Host-independent artificial rearing of Eucryptorrhynchus brandti (Coleoptera: curculionidae)†

Eucryptorrhynchus brandti (Harold) is a trunk boring pest of Ailanthus altissima in China and is a potential biological control agent for invasive A. altissima in the USA. In this study, we developed a host-independent artificial rearing method for E. brandti adults and larvae, including fresh thin slices of potato for adults and a potato-based diet (referred to as diet 6) for larvae. Adults reared on thin slices of potato oviposited normally and larvae reared on diet 6 exhibited successful pupation and eclosion and short developmental duration. The rates of larval survival, pupation, and adult emergence were 63.3?±?0.26, 86.7?±?0.42, and 93.5?±?0.33%, respectively. This method could be used for the mass rearing of E. brandti.     

Assessing Eucryptorrhynchus brandti (Coleoptera: Curculionidae) as a potential carrier for Verticillium nonalfalfae (Phyllachorales) from infected Ailanthus altissima

Two potential biological control agents for the invasive tree-of-heaven, Ailanthus altissima (Mill.) Swingle, have been extensively studied: a vascular wilt fungus, Verticillium nonalfalfae Inderb. (formerly Verticillium albo-atrum Reinke and Berthold), and a host-specific weevil from China, Eucryptorrhynchus brandti Harold, which is currently pending quarantine release. In 2002, V. nonalfalfae was observed in Pennsylvania causing significant mortality to A. altissima. Quarantine experiments were conducted to test different forms of transmission of the fungus by E. brandti to A. altissima. In one experiment, 75% of adult E. brandti transmitted V. nonalfalfae to A. altissima seedlings after contact with a culture and feeding on infected plant material. In another study, 14.7±1.3% of adult E. brandti ingested and passed viable V. nonalfalfae propagules into faeces after feeding on infected A. altissima stems for 24, 48 and 72 h, respectively, and the number of propagules increased at 72 h. Eighty-three per cent of surviving weevils overwintering in naturally infested potting mix carried viable V. nonalfalfae propagules externally. All weevil progeny that emerged from infected A. altissima billets appeared to be as healthy as weevils reared from non-infected billets. Our studies have shown that ingestion of V. nonalfalfae after feeding on infected plant material plays an important role in assessing E. brandti as a potential carrier. Results from these laboratory studies indicate E. brandti has the ability to transfer V. nonalfalfae to A. altissima seedlings in a laboratory setting.     

Micro-habitat niche differentiation contributing to coexistence of Eucryptorrhynchus scrobiculatus Motschulsky and Eucryptorrhynchus brandti (Harold)*

Temporal, spatial, and trophic niche differentiation usually occurs among species living in similar habitats which can reduce interspecific competition under limited resources. Eucryptorrhynchus scrobiculatus and Eucryptorrhynchus brandti are sympatric and closely related species and are host-specific to Ailanthus altissima (Mill.) Swingle in China. However, the possibility of niche differentiation between the two species is not clear. Therefore, we investigated the density of the two weevils temporally, spatially, and trophically (plant parts of A. altissima) at Lingwu farm and Haojiaqiao town, Lingwu city, Ningxia Hui Autonomous Region. No differences were found in temporal Levin’s niche breath index values ranging from 3.74 to 3.95 and temporal Pianka’s niche overlap values (0.98–0.99). There was little differentiation in the vertical spatial niche. The vertical distribution of E. scrobiculatus was mainly located from 0?cm (ground) to over 250?cm on tree-of-heaven. Eucryptorrhynchus brandti was found predominantly from 0.1 to 50?cm to over 250?cm on tree-of-heaven. The overlap of the cardinal direction spatial niche was 0.90–0.98, indicating no significant overlap in the cardinal direction at Lingwu farm and Haojiaqiao town. Significant differentiation of trophic niche occurred with E. scrobiculatus feeding on 1-year-old branches, perennial branches, and petioles, while E. brandti feed on the stem.     

