Dendroctonus Brevicomis Research Articles

TREE UTILIZATION AND DENSITY OF ATTACKING AND EMERGING POPULATIONS OF THE WESTERN PINE BEETLE (COLEOPTERA: SCOLYTIDAE) AND ITS NATURAL ENEMIES, BASS LAKE, CALIFORNIA, 1970–1971,

AbstractTree size and bark surface area infested in trees killed by the western pine beetle (WPB), Dendroctonus brevicomis LeConte, and the density of attacking and emerging WPB were measured on 91 trees spanning five consecutive generations of the insect. The emergence densities of six natural enemies were also estimated.Trees averaged 50.9 cm in diameter at breast height (DBH) with a mean height to base of infestation (HBI) of 1.1 m. Heights to top of infestation (HTI) averaged 16.0 m, but were significantly lower in trees attacked by the second [70(1)] and third [70(2)] generations, during synthetic pheromone elution, than in the first [69(3)], or fourth [70(3)], and fifth [71(1)] generations, before and after the treatment, respectively. Infested bark area averaged 2005 dm2 per tree for all generations.WPB attack density declined steadily from 4.36 beetles/dm2 in generation 69(3) to 0.86 beetles/dm2 in 71(1). Sampling errors ranged from 6.67 to 26.27%, higher than the desired 15% in some cases. WPB emergence in field sticky traps (STIK) followed an opposite trend from 1.66 beetles/dm2 in 69(3) to 5.43 beetles/dm2 in 71(1). Sampling errors ranged from 8.39 to 28.26%. WPB emergence in laboratory rearings (REAR) averaged 4.03 beetles/dm2 with no significant differences among the generations. Sampling errors ranged from 8.20 to 28.77%. Because of inconsistent differences between these two methods of measuring WPB emergence, we have reported estimates of both.Densities of attacking and emerging WPB were found to be uncorrelated with tree diameter, indicating that density was not a function of tree size and that these two variables may be treated as independent random variables when used in product models to estimate area-wide population totals.Sampling errors for natural enemies were quite large, ranging up to 400%; therefore few conclusions could be drawn. Predators, in descending order of abundance, were Aulonium longum, Medetera aldrichii, Enoclerus lecontei, and Temnochila chlorodia. Parasitoids were less abundant overall than predators, with Roptrocerus xylophagorum more consistently present and at higher average densities than Dinotiscus burkei.The suppression treatment was applied during the collapse phase of the population cycle and apparently prolonged that phase for two generations. This delay resulted in the death of an additional 120 trees. WPB productivity increased with decreasing density/square decimetre of attacking beetles. Density of attacking beetles appears regulated by exogenous processes acting immediately in an inverse density-dependent manner. The WPB population at Bass Lake would be released from endemic to epidemic status at the equilibrium point reached at a density of attacking adults of loge 1.65 beetles/dm2. Mortality of the developing within-tree life-stages appears regulated by delayed density-dependent processes, but the details of the relationships differ depending upon the assessment method (STIK or REAR) used.

Biochemical Diversity of Ponderosa Pine and Predation by Bark Beetles (Coleoptera: Scolytidae)

To determine if mountain pine beetle, Dendroctonus ponderosae Hopkins, influences patterns of biochemical diversity in ponderosa pine, Pinus ponderosa Laws., monoterpene composition of xylem resin of trees that survived an infestation was compared with a random sample of living trees adjacent to the infestation. No significant differences were detected in means or variances between the two groups of trees. A comparison of these populations to populations of ponderosa pine with a history of western pine beetle, D. brevicomis LeConte, infestation revealed large differences in biochemical diversity between the two geographic areas. Association of geographic differences in biochemical diversity with insect species exhibiting different feeding habits suggests possible causal relationships between these two patterns.

