WARREN ROOTCOLLAR WEEVIL, HYLOBZUS WARREN1 WOOD (COLEOPTERA: CURCULIONIDAE), IN CANADA: ECOLOGY, BEHAVIOR, DAMAGE RELATIONSHIPS, AND MANAGEMENT

H.F. CEREZKE Canada Department of Natural Resources, Canadian Forest Service, 5320 - 122 Street, Edmonton, Alberta, Canada T6H 3S5

Abstract The Canadian Entomologist 126: 1383- 1442 (1994) Warren rootcollar weevil, Hylobius warreni Wood, is a pest of several conifer species and is distributed widely throughout the boreal forest in Canada. Literature on this weevil is reviewed and interpreted to provide comprehensive coverage of its ecology, behavior, and impacts, and the implications for its management. New information is provided to fill gaps in our knowledge of H. warreni. These include distribution and hosts, immature stages, sex ratios, and daily and seasonal activity patterns of adults. Sex ratios, abundance, longevity, and pedestrian dispersal behavior of adults within the forest and on trees are described from mark, release, and recapture studies conducted over several years using a newly designed interception trap. Daily trap captures are correlated with previous night temperatures and this relationship is a tool for predicting adult captures. Fecundity and oviposition behavior on the host tree are described from laboratory- and field-reared adults. Population levels of H. warreni are compared across a variety of lodgepole pine stands in Alberta. Weevil numbers within forests are described in relation to tree size and age, depth of duff material around tree bases, and stand density. Analysis of weevil feeding scars distributed at the root collar base of mature pine stems were used to describe the likely temporal pattern of population abundance and change during stand develop- ment. Information supportive of this pattern is presented from surveys in young and mature stands. A new method of assessing stands of lodgepole pine for suitability of habitat for H. warreni takes into account the cumulative nature of this weevil's injury and reflects its temporal pattern of success in relation to stand conditions. The effects of a pre- commercial thinning treatment on H. warreni populations and its girdling injury were investigated in a 25-year-old lodgepole pine stand over an 8-year period. Compared with control plots, thinning treatment caused a 5-fold increase in weevil numbers per tree and increased the tree attack incidence by 2-fold, but resulted in an average 6% reduction in partial stem girdling of attacked trees. Information about the effects of various forest management practices on H. warreni abundance and survival is reviewed and areas requiring research are identified.

Cerezke, H.F. 1994.Le Charanqon de Warren, Hylobius warreni Wood (Coleoptera:Curculionidae) au Canada. The Canadian Entomologist 126: 1383- 1442.

Resume Le Charan~conde Warren, Hylobius warreni Wood, parasite plusieurs espbces de conifbres et est bien rCpandu dans la for& borCale canadienne. Les travaux sur cette espbce ont CtC rCvisCs et interprCtCs dans le but d'obtenir le plus d'informations possible sur l'Ccologie, le comportement et les effets de ce parasite avant d7Ctablirdes programmes de contrble. De nouvelles donnCes viennent combler les lacunes dans nos connaissances de l'espbce: rkpartition des hbtes, stades immatures, rapports m2les:femelles, activitCs quotidiennes et saisonnibres des adultes. Les donnCes sur les rapports miiles:femelles, l'abondance, la longCvitC et le comportement de dispersion pCdestre des adultes dans la forEt et sur les arbres ont CtC obtenues par marquage-capture-recapture durant plusieurs anntes au cours desquelles un nouveau type de pibge a CtC utilisC. Les captures quoti- diennes dans les pibges se sont avCrtes en corrClation avec la tempCrature de la nuit preckdente et celle relation permet de prCdire les captures des adultes. La fCconditC et le 1384 THE CANADTAN~MoLOGIST November/December 1994, comportement de ponte sur les arbres hates sont dCcrites B partir de donnCes sur des adultes ClevCs en laboratoire et en nature. Les densitks de population d'H. warreni ont ttt comparkes au sein de plusieurs for& de pins de Murray en Alberta. Le nombre de charan~onstrouvts a CtC mis en relation avec la taille et l'2ge des arbres, avec la profondeur de la couche d'humus autour de la base des arbres et avec la densit6 de la forCt. L'analyse des cicatrices laissts par les charan~onsse nounissant B la base du tronc d'arbres B maturitt, B la naissance des racines, a permis de dCcrire la courbe probable d'abondance de la population en fonction du temps au cows du dCveloppement de la forCt. Le pattern obtenu est confirm6 par des donntes obtenues dans des for& jeunes et des for& B maturitC. Une nouvelle mCthode d'kaluation des forCts de pins de Murray comme hates de populations d'H. warreni tient compte de la nature cumulative des blessures causCes par le charan~onet reflkte son succ&sen fonction du temps en relation avec les conditions de la forst. Les effets d'un Cclaircissement prkliminaire de la forCt pour des fins commerciales sur les populations d'H. warreni et ceux des blessures d'annklation ont CtC Ctudits pendant 8 ans au sein d'une forCt de pins de Murray de 25 ans. La comparaison avec des for& tCmoins a rtvtlt que 1'Cclaircissement a entrain6 une augmentation considerable (X5) du nombre de LharanCons par arbre, a augment6 l'incidence des attaques aux arbres par un facteur de 2, mais a rksultt en une rkduction moyenne de 6% des anntlations partielles des tiges des arbres attaques. L'information sur les effets des pratiques d'am~na~ementdes for& sur l'abondance et la survie d'H. warreni est rtvisCe et les zones de recherche qui doivent Ctre approfondies sont indentifkes. [Traduit par la RCdaction]

INTRODUCTION In North America, there are seven known species of weevils in the genus Hylobius. The following species occur in Canada: H. congener Dalla Torre, Shenkling, and Marshall, H. pales (Herbst), H. pinicola (Couper), H. radicis Buchanan, and H. warreni Wood. All attack and feed on coniferous hosts (Wood 1957; Warren 1958; Warner 1966). Warren rootcollar weevil, Hylobius warreni Wood, first described in 1957, is indigenous to coniferous forests in North America (Wood 1957; Warner 1966). Its larvae feed on the root and root collar region of trees, causing partial to complete girdling of roots and stem, large open wounds, and resinosis (Warren 1956b; Cerezke 1970~).Live healthy trees are susceptible to attack at a young age and these trees are subject to repeated attacks at irregular intervals through to stand maturity or harvest (Cerezke 1969, 1970~).Highest populations of the weevil and its incidence of attacks tend to occur on trees of vigorous crown classes and on high-productivity sites (Cerezke 1969, 1970b, 1970~;Ives and Rentz 1993). Trees may be killed directly from the girdling injury, and their wounds may provide entry courts for root and stem diseases (Warren 1956b; Whitney 1961; Cerezke 1974). Partially girdled trees may also accumulate losses in growth from repeated attacks and be made less windfinn because of weakened roots and stems (Cerezke 1974). Different habitat conditions are created during the process of forest removal and the early establishment of the new forest, and most of these conditions influence the population dynamics of H. warreni. The cut stumps left behind after harvesting allow established resident populations of H. warreni to complete their development, but the newly planted or naturally grown seedlings provide continuity of habitat as breeding sites for subsequent generations of the weevil (Cerezke 1973~).Thus early establishment of H. warreni into young stands is often assured at an age when the risk of tree mortality from larval girdling is maximal (Cerezke 1970c, 1974; Ives and Rentz 1993). Various silvicultural treatments are often applied in young stands to help achieve optimal growth. Studies in stands of white spruce [Picea glauca (Moench) Voss] and lodgepole pine (Pinus contorta Dougl. var. latifolia Engel.) in western Canada have shown that this weevil is distributed in relation to various site and stand parameters. Its abundance and survival can therefore be influenced Volume 126 THE CANADIAN ENTOMOLOGIST 1385 by harvesting practices and probably also by post-harvest treatments including prescribed bums, scarification, and stump removal (Warren 1956b, 1956d; Stark 1959~;Cerezke 1969, 1970a, 1970b, 1973~;Byford and McLean 1991). Such treatments as precommercial thinnings and spacings, stand fertilization, and alternate species selection may all influence H. warreni abundance and its injury (Goyer and Benjamin 1972; Wilson and Millers 1983; Selander and lmmonen 1992; Hunt et al. 1993). The earliest collections in Canada of adult H. warreni were probably made during 1930-1935, but concern for its injury to trees did not develop until the late 1940s and early 1950s (Daviault 1949). Early investigations in Saskatchewan and Manitoba were prompted by the concern that its larval wounds on white spruce provided courts of entry for root and stem diseases (Warren and Whitney 1951). Since 1949, a considerable body of information has accumulated on the biology, ecology, behavior, and tree damage relationships of H. warreni, especially in western Canada. Much of this information is contained in published reports, a number of unpublished file and internal reports, theses, and as unpublished data, much of which is not readily available. There is a need to compile and synthesize this information into a single document and thereby make it available to land managers and researchers. The objectives of this paper are to review all sources of information on H. warreni in Canada, present a synthesis and interpretation of the knowledge about this weevil, and formulate guidelines for coping with this insect in managed forests and plantations. The content of this document is arranged under four main sections. The first three sections (geographical distribution and hosts; life history and behavior; and population dynamics and impact) present the main body of scientific information; the last section focuses on forest management guidelines and research needs.

GEOGRAPHICALDISTRIBUTION AND HOSTS

Materials and Methods Records of the distribution and host tree species of H. warreni were compiled from a variety of published and unpublished sources (Warren 1954, 1956~;Wood 1957; Stark 1959a; Warren and Parrott 1965; Warner 1966; Cerezke 1969, 1970b; Warren and Singh 1970), from collection records reported in the annual reports of the Forest Insect and Disease Survey (Anon. 1939-1992), and from field collections made by the author.

Results and Discussion Geographical Distribution The distribution of Warren rootcollar weevil extends throughout most of the forested areas in Canada, from Newfoundland to coastal British Columbia, and at least into southern parts of the Northwest Territories (Fig. 1) (Warren 1954; Anon. 1956; Wood 1957; Warren and Parrott 1965; Grant 1966; Warner 1966; Cerezke 1969). Records of its presence in the United States are few, only in Maine, Michigan, New York, and North Carolina (Warner 1966). Within its wide range in the boreal forest of Canada, populations of H. warreni are well established on several islands off coastal British Columbia, in Newfoundland, Cape Breton, and in the Cypress Hills in southern Alberta and Saskatchewan (Warren and Parrott 1965; Cerezke 1969; Anon. 1975). Populations in these semi-isolated habitats may have, over the long term, developed behavioral and morphological differences. In general, the incidence of H. warreni correlates well with site conditions, being most abundant on moist to wet sites (Warren 1956b; Anon. 1959; Stark 1959~;Warren and Parrott 1965), or those sites characterized as high-productive and often with a rich component of ground floral species (Cerezke 1969; Ives and Rentz 1993). THE CANADIAN ENTOMOLOGIST

FIG.1. Probable range of Hylobius warreni in Canada.

There is considerable overlap in the distribution and host selection of H. warreni and H.pinicola; in western Canada the latter species appears to extend farther north in the Yukon Territory and may also occur at higher altitudes (Warren 1954; Wood 1957; Grant 1966; Cerezke 1969). The most northerly known location of H. warreni is near Enterprise, Northwest Territories (Cerezke 1969). Within the forested areas of Alberta and British Columbia, populations of H. warreni appear to be confined to altitudes below 1585 m (Cerezke 1970b). Hosts The tree hosts of H. warreni include most pine and spruce species native to Canada, as well as several exotic species. In natural mature forests, its populations appear to be maintained primarily on three major hosts: jack pine (Pinus banksiana Lambert.), lodgepole pine, and white spruce. There are, however, some regional and local variations in tree species susceptibility. In extensive surveys conducted in the major forest districts in Saskatchewan and Manitoba, H. warreni was found in most moist and wet white spruce habitats and was the cause of at least 95% of the root-feeding wounds on this host; the remainder of the wounds were attributed to H. pinicola (Anon. 1959, 1960; Whitney 1961). Other surveys have confirmed that jack pine is also a prime host throughout most of this weevil's range from the southern part of the Northwest Territories and central Alberta to the Maritime provinces (Warren and Ives 1957; Wood 1957; Warren 1958,1960~;Warner 1966; Rose and Lindquist 1973, 1977; Howse 1984; Martineau 1984). In the foothills of Alberta and in British Columbia, lodgepole pine is the preferred host on most sites and white spruce and black spruce are attacked if they occur intermixed with lodgepole pine (Stark 1959~;Grant 1966; Cerezke 1969,1970~;Herring and Coates 1981; Duncan 1986; Wood and Van Sickle 1986; Byford and McLean 1991). Other less frequently reported host species supporting Volume 126 THE CANADIAN ENTOMOLOGIST 1387 TABLE1. List of native and exotic coniferous hosts in Canada on which adults of Hylobius warreni have been collected and a designation of their present economic importance

Provinces with reported mortality

Tree species BC A S M 0 Q NB NS PEI NF

Prime hosts* Jack pine, Pinus banksiana Lodgepole pine, Pinus contorta Red pine, Pinus resinosa Scots pine, Pinus sylvestris White spruce, Picea glauca Occasional hostst Eastern white pine, Pinus strobus Western white pine, Pinus monticola Black spruce, Picea mariana Engelmann spruce, Picea engelmannii Norway spruce, Picea abies Sitka spruce, Picea sitchensis Rare hostst Balsam fir, Abies balsamea Subalpine fir, Abies lasiocarpa Douglas-fir, Pseudotsuga meuziesii Eastern larch, Larix laricina Western hemlock, Tsuga heterophylla