Application of a frequency distribution method for determining instars of Eucryptorrhynchus brandti (Coleoptera: curculionidae) from several morphological variables

Eucryptorrhynchus brandti (Harold) (Coleoptera: Curculionidae) is a major pest of Ailanthus altissima (Mill.) Swingle (Simaroubaceae), commonly known as tree-of-heaven, and A. altissima var. Qiantouchun in China. It is considered a potential biological control agent for tree-of-heaven in North America. The aim of this study was to use a frequency distribution method to determine the instars of field-collected larvae of E. brandti. We collected larval samples of various sizes from both the field and the laboratory and measured five morphological variables, including antenna spacing, mandible width, head-capsule width, ocellus spacing, and pronotum width. Based on the results of a frequency distribution method and Dyar’s rule, the larvae of E. brandti were divided into seven instars. Of the five variables measured, the width of the head capsule provided the best measurement for determining instar stage. The regression equation between the head-capsule widths and the instar number was y?=?0.324e^0.096x (R²?=?0.970).     

Comparative morphology of sensilla on antenna,maxillary palp and labial palp of larvae of Eucryptorrhynchus scrobiculatus (Olivier) and E. brandti (Harold) (Coleoptera: Curculionidae)

Eucryptorrhynchus scrobiculatus (Olivier) and E. brandti (Harold) are two wood boring pests of Ailanthus altissima (Mill.) Swingle (tree of heaven) and the variety Ailanthus altissima var. Qiantouchun. These beetles attack healthy trees and bore into roots and trunks during the larval stage. We studied the typology, distribution and morphostructure of the sensilla on the antennae, maxillary palps and labial palps of E. scrobiculatus and E. brandti larvae using scanning and transmission electron microscopy. The results showed the following: (i) the antennae of the two weevil larvae had two types of sensilla, sensilla basiconica (S.b.1 and S.b.2) and sensilla twig basiconica (S.tb.1‐S.tb.3), with S.tb.4 observed only on the antennae of E. brandti larvae; (ii) the maxillary palps had three types of sensilla, S.b.2, S.tb. (S.tb.2, S.tb.3 and S.tb.5) and digitiform sensilla; (iii) the labial palps had two types of sensilla, S.b.2 and S.tb. (S.tb.2, S.tb.3 and S.tb.5); (iv) the quantity and distribution of sensilla on the antennae, maxillary palps and labial palps remained constant between E. scrobiculatus and E. brandti larvae; and (v) sensilla basiconica had distinct sidewall pores, an apical pore was observed on sensilla twig basiconica, and digitiform sensilla were oval in shape, with a distinct apical pore. Based on the microstructure of the cuticle wall and dendrite, we hypothesized that these sensilla functioned as olfactory, gustatory and hygro‐/thermo‐receptors, respectively. We discuss the relationships among types of sensilla and the types of damage caused by the larvae inside the host tree to understand olfactory and gustatory receptor mechanisms. The results of this study will provide a firm basis for future electrophysiological studies.     

Phototactic behaviour of Eucryptorrhynchus scrobiculatus and E. brandti (Coleoptera: Curculionidae) adults*

Eucryptorrhynchus scrobiculatus and E. brandti (Coleoptera: Curculionidae) are destructive weevils on Ailanthus altissima in China. This study examined phototactic behaviour of E. scrobiculatus and E. brandti in response to eight light-emitting diodes (LEDs) in the laboratory and field. Effects of gender, starvation, and light and dark experience on the phototactic behaviour of the insects were evaluated. The results demonstrated that, the two species of weevil were phototactic insects and most sensitive to violet light (400–405?nm), followed by blue–violet light (420–430?nm). They were less sensitive to red (655–660?nm), white (6000–6500?k), blue–green (470–480?nm), yellow (590–595?nm), blue (450–455?nm), and green (515–530?nm) light. In the light intensity range of 200–1000?lux, the light intensity had no significant effect on the phototatic behaviour of E. scrobiculatus and E. brandti. Phototactic behaviour of the insects was affected by gender. The phototaxis indices of the two species of weevil increased with starvation, reaching a plateau after 2 or 3?d of starvation. The phototaxis indices of E. scrobiculatus and E. brandti were significantly affected by various wavelengths of light following exposure to the light for 3?h or in different dark experience time. In the mark-release-recapture test, the number of E. scrobiculatus and E. brandti adults trapped by violet (400–405?nm) light traps is the largest. The information provided here provides a basis for survey and control of E. scrobiculatus and E. brandti.     