Isolation of Fomitopsis pinicola from in-flight bark beetles (Coleoptera: Scolytidae)

Isolations of Hymenomycetes on a preferential medium were attempted from preflight pine engraver beetles, Ips pini, and the following in-flight bark beetles: pine engraver beetle, I. pini; western pine beetle, Dendroctonus brevicomis; mountain pine beetle, Dendroctonus ponderosae; and red turpentine beetle, Dendroctonus valens. Thirty pine engraver beetles removed from ponderosa pine slash (preflight) yielded no hymenomycete. However, Hymenomycetes were isolated from 50 of 114 beetles (all species) trapped in flight; Fomitopsis pinicola from 44, and other unidentified suspected Hymenomycetes, from 6. Cryptoporus volvatus was not isolated from any of the in-flight beetles. Since most of these isolates were without clamps (monokaryotic), the beetles may acquire basidiospores after emergence from beetle galleries in coniferous trees as hypothesized previously for the Douglas-fir beetle, Dendroctonus pseudotsugae. The isolation of F. pinicola from all species of in-flight bark beetles indicates that these beetles may be important in the dissemination of this hymenomycete.

Estimating and Valuing Western Pine Beetle Impacts

Abstract A tree growth and mortality model was developed to simulate timber production with and without tree mortality caused by the western pine beetle, Dendroctonus brevicomis LeConte. Stumpage value at time of harvest was discounted back to the time of mortality. A logging cost model was used to estimate revenue generated from salvaging killed trees. These values were assembled to estimate the value at risk from western pine beetle-caused tree mortality. Simulated estimates of beetle impact were affected by interest rate, time of final harvest, spatial aggregation of mortality, and distribution of mortality in relation to tree diameter and stand density. The model developed here simplified certain biological relationships. Its development highlighted the lack of quantitative data on biological factors affecting western pine beetle impact. Forest Sci. 32:325-338.

VISITATION FREQUENCIES OF SOME INSECT SPECIES ON CERATOCYSTIS WAGENERI INFECTED AND APPARENTLY HEALTHY PONDEROSA PINES

AbstractTo test the hypothesis that bark beetles and some associated insect species are attracted to ponderosa pines infected by Ceratocystis wageneri, insect visitations on 11 severely diseased, 9 moderately diseased, and 10 apparently healthy trees were monitored from 1 August to 15 October 1972. Larger numbers of Dendroctonus brevicomis, D. ponderosae, Temnochila chlorodia, and buprestids were captured on diseased trees uninfested by bark beetles than on apparently healthy ones, thus possibly indicating attraction to diseased trees. There was strong evidence that D. valens and Spondylis upiformis were attracted more frequently to wounds on diseased than on healthy trees. Arrival patterns of beetles were recorded for trees that became infested during the study. Predators became abundant on traps as bark beetle catches increased.

Behavior of the western pine beetle during host colonization

After living ponderosa pines were baited with either female-infested bolts or synthetic pheromones,Dendroctonus brevicomis were caught on sticky screens throughout trapping periods of 15-46 days; however, large numbers of beetles were trapped during only a small portion (5-10 days) of these trapping periods. The most attractive portions of trees attacked contained 3-6 beetles dm(2), in galleries ca. 2 cm long. Catch increased following addition of males to female-infested bolts, supporting the hypothesis that male-produced frontalin is an attractive pheromone of the western pine beetle. Catch at bolts removed from trees under attack was strongly dependent upon levels of boring activity. We found no evidence of interruption of the response to attractants during host colonization.

Field response ofDendroctonus brevicomis toexo-brevicomin, frontalin, and myrcene released at two proportions and three levels

Racemicezo-brevicomin, racemic frontalin, and myrcene were released at two proportions (5∶1∶400 and 1∶1∶1), each at three levels (1 ×, 10 ×, and 100 ×) in a ponderosa pine forest in central California. The 5∶1∶400 mix was based on an estimate of the relative amounts released from a ponderosa pine under attack by the western pine beetle,Dendroctonus brevicomis. MoreD. brevicomis were trapped at a source of the three compounds released at 5∶1∶400 than were trapped at a source released at 1∶1∶1, at all three levels, but this difference was statistically significant only at the 1 × and 10 × levels. Sex ratio of trapped beetles and distribution of catch at the source of attractant and 5 m away apparently did not differ between relative release rates.