'Prime hosts are tree species that have sustained most of the reported economic injury. toccasional hosts are tree species that have sustained some injury but mostly in localized areas or plantations. $Rare hosts are tree species on which adult Warren rootcollar weevils have been collected, but without root or root collar feeding injury. populations of H. warreni in British Columbia include western white pine (Ross 1955; Anon. 1957,1961), and probably Engelmann and Sitka spruces (Duncan 1986). In eastern Canada, eastern white pine, red pine, and black spruce have been commonly reported as hosts (Wood 1957; Warner 1966; Rose and Lindquist 1973, 1977; Martineau 1984; Syme 1985; Howse and Applejohn 1993). Most surveys of H. warreni injury in Canada have been conducted in young natural stands and plantations to assess tree mortality. These surveys have indicated a wide range of susceptible tree hosts, especially when growing on moist to wet sites (Table 1) (Warren 1956b, 1956c; Warren and Parrott 1965; Cerezke 1969). Exotic species such as Scots pine and Norway spruce, and some native species planted outside of their natural range have been girdled and killed by H. warreni. The native eastern larch [Larix laricina (Du Roi) K. Koch] and exotic species of Larix have thus far appeared immune to H. warreni attacks, but they are likely prime hosts of H. pinicola (Wood 1957; Warren and Parrott 1965). The susceptibility and relative economic importance of the tree species on which adult H. warreni have been collected are summarized into three groups (Table 1). The first group includes those species that are known to be "prime hosts" and on which economic injury (tree mortality) has been reported. The second group includes "occasional hosts" that have sustained some injury but mostly in localized areas or plantations. The third group includes "rare hosts" or those species on which adults have been collected, and represents perching records only or occasional adult feeding sites. LIFE HISTORY AND BEHAVIOR Studies of the life history and behavior of H. warreni were conducted within a variety of lodgepole pine stands in west-central Alberta between 1961 and 1968 and were first presented by Cerezke (1969). The stands occur within the Lower and Upper Boreal Cordil- leran ecoregions (Corns and Annas 1986) where lodgepole pine is the dominant tree species. 1388 THE CANADIAN ENTOMOLOGIST November/December 1994 Materials and Methods Life Stages Larval and Pupal Stages. Observations of larvae were made over a 6-year period during population sampling and surveys. All larvae collected from mature lodgepole pine during 2 separate years (1961 and 1962) were measured for head capsule width and measurements were analyzed to determine larval instars. Mature larvae removed from pupal chambers were readily recognized as prepupae and were recorded separately to identify their range of size. Data were collected on the origin, orientation, and structure of feeding galleries on the roots and root collar, length of excavation in the phloem during development, and position of placement of the pupal chamber. Depth of gallery penetration in the phloem was measured and related to early larval instar development. Measurements were made of the total gallery length scored through to xylem tissue of four mature larval wounds to indicate the total amount of feeding required per larva and to assess potential for girdling damage. Observations were made of differences in gallery pattern orientation on young and mature trees. Data collected during population sampling provided information on time of pupation and eclosion. Observations were made of the structure and size of the pupal chamber. Young unmated adults were obtained from field-collected pupae, which were reared successfully to adults by wrapping them individually in soft tissue and placing them in moistened containers. Egg and Adult Stages. Eggs collected from adults reared under field conditions were measured for mean length and width. Fecundity and oviposition. The base of all trees within two circular plot arenas was monitored annually during the fall from 1965 to 1968 to estimate egg and larval populations of H. warreni and the location of eggs deposited on the tree base or in adjacent moss and soil. The two circular plot arenas, each 6.1 m in diameter, were established adjacent to one another within a 25-year-old lodgepole pine stand. Each plot was enclosed with a 15-cm-high plywood fence with its base submerged a few centimetres into soil. The inside surface of the fence was coated with a band of Tree Tanglefoota; this material prevented the escape of adults as they showed a repellency toward it and no adults were ever found stuck in it. One application of the material each spring appeared to be adequate. The site was isolated from surrounding pine forests by a bog area and a stream, and was selected (a preliminary survey of the site indicated no evidence of H. warreni wounds) as being free of any evidence of the presence of a residual population of H. warreni. The plot arenas contained 49 and 47 lodge- pole pine trees, respectively. In the fall of 1964, 50 newly developed adult H. warreni (including 30 virgin females and 20 males) were released into each arena after each adult had been coded with a paint mark for individual recognition. The marked adults were monitored annually from 1965 to 1968 by capture, release, and recapture procedures (see details of trap design, trap placement within plots, and adult capture procedures in following sections) to record survival, daily and seasonal activity patterns, and annual egg productivity in each plot. Egg productivity in a field situation was assessed in the fall of each year from 1965 to 1968, by examining the root and root collar bark and adjacent moss and soil of all trees in each plot. The total numbers of eggs and larvae (first three instars only) observed each year were considered to have resulted from eggs deposited during the same year by the females captured during the same year. Thus egg productivity (eggs + larvae) per captured female was estimated each year, and the yearly values were summed to estimate egg productivity per female likely occurring over the total period of adulthood (1964-1968). The effect of artificially increasing the depth of duff around tree bases upon egg laying behavior was evaluated in the two arena plots. Alayer of fresh sphagnum mosses was placed around each tree base in the spring of 1966, increasing the depth of duff to an average 10-12 cm in one of the plots. The other plot (duff layer 3-5 cm) served as a control and had volume 126 TIE CANADTAN ENTOMOLOGIST 1389 no moss added. Egg and larval numbers counted at the end of the summer were plotted over tree diameter and compared in the two plots. Fecundity and egg laying frequency were further examined in a laboratory situation during a period from 1 June to 23 August. Adult pairs were each enclosed in paper cups inverted over fresh pine bark sections kept moist in Petri dishes, and a fresh pine branch tip was added frequently as food. Oviposition was recorded daily for each female (total of 24 pairs) and a record maintained of the total eggs laid per female. Egg productivity was expressed as the number of eggs laid per female per day. Maximum potential fecundity per female during the total summer period was estimated as the average rate of egg laying times the number of egg laying days (estimated to be about 103 days, extending from 20 May to 31 August). Rate of egg laying per female was calculated for consecutive 10-day intervals during the summer and plotted over time to describe seasonal oviposition pattern. Egg viability and period of embryonic development were described from egg laying data collected from 39 paired adults reared in 70-mL vials in which moss and a few drops of water were added to maintain a high humidity. Fresh pine tips were added regularly as food. The vials were stored in a shaded location in the field and submerged a few centimetres below ground level. The rearing period extended from 1 July to early September. Eggs were collected at 10- to 19-day intervals, placed in sealed vials with a moisture-saturated environment, and stored below ground level until hatching was complete. The average period of embryonic development and percentage hatch were estimated for each group of eggs laid during each interval. Paired adults were also reared in a specially designed plastic cage constructed to enclose part of a pine stump, and thus simulated the natural habitat (Cerezke 1967). A total of 30 cages were thus prepared; each contained one pair of adults. The cages were divided into three groups of 10 cages, and each group was reared for 50 days at a different constant temperature: 21.5, 15.5, and 10°C, respectively. At the termination of the experiment, all cages were examined for numbers of eggs and larvae, and the position of eggs in bark niches or adjacent moss was noted. Egg productivity (eggs + larvae) for each group of 10 cages was expressed as number of eggs laid per female per day. Female dissections. Females (total of 36) live-captured at intervals between early June and early September were dissected and provided additional information on seasonal ovary development and mating activity. Criteria used to assess stage of ovary development included their relative size and opaqueness and the number and size of immature and mature oocytes in the ovarioles. Mating was assessed by the presence of sperm in the spermathecal gland, presence or absence of a spermatophore, and condition of the spermatophore. Freshly deposited spermatophores were compact and pearly white, whereas older spermatophores did not have these characters. Adult collections and sex ratios. The proportion of the sexes in natural populations was determined from a variety of collection methods. During population sampling, dead female and male adults were often found in the litter near the tree base. These adults had probably died of natural causes. Live adults were collected from the lower stem or roots of trees, or from within the litter material adjacent to the roots. Sex ratios at eclosion were also calculated from virgin adults reared from pupae and tenerals collected in pupal chambers. Chi-square tests were performed on numbers of adults to establish departures from an expected 1:l ratio of females to males (Steel and Tome 1980). Adults were collected daily or during seasonal intervals in a trap of a design modified from that used by Embree (1965) to collect winter moths (Fig. 2). The trap consisted of a 2-L, wax-coated container with a 5-cm hole cut in the bottom. The top rim of a paper cup was inverted over the hole inside the container and glued. The bottom of the cup was also removed. Nylon tubing was passed through the bottom of the container, through the inside of the cup, and glued to its outside rim. The lower end of the tubing formed a cone that was THE CANADIAN ENTOMOLOGIST November/December 1994

FIG.2. Components of a trap design for live-capture of Hylobius warreni adults on tree stems.

fastened to a loop of a metal strip that was attached firmly at an oblique angle around the lower tree stem. The container was affixed to the tree above the loop. Each metal strip was about 4 cm wide and was bent at right angles along its length so as to provide a 2-cm-wide flange when nailed around the tree stem. The design of the trap took advantage of the entire tree circumference as a collecting surface, and of the adult habit of ascending trees during hours of darkness to feed in the tree canopy (Reid 1952). The adults were live-trapped as they ascended trees, being guided by the metal flange to the nylon cone, thence into the container where they remained until the following morning. A small pine branch tip was placed at the bottom of each container as food. The top of the container was covered with clear transparent plastic to prevent escape of adults and prevent moisture from entering; the transparency appeared to be necessary to maintain a light source from above for adult orientation. Adult mark, release, and recapture experiments. The traps were deployed in a number of experiments to investigate adult weevil behavior in relation to tree selection, sex ratios, dispersion, and daily and seasonal activity patterns. Traps were placed on 73 live, 70-year-old lodgepole pine trees bordering recent clearcut areas to examine numbers of H. warreni captured and their sex ratio; these values were compared with those of captures made within the stand. Traps were also placed on all 251 trees enclosed within two 0.08-ha circular plots located within a nearby 70-year-old lodgepole pine stand. The trapping of adults in the two plots was not carried out continuously throughout the summer, but during varying periods ranging from 4 to 13 days between early June and early September, 1964-1966. Adults captured within the plots were sexed and coded with colored paint for individual recognition, then released at the same tree base. The numbers of each sex were expressed as mean numbers captured per day during each of four sequential trapping periods. Volume 126 THE CANADIAN ENTOVOLOFIST 1391 These served to indicate the seasonal activity pattern. For plot and year comparisons, rate of capture was expressed as numbers of captures per trap, per trapping day. All trees within the two plots were measured for diameter at 0.3 m d.s.h. (diameter at stump height) so that captures could be examined in relation to tree size. Each tree within each plot was identified by code number and its location was measured to scale on large sheets of paper in order that the path of subsequent recaptures of marked weevils could be plotted. Individuals recaptured on consecutive nights provided information about linear distance travelled between trees and directional movement when leaving a tree of origin. The direction of dispersion was analyzed from adults captured on two consecutive nights. In each case, the tree with the first capture was considered as the tree of origin and from it the direction of the second tree was measured as a deviation in degrees from cardinal north. For analysis, the directional values were distributed into one of eight 45" directional sectors and analyzed using techniques for evaluating circular distributions (Zar 1984). During their movement from one tree to another, it was hypothesized that dispersal distance each day might relate to either distance to nearest neighbor tree, or to the average distance between trees. Within the two plots, mean distance to nearest neighbor tree was calculated directly from measurements of the plotted tree locations. As well, the average distance between trees was estimated by first calculating the mean area within the plots occupied by each tree. The distance from the center of this theoretical area occupied by one tree to the centers of its adjacent neighbor tree areas was used as an estimate of average distance between trees. The trapping procedures carried out in the two plot arenas in a 25-year-old lodgepole pine stand were similar to that in the 70-year-old stand. In these plots, however, traps were not placed on all of the trees, but only on 20 trees within the largest diameter size range within each plot. All captured weevils were identified by their individual paint mark, recorded as to tree diameter associated with, then released at the same tree base. Weevil captures were conducted during five intervals (over 4-13 consecutive days each) each year from 1965 to 1968 to determine adult survival and daily and seasonal activity patterns. A hygrothermograph enclosed in a Stevenson's screen was positioned adjacent to the two plot arenas to record temperatures at ground level and to provide a continuous record of daily temperatures during June (month of peak adult activity), 1965 and 1966. The influence of night temperatures during each night of capture was examined in relation to the numbers of adults captured. This was to explore the use of temperature data as a prediction tool for numbers of captured adults. Daily captures were regressed over temperatures recorded at hourly intervals from 2000 to 0100 hours (Mountain Standard Time) to identify the time that might reflect maximum activity. The hour yielding a maximum r2value was accepted as the best predictor of adult catch. Adult feeding pattern. Two small plywood arenas were constructed, as described previously for the two 6.1-m-diameter plot arenas; each enclosed one 25-year-old lodgepole pine. The inside surface of the plywood was coated with Tree Tanglefoot@to prevent escape of adults. Several female and male adults, each individually marked with paint for sex identification, were released into each arena and left throughout the summer. Their feeding pattern on the stem and branches was analyzed at the end of the summer, based upon the number and distribution of feeding scars.

Results and Discussion Description of Life Stages Taxonomy. Confusion existed in the early identification of H. pinicola and H. warreni because the two species are similar morphologically and in habits, and were often found within the same spruce habitats (Warren 19566; Wood 1957; Warren 1958; Whitney 1961; Finnegan 1962b; Warren and Singh 1970). The insects referred to in early studies in 1392 THE CANADl4N ENTOMOLOGlSr November/December 1994 TABLE2. Mean and range of head capsule widths of Hylobius warreni larvae collected on lodgepole pine in Alberta

Mean and (range) of head Number examined capsule width (mm)*

*Means and ranges of head capsule widths are estimated from frequency peaks of numbers of larvae measured. Only the first four instars are represented because of the wide variability of older instar sizes.

Manitoba (Warren and Whitney 1951; Warren 1954, 1955, 1956a, 1956b) in fact consisted of these two species combined under one taxonomic entity, namely Hypomolyx piceus (De Geer) (Wood 1957; Warren and Parrott 1965). Their taxonomy was clarified by Wood (1957) who invalidated the name Hypomolyx, erected H. warreni as a new species, and pro- vided a key to separate the two North American species, H. pinicola and H. warreni, from the Eurasian species, Hylobius piceus (De Geer). Manna and Smith (1959) also provided strong cytological evidence that H. pinicola and H. warreni differed in chromosomal counts, and differences in the external and some internal morphology of adults of the two species have been described and compared (Wood 1957; Warren 1960b). It is noteworthy that Martineau (1984) includes a description of the "large spruce weevil" Hylobius piceus (De Geer) in Quebec; however, the species is more likely H. warreni. The accepted common name given to H. warreni is Warren rootcollar weevil. Additional taxonomic keys to separate the adult H. warreni from other members of this genus were prepared by Finnegan (1961), Millers et al. (1963), Warner (1966), and Goyer and Hertel(1970). No keys are available to separate the immature forms. Important diagnostic characters that define the adult of H. warreni include the following: length of body varies from 11.7 to 15.1 mm; femoral spur is inconspicuous or absent; rostrum (snout) is fairly stout, less than 2.6 times as long as wide, and wider at the distal end; apical umbones on the elytra are obscure or undefined; and metathoracic wings are vestigial and do not extend beyond the posterior margin of the first visible abdominal sternite (Wood 1957; Warren 1960b; Finnegan 1961; Warner 1966). Egg. Freshly laid eggs are pearly white and ellipsoidal. They turn yellowish as they develop. Average dimensions of a sample of eggs were 2.17 + 0.15 mm long by 1.38 + 0.08 mm wide (mean + SE; n = 20). Larva. The larva of H. warreni is white, legless, and falciform in body shape, with a brown head capsule (Fig. 3A). The number of larval instars is somewhat uncertain and may vary from five to seven, similarly as described for H. radicis (Finnegan 1962~).Seven larval instars were identified from artificially reared H. warreni (Warren 1960a), but Stark (1959a, 1959b) estimated six larval instars on the basis of head capsule width measurements. Only the first four instars (Table 2) are clearly defined by measurements; beyond the fourth instar, however, the range of head capsule sizes is obscured by developmental variability even between years, and possibly due to sex differences. Finnegan (1962~)observed, for arti- ficially reared H. radicis, a similar overlap of head widths of late instars and reported differences in instar size between females and males. Difficulties in establishing numbers of larval instars of field-collected H. abietis were also experienced by Bejer-Petersen et al. (1962). It can be concluded for H. warreni that instar sizes and number beyond the fourth cannot be determined from field-collected larvae (Fig. 4). The last instar, designated as prepupa (Fig. 4), occurs within a wide range of head capsule widths (from 2.915 to 4.015 mm). This stage of development always occurrs within Volume 126 VIE CANADIAN ENTOMOLOGI.ST 1393

1 .>>- .%au T-.?. :.=.-*--<

FIG.3. Larva (A) and adult (B) of Hylobius warreni. the pupal cell 1 or 2 weeks before pupation. Newly emerged larvae have a body length of about 5.5 mm and grow to a length of about 18.0 mm at maturity. Pupa. The pupa is white throughout its development and turns a creamy color when newly transformed to the adult. It resembles an adult but is slightly longer in body length and has its appendages folded under the body. Separation of the sexes may be possible in the pupal stage by examination of differencs in the folds and ridges of the last sternites, as described for H. radicis (Wilson and Millers 1983). Adult. The adult is a large, robust, and somewhat cylindrical weevil with a prominent rostrum that curves in slightly (Fig. 3B). Males average 13.0 mm long (11.7-14.4 mm) and 1394 THE CANADLW E~TOMDIL~IST NovemberPecember 1994 Larval instars

I II 111 IV L Prepupa size distribution b 6- 6- - I-

Larval head capsule widths (rnrn)

FIG.4. Frequency distribution of Hylobius warreni larval head capsule widths (mm), collected in mature lodgepole pine stands in 1961 and 1962. The range of head widths is shown for instars 1-4 and for prepupae. Number of larvae measured: n = 1345 (1961) and 914 (1962). females average 13.7 mm (12.0-15.1 mm) (Wood 1957). Its nearest relative, H. pinicola, is slightly smaller, 11.3-14.3 mm long with an average of 12.5 mm (Wood 1957). The head, pronotum, and elytra of H. warreni are coarsely sculptured and the body is sparsely clothed with white to pale-yellow hairs and slender scales that form irregular pale-yellow patches on the elytra (Warren 1960b). Both sexes are a reddish-brown to purple color as young teneral adults, but turn darker and greyish with age. Warren (1960b) noted that examination of genitalic structures was the only reliable means of separating the sexes, although his illustrations depicted a difference in the number of visible tergites: seven visible in the female, eight in the male. A circular depression on the last stemite of male Hylobius species (less prominant and more concave in the females) has been used to identify the sexes in the field (Wilson et al. 1966). This character on H. warreni males, however, appears to be weakly developed and may not be reliable to identify the sexes. Life Cycle. Two years is required to complete one generation of H. warreni (egg to adult) throughout most of its range in Canada (Reid 1952; Warren 1955, 195617; Stark 1959b; Cerezke 1969, 1970~;Martineau 1984). In Quebec, Martineau (1984) noted that the length of one generation may occasionally extend beyond 2 years because of variable environ- mental conditions, as well as differences in latitude, altitude, and degree of shade. During artificial rearing studies in Manitoba, Warren (1955, 1956a, 1958, 1960a) found the life history of H. warreni to be complicated by a prolonged duration of the larval stage (some- times 3-4 years) and by an overlap of generations, but concluded that the 2-year cycle was probably the normal occurrence. Life history studies in Alberta corroborate this (Reid 1952; Stark 1959b; Cerezke 1969). The 2-year cycle is also consistent with field observations and has been described similarly for the pine rootcollar weevil, H. radicis (Wilson and Millers 1983). Oviposition and the Egg Stage. The oviposition period of H. warreni probably extends from late May to early September. Stark (1959~)suggested late June as the start of oviposition, but others have observed eggs in May and in late August (Warren 1956a; Volume 126 THE CAUADIAN ENWMOLOGlST 1395

0) $ 0.1 2Q) 0.0 , L I I I I I I

Consecutive 10-day periods

FIG. 5. Seasonal oviposition pattern of Hylobius warreni adults reared in captivity, summarized by consecutive 10-day intervals from 1 June to 23 August. Data based on 24 adult pairs. Values above each data point are total numbers of eggs collected.