ALLELOPATHIC AND HERBICIDAL EFFECTS OF EXTRACTS FROM TREE OF HEAVEN (AILANTHUS ALTISSIMA)

Mature trees of Ailanthus altissima produce one or more potent inhibitors of seed germination and seedling growth. Inhibitor activity is highest in bark, especially of roots, intermediate in leaflets, and low in wood. Crude extracts of Ailanthus root bark and leaflets corresponding to 34 and 119 mg water extractable material/L, respectively, caused 50% inhibition of cress radicle growth. Ailanthus seeds also contain one or more inhibitors. These are bound within the seed by the pericarp but diffuse into water agar when the pericarp is removed. The inhibitor(s) could readily be extracted from Ailanthus tissues with methanol, but not dichloromethane, indicating polar characteristics. Ailanthus leaflets had highest inhibitory activity during expansion in spring, whereas activity of trunk bark peaked just before emergence of leaves. This pattern suggests transport of allelochemicals from bark into new leaves. A comparison of seven plant species for sensitivity to the inhibitor(s) from Ailanthus root bark showed little selectivity, although velvetleaf was somewhat more resistant. The inhibitor(s) from Ailanthus root bark exhibited strong herbicidal effects when sprayed pre- and postemergence on plants in soil in the greenhouse. Postemergence effects were striking, with nearly complete mortality of all species, except velvetleaf, at even the lowest doses tested. The results suggest the allelochemical(s) from Ailanthus may have potential for development as natural-product herbicides.     

Patterns in the within-tree distribution of the emerald ash borer Agrilus planipennis (Fairmaire) in young, green-ash plantations of south-western Ontario, Canada

1 The emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) is a serious exotic pest of ash trees (Fraxinus spp.) in North America, and is responsible for the deaths of millions of trees in Ontario and Michigan. One of the greatest challenges facing the successful management of the pest is the ability to accurately detect its presence in a tree. 2 Observations were made on A. planipennis larval feeding galleries found within 65 young, green‐ash trees cut from plantations in Essex County, Ontario, Canada. The within‐tree distributions of feeding galleries were described in relation to height‐above‐ground, stem diameter, bark thickness and stem aspect. 3 Galleries were not distributed randomly or evenly; minimum boundaries of stem diameter and bark thickness and a maximum boundary of height‐above‐ground were detected. Indications of maximum boundaries for stem diameter and bark thickness were also observed. Galleries were found most often on the south‐west side of the tree. 4 Using the technique of upper boundary regression, we were able to identify significant quadratic relationships between A. planipennis gallery density and stem diameter and bark thickness, as well as a significant negative linear relationship between gallery density and height‐above‐ground. 5 Agrilus planipennis gallery density in newly‐infested trees was lower than in previously‐infested trees, and was observed to peak at smaller stem diameters and bark thicknesses than in previously‐infested trees. 6 Survey teams would increase their probability of detecting new A. planipennis infestations by initiating searches for exit holes and feeding galleries in trunk sections and branches of approximately 7 cm in diameter.     

Skewed adult sex ratios observed early in the North American invasion of Lycorma delicatula (Hemiptera: Fulgoridae)

The spotted lanternfly, Lycorma delicatula, (Hemiptera Fulgoridae) is an invasive pest in Korea and the United States, but originating from mainland Asia. Both tree of heaven, Ailanthus altissima, and grapevine (Vitis) are known to be preferred hosts of adults. However, much is unknown about its adult behavior with respect to mating or dispersal patterns. In 2015, just after it was discovered in the United States, we performed an observational study to elucidate movement by adults in relation to host plants. We noted weekly changes in their presence and sex ratio on host plants at four sites in a quarantine zone in Berks County, PA. Just after adult emergence, the trunks of large (>15 cm diameter at breast height) A. altissima hosted nearly exclusively females, while smaller A. altissima, Vitis, Salix nigra, and other less commonly inhabited tree species, had high proportions of males. By October 1st, greater proportions of males were observed on the trunks of the larger A. altissima trees. Pairings of males and females were observed most frequently on the smaller A. altissima and Vitis. At the very end of the season, a large mixed-sex population was found on Salix nigra, which was the only deciduous tree species in the area still bearing green leaves.     

Breeding behaviour of Nuthatch Sitta europaea in relation to natural hole attributes in a primeval forest

Capsule Nuthatches used holes with strong walls, typically in live trees with entrances reduced by plastering, and ‘oversized’ interiors filled with bark flakes.

Aims To describe patterns of nest-site utilization by Nuthatches in primeval conditions, to examine the influence of various hole attributes on nesting success and to consider the adaptive value of nest-site choice.