Effective Residual Life of Carbaryl for Protecting Ponderosa Pine from Attack by the Western Pine Beetle (Coleoptera: Scolytidae)

The effectiveness of carbaryl in protecting high-value ponderosa pine trees from attack by Dendroctonus brevicomis LeConte was tested at reduced concentrations or for longer than one beetle flight season. A 2.0% suspension of carbaryl provided substantial protection of ponderosa pine from attack by D. brevicomis for the 5 months adults are actively attacking trees. Lesser concentrations, notably 1.0 and 0.5%, provided some protection but with greater tree mortality. Neither 2.0% Sevimol® nor 2.0% Sevin XLR® provided adequate protection for 9 or 12 months, respectively, after application.

Microsomal Polysubstrate Monooxygenase Activity in Western and Mountain Pine Beetles (Coleoptera: Seolytidae)

On the basis of polysubstrate monooxygenase (PSMO) activities in midgut tissue, we detected no difference in the biochemical breadth of diet of western pine beetles, Dendroctonus brevicomis Le Conte, and mountain pine beetles, D. ponderosae Hopkins. This result suggests that the number of taxa that these insects encounter may not be an accurate indicator of the diversity of toxins to which they are exposed. The biochemical diversity encountered by the host-restricted western pine beetle appears to be as great as that of the less host-restricted mountain pine beetle. PSMO activity of mountain pine beetles in their alternate host was significantly lower than that of mountain pine beetles in their preferred host; toxins in the alternate host may thus inhibit PSMO activity. Such inhibition may explain why, although mountain pine beetles colonize several different taxa throughout their geographic range, they prefer to colonize one taxon in any given locality and they shift to alternate hosts only rarely.

Attractive and inhibitory pheromones produced in the bark beetle,Dendroctonus brevicomis, during host colonization: Regulation of inter- and intraspecific competition

Quantities of attractive (exo-brevicomin and frontalin) and inhibitory (trans-verbenol, verbenone, and ipsdienol) pheromones were monitored in both sexes ofDendroctonus brevicomis during their colonization of a ponderosa pine. Verbenone was found in males in the greatest amounts at the time of landing, and it declined more rapidly than the other pheromones in either sex. The amounts of frontalin andexo-brevicomin in males and females, respectively, increased after initial boring within the host but began to decline after mating. The quantity oftrans-verbenol in both sexes (females had significantly more) declined more gradually thanexo-brevicomin, frontalin, and verbenone. Ipsdienol was found only in males during the initial stages of attack when encountering the resin. It is suggested that along with a general decline in all pheromonal components, a sufficient change in the ratio of the attractive pheromones to an inhibitory pheromone,trans-verbenol, may play a role in termination of aggregation.trans-Verbenol may also function along with verbenone and ipsdienol in limiting the density of attack and thus intraspecific competition. These inhibitory pheromones also appear to cause several competing species of bark beetle to avoid landing in areas infested withD. brevicomis, even when their own pheromone is present.

Effectiveness of Insecticides for Protecting Ponderosa Pines from Attack by Red Turpentine Beetle (Coleoptera: Scolytidae)

In a series of experiments conducted from 1979 to 1982, the efficacy of carbaryl (Sevimol 4 and Sevin XLR), chlorpyriphos, fenitrothion, and permethrin was tested for protection of ponderosa pines from attack by the red turpentine beetle, Dendroctonus valens LeConte. Insecticide-treated trees and untreated controls were baited with western pine beetle, D. brevicomis LeConte, semiochemicals to subject them to attack by D. valens. Only 4% carbaryl (Sevimol4), 2% carbaryl (Sevin XLR), and 4% fenilrothion were effective in protecting trees from D. valens attack.

