B. Staffan Lindgren

Effect of verbenone on five species of bark beetles (Coleoptera: Scolytidae) in Lodgepole pine forests

Abstract The response by five species of bark beetles to a range of verbenone doses were tested in bioassays using Lindgren funnel traps baited with attractant semiochemicals. The objective was to determine how these bark beetles respond to verbenone, a purported anti-aggregation pheromone of several economically significant bark beetle species. Catches of Dendroctonus ponderosae Hopkins, a species attacking live trees, were unaffected relative to a control trap (no verbenone) at release rates of 0.2 mg/24 h or less, but were significantly reduced at rates of 1.8 mg/24 h or more. Catches of Ips pini (Say) and I. latidens (LeConte), two opportunistic species normally attacking fresh, dead host material, were gradually reduced with increasing verbenone dose. Verbenone did not affect catches of Hylurgops porosus (LeConte) and Hylastes longicollis Swaine, two species normally associated with bark in contact with the ground, where saprophytic microorganisms quickly invade phloem tissue. The effect by verbenone on catches of the five species was consistent with differences in host-age preference. Catches of species requiring relatively fresh host tissue were reduced by verbenone, whereas catches of species accepting aged tissue were unaffected.

Spatial genetic structure of the mountain pine beetle (Dendroctonus ponderosae) outbreak in western Canada: historical patterns and contemporary dispersal

Environmental change has a wide range of ecological consequences, including species extinction and range expansion. Many studies have shown that insect species respond rapidly to climatic change. A mountain pine beetle epidemic of record size in North America has led to unprecedented mortality of lodgepole pine, and a significant range expansion to the northeast of its historic range. Our goal was to determine the spatial genetic variation found among outbreak population from which genetic structure, and dispersal patterns may be inferred. Beetles from 49 sampling locations throughout the outbreak area in western Canada were analysed at 13 microsatellite loci. We found significant north‐south population structure as evidenced by: (i) Bayesian‐based analyses, (ii) north‐south genetic relationships and diversity gradients; and (iii) a lack of isolation‐by‐distance in the northernmost cluster. The north‐south structure is proposed to have arisen from the processes of postglacial colonization as well as recent climate‐driven changes in population dynamics. Our data support the hypothesis of multiple sources of origin for the outbreak and point to the need for population specific information to improve our understanding and management of outbreaks. The recent range expansion across the Rocky Mountains into the jack/lodgepole hybrid and pure jack pine zones of northern Alberta is consistent with a northern British Columbia origin. We detected no loss of genetic variability in these populations, indicating that the evolutionary potential of mountain pine beetle to adapt has not been reduced by founder events. This study illustrates a rapid range‐wide response to the removal of climatic constraints, and the potential for range expansion of a regional population.

Quantitative Association of Bark Beetles with Pitch Canker Fungus and Effects of Verbenone on Their Semiochemical Communication in Monterey Pine Forests in Northern Spain

Abstract The association between 11 species of bark beetles (Coleoptera: Scolytinae) and one weevil (Coleoptera: Entiminae) with the pitch canker fungus, Fusarium circinatum Nirenberg and O’Donnell, was determined by crushing beetles on selective medium and histone H3 gene sequencing. Pityophthorus pubescens (Marsham) (25.00%), Hylurgops palliatus (Gyllenhal) (11.96%), Ips sexdentatus (Börner) (8.57%), Hypothenemus eruditus Westwood (7.89%), Hylastes attenuatus Erichson (7.40%), and Orthotomicus erosus (Wollaston) (2.73%) were found to carry the inoculum. In addition, the root weevil Brachyderes incanus L. (14.28%) had the second highest frequency of occurrence of the fungus. The responses of the insects to a range of verbenone doses were tested in field bioassays using funnel traps. Catches of P. pubescens, a species colonizing branch tips of live trees, were significantly reduced in a log-linear dose-dependent relationship. Catches of I. sexdentatus, an opportunistic species normally attacking fresh dead host material, were also gradually reduced with increasing verbenone dose. Catches of Tomicus piniperda L., O. erosus, Dryocoetes autographus (Ratzeburg), H. eruditus, Xyleborus dryographus (Ratzeburg), Hylastes ater (Paykull), Hylurgus ligniperda (F.), H. attenuatus, and B. incanus were not significantly affected by verbenone. The effects of verbenone were consistent with differences in host-age preference. Semiochemical disruption by verbenone in P. pubescens and I. sexdentatus could represent an integrated pest management strategy for the prevention of the spread of pitch canker disease between different stands. However, several species associated with F. circinatum were unaffected by verbenone, not supporting this compound for prevention of the establishment of potential vectors in Northern Spain.

