Fitness consequences of pheromone production and host selection strategies in a tree-killing bark beetle (Coleoptera: Curculionidae: Scolytinae)

Abstract

Timing of arrival at a resource often determines an individual's reproductive success. Tree-killing bark beetles can reproduce in healthy trees by attacking in adequate numbers to overcome host defences that could otherwise be lethal. This process is mediated by aggregation and antiaggregation pheromones. Beetles that arrive early in such a "mass attack" must contend with undiminished tree defences, and produce enough pheromones to attract more beetles, but have a head start on gallery construction and egg-laying. Beetles that arrive late may be impeded by competition and diminishing availability of phloem, but should experience fewer costs associated with pheromone production and battling tree defences. We investigated relationships between timing of arrival, body size, pheromone production and fitness in the southern pine beetle, Dendroctonus frontalis. In field experiments, we captured beetles that arrived early (pioneers) and late on slash pine trees, Pinus elliottii, and measured pheromone amounts in their hindguts. We marked gallery entrances of beetles as they landed on a tree and measured their reproductive success after the attack terminated. We found no difference in body size or pheromone amounts between early and late arrivers. Most beetles arrived at the middle of the attack sequence, and excavated longer galleries per day than early arrivers. The number of offspring produced per day by beetles that established galleries midway through mass attack was higher than those that arrived early or very late in the sequence. Our results suggest that beetles do not exhibit adaptive phenotypic plasticity in pre-landing pheromone production, depending on the extent of previous colonisation of a host. Rather, it appears that stabilising selection favours beetles that attack in the middle of the sequence, and contributes to attack synchrony. Synchronous attack on trees is essential before population booms characteristic of tree-killing bark beetles can occur in nature.

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

“…It is present in newly emerged, host-arriving, and gallery-establishing females Pureswaran et al, 2007;Renwick and Vit e, 1968;Sullivan et al, 2007bSullivan et al, , 2012 and generally is undetectable in males (although see Grosman, 1996;Grosman et al, 1997;Pureswaran et al, 2006;. Evidence of its uniqueness to females is consistent with the observation that logs infested with solitary D. frontalis females are attractive whereas those with forced male attacks are not .…”

“…endo-Brevicomin is produced by newly emerged D. frontalis males, those alighting on mass-attacked trees (Pureswaran et al, 2006;Vit e and Renwick, 1971), and males paired with a female in a gallery (Pureswaran and Sullivan, 2012;Sullivan et al, 2007b). For populations examined in Mississippi, United States, solitary males feeding in phloem (ie, forced to initiate a gallery on a host log, a behaviour that does not occur in nature), did not produce significantly greater amounts than newly emerged beetles whereas pairing caused production to increase nearly 10-fold (Sullivan et al, 2007b).…”

Evidence that (+)-endo-Brevicomin is a Male-Produced Component of the Southern Pine Beetle Aggregation Pheromone

“…The potential fitness benefits to pheromoneproducing males are enhanced survival for both themselves and their offspring, as attracting greater numbers of attacking conspecifics should help assure rapid and complete disruption of host defenses. Alternately, males and females responding to hosts releasing (+)-endobrevicomin, frontalin, and host terpenes (hosts infested with at least some beetle pairs) may avoid the high risks of mortality encountered by pioneer beetles that are first to initiate attacks on a particular tree (Pureswaran et al 2006). Our data also indicate that the attractant currently used for monitoring populations of D. frontalis with traps (frontalin and turpentine; Skillen et al 1997) is incomplete and that the addition of (+)-endo-brevicomin may enhance detection of low-density beetle populations.…”

Maintenance of endemic Dendroctonus ponderosae populations through interactions with a secondary bark beetle, Pseudips mexicanus.

“…Beetle size significantly affects the egg-laying capacity, with larger beetles able to lay more eggs (McGhehey 1971). Larger size also confers a greater ability to disperse and locate new hosts, and energetic requirements for the attacking sex are usually greater than for the sex responding to aggregation pheromones (Pureswaran et al 2006). Beetles from populations in Mexican white pine were reported to be larger (Schwerdtfeger 1956) than the ones I found in lodgepole pine, possibly contributing to the greater reproductive potential.…”

“…Very little is known about the fungi or yeasts associated with P. The ability to develop quickly with minimal loss in body mass could confer a number of benefits to a beetle. Earlier emergence would give beetles the opportunity to locate and choose from among the best available hosts (Pureswaran et al 2006). Once a host is selected, an optimum attack site can be located and oviposition commenced.…”