Cerezke 1969). In my experiment with field-reared adults, oviposition commenced in early June, reached a peak in early July, and then tapered off toward September (Fig. 5). Adult females collected and dissected at intervals during the summer tended to show peak ovariole development (i.e. larger size of ovaries, greater number of oocytes, and greater numbers of mature oocytes) in late June. Mating activity of dissected females also peaked in June and July, indicating these months to reflect peak oviposition. Warren (1956~)had also observed that the peak period of oviposition occurred in May, June, and July. Based on 24 field-reared females, the maximum number of eggs laid per female during a period of 84 days varied from 2 to 36 (average 12.2 eggs per female or 0.236 eggs per female per day). Using the value of 0.236 eggs per female per day and a maximum egg laying period of 103 days, average egg productivity during a season can be estimated at 24.3 eggs (103 X 0.236) per female. Other estimates of total seasonal egg productivity range as high as 24.9-28.4 (Table 3) and 28.6 (Cerezke 1967). In a laboratory experiment where adults were reared in plastic cages, the rate of egg laying per female and total numbers of eggs laid were similar for those adults reared at constant temperatures of 15.5 and 21S°C, but fewer eggs were laid in cages stored at 10°C (Table 3). The low rate (0.082 eggs per female) of egg laying at 10°C probably was a direct result of the lower temperature because adult activity was reduced and no egg hatch occurred during the 50-day rearing period. The data are similar to those recorded by Cerezke (1967) where an average of 16.4 eggs per female (range 0-27) were laid over a period of 59 days. Warren (1955, 1956a) reared females of different ages and obtained an average of only 7.5-8.6 (range 1-33) eggs per female. Female adults are long-lived (4-5 years) and appear to lay few if any eggs during their 1st year. My observations indicated that egg productivity per female may actually increase with age of the female, although Warren (19566) suggested otherwise. Egg productivity 1396 THE CANADIAN ENTOMOLOGIST NovemberPecember 1994 TABLE3. Summary of the rearing of adult Hylobius warreni and its egg productivity in plastic cages enclosing lodgepole pine stumps, at three temperatures for 50 days*

No. of Eggs in bark No. of eggs per paired Temp., Total eggs niches Total Percentage female per females "C deposited (%) larvae hatch day

*Descriptionof cage and rearing method are detailed in Cerezke (1967). ?No hatch occurred, probably because rearing temperatures were too low. assessed over the duration of adulthood within two field plot arenas in which newly eclosed adults were released and monitored over 4 years, indicated that 1-year-old adults apparently laid few eggs (average 0.11 per female recorded in 1965) (Table 4). There is evidence that adult females require one full season to become sexually mature (Warren 1956~;Raffa and Hunt 1988). Estimated egg productivity per female over the next 3 consecutive years increased (respectively, 4.7, 5.8, and 9.7; average 6.7 per year), yielding a total of about 20 eggs per female over the 4-year period (Table 4). This is a minimum estimate, however, because a portion of the eggs likely were not found or were preyed upon and some larvae may also have died. The large difference in yearly estimated egg productivity of adults reared in captivity (24.3-28.6 eggs per female) and those surviving within a natural habitat (6.7 eggs per female) probably indicates the magnitude of mortality factors that affect eggs and early-instar larvae in the field. The addition of sphagnum mosses around the tree bases to increase the depth of duff had the effect of increasing the bark surface area available for oviposition (some adults laid eggs directly beneath the moss), and may have increased the moisture at the root collar base. This treatment of increasing the duff layer resulted in increased oviposition on all tree sizes, compared with trees in the control plot (Fig. 6). At the end of the 1966 field season, weevil numbers (eggs and larvae) on treated trees were about twice those on untreated trees. This trend continued through 1967 and 1968 even though the estimated female survivors in each

TABLE4. Summary of surviving female Hylobius warreni adults and their oviposition behavior in two field plot arenas enclosing 25-year-old lodgepole pine trees. Plot A had the duff layer increased artificially to 10-12 cm, and plot B arena remained untreated and had a duff layer of 3-5 cm

Eggs in No. of eggs +. No. of No. of eggs + Percentage bark No. of eggs larvae per Plot: Year females* larvae? hatch niches (%) per female tree

*Numbers of surviving females were total numbers that had been marked and released in 1964, and recaptured in subsequent years. tLarvae in fourth instar and older were excluded as they likely were present during the previous year. $No values obtained. Volume 126 THE CANADIAN ENTOMOLOGIST 1397

Tree diameter at stump height (cm)

FIG. 6. Relationship between numbers of Hylobius warreni eggs and larvae and tree diameter of 25-year-old lodgepole pine trees enclosed in two circular arena plots after the duff thickness had been modified to 10-12 cm in one of the plots; the other plot was untreated and had a duff thickness of 3-5 cm. Error bars indicate 2 1 SE. plot were about the same (Table 4). This indicates the importance of the duff layer for H. warreni populations. Egg viability and embryonic development. High moisture content throughout embry- onic development seems to be required for successfulhatch. When eggs were stored in sealed vials with a high moisture content, percentage hatch of eggs laid during consecutive 10- to 19-day intervals varied from 36.8 to 68.4 (average 46.9%), but showed no seasonal trend (Table 5). The average period of embryonic development for the season varied from 29 to 54 days (average 42.2 days), but declined over consecutive intervals from early July to September (Table 5). The reason for this trend is unknown. Warren (1955) reared H. warreni adults of different ages collected on white spruce in Manitoba and observed a variable rate of hatch. Newly eclosed adults laid some eggs but hatch was low (5.0-7.6%), whereas for eggs that were collected from adults that were more mature, the rate of hatch was 56 and 70% during 2 separate years. All females, however, produced some eggs that did not hatch (Warren 1956~). My observations indicated that, during oviposition, most eggs were deposited on the roots and root collar areas. Some were loosely placed under bark scales or in the adjacent

TABLE5. Seasonal trend of egg hatch (%) and embryonic development time for Hylobius warreni eggs laid under laboratory conditions. Number of adult female and male pairs was 39

Period of No. of eggs Percentage Average period of embryonic oviposition laid hatch development (days)

1-19 July 44 19-29 July 46 29 July - 10 August 50 10-23 August 60 23 August - 2 September 19 2-20 September 22 Averages - 1398 THE CANADIAN ENTOMOLOGIST November/December 1994 soil, but most were deposited in small niches chewed in the bark. Each niche was chewed, usually in the outer bark; after a single egg was deposited, the niche was covered over with bark particles or excreta, similarly as observed for H. radicis (Wilson and Millers 1983). Niches with more than one egg were never observed, but several eggs were sometimes deposited in localized areas of the root or root collar of large-diameter-size lodgepole pine trees. In the above experiments, the proportion of eggs deposited in bark niches varied from 51 to 85% (Table 3; Cerezke 1967), and was similar to data recorded from field-caged adults monitored over 3 years (56-82%) (Cerezke 1969). Some of the variability in selection of oviposition sites appeared to relate to moisture conditions in the zone of egg laying, as a higher proportion were deposited in niches on trees having a thick moss layer (Table 4; Fig. 6). In naturally infested stands of lodgepole pine, eggs were generally difficult to locate but were observed most commonly in bark niches and in adjacent moss and soil. Larval Stages. First-instar larvae eclose about 42 days (range 29-54 days) after oviposition (Table 5) and were observed in the field from May to September on mature lodgepole pine (Cerezke 1969). The young larvae can survive for at least 5 days without food (Cerezke 1969). Presumably this allows them to make their way to host bark even if they emerge from eggs deposited in the adjacent soil. Larvae that emerged from eggs deposited in bark niches began immediately to excavate their tunnels. Initially, the gallery is shallow in the outer phloem and may be oriented in any direction. Most galleries remain localized until after larvae are in the second or third instar, when many are seen to follow a more directional path on the roots and root collar. Throughout larval development, feeding and gallery excavations are confined mostly to the zone of the root collar and roots lying between the surface mineral soil and the upper surface of the duff (Fig. 7). Within this zone (designated as the "larval universe") gallery orientation may extend in almost any direction. Larvae of all instars responded negatively to the presence of light, and probably sense the upper limit of their universe visually by the presence of two anterior ocelli. Throughout the feeding period, fine particles of chewed-off bark are mixed with fresh resin to form a matrix which the larva moulds into a protective covering. The resin material produced during feeding of young larvae often hardens and becomes crumbly but that of later feeding stages tends to remain sticky and pliable. In contrast, the pupal chamber formed at the end of the feeding gallery hardens fairly quickly to form a firm protective structure. The resin-bark mixture is generally pinkish-brown when fresh, turning whitish when dry and hard. The depth of feeding increases with size of larva, generally penetrating to the cambium and sapwood layers by the fourth instar. Thus most of the injury on trees occurs during the late larval stages. During larval development, the feeding tunnel may score the cambial and xylem tissues, either continuously or intermittently along its path. Completed individual larval galleries scored through to xylem tissue have extended up to 24 cm long by 0.7 cm wide. As feeding progresses, however, the exudation of resin may become excessive over the damage area and the resultant gallery pattern may become convoluted through the resin mass and become three-dimensional in form (Fig. 7), as also observed by Stark (1959~). Some differences in the feeding galleries of late-instar larvae were observed on young and mature lodgepole pine. In 10- to 25-year-old stands, most galleries were more circum- ferentially oriented around the lower stem, and extension of the gallery onto roots was less common than on older and larger trees (Fig. 8A, B). As well, penetration into the sapwood was generally more pronounced on the younger trees, probably because of the thinner bark. In Manitoba and Saskatchewan, Warren (1960~)observed a higher incidence of feeding on the roots of white spruce compared with the root collar, and the reverse pattern on jack pine. Volume 126 THE CANADIAN ENIKlMOLWilST

FIG.7. Profile of tree base and lateral roots showing the feeding universe of Hylobius warreni larvae by the presence of accumulated wounds, position of the pupal chamber away from tree base, duff layer, and resin accumulation. Abbreviations: D, duff; LW, larval wound; MS, mineral soil; PC, pupal chamber with larva; RCZ, root collar zone; R-SM, resin-soil mass.

When mature, the larva constructs a special chamber at the terminal end of the feeding gallery that serves for the protection of prepupa, pupa, and teneral stages. Its construction is evident by mid-May but the prepupal stage does not begin until the early part of June. For its construction, the larval gallery is usually extended 2-15 cm into the soil away from the tree base or root and within 2-10 cm from the duff surface. Rotting logs lying at the base of trees were also a common medium for the extension of the gallery and pupal chamber as also reported by Warren (19566). When completed, the chamber measures 8-10 mm inside diameter and about 25 mm long with a wall thickness of 4-6 mm (Fig. 7). The inside wall is smoothed and the chamber is sealed off behind and in front of the larva. Most chambers lie in a near horizontal plane with the head capsule facing away from the tree. This orientation and position away from the tree base may minimize entry of moisture from stem run-off during pupation, and thus enhance survival. Temperature in the larval universe was an important factor determining rate of develop- ment. Higher temperatures adjacent to root collars in clearcut sites, compared with uncut sites, shortened larval and pupal development time by about 1 month (Cerezke 1969,1973~). Pupal Stage. In west-central Alberta, pupation was recorded over a 6-year period and commenced between the 3rd week of June and early July with a peak near mid-July, and lasted until mid-August. Observations in Quebec were similar (Daviault 1949; Martineau 1984). In Manitoba during 1952 and 1954, pupae were observed during two 37-day periods, the first was between 10 June and 16 July 1952, and the second was between 5 July and 10 August 1954 (Warren 1955). This difference of about 25 days in the start of pupation was attributed in part to warmer daily temperatures in 1952. Pupae reared to adults during the same 2 years required an average of 32.9 days (range 29-36) and 29.5 days (range 21-34), respectively. Combined, the prepupal and pupal stages may last up to 8 weeks in the pupal chamber. Teneral adults in the pupal chamber were generally observed after mid-August and into September, similarly as noted by Warren (1956~). 1400 THE CANMIAN EN~OMOLO~IST November/December 1994

FIG.8. Typical root collar and root injury by Hylobius warreni larvae on a 15-year-old (A) and a 70-year-old (B) lodgepole pine. Arrows in A indicate an engraved gallery by one larva oriented circumferentially around the lower stem.