Methods Observations of birds living in undisturbed conditions in a strictly protected part of the Bia?owie?a National Park (Poland) during 27 breeding seasons coupled with measurements of hole attributes and observations of nests' fate.

Results Tree species used for breeding differed among habitats. Holes were on average 14.0 m above the ground, in trees with girth at breast height 206 cm; both parameters varied strongly among tree species. They were situated mainly in tree trunks (76%), in living trees (89%), in conical knotholes (51%); woodpecker-made holes constituted 32%. Nuthatches bred in very large (mean bottom area: 325 cm²) holes, the preferred tree species (Maple Acer platanoides, Ash Fraxinus excelsior) had larger holes than other tree species. Nuthatches reduced entrances by ‘plastering’ to a mean size of 2.9 × 3.3 cm. They made the holes substantially shallower by filling them with bark flakes (mean depth to nest level: 10 cm), eggs were laid in depressions among flakes, far from the entrance (mean distance: 21 cm), their ‘nests’ occupied only a fraction of the hole area. Broods in holes with smaller entrances were the most successful. Eggs and small young were covered with bark during the absence of the female. Larger nestlings, when endangered, moved to the rear wall of the hole, where they stayed tightly pressed. These behaviour patterns reduced the risk of predation.

Conclusion The features of holes used by Nuthatches (combination of strong walls, small entrances and large bottoms with copious filling) are probably an evolutionary solution to the need to evade predators while keeping contents of the nest dry.     

Distribution and survival of overwintering adults of the Dutch elm disease vector, Hylurgopinus rufipes (Coleoptera: Scolytidae), in American elm trees in Manitoba

Abstract 1 The native elm bark beetle, Hylurgopinus rufipes, is the principal vector of Dutch elm disease in Manitoba, Saskatchewan and North Dakota, and disease management measures include applying residual insecticides to the lower part of elm tree trunks where the adult beetles overwinter. 2 In American elm trees in southern Manitoba, we counted entrance holes produced by beetles then felled and dissected trees to determine numbers of tunnels and numbers and survival of overwintering beetles. 3 Densities of entrance holes, tunnels and beetles followed a logistic relationship with tree trunk diameter; densities were near zero at diameters < 10 cm and reached a site‐specific asymptote at diameters > 20 cm. 4 Asymptotic densities of holes, tunnels and beetles in samples from 55 to 190 cm above the ground were, respectively, 22%, 22% and 0.7% of those within 25 cm of the ground. 5 Within the height range 0–190 cm, the proportion of living beetles declined steeply with increasing height. 6 Average density of holes at height 0–25 cm estimated from a sample of several trees of diameter ≥15 cm could be used to predict the asymptotic maximum density of overwintering beetles in the site; predictions of beetle densities for individual trees were not reliable.     

Life history of the Asian longhorn beetle Anoplophora glabripennis (Coleoptera Cerambycidae) in southern Europe

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Biology and associated fungi of an emerging bark beetle pest,the sweetgum inscriber Acanthotomicus suncei (Coleoptera: Curculionidae)

The sweetgum inscriber (SI) Acanthotomicus suncei Cognato is an emerging bark beetle pest that seriously damages American sweetgum trees (Liquidambar styraciflua) and Chinese sweetgum trees (L. formosana) in China. Since 2013, SI has killed more than 30,000 sweetgum trees in Shanghai and adjacent areas. In Shanghai, SI was observed to emerge from infested wood between April–September and exhibited two generations per year. Both the flying populations and those in colonized logs were female-biased. After the parental adult initiates a gallery, the emergence of new adults required 73.4 ± 0.7 days at 30°C and 163.5 ± 0.9 days at 20°C. SI could not sustain population development at constant temperatures ≤15°C. The fungi Geosmithia spp. and Phaeoacremonium tuscanum were common associates of SI. The results suggest that SI has a long flight period, and its development is sensitive to low temperatures. Fungi associated with SI were not pathogenic to American sweetgum trees, but their presence may indirectly increase the probability of tree mortality. Our findings contribute to the prevention and control of this important emerging bark beetle pest.     

