Can spruce beetle (Dendroctonus rufipennis Kirky) pheromone trap catches or stand conditions predict Engelmann spruce (Picea engelmannii Parry ex Engelm.) tree mortality in Colorado?

1. Bark beetles (Coleoptera: Curculionidae: Scolytinae) can cause extensive tree mortality in forests dominated by their hosts. Among these, the spruce beetle (Dendroctonus rufipennis) is one of the most important beetles in western North America causing Engelmann spruce (Picea engelmannii) tree mortality.
2. Although pheromone traps with attractants are commonly used to monitor spruce beetle populations, the relationship between the numbers of beetles caught in pheromone traps and subsequent tree mortality has not been investigated adequately.
3. We used pheromone traps to catch spruce beetles in plots throughout the insect flight period, quantified subsequent tree mortality, and modelled spruce tree mortality as a function of spruce beetle trap catches and stand conditions.
4. The number of beetles caught was not different between years. It was also positively associated with tree mortality, as was the amount of available host. The year of sampling was significant in all models as a result of different mortality levels between years.
5. We conclude that, although the models had good fit, the difference in mortality between the years with a similar beetle catch negates reliable estimates of tree mortality across years. Managers and forest health specialists will be better served by continued monitoring of spruce beetle populations with pheromone traps and the use of stand variables to identify susceptible stands.

     

Evaluation of traps used to monitor southern pine beetle aerial populations and sex ratios

1 Various kinds of traps have been employed to monitor and forecast population trends of the southern pine beetle (Dendroctonus frontalis Zimmermann; Coleoptera: Scolytidae), but their accuracy in assessing pine‐beetle abundance and sex ratio in the field has not been evaluated directly. 2 In this study, we used fluorescent powder to mark pine beetles emerging from six isolated infestations. We then compared estimates of total abundances and proportions of males emerging from within each infestation to the estimates from three types of traps: passive sticky traps (2, 5, 10 and 20 m away from the source of beetles), multi‐funnel traps baited with pine beetle attractants (100 m away) and pine trees baited with attractants (also 100 m away). 3 We found that the proportion of males captured in traps was significantly affected by the type of trap used. 4 Within an infestation, equal proportions of males and females were marked (0.53 ± 0.02 males; mean ± SE), but the proportions captured in trap trees and passive traps were more female biased (0.42 ± 0.03 and 0.46 ± 0.01 males, respectively). On the other hand, funnel traps provided an estimate of the proportion of males that was nearly identical to the proportion from within infestations (0.51 ± 0.03). 5 Numbers of marked beetles captured in traps were uncorrelated with the numbers of marked beetles emerging from the focal infestations. This suggests that traps positioned around an infestation may not be effective at estimating relative abundances of beetles within the infestation.     

Scramble competition in the southern pine beetle, Dendroctonus frontalis

Abstract .1. The nature of intraspecific competition was investigated in the southern pine beetle, Dendroctonus frontalis , a highly destructive pest of pine forests in the southern U.S.A. Data were analysed from an observational study of naturally-attacked trees, and from field experiments where attack density was manipulated by adding different numbers of beetles to caged trees.
2. The effect of attack density on gallery construction, oviposition, brood survival, and the overall rate of increase was examined, and a flexible model of intraspecific competition used to classify the type of competition (contest or scramble) at different points in the life cycle.
3. The results of these analyses suggest that contest competition occurs during gallery construction and oviposition, in accord with previous work on D. frontalis . Strong scramble competition occurs later on in development, however, and the overall competitive process is better characterized as scramble competition, similar to other bark beetles. Trees with attack densities sufficiently high to produce significant competition are common in the field.     