Adult Stage. In west-central Alberta, most teneral adults vacated pupal chambers in the fall after mid-August, but some remained in the chamber until the following May or early June. Presumably some larvae from eggs laid late in the season finish development later because of cooler temperatures. Newly eclosed adults emerged from the chamber by chewing through its distal end. Young and older adults overwinter within the duff, probably within a few centimetres of the duff surface. Sex ratios. Sex ratios of adult H. warreni collected by a number of different methods are shown in Table 6. Field-collected pupae reared to adults indicated that females were Volume 126 THE CANADIAN ENTOMOLOGIST 1401 TABLE6. Numbers of adults and the sex ratios of Hylobius warreni collected by different methods in a mature lodgepole pine forest

Total No. of no. of Percentage Method of collection females adults females x2 r~

Pupae collected in chambers and reared to adults: 115 214 53.7 1.196* 0.50 < p < 0.25 Tree-base and duff search within stand: Dead adults?: 29 60 48.3 0.067 0.90

*Chi-square values of goodness-of-fit test of an expected 1:l sex ratio. tDead adults were recovered within the duff near tree bases and represent mortality over more than 1 year

slightly more abundant (53.7%) than males but did not depart significantly from an expected 1: 1 ratio (Table 6). A similar 1: 1 sex ratio of H. warreni had been reported by Stark (1959a, 1959b). Numbers of dead and living females and males collected on or near the base of trees within pine stands also did not deviate significantly from an expected 1:l ratio, although 58.5% of live adults were females. Females caught in traps within stands, however, were significantly (p > 0.01) more abundant than males. Of the adults collected at tree bases and in traps on trees bordering clearcuts, males were significantly (p > 0.01) more abundant than females (Table 6). These data suggest that within stands, females are more readily found as they often occurred at the root collar base, whereas males were more common near the surface of the duff within a radius of about 35 cm from the tree base. Higher numbers of females in trap catches within stands may also indicate they were more active than males in terrestrial movement during host finding and in ascending trees to feed. Other explanations ' to account for differences in sex ratios of adults at margins and within stands may include differential mortality and longevity. Lower numbers of males in trap catches and from tree-base searches may reflect reduced male feeding and dispersal activities, compared with females. The response of males to seek out moist conditions in the root collar zone may also be less strong than that of females. Adult longevity. Adult H. warreni are flightless and long-lived. Daviault (1949) had suggested they may live up to 3 years, and 2 years was suggested by Stark (1959~)and Warren (1956b). In a field experiment in Alberta, in which newly eclosed adults were individually marked and released in 1964 into small plot arenas within a natural pine stand, and monitored for survival over the next 4 years, a portion of the original weevils released were still alive in 1968. This indicated that adults can survive up to 5 years. Although the survival curves appear similar for females and males, the ratio of females to males declined steadily in the two plots from 1964 to 1968: respectively, 1.50, 1.31, 1.29, 0.96, and 0.71 (Fig. 9). This suggests that male survival is better than female survival, perhaps because of their reduced activity. Almost half of the 4-year-old female and male adult survivors in 1968, however, had damaged appendages, either a missing antenna1 club, missing tarsi on one or more legs, or both. Mating activity. The sexual activity of H. warreni has been investigated only in a limited way. Mating probably occurs from May to September, similarly as for H. radicis (Wilson and Millers 1983), but appeared to occur mostly during June and July. Females THE CANADIAN mMOLOGIST November/December 1994

0 I I I I 1664 19165 1966 1967 1968 1969 Year

FIG.9. Survival rate of Hylobius warreni adults determined by mark, release, and recapture methods within field plot arenas. A cohort of 60 marked virgin females and 40 males was released into the arenas in fall 1964 and recaptured during subsequent years. dissected after July were all mated and none contained fresh spermatophores, whereas most females dissected in June and July had either not mated or they contained a freshly deposited spermatophore. In tree-cage experiments, mating adults were observed at night on tree stems, on the ground surface, and in the duff. Feeding behavior. Adults feed on bark of small roots and twigs, and on needles of white spruce and pine hosts (Warren 1956b; Martineau 1984). On lodgepole pine, some adult feeding occurred on the bark at the root collar and base of roots, but most scars were on branches and some on terminal buds; none were observed on the needles. When adults were enclosed in arenas around the base of young lodgepole pine trees, the distribution of feeding scars was bimodal with respect to height on the stem, showing that weevils favored either lower or upper branches as feeding sites (Fig. 10). Many of the feeding sites in the upper part of the tree occurred in the terminal buds where females were more commonly observed than males. Most feeding scars were on the upper surface of branch bark, free of needles and within 5-7 cm from the main stem. During movement or when at rest on a branch, the adults clung tenaciously. Adult weevils also ascended the stems of mature trees to feed; their feeding scars have been observed at least 6.4 m above ground and probably extend into the upper crown (Cerezke 1969). Feeding injury on young seedlings appeared to be rare (Cerezke 1969). Diurnal behavior. The adults display a strong diurnal pattern of activity, being most active at night and resting during the day. Observations by Reid (1952) first drew attention to the adult behavior of ascending tree stems during darkness and returning to the forest duff by early morning. He considered low light intensity, relative humidity greater than 70%, and temperatures above 4.4-7.2"C to be important factors stimulating their pedestrian and feeding activities (Reid 1954). In my studies, day -night observations of adults in enclosed arenas indicated that nearly all above ground pedestrian activity occurred between 1900 and 0500 hours, with a peak period after 2200 hours (Mountain Standard Time) (Cerezke 1969). When daily numbers of adults captured in traps within the young lodgepole pine stand were regressed over hourly temperatures recorded during the night of capture, a maximum r2value of 0.71 was obtained Volume 126 THE CANADIAP: ENTOMOLOGILT

--I# --I# TreeA - Tree B

Height above ground to branch whorls (cm)

FIG. 10. Distribution of adult Hylobius warreni adult branch feeding scars in relation to height above ground on two 25-year-old lodgepole pine trees. Number of feeding scars was 182 (Tree A) and 97 (Tree B). for temperatures recorded at 2300 hours. This suggested that most night pedestrian activity commenced shortly before this hour. The strong association between temperature and catch indicates this to be a useful tool to predict daily captures in traps. Weevil captures are plotted over temperatures at 2300 hours and show a strong linear relationship (r2= 0.82) (Fig. 11). Little or no activity, however, occurred if the temperature fell below 2.2"C by 2300 hours. Daily and seasonal dispersal behavior. Results of the daily and seasonal captures of adults in traps deployed in young and mature stands of lodgepole pine provided information on the activity patterns of males and females. Several conclusions can be stated from these studies. The seasonal trend in captures of females and males was similar between stands and generally fewer males were caught than females. Highest catches, indicating greater pedes- trian and feeding activity, occurred in June and decreased toward September (Fig. 12). Within the mature stand, the percentage of females (41.2%) recaptured one or more times was similar to that of the males (44.0%). The rate of capture for females, expressed as numbers of adults per trap per trapping day, was at least twice as high as it was for males except during 1966 when it declined; the rate of male captures remained near constant over time within the same plots (Table 7). Some of this decline in female catch may be partly attributed to mortality, but may also have resulted from behavioral differences due to increased oviposition. The recapture of marked adults on different trees within the mature stand during con- secutive nights indicated the adults may disperse laterally up to 11.3 m during any one night, but the average dispersal distance during a single night was only 2.3 m for both sexes. This 1404 THE CANADIAN EN'KIMOLOGIn November/December 1994,

1965 data • 1.4 + + 1966 data

:::; 0.2

0.0 -4 0 4 8 12 16 Temperature at 2300 hrs ("C)

FIG.11. Relationship between numbers of adult Hylobius warreni captured in traps affixed to tree stems and tempera- tures ("C) recorded at 2300 hours (Mountain Standard Time) during their night of capture. distance corresponded closely to the estimated average distance between trees (2.5 m), rather than to the average distance of nearest neighbor tree (1.2 m). Adult weevils may visit one or more trees during a single night. Hosts are probably selected visually according to the prominence of stem silhouette because weevil capture frequency closely matched tree diameter frequency (Fig. 13). When leaving a tree of origin to travel across the duff, both females and males showed no preferential direction (x2,goodness-of-fit; 0.75 < p < 0.50), based on recaptures at tree bases on two consecutive nights (Fig. 14A, B). Mortality Factors Egg Stage. Mortality factors affecting the egg stage of H. warreni have not been investigated in detail. During rearing studies of adult weevils in vials and in cages, it was observed that a portion of the eggs laid by most females failed to hatch. Similar observations were noted by Warren (1955). Although some eggs were likely infertile, some of the failure to hatch was likely due to an inadequate moisture level maintained throughout the long (29-54 days) duration of embryonic development. The placement of eggs in bark niches seems to meet the high moisture requirement, and the niches may also protect them from predation (Cerezke 1967). To date, however, no parasitoids or predators of the egg stage have been observed. During rearing studies in Manitoba, Warren (1955) reported eggs with soft shells that were easily crushed, and observed some adults in captivity eating their own eggs. These difficulties with artificial rearing probably resulted from an inadequate level of moisture and a reaction to the artificial medium (Warren 1958). On young lodgepole pine trees, the zone of oviposition and larval feeding occurs mostly where bark thickness is maximal and where the density and proportion of bark resin cavities are comparatively low. These physical characteristics of the inner bark were indicated to be important to the survival of eggs deposited in bark niches (Cerezke 1973b). Larval Stage. During intensive sampling of H. warreni populations in lodgepole pine stands between 1961 and 1966, observations showed that larval mortality was relatively uncommon (Table 8). The most common cause of death for young larvae appeared to be excess mositure in the gallery. Moisture from stem run-off can accumulate in galleries and other cavities Volume 126 THE CANADIAN ENTOMOLOGIST 25-year-old stand

P I I I I I I I I I 5 I t \ t I ---- Males 4 -Females - \ \ \ 1 3 - \

2

1

0 r I 20 30 9 19 29 9 19 29 8 18 28 May June July August

7Oyear-old stand

4 .I t

)r m I---Males g -Females 3 C ma 0 .--V) 2 Q, 3 $ Q) 1 0 -z -2 2 **,,--*

0 i0 30 9 19 29 9 19 29 8 18 28 May June July August

FIG. 12. Seasonal pattern of activity of female and male Hylobius warreni adults based on trap captures in a 25-year-old and a 70-year-old stand of lodgepole pine. Horizontal bars indicate trapping periods, ranging from 4 to 13 days. within the resinous matrix around attacked tree bases. Early-instar larvae may also be prone to predation and to excess resin flow, but the effects of these factors have not been quantified. In areas of clearcuts, larval development continued in the cut stumps of lodgepole pine for 2 years after tree removal but an estimated 88% of the larval population apparently died as a result of harvesting (Cerezke 1973a). The most important parasitoid of H. warreni was the ichneumonid wasp, Dolichomitus tuberculatus tuberculatus (Fourc.), which is known to occur transcontinentally in Canada 1406 THE CANADIAN ENTOMOLOGIST November/December 1994 TABLE7. Summary of the relative abundance and recapture* characteristics of female and male Hylobius warreni in a 70-year-old lodgepole pine stand in western Alberta during 1964-1966

Plot A Plot B

191% 1965 1966 1965 19M

% females captured 1 + times: 37.5 37.0 51.5 36.8 43.2 % males captures 1 + times: 59.1 33.3 44.0 40.0 44.0 No. female captures per trap per trapping day: 0.025 0.022 0.014, 0.027 0.016 No. male captures per trap per trapping day: 0.012 0.010 0.011 0.011 0.011

*Adult H. warreni were captured alive in tree-stem-attached traps, marked for individual recognition, released, and recaptured. Total number of traps in plots A and B was 251.

(Townes and Townes 1960). In Alberta, D. tuberculatus tuberculatus accounted for up to 5% mortality of last-instar larvae over the 4 years of study (Cerezke 1973c) and Stark (1959~)observed less than 3% mortality due to parasitism. Adults of this parasitoid eclosed between mid-June and mid-July and oviposition occurred during July with the deposition of a single egg placed in the weevil pupal chamber. The newly emerged parasitoid larva feeds externally on its host while in the chamber and matures in about 2 weeks; it then prepares a leathery pupal case within the weevil pupal chamber where it rests until the following spring. Warren (1955) collected Hylobius larvae in Manitoba and reported 39% parasitism on those larvae collected after 1 August. The species was tentatively identified as Ephialtes sp., which now appears to be a synonym of D. tuberculatus tuberculatus (Townes and Townes 1960). Warren's larval material may have included both H. warreni and H. pinicola; the latter species was also listed as a host of this parasitoid by Townes and Townes (1960). The infrequent predation on H. warreni larvae and pupae surviving in recently cut lodgepole pine stumps seems mainly attributable to a Laphria species (family Asilidae) (Cerezke 1973~).This predator may not be present on infested live standing trees.

- 20 -8 cn a - 15 0 Sr 0 5 10 3 0- ?? LL 5

0 10 15 20 25 30 35 Tree diameter at stump height (cm)

FIG. 13. Frequency distribution of tree diameters in a 70-year-old lodgepole pine stand and the distribution pattern of Hylobius warreni adults captured in stem-attached traps within the stand. Number of trees with traps was 251; numbers of female and male captures were 407 and 229, respectively. Volume 126 THE CANADIAN ENTOMOMGISl

Females n= 120

FIG. 14. Circular histograms of the direction from the traps where Hylobius warreni female adults (A)and male adults (B) were captured to the traps in which they were recaptured 1 day later. Concentric circles represent fre- quency increments of 5, Females and males showed no directional preference (goodness-of-fittest, 0.75

Pupal Stage. Several mortality factors of the prepupal and pupal stages were identified (Table 8). Pupae were particularly susceptible to moisture accumulated in their chamber. In some cases, free water appeared to weaken the chamber structure and allowed development of black mycelial fungi on the inside wall. A few dead last-instar larvae, pupae, and teneral adults in the pupal chamber were covered with a white mycelium believed to be the entomogenous fungus, Beauveria bassiana (Balsamo) Vuillemin. This fungus was posi- 1408 THE CANADIAN ENTOMOLOGIST November/December 1994 TABLE8. Summary of the incidence of mortality of immature stages of Hylobius warreni recorded in a variety of mature lodgepole pine stands in west-central Alberta during 1961-1966

% % Total* No. of mort. in popn. Sites Year weevils Larvae Prepupae Pupae Tenerals Hym.t cells mort.

I$ 1961 636 0 1 0 0 0 1.4 0.16 1 1962 647 0 0 4 5 1 7.0 1.39 1 1963 804 0 2 8 4 4 18.9 1.74 1 1965 633 1 2 17 + 15 8 3 44.3 4.58 2 1961 150 1 0 0 0 0 0 0.67 2 1962 160 0 0 1 0 1 4.2 0.62 2 1963 108 0 1 0 2 0 50.0 2.78 3 1962 121 0 2 4 6 0 30.8 9.92 3 1963 110 0 0 0 3 0 17.6 2.73 4 1963 306 1 0 4 5 0 34.6 3.27 5 1966 169 1 3 +I$ 0 1 0 22.7 3.55 6 1966 57 0 0 0 2 0 20.0 3.51

'Total population included all stages of larvae, pupae, and tenerals in pupal chambers. tAll parasitoids were identified as Dolichomitus tuberculatus tuberculatus. $Sites with the same number were sampled in consecutive years. §Indicates specimens covered with white mycelium, believed to be Beauveria hassiana. tively identified on several dead adults but it is unknown whether it was the cause of death (Cerezke 1973~).Pupae that developed late in the season did not survive overwintering, whereas teneral adults that remained in the pupal chamber during winter did survive. Adult Stage. Adult H. warreni appear to have few enemies; many of the adults seem to simply die of old age. Predation by birds and small mammals has not been observed; this may contribute to a low incidence of mortality because of the weevil's tree climbing and nocturnal activity behavior. The masked shrew, Sorex cinereus cinereus Kerr., was com- monly trapped in a weevil-infested lodgepole pine forest but examination of stomach con- tents of 46 individuals failed to reveal sclerital remains of the weevil (Cerezke 1973~).This may have been because the adult weevils were relatively scarce compared with other more abundant nocturnal insects such as carabid beetles; sclerital remains of these insects were readily identified. A mite, identified as Hericia species (near H. fermentationis Vitz.), family Sapro- glyphidae, subfamily Carpoglyphinae, was common on adults, especially females, after June and was attached externally on the ventral abdomen (Cerezke 1973~).The mites were present as immatures and may use the host weevil for phoresy as well as a food source. Only one species of internal parasite has been identified in the abdomen of a female weevil and was classified in the nematode superfamily Tylenchoidea. The adult weevil was collected in late August and contained 10 nematodes, each about 3 mm long, that lay in a dorsal position external to the digestive tract and in the space of ovary expansion. Its effect on the weevil is unknown but it likely reduces the fecundity or shortens the life of the adult (Cerezke 1973~).