Influence of the mycangial fungi of the western pine beetle on water conduction through ponderosa pine seedlings

The mycangial fungi Ceratocystis nigracarpa Davidson and a basidiomycete associated with western pine beetle reduce water conduction through seedling ponderosa pine. Only after the trees had been severely water stressed was the water tension in control treated trees not significantly different from that of a fungus treatment. There were no differences in the lengths of the lesions produced in a hypersensitive response to inoculated fungi or in the controls. This suggests that the reduction in water movement is a result of some factor other than destruction of conductive tissue.

Seasonal response of ponderosa pine to inoculation of the mycangial fungi from the western pine beetle

The hypersensitive response obtained by inoculating the two mycangial fungi of the western pine beetle, Dendroctonus brevicomis LeC, and the blue-stain fungus, Ceratocystis minor Hedge, into ponderosa pine was measured during three different seasons in the same 12-month period. The lesions were produced faster and were significantly longer in the fall than in the summer. Similarly, lesions were longer and were produced faster when inoculations made in the summer were compared with spring inoculations. However, the response to a nonpathogenic fungus, a Penicillium sp., was not different from the response to mycangial fungi, suggesting that lesion production is a generalized response to infection that isolates fungus-colonized tissue from the rest of the tree. Ethanol extracts of hypersensitive-response lesions produced during the spring did not reduce growth of the mycangial fungi or C. minor when bioassayed at concentrations similar to those found in host tissue. This is different from other bark beetle–host tree systems that have been investigated.

Southern Pine Beetle (Coleoptera: Scolytidae) Brood Adults: Reverse Emergence

The emergence of southern pine beetle (Dendroctonus frontalis Zimmermann) brood adults from the inner surface of removed Pinus taeda L. bark is described. It is well known that bark beetles normally emerge through the outer bark. The parent adults bore the so- called ventilation holes (Melnikova 1964, Payne 1980), while the brood adults bore the more frequent exit holes. However, Miller and Keen (1960) reported that when bark was removed from trees infested with the western pine beetle Dendroctonus brevicomis LeCompte 1876, the adults reversed their normal direction of emer- gence and emerged through the inner surface. If the bark were kept in a container with light excluded, the beetles emerged from both the outer and inner bark surfaces. This note reports similar behavior for the southern pine beetle, D. frontalis Zimmermann 1868.

Attraction of Dendroctonus valens (Coleoptera: Scolytidae) to Ponderosa Pines Baited with Dendroctonus brevicomis (Coleoptera: Scolytidae) Pheromone

From 1979 to 1981, the number of ponderosa pines attacked by Dendroctonus valens LeConte was monitored in conjunction with a series of experiments on Dendroctonus brevicomis LeConte. During these experiments, over 100 trees were baited with D. brevicomis pheromone. In four replications, trees baited with pheromone were attacked in greater numbers than were unbaited trees. Thus, I suggest that D. valens is attracted to ponderosa pines by compounds released from the tree during D. brevicomis attack. Alternative explanations are offered.

Bark Beetle Conversion of a Plant Compound to a Sex-Specific Inhibitor of Pheromone Attraction

Both sexes of the bark beetle Dendroctonus brevicomis convert the (+) and (-) enantiomers of the tree terpene alpha-pinene to the corresponding enantiomers of trans-verbenol at about equal rates. (-)-trans-Verbenol inhibited the response of females, but not of males, to a mixture of attractive pheromone components. Since the female initiates the attack on a pine tree, (-)-trans-verbenol may play a role in reducing intraspecific competition for breeding areas.