Sampling saproxylic beetle assemblages in dead wood logs: comparing window and eclector traps to traditional bark sieving and a refinement

The use of saproxylic beetle community as a metric to evaluate nature conservation measures in forests requires efficient methods. We first compare traditional bark sieving to a potential improvement (extracting beetles from whole bark with Tullgren funnels) to determine the most efficient. Secondly we compare this most efficient bark sampling to eclector and window traps. At the species, family, and functional group levels, we consider species richness, abundance and practical aspects. Traditional bark sieving missed >50% of the individual beetles compared to whole bark sampling so we recommend the latter. Window traps caught large numbers of mobile saproxylic beetles, but a high proportion of non-saproxylics results in high sorting cost; bark sampling and eclector traps had a high proportion of saproxylics and obligate saproxylics. Compared to bark sampling, eclector traps are non-destructive, and monitor the whole saproxylic assemblage (i.e. also beetles inside the wood). Overall, window traps are useful because they capture saproxylic beetles attracted to dead wood and sample the local species pool, whereas eclector traps capture the saproxylics that actually emerge from a particular piece of dead wood, and thus are suited to detailed studies. Overall, we suggest that a combination of these two best methods is highly complementary.     

Variations in bark acidity and conductivity over the trunk length of silver fir and Norway spruce

 Before using bark to determine the degree of acidity in the environment due to atmospheric pollution, a better understanding of the internal factors which are involved in the evolution of the physico-chemical characteristics of bark is necessary. In this paper, variation of acidity and bark conductivity over the trunk length of silver fir and Norway spruce are examined. First, we show that it is more accurate to measure average bark pH and conductivity in each 2 m section of a tree by starting at the top than by starting at the base of the tree. A positive pH and conductivity gradient is observed over the trunk length; bark thickness decreases towards the top of the trunk. In the upper part of both silver fir and Norway spruce there are good correlations between acidity, conductivity, bark thickness and height, but in the lower part of the trees, silver fir and Norway spruce show contradictory behaviour. In silver fir, pH is linked with bark thickness and distance from the ground, while conductivity is not correlated with these two criteria. In Norway spruce we observe opposite results. It appears that conductivity measured on the external part of bark is directly influenced by the proximity of internal tissues, which are rich in ions, while acidity depends on the length of exposure to leaching due to water flowing down the trunk. Received: 15 June 1993/Accepted: 30 January 1995     

A comparison of three methods to survey saproxylic beetles in hollow oaks

One of the most endangered assemblages of species in Europe is insectsassociated with old trees. For that reason there is a need of developing methodsto survey this fauna. This study aims at comparing three methods – windowtrapping, pitfall trapping and wood mould sampling – to assess speciesrichness and composition of the saproxylic beetle fauna in living, hollow oaks.We have used these methods at the same site, and to a large extent in the sametrees. Useful information was obtained from all methods, but they partiallytarget different assemblages of species. Window trapping collected the highestnumber of species. Pitfall trapping collected beetles associated with treehollows which rarely are collected by window traps and therefore it isprofitable to combine these two methods. As wood mould sampling is the cheapestmethod to use, indicator species should preferably be chosen among specieswhich are efficiently collected with this method.     

Evaluation of genetic variation of attack and resistance in lodgepole pine in the early stages of a mountain pine beetle outbreak