POPULATION DYNAMICS AND IMPACT

Methods and Materials Weevil Abundance and Distribution within Forests Populations of H. warreni were sampled in a variety of even-aged lodgepole pine stands of different age classes in west-central Alberta to ascertain patterns of abundance and to Volume 126 THE CAEADlAN ENMMOI.OGlST 1409 identify mortality factors. Population patterns were considered most likely to be influenced by stand age and tree size, stand density, and depth of duff (defined here as the living and dead organic matter measured to the depth of mineral soil) around tree bases. These variables define much of the physical structure of the weevil habitat. Individual trees, consisting of the bark surface area on the root collar and main lateral roots between mineral soil and the upper surface of the duff, were considered as the basic sample units. Each tree was examined for weevils by removing the litter from around the tree stem to expose lateral roots as described by Cerezke (1969,1970c, 1973~).All larvae, pupae, and teneral adults were tallied for population estimates; eggs and mature adults were excluded because they were difficult to locate and not often encountered. Population estimates were expressed as numbers per tree (population intensity), or as numbers per unit area of forest land (absolute populations) (Southwood 1978). Estimates of absolute numbers allow comparisons to be made between different locations, sites, years, and different stand conditions. Populations were sampled within the same plot areas over I-, 2-, 3-, and 6-year periods. Trees selected for sampling within plot areas either were chosen randomly to provide representation of all tree sizes or were all sampled within fixed plot areas. In all plot areas, measurements were made of tree diameter (diameter at stump height or d.s.h.), tree height (in young stands only), stand density (stems per hectare), and average depth of duff at tree bases. The depth of duff was calculated as an average of three measurements taken a few centimetres away from around the tree base. Sample sizes per site ranged from 107 to 389 trees. Population estimates were calculated for each site and year. The location of current larval feeding areas was recorded, whether on lateral roots or on the root collar. Incidence of attack was calculated as a percentage of trees with current attacks (live weevils present) and as a percentage of trees with old weevil wounds. nee Size and Age Relationships. The relationships of weevil numbers per tree and tree size are described and compared graphically for two natural stands of lodgepole pine, both of fire origin: one was a 25-year-old stand, the other was a 70-year-old stand. For the preparation of these graphs, plot data were divided into four approximate equal density classes. Trees within each density class were stratified into four height classes for the 25-year-old stand and into four diameter (d.s.h.) classes for the 70-year-old stand. The percentages of trees with old and current H. warreni wounds were calculated for each tree size and density class in the 25-year-old stand, but only current attacks were considered in the 70-year-old stand. Because plot areas and their corresponding number of trees were known, estimates of the numbers of weevils per tree and per hectare were calculated for each density class within each of the two stand age classes. Duff Depth Relationships. The relationship of weevil numbers per tree and duff depth around the tree base is complicated by the fact that average duff depth seems to increase with tree size within the same stand. This aspect was examined in a 70-year-old stand and a 25-year-old stand of lodgepole pine. In the 70-year-old stand, the relationship between weevil numbers per tree and duff depth is described for trees in three diameter classes, representing small, medium, and large trees. A further complicating factor results from the distribution of weevils on roots and root collar, and how this might vary with increasing tree size and duff depth. During population sampling, weevil numbers occurring on roots were recorded separately from those on the root collar. The two population values were plotted separately over average duff depth at trees within three broad diameter classes. The ratio of weevils on roots to those on the root collar within the same diameter classes was regressed over tree diameter to determine the influence of tree size on the distribution pattern of weevils on their host. Stand Density Relationships. Weevil numbers and stand density relationships were examined in a 70-year-old stand. Estimates of weevil numbers were obtained from a sample 1410 THE CANAD1 AN EFirOMOLOGlST NovemberDecember 1994 of 10 randomly selected trees within each of 96 plot areas. Each plot measured 15.1 by 45.7 m (0.069 ha). A count of the total number of living trees was made in each plot and expressed as density per hectare. The plots were grouped into similar density classes and an estimate was made of the weevil population within each class and expressed as numbers per hectare. Weevil density estimates were plotted over stand density values. Weevil Population lkend during Stand Development. During population sampling in lodgepole pine stands, it became apparent that weevil numbers were strongly influenced by tree size and age. It was hypothesized that weevil abundance may follow a characteristic pattem temporally as trees grow and mature during stand development. One approach con- sidered to examine this aspect was by dating of the larval feeding scars that remain visible as a permanent record on the lower stem. This method was used on the assumption that the number of old feeding wounds was a reflection of weevil abundance. A total of 3 1 lodgepole pine stems in a 70-year-old stand were cut transversely at a level on the stump that was visually judged to represent the region of maximum weevil damage. The trees were selected within a range of diameter sizes representative of the stand. Each stump cross section was smoothed with a rotary sander to clarify annual increment bound- aries and to date old weevil scars. The scars were dated according to approximate year of attack and were grouped into consecutive 5-year age intervals on each stem. An average number of scars per tree was calculated for each 5-year interval and plotted over age class. Weevil Population Characteristics. The frequency distribution of H. warreni numbers per tree conformed to the negative binomial distribution. Two parameters describe this distribu- tion; mean (i5)and an exponent k. As described by Southwood (1978), the k-value provides a measure of the degree of dispersion in a population and is a useful characteristic for comparing different populations from different habitats and years, providing that a standard sampling unit (i.e. individual tree in this case) has been used. Values of k were calculated from data obtained from a number of plot areas within mature lodgepole stands by the iterative solution described by Southwood (1978). lkee Host Attack Pattern and Injury Attack Pattern in Young Stands. Invasion by H. warreni into young lodgepole pine stands begins when the trees are a few years old, depending upon the nearness of population sources. Surveys in young stands were conducted in western Alberta to examine the pattern of initial tree selection for attack, tree mortality, and the accumulated injury in relation to stand maturity. Surveys conducted in a 3- to 9-year-old stand and in a 25-year-old stand were made by describing attacked trees in relation to tree size distribution. Methods of Assessing Stand Susceptibility, Weevil Abundance, and Injury Diameter at 50% Damage Incidence (D,,-value). Extensive surveys for H. warreni abundance and incidence were conducted at 56 locations in lodgepole pine stands in western Alberta (Anon. 1969; Cerezke 1970b). Stands ranging in age from 18 to 162 years and occurring over an altitudinal range of 820-1830 m were sampled using the procedure described by Cerezke (1970~).Trees in each sampled stand were divided into 2.54-cm diameter classes and the percentage of trees with old attacks was calculated for each diameter class. When the percentage values were plotted over diameter class, a diameter-value was obtained, representative of each stand, at which damage incidence had accumulated to 50% (i.e. D,,-value). This value reflects the cumulative nature of attacks during stand development and suggests that a fairly stable pattem exists for all age classes within a broad range of sites. Values of D,, were obtained for stands classed into 10-year age classes within the Lower Foothills (I220 m) sections of Alberta (Rowe 1972). The data are presented graphically for sampled stands 61-70 years old to illustrate differences related to altitude and site. Volume 126 THE CANADIAN EhTOIOLOGIST 1411 Precommercial Thinning Effects on Weevil Abundance and Injury Two 0.081-ha plots within a 25-year-old stand of lodgepole pine in western Alberta were thinned to about 2-m spacing and had a post-thin density of 2750 stems per hectare. A natural population of H. warreni had been present in the stand for many years. Populations of the weevil were monitored over the following 8 years to assess changes in numbers of weevils and related girdling injury, and to compare these changes with similar information gathered in two adjacent control plots in which no thinning treatment took place. The two plot areas were treated in 1967 and observations were made subsequently at 2-year intervals: 1969, 1971, 1973, and 1975. Observations in the control plots began in 1969. Data recorded included tree diameter (d.s.h.), populations of the weevil (expressed as numbers per tree and per hectare), percentage of attacked trees, and percentage root collar circumference girdled (data obtained for 197 1, 1973, and 1975).

Results and Discussion Numerical Relationships Numerical Trends and Abundance. Estimates of populations of H. warreni have been difficult to obtain because of the subterranean habits of this insect. The accuracy of estimates may vary with the size and age of host trees and with host species. As well, the lengthy life cycle has added to the problems of population census. Warren (1956b) recognized these difficulties and developed a Damage Index (D.I.) method that characterized levels of injury. He attempted to correlate D.1.-values with weevil numbers on dry to moist sites but was only partly successful. My population estimates include larvae, pupae, and teneral adults within pupal chambers, and have been expressed as numbers per unit diameter of tree stem or per tree (population intensity), or as numbers per unit area of forest land (absolute populations) (Cerezke 1969, 1970b, 1970~).Table 9 presents a summary of population estimates expressed as weevils per tree and per hectare for a variety of habitats within stands of lodgepole pine. Additional data on population estimates of H. warreni in white spruce and jack pine habitats are included (Warren 1956a, 1960c; Stark 1959~).The range of absolute estimates (215-2760 weevils per hectare) indicates that populations of H. warreni are maintained in relatively low numbers within forests, and probably undergo minor fluctua- tions from year to year. Similar levels of population abundance may occur in both young and mature stands and on different hosts. This results from the fact that young stands often have a low attack rate of trees and a low population intensity, but the stands exist with high numbers of stems per hectare. In contrast, a mature stand will likely have a higher attack rate, a higher population intensity, but with fewer stems per hectare. In an intensive survey of H. warreni in lodgepole pine stands in west-central Alberta, population estimates obtained by an indirect method of measurement (Cerezke 1970c) provided numerical trends similar to those shown in Table 9 (Cerezke 1970b). Many surveys of tree mortality in various conifer plantations and other managed stands established after disturbances such as harvesting have indicated much higher population levels than those in Table 9 (Warren 1956a; Finnegan 1962b; Warren and Parrott 1965; Hemng and Coates 1981; Wood and Van Sickle 1986; Byford and McLean 1991; Cerezke 1991). Some of these plantations have included exotic species such as Scots pine and Norway spruce. Weevil Abundance and Site Factors. Warren (1956b) investigated site factors affecting the abundance of H. warreni in Manitoba and Saskatchewan and showed that accumulated girdling injury (D.1.-values) on white spruce increased directly with moisture content of humus. Soil pH was also examined as a possible factor influencing weevil abundance on white spruce (Warren 1956d). Although the data suggested that D.1.-values increased inversely with pH, the results were inconclusive due to the complication of interacting variables such as climate, soil type, moisture, location, and tree species. His studies of site 1412 THE CANADIAN ENTOMOLOGIST November/December 1994. TABLE9. Summary of population* estimates of Hylobius warreni sampled on different host species, stand ages, locations, and yearst

Site$ Year Hosts Age 41 Weevils per tree Weevils per ha

100 Mature 15 75 15 25 25 25 45 65 66 67 69 70 65 66 67 66 67

*Population estimates were based on numbers of larvae, pupae, and teneral adults in pupal chambers ?Data used were from Cerezke (1969, 1970c), Stark (1959a), and Warren (1956a, 1960~). $Some sites were sampled for 2 or more consecutive years. $Host species include: wS = white spruce; jP = jack pine; IP = lodgepole pine. I(n = number of trees sampled. (/Indicates no data available.

factors included plant indicator species, soil characteristics, and measurements obtained from analysis of the humus (e.g. moisture equivalent and loss on ignition) lying over the tops of roots of attacked trees. These factors provided useful predictive indicators of habitats suitable to the weevil (Table 10). In west-central Alberta, Ives and Rentz (1993) rated lodgepole pine stands up to 30 years old into low-, medium-, and high-productivity sites based on soil associations, drainage classes, and altitudes. They recorded highest incidence of tree mortality by H. warreni girdling in sites rated high-productive. Overall mortality in the high-productive sites was about twice that in low- and medium-productive sites, and included trees in all age classes from 5 to 30 years old. It is assumed that the different levels of mortality on these sites correlate with H. warreni abundance. In mature lodgepole pine stands, highest populations of Warren rootcollar weevil occurred on high-productive sites, characterized by soil profile and plant indicator species (Cerezke 1969, 1970~);ecosystem associations rated for these stands have mean annual increment values of 3.8-4.3 m3 per ha per year (Corns and Annas 1986). Weevil Abundance and Stand Parameters. Weevil numbers can be related to four stand parameters: tree size and age, depth of duff material at tree bases, and stand density. Tree size and age relationships. Within naturally stocked stands of lodgepole pine, weevil numbers (larvae, pupae, and young adults in pupal chambers) per tree increased directly with tree size, regardless of stand age, density, and site (Figs. 15,16, 17), but tended to vary inversely with stand density in a 25-year-old stand (Fig. 16). Warren (1960~) observed a similar tree size relationship in white spruce and jack pine stands and indicated that the incidence of attack increased with stand age as well. He suggested, as with lodgepole pine, that size was a more important factor than age. In studies of plantation-grown lodgepole Volume 126 THE CANADW ENTOMOLOGIST 1413 TABLE10. Comparison of percentage moisture equivalent and loss on ignition values of humus over roots of white spruce attacked by Hylobius warreni with corresponding Damage Index (D.I.) at sites in Manitoba, Saskatchewan, and Alberta*

Moisture D.1. Loss on D.I. equivalent ignition (%) Man.t Sask.? A1ta.t (%) Mnn. Sask. Alta.

*Data after Warren (19566). ?Locations in each province were as follows: Manitoba, Riding Mountain National Park; Saskatchewan, Candle Lake; Alberta, Strachan. $Indicates no data available. pine in west-central British Columbia, Byford and McLean (1991) showed that the percentage of pine attacked by H. warreni increased linearly with plantation age and tree height. In the studies in Alberta, large trees consistently supported more weevils than did small trees within the same stand and age class of lodgepole pine, and fewer weevils per tree occurred in young stands compared with older stands (Figs. 15, 16, 17) (Cerezke 1969, 1970b, 1970~).The maximum number of weevils found on single mature trees was 31, but in 20- to 25-year-old stands the maximum numbers rarely exceeded five weevils. Similarly, the percentage of trees within stands with current-year attacks was strongly correlated with average numbers of weevils per tree over a broad range of stand age classes (Cerezke 1970~). In a general survey of lodgepole pine forests in Alberta, mean tree diameter per sampled plot was the single most important factor accounting for the variability in percentages of trees with both old and current attacks (Anon. 1969; Cerezke 1970b).

Tree diameter at stump height (cm)

FIG.15. Relationship of numbers of Hylobius warreni per tree and tree diameter at stump height in 25-year-old (A) and 70-year-old (B) stands of lodgepole pine. Number of trees sampled in A was 632, and 1599 trees in B. 1414 THE CANADIAN ENTOMOLOGIST Novemher/Dewmber 1994

Average no. weevlldtree: 0.20 0.14 0.12 0.08 Average no. weevilslha: 684 964 1485 1a5 I

Stemslha ('0001 G'-

FIG. 16. Histogram of Hylobius warreni attack incidence (old and current attacks) in relation to stand density and tree height in a 25-year-old lodgepole pine stand. Population estimates are given for each stand density class. Plot areas were grouped into four equal density classes, and trees within each class were grouped into four height classes. Estimates of weevil numbers were calculated for each density class.

The relationships with tree size and age suggest that adult females distribute their eggs approximately in proportion to the available healthy bark surface area of roots and root collar. During stand development weevil wound areas accumulate on the tree and thus have the effect of reducing potential feeding areas and oviposition sites. Many of the wound areas heal over in time, and at the same time, root and root collar areas expand through normal growth. Bark areas with old wounds and resinosis are generally avoided as new egg laying and feeding sites. Because most attacked trees survive the accumulated wounds and resinosis, this injury over the long term may provide a regulatory mechanism for the weevil by restricting the areas for subsequent egg laying and feeding activity.

Average no, weevlls/tree: 2.10 1.41 1.S9 1.M Average no. weevlldha: 1974 1693 2313 1737

Stemslha ('000) \-'

FIG.17. Histogram of Hylobius warreni current attacks in relation to stand density and tree diameter in a 70-year-old lodgepole pine stand. Population estimates are given for each stand density class. Plot areas were grouped into four density classes, and trees within each class were grouped into four diameter classes. Estimates of weevil numbers were calculated for each density class. Volume 126 THE CANADIAN ENTOMOLOGIST 1415

8 12 16 20 Depth of duff (cm)

FIG.18. Relationships between numbers of Hylobius warreni per tree and depth of duff around tree bases for three tree diameter classes in a 70-year-old lodgepole pine stand. Trees of three diameter classes, representing small, medium, and large trees, were selected from within six 1.2-ha plots. Average duff depth was measured at the base of each tree. Trees within each diameter class having the same duff depth were grouped together and plotted against the corresponding average numbers of weevils per tree.