Facilitation in bark beetles: endemic mountain pine beetle gets a helping hand

1 Endemic populations of the bark beetle Dendroctonus ponderosae attack weakened lodgepole pine (Pinus contorta var. latifolia) trees that are often previously infested by other bark beetle species, such as Pseudips mexicanus. 2 The effect of interactions on D. ponderosae was assessed by examining host selection and productivity of D. ponderosae in trees containing P. mexicanus and trees infested solely by D. ponderosae. 3 The findings obtained show that D. ponderosae attacked hosts previously occupied by P. mexicanus at greater densities, and offspring emerged earlier compared with hosts infested by D. ponderosae alone. Additionally, D. ponderosae larvae in P. mexicanus‐infested trees were found to require a significantly lower amount of resource to complete development with no loss in size. 4 The presence of P. mexicanus may affect host condition, improving the subcortical environment for endemic D. ponderosae, ultimately aiding in population maintenance at low levels. Hosts in this state should be preferentially attacked by D. ponderosae.

Comparison of lodgepole and jack pine resin chemistry: implications for range expansion by the mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Curculionidae)

The mountain pine beetle, Dendroctonus ponderosae, is a significant pest of lodgepole pine in British Columbia (BC), where it has recently reached an unprecedented outbreak level. Although it is native to western North America, the beetle can now be viewed as a native invasive because for the first time in recorded history it has begun to reproduce in native jack pine stands within the North American boreal forest. The ability of jack pine trees to defend themselves against mass attack and their suitability for brood success will play a major role in the success of this insect in a putatively new geographic range and host. Lodgepole and jack pine were sampled along a transect extending from the beetle’s historic range (central BC) to the newly invaded area east of the Rocky Mountains in north-central Alberta (AB) in Canada for constitutive phloem resin terpene levels. In addition, two populations of lodgepole pine (BC) and one population of jack pine (AB) were sampled for levels of induced phloem terpenes. Phloem resin terpenes were identified and quantified using gas chromatography. Significant differences were found in constitutive levels of terpenes between the two species of pine. Constitutive α-pinene levels – a precursor in the biosynthesis of components of the aggregation and antiaggregation pheromones of mountain pine beetle – were significantly higher in jack pine. However, lower constitutive levels of compounds known to be toxic to bark beetles, e.g., 3-carene, in jack pine suggests that this species could be poorly defended. Differences in wounding-induced responses for phloem accumulation of five major terpenes were found between the two populations of lodgepole pine and between lodgepole and jack pine. The mountain pine beetle will face a different constitutive and induced phloem resin terpene environment when locating and colonizing jack pine in its new geographic range, and this may play a significant role in the ability of the insect to persist in this new host.

Successful colonization, reproduction, and new generation emergence in live interior hybrid spruce Picea engelmannii×glauca by mountain pine beetle Dendroctonus ponderosae

1 Although mountain pine beetle Dendroctonus ponderosae Hopkins are able to utilize most available Pinus spp. as hosts, successful colonization and reproduction in other hosts within the Pinaceae is rare.

Effect of Verbenone on Attraction of Predatory and Woodboring Beetles (Coleoptera) to Kairomones in Lodgepole Pine Forests

Abstract The response of bark beetle predators and woodboring beetles to the bark beetle anti-aggregation pheromone, verbenone, was tested in the field with multiple-funnel traps baited with attractant kairomones. Catches of the predators Thanasimus undatulus (Say), Enoclerus sphegeus (F.), Enoclerus lecontei (Wolcott) (Coleoptera: Cleridae), and Lasconotus complex LeConte (Coleoptera: Colydiidae) declined significantly with increasing release rates of verbenone. Lasconotus subcostulatus Kraus, and Corticeus praetermissus (Fall) (Coleoptera: Tenebrionidae) (in two of three experiments), showed no significant response to verbenone. In a third experiment, catches of C. praetermissus increased with verbenone dose. Likewise, catches of the striped ambrosia beetle, Trypodendron lineatum (Olivier) (Coleoptera: Scolytidae), increased with verbenone dose in one experiment, but there was no effect in two other experiments. Verbenone had no effect on the response of Spondylis upiformis Mannerheim (Coleoptera: Cerambycidae). We hypothesize that predators specializing on early successional bark beetles are repelled by verbenone since this compound indicates a late stage attack. Generalist predators and woodborers either do not respond to verbenone at all, or they may be attracted by it.