We examined variation of attack by mountain pine beetle (MPB) (Dendroctonus ponderosae) (Coleoptera: Scolytidae) in a 20-year-old lodgepole pine open-pollinated (OP) family trial composed of 165 OP parent-trees originating from local and nonlocal provenances. Trees were assessed in the summer of 2005 for traits relating to attack, survival, gallery formation, and infection from the fungi associated with MPB, Ophiostoma sp. Successful initial attack was determined by the presence of dead (i.e., red or gray foliage) crowns and the presence of entrance holes from MPB. Eighty-seven percent of the trees still had green crowns in the fall of 2005 (GC05), with family mean differences ranging from 46 to 100%. The mean number of pitch tubes per tree (PT#05) (in a sampling area of 225 cm² at breast height) was 1.5 with a range from 0 to 14 per tree. However, for pitch tubes indicating presence or absence (PTP05) of MPB on each tree, 63% of the trees had pitch tubes and family means ranged from 7 to 100%. Significant levels of genetic variation were found for GC05 and PTP05 with narrow-sense heritabilities of 0.20 (SE = 0.11) and 0.26 (SE = 0.07), respectively. Provenance differences were also significant, indicating that some population structure is present for these “resistance” attributes. The family breeding value correlations between 10-year height growth and PTP05 was 0.22, indicating that at the population level faster growing families may be slightly more subject to attack. An intensive survey of a subsample of 442 trees in the test (selected from 50 families with a range of attack levels) was conducted, and trees were reassessed for the presence of attack, presence of blue stain in the wood, and presence of galleries and egg chambers/eggs in the gallery. Family means ranged from 0 to 57% for blue stain, 11 to 63% for galleries, and 0 to 57% for egg chambers/eggs; however, due to the relatively small sample sizes and the nature of the binary data, family differences were not highly statistically significant. Further research is underway to improve the quantitative genetic parameters and determine the actual mechanisms at work; however, it is clear the MPB does react differently to host genotypes in terms of initial attack.     

不同方法对蜜蜂总科昆虫资源与多样性监测效果的比较

蜜蜂总科昆虫是重要的生物资源, 可为人类提供蜂产品、为生态系统提供授粉服务等。当前全球蜜蜂资源呈下降趋势, 亟需加强监测和保护。虽然调查和监测蜜蜂总科昆虫的方法有多种, 但各方法适用的监测类群还不甚清楚。为了对蜜蜂总科昆虫进行系统监测, 更为了全面揭示蜜蜂总科昆虫的多样性, 本研究选择生物资源极为丰富的中国科学院西双版纳热带植物园, 利用样线法、马来氏网法和黄盘法对蜜蜂总科昆虫资源及多样性进行监测, 比较了不同方法的监测效果。经过一年期系统监测, 收集到蜜蜂总科(包括蜜蜂科、隧蜂科、切叶蜂科、分舌蜂科、泥蜂科、方头泥蜂科和蠊泥蜂科)昆虫14,896头, 隶属于7科54属345种。稀释曲线显示3种方法采样覆盖度均充分, 但收集的主要类群有差异。样线法监测到6科33属133种, 蜜蜂科、切叶蜂科和隧蜂科的多样性较高, 有3个优势种及44个稀有种。马来氏网法监测到7科50属260种, 方头泥蜂科、切叶蜂科和隧蜂科的多样性较高, 有6个优势种及130个稀有种。黄盘法监测到6科29属122种, 方头泥蜂科多样性高, 而蜜蜂科个体数多, 有6个优势种及49个稀有种。结果显示不同方法适合监测蜜蜂总科昆虫中不同的类群及种类, 组合使用可监测到更多物种, 这将为蜜蜂总科昆虫的调查、种群监测提供方法选择, 也为有效保护蜜蜂总科昆虫资源提供基础数据。     

Complex emergence patterns in a bark beetle predator

1 The emergence pattern of Thanasimus dubius (F.) (Coleoptera: Cleridae), a common predator of the southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), was studied under field conditions across different seasons. A simple statistical model was then developed to characterize the emergence data, using the truncated geometric distribution. Data are also presented on the mortality of T. dubius eggs at various temperatures and humidities in an effort to explain certain aspects of emergence behaviour. 2 Emergence of T. dubius from a given tree usually occurred in several discrete episodes across a two‐year period, with most individuals emerging in spring or autumn. Almost no emergence occurred in July and August, which may be an adaptation to avoid high temperature mortality. Emergence patterns appeared similar across seasons, with the time of year serving mainly to shift the pattern through time. 3 Cycles in D. frontalis abundance may be the result of delayed density dependence generated by its natural enemy complex. The predator T. dubius is likely to be an important component of this delayed density dependence, because of its lengthy development time and apparent impact on D. frontalis.