Duff depth relationship. The thickness of the duff layer may reflect both moisture conditions and quality of site as a result of the soil characteristics, physical structure of the ground floral species, stand density, and stand maturity. A shallow duff layer, for example, was characteristic of a dry site that included lichen species (Cladonia spp.) and a low attack incidence, whereas moist sites generally supported a rich complex of mosses, herbs, and shrubs and had a higher attack incidence (Cerezke 1969). The depth of the duff layer around tree bases may influence the amount of oviposition, largely determines the size of the larval universe, and provides habitat and protection for the pupae and adults. In an experiment in which the depth of duff was artificially increased, subsequent egg productivity per tree increased, compared with adjacent untreated trees, and the portion of lower stem covered by introduced duff was utilized by females as egg laying sites (Fig. 6). In older stands, weevil abundance generally increased with thickness of duff (Fig. 18). Excessively deep duff (i.e. >17 cm) layers, however, consisting largely of Sphagnum species of moss, were detri- mental to the weevil by retaining a high moisture level around the root collar base (Fig. 19). There is an apparent interaction between tree size and duff depth as larger trees tend to have deeper duff than smaller trees within the same stand (Figs. 18, 19,20). The effects of the duff layer may act differentially on different size trees as weevil numbers per tree De~thof duff (cm)

FIG. 19. Relationships between numbers of Hylohius warreni on roots (R) and root collar (RC) and depth of duff around tree bases for three diameter classes in a 70-year-oldstand of lodgepole pine. Note decline in weevil numbers at highest duff depth level. Weevil numbers were recorded separately on roots and root collar areas of trees within three broad diameter classes. Trees within each diameter class were grouped according to the depth of duff measured at each tree base. Average number of weevils per tree within each diameter class was plotted over duff depth. increased more sharply with increasing duff depth on dominant-size trees than they did on suppressed trees (Figs. 18, 19). Byford and McLean (1991) measured the duff layer depth in young lodgepole pine plantations in west-central British Columbia but found no correlation with incidence of attack. They attributed the lack of a relationship to the fact that their measurements were made in the open rather than at tree bases. Duff depth measurements taken away from tree bases during an extensive survey of H. warreni in Alberta also did not show any clear relationship with weevil abundance (Cerezke 1970b). When weevil numbers were tallied separately on roots and on the root collar, their relationships with duff depth were similar and increased with increasing tree size (Fig. 19). In mature lodgepole pine stands, however, there was considerable variation in the proportion of weevils on roots and root collar; percentages varied among stands and among years within the same stand. This may have resulted from yearly or seasonal variations in moisture conditions around tree bases that required egg laying females and larvae to adjust their positions (Table 11). The ratio of weevils on roots versus root collar increased directly with tree size and stand age, suggesting that this weevil increases its utilization of the lateral root surfaces as stands grow and mature (Fig. 21). Utilization of lateral roots versus root collar for feeding and oviposition may also vary with the host species. Warren (1960~)observed a higher Volume 126 THE CANADIAN ENTOMOLOGIST 1417

0 I I I I I I I 1 1 2 3 4 5 678 Tree height (m)

FIG.20. Relationship of depth of duff and tree height in a 25-year-old lodgepole pine stand. Trees within the same height class were grouped and the average depth of duff was calculated for each height class.

D.1.-value on the roots than on the root collar of white spruce, and the reverse situation was observed on jack pine. Stand density relationship. The relationship of H. warreni abundance and stand density was not investigated by Warren (1960c), although he suggested that density appeared to have little or no effect in young white spruce stands. He observed, however, low D.1.-values in very dense stands with complete crown closure and attributed this to a dry humus layer. In young naturally grown stands of lodgepole pine, excessively stocked (e.g. >12 000 stems per ha in 25-year-old stands or >4500 stems per ha in a 45-year-old stand) stands appeared to provide poor weevil habitat with a low incidence of attack (Cerezke 1969, 1970b). Millers (1965) suggested that cooler soil temperatures associated with dense stands compared with open-grown stands caused H. radicis to be nearly absent in dense stands. In the Nordic countries, thermal climate variations reflected in latitude and altitude were believed primarily responsible for influencing the development rate and generation

TABLE11. Summary of the percentages of Hylobius warreni larval feeding on roots and on root collar areas of mature lodgepole pine in west-central Alberta

No. of trees % of weevils % of weevils Site Year sampled on roots on root collar THE CANADIAN ENTOMOLOGIST NovemberDecember 1994

Tree diameter at stump height (cm)

FIG.21. Relationship of the ratio of Hylobius warreni on roots to root collar areas of the host and tree diameter in a 70-year-old stand of lodgepole pine. Weevil numbers were recorded separately on roots and root collar areas of individual trees. Trees were then grouped into diameter classes and average ratio was calculated for each class. time of H. abietis (Bejer-Petersen et al. 1962). In young, plantation-grown lodgepole pine stands with densities ranging from 1000 to 7000 stems per hectare, Byford and McLean (1991) found no apparent relationship between density and incidence of weevil-attacked trees. This density range was not considered excessive for young stands. In another study in west-central Alberta, Ives and Rentz (1993) separated stand density into two categories: those over 6000 stems per ha and those under 6000 stems per ha, and compared the incidence of tree mortality caused by H. warreni for different years and age classes. The incidence of total mortality appeared to be slightly higher in the dense stands for age classes up to 20 years, but they reported mortality in the 20- to 25-year age class only in the less dense stands. The density relationships with weevil abundance within these young stands are not entirely consistent and require further study. The relationship between weevil numbers and stand density was examined in 70-year-old lodgepole pine stands in west-central Alberta. In these stands, maximum weevil population levels (weevils per hectare) occurred within the range 900-1300 stems per hectare (Fig. 22). This "optimum level" may vary according to different ages and site conditions and reflect a balance between minimal tree spacing and stem diameter; the former characteristic may relate to adult weevil host and mate finding efficiency and the latter factor may relate to total habitat space available for egg laying and larval feeding sites. The influence of crown closure at the higher density range may also be implicated. Numerical trend during stand development. Numbers of feeding scars made by H. warreni larvae at the root collar base of stems are plotted over tree age and indicate a pattern of attack during stand development (Fig. 23). Initial attack in the stand probably commenced between ages 10 and 15 years and was followed by a slow rate of increase to about age 30 years. After 30 years, there was a rapid rate of increase to about age 45, then an apparent decline. This period of decline, however, does not reflect all events associated with stand maturity as only scars at the root collar level were counted. The graph does not take into account the trend of increasing weevil attacks on roots with increasing tree size and age (Fig. 21). The declining trend after age 45 may therefore incorrectly represent weevil Volume 126 TCW CANADIAN ENTOMOLOGIST

FIG. 22. Relationship of Hylohius warreni population estimates per hectare and stand density in a 70-year-old lodgepole pine stand. Estimates of weevil numbers were based on samples of 10 trees selected randomly within 96,0.076-ha plot areas of known stem density. The plots were grouped into similar tree density classes and plotted against weevil population estimates. abundance and should perhaps indicate a levelling off to at least age 60. It is perhaps noteworthy that the basal area of fully stocked lodgepole pine stands attains a maximum at about age 60 years (Smithers 1957). This suggests that weevil population intensity levels may not increase significantly beyond this age. The period of most rapid weevil increase coincides with the age of most rapid growth in natural stands of lodgepole pine (between 15 and 45 years), and probably also with the interval when most natural thinning takes place (Smithers 1962). During the period of apparent rapid population growth (30-45 years), the pattern of feeding scars probably reflects more of an increase in population intensity rather than in absolute number. The increasing tree size and reduction in stem density during stand development have the effect of making weevil populations more highly aggregated. The estimates of absolute weevil numbers per hectare indicate that, although weevil numbers increased with tree size, similar levels of abundance occurred in young and old stands. This suggests that absolute abundance remains relatively constant in time. During stand development, stand density changes as a result of the natural thinning process, and with the continued growth of surviving trees. Thus weevil population intensity increases temporally with increasing tree size and age and reaches a maximum, whereas absolute numbers tend to remain fairly constant in time, perhaps decreasing at stand maturity. Weevil population characteristics. The frequency of weevil numbers per tree conformed to the negative binomial distribution as described by two parameters, a mean 6 t-) and an exponent k (Southwood 1978). In a variety of mature stands sampled in Alberta, estimates of k-values varied from 0.09 for the lowest population to 0.68 for the highest population, indicating a high degree of contagion. Contagion in the weevil habitat appeared to be due to two characteristics: the behavior of adult weevils in selecting large-diameter-size trees for greater oviposition compared with small trees, and the gradient of tree sizes within natural stands. The k-values may be used to compare different 'populations from different habitats and years. 1420 THE CANADIAN ENTOMOLOGIST Novemberpecember 1994

Stand age (years)

FIG.23. Frequency distribution of scars made by Hylobius warreni larvae at the root collar level of stems of 70-year-old lodgepole pine. Each bar indicates numbers of scars ? 1 SE accumulated during a 5-year growth increment period. Number of stems sectioned was 3 1. nee Host Attack Pattern and Injury Tree Mortality. Adult H. warreni initially invade young natural stands of lodgepole pine as early as 5 years following fire, harvesting, or other forest disturbances. Within the new stand they disperse while selectively attacking dominant and codominant trees (Figs. 24,25). As the stand develops, incidence of attack increases and accumulates progressively from largest- to smaller-diameter-size trees. By age 40-60 years in natural stands, virtually all trees may have sustained old or current-year attacks, or both (Figs. 15, 16, 17) (Cerezke 1969, 1970b, 1970~).Weevil-caused mortality within natural stands occurs up to about age 30 years but appears to reach a peak between 5 and 10 years (Ives and Rentz 1993). Except in some plantations and intensively managed stands, trees rarely die directly from girdling injury after age 30 years but the wounds can provide entry for decay organisms and cause growth reductions (Warren 1960~;Whitney 1961; Cerezke 1970~).During intensive surveys of factors affecting the survival of lodgepole pine up to 30 years old in west-central Alberta, Ives and Rentz (1993) observed an overall average of 0.84% of trees killed by weevils per year. Other surveys in natural stands of lodgepole pine have indicated similar annual mortality rates within the range of <1-3% (Anon. 1958-1989; Amirault and Pope 1989; Cerezke and Brandt 1993). Accumulated mortality by age 30 years may generally range between 5 and lo%, but often exceeds 15% in intensively managed stands and in plantations (Table 12) (Cerezke 1970~). The reasons for the occurrence of mortality of young confiers, compared with older trees, are that girdling injury tends to occur more frequently on the root collar than on roots and is often more circumferentially oriented around the stem base of smaller trees. Also, complete girdling of a 5- to 15-year-old tree can be achieved by only one to three larvae: on average, one larva girdles a stem circumference distance of 5.9 cm (SE f 0.4 cm) (Cerezke 1970~).On older trees, feeding injury occurs more frequently on roots (Figs. 19,21), thus decreasing the risk of complete girdling at the stem base as well as diluting the overall effects of wounds on the host tree (Cerezke 1970c, 1974). Most trees die from girdling when they Volume 126 TIIE CANADl4N ENWMOLOGIST - 1421

Tree height (m)

FIG. 24. Frequency distribution of tree heights in a 3- to 9-year-old lodgepole pine stand and early attack pattern of Hylobius warreni. have feeding wounds scored through the cambium and encircling over 90% of the root collar circumference, or when the majority of roots are girdled (Warren 1956b; Cerezke 1974). Anatomical Effects of Girdling. The feeding wounds of larvae that score through the cambium and outer sapwood of the host tree stimulate a response to wounding and result in the formation of traumatic resin ducts. These are produced in the outer xylem ring and extend above and below the wound. They continue to form until larval feeding is terminated

25

0 2 4 6 8 10 12 Tree diameter at stump height (cm)

FIG.25. Frequency distribution of tree diameters in a 25-year-old stand of lodgepole pine and the accumulation of Hylobius warreni attacks. 1422 THE CANADlAN ~.MOLOTJIST NovemberDecember 1994 TABLE12. Examples of accumulated tree mortality caused by Hylohius warreni in high-value stands of different hosts, ages, and provinces - -- - - Accumulated Province Host species Age, years mortality Reference

British Columbia Lodgepole pine 4-20 5% Wood and Van Sickle (1989) British Columbia Lodgepole pine 15 5% Koot and Tunquist (1984) British Columbia Lodgepole pine 7 29% Garbutt and Stewart (1991) British Columbia Engelmann spruce Young stand 8% Humphreys and Clark (1989) Alberta Lodgepole pine 11 7.1% Cerezke (1991) Alberta Lodgepole pine 12 10.4-22.8% Cerezke unpubl. data Manitoba Jack pine 15 2-10% Warren (1960~) Quebec Scots pine 40 63% Finnegan (1962b) Newfoundland Scots pine 14 29.2% Warren and Parrott (1965) Scots pine 23 18.6% Jack pine 23 15.6% Newfoundland Sitka spruce 14 16.5% Warren and Singh (1970) Norway spruce 14 3.6%