Influence of decay fungi on species composition and size class structure in mature Picea glauca × engelmannii and Abies lasiocarpa in sub-boreal forests of central British Columbia

Abstract Disturbance patterns in the sub-boreal spruce forests of central British Columbia have long been thought to result from frequent stand-initiating fires. However, recent evidence suggests that fires in the wetter areas of this region are infrequent (>500 years) and the uneven-aged stand structures have been shown to be self-maintaining in the absence of fire. The importance of decay fungi as agents of gap-formation and facilitators of uneven-aged stand structure was investigated. Three plots on each of two recently clearcut sites were established. Each stump in the plots was stem mapped and the species and diameter recorded. Decay at the stump top was recorded as white or brown rot, and the area occupied by decay was measured. Spruce stumps dominated the larger diameter classes but had less butt rot than sub-alpine fir stumps. Decay fungi contribute to stem breakage in living trees with heart rot, and as saprots of dead trees. Therefore, the results suggest that decay fungi play an important role in removing sub-alpine fir trees from the canopy of these wetter sub-boreal ecosystems, and in enabling spruce recruitment. The type of decay observed in sub-alpine fir suggests that breakage is predominantly due to white rot fungi causing heart rot, such as Echinodontium tinctorium and Stereum sanguinolentum. In spruce, brown rot fungi, which are predominantly saprot or wound-entry decay fungi, became more common in larger spruce, and may result from wounding as sub-alpine fir fall from the canopy. Spatial analysis indicated the stumps with stem decay were clumped. However, this is more likely due to strong clumping of the host, rather than spreading of butt rot pathogens through the roots.

Dose-Dependent Pheromone Responses of Mountain Pine Beetle in Stands of Lodgepole Pine

Abstract We conducted seven behavioral choice tests with Lindgren multiple-funnel traps in stands of mature lodgepole pine in British Columbia, from 1988 to 1994, to determine the dose-dependent responses of the mountain pine beetle, Dendroctonus ponderosae Hopkins, to its pheromones. A multifunctional dose-dependent response was exhibited by D. ponderosae to the pheromones cis- and trans-verbenol in areas with low population numbers. In an area with a high population level of D. ponderosae, the response was directly proportional to release rates. No dose-dependent response was exhibited by D. ponderosae to exo-brevicomin at low release rates. At rates of release >0.5 mg/d, exo-brevicomin interrupted the attraction of D. ponderosae in a dose-dependent fashion. The bark beetle predators, Enoclerus sphegeus (F.) and Thanasimus undatulus (Say), showed dose-dependent responses to only a few pheromones, with trap catches directly proportional to release rates. The multi-functional response of D. ponderosae to verbenols is consistent with an optimal attack density hypothesis.

The role of vision in the host orientation behaviour of Hylobius warreni

1 Visual stimuli, often in combination with olfactory stimuli, are frequently important components of host selection by forest‐dwelling phytophagous insects. 2 Warren root collar weevil Hylobius warreni Wood (Coleoptera: Curculionidae) is a native insect in western Canada, where larvae feed primarily on lodgepole pine Pinus contorta and can girdle and kill young trees. This weevil is an emerging problem in areas heavily impacted by mountain pine beetle Dendroctonus ponderosae Hopkins. 3 No olfactory attractants have been identified for this insect, making monitoring and management difficult. Thus, we investigated the role of vision in the host‐finding behaviour of Warren root collar weevil in the absence of known olfactory cues. 4 We conducted three experiments in field enclosure plots aiming to characterize aspects of host‐finding behaviour by adult Warren root collar weevil. 5 We found that both male and female weevils were readily attracted to vertical plastic silhouettes in the shape of a trunk, crown or tree at distances of less than 4 m. This pattern of attraction persisted over 2 years in two slightly different study designs. Blinding the insects removed their ability to orient to these silhouettes, indicating that host‐finding behaviour has a strong visual component. The use of different colour trunks and crowns (black, white and green) did not change the patterns of attraction of the insects to the silhouettes. 6 Exploiting visual attraction in this walking insect may present a new management tool in forest protection strategies.