the pheromone blends associated with any of the Ips species in the southern guild or to Ips more generally Hofstetter et al, 2012;Svihra et al, 1980) and (2) the other Ips species display no attraction to D. frontalis with the possible exception of a weak positive response by I. grandicollis . Crossinhibition of the Ips spp.…”

“…As discussed earlier, responses to mutually produced, attractive pheromone components by D. terebrans and D. frontalis could potentially mediate cross-attraction and joint host colonization (Smith et al, 1990), but this possibility has not been sufficiently examined. Additionally, given evidence for cross-attraction between D. frontalis and D. brevicomis (Hofstetter et al, 2012;Pureswaran et al, 2008a) and between D. frontalis and D. mesoamericanus (Niño-Domínguez et al, 2015a), it would appear that for D. frontalis that bark beetle cross-attraction may be limited to congeners.…”