(Cerezke 1972, 1974). Only vertical traumatic resin ducts were observed adjacent to the larval wounds and were a source of the resinosis accumulating at wound openings. On lodgepole pine, the external resin flow at the wound site as well as some infiltration of resin in the tracheids centripetally from the wound probably confer resistence to entry of decay- causing fungi. Surveys of lodgepole pine have generally found less evidence, compared with white spruce, that the larval wounds contributed significantly as courts of entry for disease organisms (Nordin 1956; Stark 1959a; Baranyay and Stevenson 1964; Cerezke 1970~). Growth Loss Effects. Several authors have studied the effects of weevil girdling injury on the growth of trees. Warren (1956~)measured radial increment at stump height level on 100-year-old white spruce in northern Saskatchewan and found no correlation between D.1.-values and increment reduction, or between D.1.-values and apparent vigor (rated as good, fair, and poor). His conclusion about H. warreni attacks on plantation-grown Scots pine in Quebec was similar, and suggested that the stump height level of these tree species showed little response to girdling effects, even on stems with near complete girdling. A study of radial growth measurements at breast height level on young lodgepole pine trees also failed to show a significant difference between trees 0-30% girdled and trees >70% girdled (Garbutt and Stewart 1991). During studies at two locations in Alberta of 20-year-old lodgepole pine with 50% girdling of the root collar circumference, radial growth reductions at stump height level ranged from 8.2 to 17.2%, but only the latter amount was statistically significant (Cerezke 1970~).On individual trees, however, growth reductions do occur immediately above root collar girdled areas as well as on lateral roots immediately below girdle wounds (Cerezke 1972,1974). These reductions presumably result from disruption of the normal nutrient flow and distribution. A consequence of reduced radial increment on lateral roots extending below partial girdles is that growth of the root system may become asymmetrical and weakened. On partially girdled stems of Scots pine and Norway spruce seedlings, Lingstrom and Hellqvist (1989) observed a higher level of mortality of the spruce seedlings but root growth was reduced considerably on both species. During a 3-year period following girdling of stems to simulate weevil wounds on young lodgepole pine, radial increment on roots below girdle wounds was reduced by an average of 50.7, 60.7, and 49.3%, respectively, for the 3 post-treatment years. In this study radial growth on the main stem increased initially with increasing amount of partial girdling to about 50% of the root collar circumference and Volume 126 THE CANADlAN ENW.WLOGIST 1423 declined significantly only after partial girdling exceeded 70% (Cerezke 1974). The response to partial girdling at the root collar level was somewhat variable at different levels up the stem, but showed the greatest reduction in radial growth near the top of the tree. Initially, growth in the stem increased above the girdle wound, then declined after 2 years, probably because of depletion of food reserves and starvation of the roots (Cerezke 1974). The effects of H. warreni girdling on height growth are more distinct and dramatic. On sapling-sized white spruce, leader growth on trees with high D.1.-values, when compared with those having low D.1.-values, was decreased 2.4,25.0, and 34.5%, respectively, during 3 consecutive years (Warren 1960~).Height growth reductions were also visually noted on attacked young lodgepole pine in British Columbia (Garbutt and Stewart 1989). In Alberta, estimates of height reduction on trees with 50% girdling by H. warreni ranged from 11.5 to 15.6% (Cerezke 1970~).On young lodgepole pine with simulated girdling treatment, reduced height growth occurred during the 1st, 2nd, and 3rd years after treatment, decIining by 28.5% over 3 years on trees with 90% root collar circumference girdled (Cerezke 1974). Similar reductions in height growth were observed on young lodgepole pine partly girdled by small mammals (Sullivan et al. 1993). Other studies in plantation-grown Scots pine and red pine 1.2-3.0 m tall indicated that stem girdling by H. radicis caused leader length to decrease in relation to the amount of stem girdled, and that the tallest trees showed higher losses than did shorter trees within the same stand (Wilson 1965). This is an important aspect because H. warreni attacks are generally concentrated on dominant and codominant trees (Figs. 24,25). Throughout development of lodgepole pine stands sustaining infestations of H. wareni, variable proportions of surviving trees will accumulate partial girdling of roots and root collar. This injury likely causes some reduction in stem volume but height reductions appear to be the main long-term effects. These losses have not been quantified on a stand or temporal basis. The accumulated weevil wounds during the life of stands may also play a role in stand decline and a hastening of stand succession by contributing to tree mortality, a reduction in stand density, and the creation of openings for understory spruce and fir species. Weevil Wounds and Disease Associations. Early studies of H. warreni in Manitoba and Saskatchewan were prompted by the concern that the feeding of this weevil contributed to root and stem decay organisms (Warren and Whitney 1951; Whitney 1952). In a mature stand of white spruce, the incidence of root decay was shown to increase directly with D.1.-values (Warren 19.56~).In a more comprehensive study of 7- to 180-year-old white spruce, Whitney (1961) identified 82.7% of trees with root rot or stain infections, over half of which were traced to wounds caused by various agents including Hylobius spp. (mostly H. warreni and a low percentage due to H. pinicola). In both of these studies, the most common root-rotting fungus was Tomentosus root and butt rot, Inonotus tomentosus (Fr.) Gilbertson. The Hylobius wounds apparently predisposed the roots to infection by this pathogen. Overall, the Hylobius wounds of girdled and non-girdled roots provided an estimated 27% of the avenues of infection for root-rotting and staining fungi (Whitney 1961), and were a significant factor in contributing to "stand-opening disease" (attributed mainly to I. tomentosus) (Whitney 1962). Merler (1985) investigated I. tomentosus-caused root disease in 50- to 70-year-old white spruce in central British Columbia and reported an association of the disease with wounds caused by H. warreni but a causal relationship was not established. Wounds attributed to H. pinicola on balsam fir in Quebec were associated with root- and butt-rotting fungi and were the most important infection courts on dominant and codominant trees (Smerlis 1957, 1961). Several studies have attempted to establish a relation between H. warreni wounds and Armillaria root rot (Armillaria spp.) in a wide variety of conifer hosts. These studies have indicated either no direct causal relationship between weevil wounds and incidence of THE CANADIAN ENTOMOLMiI!X November/December 1994 TABLE13. Classification of damage to conifer roots and root collar by feeding tunnels of Hylobius warreni larvae*

Rating? Description

No damage A few scars; less than 5% of roots or collar circumference girdled to depth of wood 6-25% girdled as above 30-50% girdled as above 60-75% girdled as above 80-100% girdled as above

*Data after Warren (1956b, 1960~). $Value ratings of 0-5 are derived separately for roots and root collar. armillaria, or the possibility of only a weak relationship (Nordin 1956; Whitney 1961,1962; Stark 1959a; Warren and Singh 1970; Whitney and Myren 1978). Methods of Assessing Stand Susceptibility, Weevil Abundance, and Damage A number of techniques have been developed to survey stands for abundance of H. warreni, assess for levels of damage on trees, and assess for site conditions that indicate weevil habitat suitability. Warren's Damage (D.I.) and Population (P.I.) Indices. Attacks by H. warreni accumulate with stand development, and are dependent upon the freqqcy and number of re-attacks. Injury associated with each attack may also accumulate. The effects of wounds on sub- sequent tree growth, however, relate partly to their distribution and quantity over the roots and root collar, and to some extent upon the defence reaction and healing capabilities of the host tree. Wounds occurring during one period may be completely healed over 5-10 years later and effects thus may not be entirely cumulative. Warren (1956b) developed a Damage Index (D.I.) method of survey for site assessment and as a means of comparing weevil injury in different sites and years. With this method damage is classified into five broad categories, and the roots are assessed separately from root collars (Table 13). Injury on individual roots is classified according to the estimated percentage of the root circumference girdled and the results are averaged for all lateral roots for a maximum rating of 5. The root collar circumference is assessed similarly for a maxi- mum of 5 points and the two values are summed for a Total Tree Damage Index (maximum of 10 points). A maximum of 5 on either roots or root collar, however, is sufficient to cause death of the tree. The D.1.-values of individual trees can be summed over all trees examined at a site to give an average Stand Damage Index; this value can be used to compare different sites, stands, years, and tree species. Additional flexibility of the D.I. method is possible by deriving separate D.1.-values for current injury, old injury, or both. Application of the D.I. method has some shortcomings. Factors that may influence the accuracy of D.1.-values include the presence of large quantities of decaying logs, a change in the ground water table, experience of the samplers, and seasonal moisture variations influencing the proportion of attacks on roots and root collar. The D.1.-values do not usually reflect current populations of the weevil (Anon. 1958; Warren 1960c) and are unsuitable for comparing effectiveness of control treatments (Warren and Ives 1957). The D.I. method was developed in white spruce and jack pine in Saskatchewan and Manitoba. Stark (1959a), however, concluded that it was inadequate for surveys of lodgepole pine and provided a poor measure of the relationship between weevil numbers present and actual injury to the tree in Alberta. In surveys of young conifer stands for weevil-caused mortality and growth reduction, it is probably sufficient to obtain D.1.-values only for the root collar circumference of trees as most tree mortality results from girdling at this level. Volume 126 THE CANADIAN E~T~MOLOC~IST 1425 The D.1.-values can be interpreted directly into broad percentage classes-(Table 13); how- ever, accurate estimates of percentage root collar circumference girdled require detailed examination and measurement of old and current wounds to ensure they have penetrated through the cambium layer. Warren's population index (P.I.) is based on detailed examination of young and mature jack pine, and mature white spruce, and is expressed as numbers of weevils (larvae older than second instar + pupae + tenerals) per unit width of tree diameter (Warren 1960~). Correlations between D.1.- and P.1.-values were considered acceptable but neither value appeared to relate to the incidence of tree mortality (Warren and Ives 1957). The D.I. method was considered the best of the two methods for appraising stand damage because it required only one-sixth of the time to assess an equal number of trees. Diameter at 50% Damage Incidence (D,,-value). During extensive surveys of H. warreni in lodgepole pine stands in Alberta, trees in each stand were divided into diameter classes and the percentage of trees with old attacks was calculated for each diameter class. When the percentage values were plotted over diameter class, a diameter-value was obtained, representative of each stand, at which damage incidence had accumulated to 50% (i.e. D,,-value). The cumulative nature of old H. warreni attacks is illustrated in Figure 26A and B, in which 61- to 70-year-old lodgepole pine stands representative of the Lower and Upper Foothills sections of the Boreal Forest region are contrasted. D,, values of 13.5 and 21.6 cm, respectively, for the two forest sections, reflect the tree selectivity pattern by the weevil over many years and take into account the full range of tree size distribution within stands. Lower D5,-values, indicating smaller average tree diameters, are characteristic of the Lower Foothills sectim and are an expression of site index and habitat suitability of H. warreni. The values reflect the weevil's relative success temporally in relation to stand and site conditions. Thus D,,-values in the range 10-15 cm indicate a high level of habitat suitability, whereas values in the range 16-24 are indicative of a lower level of habitat suitability (Table 14). The D5,-values are more easily measured than are D.1.-values because each tree is scored positive when only the first wound is located, and the method is applicable over a broad range of stand age classes. During surveys to obtain D,,-values, it is assumed that sample trees will be selected by some random means. The two methods may be equally suitable as indices for expressing stand and site conditions, or for risk-rating stands. Sequential Survey Method to Estimate H. warreni Abundance. A sequential method to survey for the abundance of H. warreni was developed for application in even-aged lodgepole pine stands, including plantations and thinned stands (Cerezke 1970~).The method may have application in stands of other tree species as well but is probably not applicable in stands that are not even-aged. This method utilizes estimates of percentage of trees with current attacks and requires the examination of the root collar and major lateral roots of sample trees for the presence or absence of larvae, pupae, and immature adults in pupal chambers. Sample trees are selected by some random process, usually along transects and within plot areas positioned in a representative manner within the stands selected for assessment. Each sample tree is scored negative if no weevil is found, and positive when the first live weevil is found. The sampler then proceeds on to the next tree. Each sampled tree may be plotted cumulatively on a specially designed sampling form illustrated in Cerezke (1970c), on which each point on the graph represents one sampled tree. Sampling is continued until a maximum of 100 trees have been examined, or until the plotted sampling line crosses the decision line. At this point of intersection, a value is read on the decision line which gives the percentage of trees with current attacks. This value is then interpolated from Cerezke (1970c, fig. 3) and is expressed as average numbers of weevils per tree, or as numbers per hectare if stand density is known. With this method, inspection of trees is most efficient in stands supporting high populations because each tree requires minimal searching to locate the first weevil. In contrast, stands with low populations I426 THE CANADIAN ENTOMOLOGIST November/December 1994

Tree diameter at stump height (cm)

FIG. 26. Accumulated attack incidence of Hylobius warreni in 61- to 70-year-old lodgepole pine stands surveyed in the Lower Foothills (A) and Upper Foothills (B) sections of the Boreal Forest region in Alberta. Numbers of trees sampled were 651 and 589, respectively, for A and B. would likely require maximal searching of the root and root collar. Stands with high and low populations also require fewer trees to sample because sample size attains a maximum when 50% of trees have current attacks. Current attacks are generally more easily detected on young trees compared with mature trees. Collection Methods for Adult Weevils. Immature adult H. warreni have been collected successfully by laboriously searching around the root collar for pupal chambers in late August or early September. This method is often inefficient because it requires familiarity with the habits of the weevil and young adults are easily damaged. Older mature adults may be collected in a trap design described earlier (Fig. 2). The trap can be deployed to remove adult populations within a stand, and to live-trap adults for behavioral studies using mark, release, and recapture techniques. These techniques were used successfully to study the dispersal behavior of H. warreni and its diurnal and seasonal activity patterns, and may have application for chemical attraction studies.

TABLE14. Summary of tree diameter size at which 50% of trees have accumulated Hylobius warreni damage incidence (Dso-values) in natural stands of lodgepole pine in the Lower and Upper Foothills sections of Alberta*

Lower Foothills section Upper Foothills section

Stand age class Dso-values (cm) Stand age class Dso-values (cm)

31-40 10.2 31-40 16.0 41-50 -i 41-50 17.0 51-60 15.0 5 1-60 16.2 61-70 13.5 61-70 21.6 71-80 12.7 7 1- 80 22.1 81-90 13.7 81-90 23.9 Average diameter 13.0 Average diameter 19.5

*Data after Cerezke (1970b). tNo data obtained. Volume 126 THE CANADIAN ENTOMOLOGIST 1427

@gCOI 50 - Thinned 40

1967 1969 1971 1973 1975 Year FIG.27. Trends in accumulated percentage trees attacked by Hylobius warreni in a 25-year-old lodgepole pine stand following precommercial thinning and in adjacent unthinned control plots. The percentage of trees attacked in 1967 was determined on residual trees after thinning treatment, and control plots were established in 1969.

Precommercial Thinning and Weevil Abundance and Injury Over the 8-year period, thinning in the 25-year-old lodgepole pine stand resulted in an increased rate of stem radial growth; this provided a more rapid increase in root and root collar surface area per tree available for weevil attack compared with control trees. Initially, thinning had the effect of concentrating weevils onto residual trees, resulting in increased population and attack incidence (Figs. 27, 28). The proportion of trees sustaining injury increased to 55% in thinned plots but only to 25% in control plots. Weevil numbers per tree within the thinned plots increased to 5.0 times (average 0.61 weevils per tree) that in the unthinned plots in the 6th year (1973), and then declined somewhat, whereas in the control plots, populations remained low (<0.2 weevils per tree), but increased steadily over the 8-year period (Fig. 28). Although the thinning treatment induced a higher frequency of attack, the average amount of partial stem girdling on attacked trees was less on thinned trees (average 25.7%) than that on attacked trees in control plots (average 31.7%) (Fig. 29). In addition, there was a declining trend in percentage of the root collar circumference girdled in relation to tree diameter in the thinned plots in 1971,1973, and 1975. This declining trend was not apparent in the control plots. The overall effects of thinning were to create a plantation-like situation where trees were fairly uniformly spaced, grew larger and faster, and the range in diameter size was reduced. Consequently, there was probably less discrimination by the adult weevils in their selection of tree size for attack. It is expected that height growth losses particularly would be higher following precommercial thinning compared with unthinned stands, because of the increased abundance of weevil and proportion of trees sustaining weevil injury. The increased wounding resulting after stand thinning may also have consequences in weevil wound and root decay incidence associations. Greater weevil-caused injury including tree mortality is likely to result in stands thinned at ages younger than 25 years (i.e. 10-15 years old) because of the smaller stems and greater damage potential per larva (Cerezke 1970c, 1974). THE ChVAOlAN ENTOMIILOGIST NovernberPecember 1994

0.6 A a Thinned plots 2? 0.5 - -.-V) ---- Control plots > a3 a, 0.4 3 .c 0 Z 0.3 n E 3 0.2 a 0) !! a 0.1 k

Year

FIG.28. Estimates of Hylobius warreni populations in plots precommercially thinned in 1967 and in adjacent control plots within a 25-year-old lodgepole pine stand, compared over an 8-year post-treatment period. Population estimates were based on numbers of larvae, pupae, and young adults still within pupal chambers, as obsewed on residual trees after thinning in 1967 and in control plots first established in 1969.