Cyclic Behavior of <Emphasis Type="Italic">Lycorma delicatula</Emphasis> (Insecta: Hemiptera: Fulgoridae) on Host Plants

Lycorma delicatula is an invasive insect species in Korea, and its populations are increasing. It sucks plant sap and can cause withering of the whole trees. To prevent damage to fruit trees, it is important to determine the behavioral characteristics of L. delicatula. We monitored migration patterns and host plant preferences, from the egg mass on the tree bark, through egg hatching to egg laying. Most eggs hatched between 0500 h and 0800 h. The nymphs ascended trees until they reached the leaves. They often fell to the ground because of physical factors, such as wind, but then ascended the trees again on the upper sides of the branches. Their falling-ascending cycle became longer as their arolia developed. The host preference changed over the course of its growth, from a broad range of plant species at the early nymph stage to a few plant species, such as Ailanthus altissima at the adult stage. We summarize the life cycle behavior as follows. Initially, there is a short-term cycle of falling and ascending, which becomes longer as the nymphs age. The other cycle is a yearly cycle of host plant preferences, with broad host preference in the early nymph stage and a narrower host preference in the adult stage. Knowledge of this cyclic behavior can be used to prevent the rapid expansion of L. delicatula populations in orchards.     

Herbicidal effects under field conditions of Ailanthus altissima bark extract,which contains ailanthone

Extracts of Ailanthus altissima stem bark were evaluated for herbicidal effects under field conditions in two outdoor trials. Previous investigations had shown A. altissima bark, extracted with methanol, yielded a strongly phytotoxic extract that contained ailanthone as one of the major herbicidal compounds. The first field trial investigated the level of activity and selectivity of the extract. A. altissima bark extract was sprayed post-emergence onto 17 species of weeds and crops at rates of 366, 177, 93, 47, 23, and 0 kg ha^–1. These application rates provided herbicidal activity equivalent to 4.5, 2.2, 1.1, 0.6, 0.3, and 0.0 kg of pure ailanthone per hectare, based on the results of a laboratory bioassay of extract and pure ailanthone. Strong herbicidal effects were observed within several days. Even the lowest rate caused mortality and injury in excess of 50% for nine of the 17 species, and a significant reduction in shoot biomass for 13 species. The second field trial tested the ability of bark extract to control weeds under field conditions with horticultural crops (bush bean, cauliflower, sweet corn, tomato). A. altissima bark extract was sprayed post-emergence at rates of 99, 50, 26, 13, and 0 kg ha^–1, providing herbicidal activity equivalent to 1.1, 0.6, 0.3, 0.14, and 0.0 kg of pure ailanthone per hectare. Extract treatment provided partial weed control (greatest reduction in weed biomass was 40%), but also caused serious crop injury. Bush bean was the only crop that showed a significant increase in shoot biomass and fruit yield, compared to the non-weeded control. None of the crops, regardless of application rate, showed a level of shoot biomass or fruit yield comparable to the hand-weeded control. The herbicidal effects of A. altissima bark extract declined within the first few weeks after application, supporting previous evidence that ailanthone is rapidly degraded under field conditions.     

Orientation of flight for physically disturbed spotted lanternflies,Lycorma delicatula, (Hemiptera,Fulgoridae)

The spotted lanternfly, Lycorma delicatula, (Hemiptera, Fulgoridae) is an invasive pest to Korea and the United States, originating from China or Southeast Asia. Immature L. delicatula feed on a wide range of plants, but the adults are more host-selective, often preferring the tree of heaven, Ailanthus altissima. We performed field studies to evaluate adult movement in relation to A. altissima after disturbance. The Ailanthus trees were in a mixed suburban forested situated at the southern border of an open grassy field. Female adult lanternflies were manually disturbed from feeding on the trunks of large A. altissima trees. In the first experiment, insects were disturbed directly from the tree using a ballpoint pen to simulate a predatory attack. These insects usually flew initially southward away from the tree line toward a sunlit field, but turned northward back toward the tree line. In the second experiment, to simulate an initially successful predatory attack, they were manually taken from trees, and allowed to escape. The females immediately opened their wings in an apparent aposematic display. They then either immediately flew toward the sunlit open field, or remained with their wings splayed open for a prolonged period.     