Simulated Natural Encounters of the Insecticides, Chlorpyrifos and Carbaryl, by Western Pine Beetle Predators Enoclerus lecontei and E. sphegeus (Coleoptera: Cleridae)1

Laboratory tests are described, using residual film and topical application methods to evaluate the toxicity of aqueous formulations of chlorpyrifos and carbaryl to two coleopterous predators, Enoclerus lecontei and E. sphegeus . The insecticide-impregnated filter paper discs simulated predators walking on sprayed substrates, and topical application evaluated intrinsic susceptibility. Chlorpyrifos was equally toxic to both species in both tests, whereas carbaryl showed very limited toxicity to both species. These tests indicate that carbaryl, a chemical which provides extensive protection of ponderosa pine trees from attack by western pine beetles, has minimal effect on the important predators of the western pine beetle

Effects of Remedial Application of Lindane on Emergence of Natural Enemies of the Western Pine Beetle, Dendroctonus brevicomis (Coleoptera: Scolytidae) 1

Field tests of remedial applications of registered 2% lindane sprays to ponderosa pine, Pinus ponderosa Laws, bark infested with the western pine beetle, Dendroctonus brevicomis LeConte (Coleoptera: Scolytidae), indicated that the overall emergence of predaceous natural enemies is reduced by 89%, and a ratio of natural enemy to western pine beetle emergence is diminished by 80%. Species showing significant effects due to lindane treatment include Enoclerus lecontei (Wolc.), Aulonium longum LeConte, and Medetera aldrichii Wheeler. Differential in situ mortality of predators and prey indicates a need for further study of dispersal stage mortality of predators and prey as well as the contribution of natural enemies to long-term population regulation before continuing registration of lindane for remedial control of the western pine beetle.

Influence of sex, maturity and host substances on pheromones in the guts of the bark beetles, Ips paraconfusus and Dendroctonus brevicomis

Pheromones and metabolites of host (ponderosa pine) compounds were found in association with the hindgut of both naturally fed and of non-fed, host vapour-exposed bark beetles, Ips paraconfusus and Dendroctonus brevicomis. Much smaller amounts were found in the corresponding heads and mid guts. Sex-specific differences in content of pheromones were observed as in earlier studies. Exposure of I. paraconfusus to vapours of a pheromone component, ipsenol and other monoterpene alcohols resulted in their accumulation in the hindgut but relatively very low amounts in the head. The possible sites of pheromone biosynthesis are discussed. Exposure of male I. paraconfusus to vapours of host compounds, myrcene and α-pinene, revealed that immature adults do not produce the pheromone components, ipsenol and ipsdienol, as mature adults do while both immature and mature sexes produced another pheromone component, cis-verbenol, as well as trans-verbenol and myrtenol. Immature D. brevicomis adults did not contain pheromones until their exposure to vapours of (−)-α-pinene which caused production of trans-verbenol but only about 10% that of mature adults treated similarly. Verbenone, a male-produced inhibitory pheromone of D. brevicomis, apparently was not synthesized from (−)-α-pinene in females nor was its synthesis in males enhanced by exposure to this host compound.

Effectiveness of Carbaryl and Chlorpyriphos for Protecting Ponderosa Pine Trees from Attack by the Western Pine Beetle (Coleoptera: Scolytidae)1

A large-scale field experiment was conducted to examine the efficacy of 1, 2, and 4% chlorpyriphos and 1,2, and 4% carbaryl for protecting high-value ponderosa pine trees from attack by Dendroctonus brevicomis LeConte. Each of the 510 trees utilized in the experiment was separated by at least 0.4 km. At 1 month, 3 months, and 1 year after insecticide application, D. brevicomis pheromone was attached to the boles of treated and untreated check trees. All six treatments were regarded as effective 1 month after application. At 3 months after application, 1 and 2% chlorpyriphos were regarded as ineffective. One year after application, low mortality of untreated check trees hindered the determination of efficacy of the remaining four treatments. At 3 months and 1 year after application, significantly more Temnochila chlorodia (Mannerheim) were found in catchment traps beneath treated than beneath untreated trees. The best explanation for this is insecticide-induced mortality of T. chlorodia . There were no significant differences in numbers of D. brevicomis or Enocleris lecontei (Wolcott) in the catchment traps.