White pine weevil performances in relation to budburst phenology and traumatic resin duct formation in Norway spruce

1 As the phenological window hypothesis was reported to be significant in influencing the fitness of many herbivores feeding on tree foliage, could it also explain the performance of an insect such as the white pine weevil Pissodes strobi mainly attacking the bark phloem of conifers? 2 Under field conditions, adult weevils were caged on Norway spruce trees presenting a natural variation in their shoot growth phenology. 3 We evaluated white pine weevil biological performances, including oviposition, the number of emerged insects, survival, adult mean weight and tree defense responses as reflected by the production of induced resin canals. 4 None of the white pine weevil biological parameters was significantly affected by Norway spruce phenology. 5 The number of eggs per hole, the number of oviposition holes per leader, the number of emerged adults and their mean weight were not affected by host phenology. 6 The intensity of the traumatic response observed was variable and not correlated with budburst phenology. 7 Trees with higher traumatic responses, forming two or more layers of traumatic ducts, had lower adult emergence and estimated survival. 8 The distance between the first layer of traumatic resin ducts and the start of the annual ring was not correlated with the number of emerged weevils. 9 Norway spruce, which is an exotic tree in North America and a relatively recent host for the white pine weevil, might not possess the defense mechanisms necessary to fight off the white pine weevil.     

Tree Holes Used for Resting by Gray Mouse Lemurs (Microcebus murinus) in Madagascar: Insulation Capacities and Energetic Consequences

I studied the insulation capacity of tree holes used by gray mouse lemurs (Microcebus murinus) in a primary dry deciduous forest in western Madagascar during the cool dry season. Tree holes had an insulating effect, and fluctuations of air temperatures were less extreme inside the holes than outside them. The insulation capacity of the tree holes peaked between 0800 and 1100 hr, when ambient temperatures ranged between 25 and 30°C. To compare tree holes, I calculated the mean difference between the internal temperature )(T_i ) and the external temperature (T_e ) for each tree hole. Thus large differences indicate good insulation capacities. The mean difference of tree holes in living trees was significantly larger than that of tree holes in dead trees, which shows that insulation in living trees is more effective. During the dry season, the insulation capacity of tree holes in living trees decreased and was lowest in July, whereas the insulation capacity of holes in dead trees remained approximately constant. Physiological studies under natural temperature and light condition in Microcebus murinus reveal that daily torpor saves around 40% of the daily energy expenditure compared to normothermia. However, torpor can be maintained only up to the threshold body and ambient temperature of 28°C, whereat Microcebus murinus have to terminate torpor actively. By occupying insulating tree holes, mouse lemurs may stay longer in torpor, which increases their daily energy savings by an extra 5%.     

Thinning Jeffrey pine stands to reduce susceptibility to bark beetle infestations in California,U.S.A.

• 1 Bark beetles (Coleoptera: Curculionidae, Scolytinae) are commonly recognized as important tree mortality agents in coniferous forests of the western U.S.A.
• 2 High stand density is consistently associated with bark beetle infestations in western coniferous forests, and therefore thinning has long been advocated as a preventive measure to alleviate or reduce the amount of bark beetle‐caused tree mortality.
• 3 The present study aimed to determine the effectiveness of thinning to reduce stand susceptibility to bark beetle infestations over a 10‐year period in Pinus jeffreyi forests on the Tahoe National Forest, California, U.S.A. Four treatments were replicated three times within 1‐ha square experimental plots. Treatments included thinning from below (i.e. initiating in the smallest diameter classes) to a residual target basal area (cross‐sectional area of trees at 1.37 m in height) of: (i) 18.4 m²/ha (low density thin); (ii) 27.6 m²/ha (medium density thin); (iii) 41.3 m²/ha (high density thin); and (iv) no stand manipulation (untreated control).
• 4 Throughout the present study, 107 trees died as a result of bark beetle attacks. Of these, 71% (75 trees) were Abies concolor killed by Scolytus ventralis; 20.6% (22 trees) were Pinus ponderosa killed by Dendroctonus ponderosae; 4.7% (five trees) were P. jeffreyi killed by Dendroctonus jeffreyi; 1.8% (two trees) were P. jeffreyi killed by Ips pini; 0.9% (one tree) were P. jeffreyi killed by Orthotomicus (= Ips) latidens; 0.9% (one tree) were P. ponderosa killed by both Dendroctonus brevicomis and D. ponderosae; and 0.9% (one tree) were P. jeffreyi killed by unknown causes.
• 5 In the low density thin, no pines were killed by bark beetles during the 10‐year period. Significantly fewer trees (per ha/year) were killed in the low density thin than the high density thin or untreated control. No significant treatment effect was observed for the percentage of trees (per year) killed by bark beetles.