STRATEGIES TO INTEGRATE INTO FOREST MANAGEMENT Forest Management Guidelines and Recommendations Information on the life history, behavior, site relationships of H. warreni, mortality factors operating on the weevil, and tree damage can be integrated to provide a sound basis for management in weevil problem areas. Several field trial studies have been undertaken

60 Thinned plots Control plots *. 1971 @ 1971 -1975 50 '\. ------\ -1973

Tree diameter (cm)

FIG. 29. Relationship of percentage root collar circumference of 25-year-old lodgepole pine trees girdled by Hylobius warreni in plots precommercially thinned and in non-thinned control plots and tree diameter. Trends in partial girdle injury in the thinned plots are shown for 3 post-treatment years whereas in the control plots, the data were combined for 1971, 1973, and 1975. Volume 126 THE CANADLAN EVTOMOLOGIST 1429 to examine the effects that various stand treatments, such as clearcutting, precommercial thinning, and insecticidal application, have on the survival and mortality in H. warreni populations. Results of these and new technologies with potential application for manage- ment and control of H. warreni are reviewed in this section, and new areas requiring further research are described. Management guidelines are formulated to offer specific guidance to reduce losses caused by this weevil species. Risk-rating of Sites and Tree Species Susceptibility. Damaging populations of Warren rootcollar weevil occur extensively throughout much of the forested area in Canada, mostly within natural stands of jack pine, lodgepole pine, and white spruce. Most other native and exotic pine and spruce species, however, are susceptable to attack if they are growing inter- mixed or planted adjacent to these species and where populations of H. warreni exist. Sites within spruce and pine forests preferred by H. warreni have (1) moist to wet soil and humus conditions and (2) a humus or organic duff layer that is relatively deep often including mosses around the base of trees (Warren 19566, 1960~;Warren and Parrott 1965; Cerezke 1969; Warren and Singh 1970; Rose and Lindquist 1973, 1977; Martineau 1984). In jack pine stands in Ontario, sites rated as fresh and moist and supporting the following herbaceous plant indicator species are likely to be the most susceptible to H. warreni: twin- flower (Linnaea borealis L.), lily-of-the-valley (Maianthemum canadense Desf.), bunch- beny (Cornus canadensis L.), bracken fern (Pteridium aquilinum L.), Labrador tea (Ledum groenlandicum Oeder), and leather leaf [Chamaedaphne calyculata (L.) Moench] (Moore 1984). Jack pine forest entities in Saskatchewan, western Manitoba, and Alberta likely to support highest populations of H. warreni include the Pinus-Vaccinium vitis-idaeal Pleurozium and Pinus-Pleurozium/Lycopdium ecosystems described by Kabzems et al. (1986). In lodgepole pine stands in Alberta and British Columbia, H. warreni survives on a wide range of site conditions but highest populations and injury occur in young stands with a high-productivity rating (Ives and Rentz 1993). Surveys in 5- to 10-year-old lodgepole pine plantations in British Columbia suggest a similar association: there was a preponderance of H. warreni injury in sites having a relatively moist duff layer that included mosses. These sites were in the Interior Cedar-Hemlock, Northwest transitional sub-zone ecosystem (Byford and McLean 1991). In mature lodgepole pine stands within the Lower and Upper Boreal Cordilleran ecoregions defined for western Alberta (Corns and Annas 1986), eco- system associations particularly susceptible to H. warreni include P1-SblLeduml Pleurozium, Sw/Viburnum/Aralia, pine facies, Sw/Vihurnum/Rubus pubescens, pine facies, and Pl/Alnus. White spruce site types in Manitoba that were characterized with a high incidence of H. warreni injury were classed intermediate to wet and supported the following plant indicator species (Warren 1956b): common horsetail (Equisetum awense L.), wild sarsaparilla (Aralia nudicaulis L.), bunchbeny (Cornus canadensis L.), tall mertensia [Mertensia paniculata (Ait.)], bishop's-cap (Mitella nuda L.), palmate-leaved coltsfoot [Petasites palmatus (Ait.)], Canada reed grass [Calamagrostis canadensis (Michx.) Nutt], and various moss species. Forest Management Guideline 1:Site conditions rated from intermediate to moist and with a moderate to high productivity in white spruce, jack pine, and lodgepole pine stands provide the highest risk for injury and population abundance of H. warreni. Site-specific ecosystem (plant association) information can be used to define high-risk areas before harvesting and planting. D.1.- and D,,-value surveys may be considered to establish stand and site conditions for risk-rating. General survey methods using an 1430 THE CANADIAN ENMMOl.OOI.ST NovemberPecember 1994

@ Strip A 4 strip B stripStrip D . ,; & - a 2 c5 a 3 5 1 a

0 1961 1962 1963 1964 1965 Year FIG.30. Histogram of Hylobius warreni population estimates in plot areas within a 65- to 70-year-old lodgepole pine stand in which half of each plot area (Strips A and B) was harvested by clearcutting after the 1961 sample was obtained. Population estimates were obtained from cut stumps in Strips A and B in 1962 and 1963, and no weevils were found in 1964. Adjacent Strips C and D remained unharvested, with population samples obtained in 1961, 1962, 1963, and 1965 [see Cerezke (1973~)for details of experimental design and sampling procedure]. Each bar represents mean + 1 SE. unbiased selection of sample trees can be deployed to generate tree impact information such as percentage trees attacked and tree mortality. Tree Harvesting Effects. Invasion by H. warreni into stands mostly occurs when they are young, and populations subsequently persist through to stand maturity or harvesting, becoming more concentrated on merchantable-size trees. Tree removal, whether by diameter or space-selective cuts or by clearcutting, will impact on the residual weevil population. In a series of experimental partial-cut treatments in mature lodgepole pine, the main effect on H. warreni populations apparently was to concentrate the surviving population onto the remaining residual trees (Stark 19.59~).This resulted (observations made in 4th year after treatment) in slightly higher weevil numbers per tree but an apparent decrease in absolute numbers, and no apparent increase in Stand Damage Index. The effects of clearcutting weevil-infested lodgepole pine were studied over a 5-year period in western Alberta (Cerezke 1973~).The objectives of this study were to examine clearcutting as a method of weevil control and to examine the behavior and survival of weevils during the post-harvesting period. Larval populations, recorded in the cut stumps within the cut area, continued to survive and develop successfully to adults during the 1st and 2nd years after tree removal, but no weevils were found during the 3rd year. About 25% more adults developed in the clearcut area during the 2nd year after harvest, compared with the adjacent residual stand. In the 4th year after cutting, there was a significant increase in the weevil population on adjacent residual trees that was assumed to have resulted from migration of adult survivors from within the clearcut (Fig. 30). Residual trees (i.e. seed trees and advanced regeneration) left within partial cuts as well as those trees around the perimeter of clearcuts may thus sustain a temporary increase in injury as a result of the redistribution of adults following tree removal. There are potentially large numbers of new adults, in addition to some older adults present in the clearcut area during the 1st and subsequent post-harvest years. These adults pose a threat to young seedlings if planted in the clearcuts Volume 126 THE CANMIAN f3TOMOLOGIS7' 1431 immediately after harvesting. Newly planted nursery stock can provide an immediate food source to sustain adult survival, and because the adults are long-lived, their oviposition on the planted trees may begin in the 4th or 5th year of growth. From the time of harvesting, adult weevils from cut stumps are potentially available in the clearcut areas for up to 7 years (2 years as larvae + 5 years as adults). This provides an explanation for the high mortality observed in some young lodgepole pine (Garbutt and Stewart 1989; Cerezke 1990,1991; Byford and McLean 1991). Regeneration that becomes established naturally following harvesting or in areas bumed by wild fires is often invaded gradually after 5 or 6 years byadult weevils that immigrate from adjacent infested timber. In this case, the newly attacked trees may first appear near the perimeter of the young stand and then advance progressively inward. In contrast, young planted or natural regeneration trees that are attacked by adults surviving from cut stumps tend to be distributed randomlv throughout.., the clearcut area. Observations in suvvort of this random pattern have been made in a number of young stand surveys in lodgepole pine (Cerezke 1990,199 1; Byford and McLean 1991). Overall, clearcutting a mature lodgepole pine stand reduced the larval population in the stumps by an estimated 88.4% (Cerezke 1973~).This mortality resulted from a combination of starvation, predation, excess moisture trapped in the larval galleries, and desiccation from rapid drying of the phloem feeding areas. Forest Management Guideline 2: Removal of trees supporting H. warreni populations, whether by clearcutting or by some form of selective logging, is in itself a method of control, but the consequences of the adult survivors and their movement and attack pattern within the clearcut area following harvesting are prime concerns. Assessment of risks to young regeneration may require a pre-harvest survey of weevil habitat suitability (risk-rating), population and damage potential, and consideration of the susceptability of tree species to be planted as well as the timing of planting. A 2- to 3-year post-harvest delay in planting may reduce weevil damage in sites where pre- harvest weevil density was high. Post-harvest lkeatment Effects. Few data are available on the effects that post-harvesting treatments such as scarification or prescibed buming may have on the survival and spread of H. warreni within clearcuts. Surveys in 10- to 20-year-old lodgepole pine stands in British Columbia were made to compare percentage weevil-killed trees in clearcut areas that had prescibed bum treatment with other similar clearcut areas that had no bum treatment. The results suggested that a higher (average 10.5%) level of mortality occurred near the perimeter in the non-bum sites compared with bum sites (average 6.0%), and that the differences between the two site conditions were even greater at the centers of the young stands: average 8.0% for non-bum and average 0.5% for bum (Unger and Stewart 1986). The effects of the bum treatment likely decreased the suitability of the weevil habitat by reducing ground vegetation and logging debris, causing increased temperatures at ground level and at tree bases, and effecting decreased moisture levels in the humus layer. Because the woody and ground vegetation layers are largely removed, air circulation at ground level is also enhanced. These factors in the bum areas likely retarded the rate of weevil dispersion and host selection within the young stands, and appear to be operative for several post-treatment years. In contrast to this study, Byford and McLean (1991) found no evidence that buming or scarification treatments had an effect on H. warreni abundance in young lodgepole pine plantations. They attributed the lack of an apparent effect to the wide spread in ages of treatment sites: broadcast bum sites averaged 16 years of age and therefore they likely had sufficient accumulation of duff materials to support weevil re-invasion, whereas the scarified and non-scarified sites that were compared in the same vicinity were mostly 5-6 years old. Cerezke (1973~)suggestd that scariccation or prescibed buming treatments, applied soon 1432 TIECANADIAN ENTOMOLOGIST Novemberpecember 1994 after harvesting to remove and disrupt the organic layer, would likely hasten and increase mortality of larvae and pupae in the cut stumps and may also cause some mortality to adults within the cleared areas. Any site preparation treatment that retards the re-invasion and spread of the weevil into young stands will have beneficial effects, especially if this can be delayed until after the stands reach 10-15 years of age. Forest Management Guideline 3: Although not field-tested, there is reasonable evi- dence that prescibed burning and scarification treatments, applied within a year after harvesting, will increase mortality of larvae and pupae remaining in the cut stumps and possibly of adults in clearcuts. These treatments may also retard re-invasion and rate of spread of adults for several years post-harvest within young stands. By delaying the spread and attack of weevils in the new stands weevil-caused mortality and growth losses will be minimized, especially during ages 5-15 years. Precommercial Thinning Effects. Precommercial thinning is becoming a standard man- agement practice in overly dense stands of lodgepole pine and jack pine mostly between ages 10 and 30 years, and especially on high-productive sites (Smith 1984; Johnstone 1985). Information on the effects of thinning a 25-year-old stand of lodgepole pine were studied over an 8-year-period in Alberta to assess changes in populations of H. warreni and its damage following treatment and form the basis of this management guideline. Forest Management Guideline 4: Excessively stocked stands (i.e. greater than 15000- 20000 stems per ha) appear to provide an unfavorable habitat for H. warreni and thus retard its buildup and spread during the early stages of stand development. Pre- commercial thinning in densely stocked stands growing on medium- to high-productive sites should be delayed to beyond 15-20 years where H. warreni is present. This would help to minimize weevil-caused tree mortality and growth loss. On sites with a high incidence of Armillaria root rot or other root diseases, and where H. warreni is also present, consideration should be given to delay as long as possible or delete thinning as an option. Direct Control Strategies. Cultural Control. Warren (1956b) suggested that H. warreni might be controlled by removing the humus from the vicinity of the root collar and basal portions of lateral roots. This treatment had been first tested for control of H. radicis on planted Scots pine (Maxwell and MacLeod 1937), and was later examined in more detail as a viable control method for this weevil in young plantation-grown red pine (Wilson 1967, 1973). The treatment consists of pruning the lower branch whorls to a height of up to 90 cm and scraping the litter and top layer of soil up to 30 cm away from around the tree base. Removal of the litter destroys the habitat necessary for adult weevil resting, mating, and oviposition, and pruning the lower branches decreases moisture and increases temperatures and air circulation. Wilson (1973) showed that the treatment reduced H. radicis populations to an acceptable level and appeared to be effective for up to 5 years. Adaptation of this method for control of H. warreni may be timed with age of the plantation (i.e. 5-15 years), and applied selectively in "hot-spot" locations such as areas with a deep moss layer, within and around the perimeter of plantations, on larger-diameter- size trees, and prior to crown closure. Reduction of the weevil population may be sufficient to allow healing of weevil wounds and increased growth rate of stems and roots to confer partial immunity. Although this cultural method has had only limited field testing for control of H. warreni, it was applied in an 8-year-old lodgepole pine plantation in Alberta (N. Dhir, Alberta Environmental Protection, pers. comm.) (Fig. 31). In addition to lower branch pruning to a 60-cm height and removal of the duff and top soil layer, larvae were also removed. Accumulated mortality from H. warreni 1 year after treatment had reached 7.6% but only 1.5% of trees had current attacks. Two years later, the treatment showed continued Volume 126 THE CANADIAN ENTOMOLOGIST 1433

FIG.31. Young plantation of lodgepole pine showing cultural treatment for control of Hylobius warreni,including duff removal around the tree bases and pruning of lower branches.

success for maintaining low weevil populations and injury, and appeared to be effective for at least 3 years post-treatment (unpublished data). Forest Management Guideline 5: The need for direct control treatment may be decided by assessment of weevil habitat suitability and by surveys for weevil abundance and damage. Cultural treatment, involving the pruning of lower branches and scraping the duff and upper soil surface away from tree bases, may be applied on trees in selected areas or on all trees in young conifer plantations, especially at ages between 5 and 15 years. Hand-removal of larvae, pupae, and tenerals, or by trapping to remove adults, will increase the effectiveness of the treatment. The treatment may be repeated at 3- to 5-year intervals if warranted. Intermixture of Tree Species. Mixtures of conifer hosts with deciduous tree species, or with non-host conifer species (e.g. Ahies, Larix, Pseudotsuga, etc.), may retard the invasion and attack of H. warreni, although no apparent field studies have investigated this. Different conifer species planted within the same area have sometimes shown different suscepti- bilities, and exotic species planted with native species have appeared to be more susceptible to H. warreni than the native species (Finnigan 1962b; Warren and Parrott 1965; Warren and Singh 1970). Wilson and Millers (1983) recommended, for H. radicis, that susceptible pine hosts not be planted together as they may be equally damaged, or that the susceptible hosts 1434 THE CANADIAN EFnnMOLWIST November/December 1994 will be attacked first with subsequent spill-over onto less-susceptible hosts. There is evidence this applies equally for H. warreni (Stark 1959a; Howse and Applejohn 1993). Forest Management Guideline 6: In areas of H.warreni populations and on medium- to high-productive sites, consider reduced planting of susceptible hosts, or planting of susceptible species with non-susceptible species (e.g. Abies, Larix, Pseudotsuga) in mixture with deciduous species. In areas where mixed conifer species plantings are contemplated, evaluate the site for weevil habitat suitability and survey adjacent areas for current H. warreni populations. Exotic tree species such as Scots pine and Norway spruce seem to be at higher risk than native species. Chemical Insecticidal Control. Several studies on insecticidal control of Hylobius species have been made, mostly with chemicals having long-residual effects. Most of these are no longer available or registered in Canada. Early studies to control H. radicis populations deployed lead arsenate, paradichlorobenzene, and carbon disulphide, but control results were not considered successful (Maxwell and MacLeod 1937; Felt and Bromley 1941). Up to 80% suppression of larvae was achieved with ethylene dichloride plus dinitro-o- cyclohexyl phenol by Schaffner and McIntyre (1944), and Shenefelt (1950) claimed 61-99% control of H. radicis with ethylene dichloride, propylene dichloride, DDT, chlor- dane, and BHC. Control studies in Ontario against H. radicis with dieldrin, lindane, BHC, and endrin, applied as soil drenches on Scots and red pines, provided up to 100% larval reduction for 4 years (Finnegan and Stewart 1962). Control of larvae, however, was often variable because of their protection in the soil, bark, and resinous galleries, whereas adults were more readily killed as they emerged from pupal chambers or when at rest within the treated forest litter. Field trials to control H. warreni were made on young lodgepole pine in Alberta using several systemic insecticides applied as soil drenches. Control of larvae was highly variable and ranged from 12 to 86% reduction in one trial and from 0 to 40% in another trial (Drouin and Kusch 1975, 1978). This method of application, aimed at the larval stage, may not be economical on young trees up to 25-30 years old as it is not likely to be as efficient nor as effective as hand removal of larvae. However, control in the short term with contact insecticides aimed primarily at the adult stage may be effective if water-based solutions are applied to the lower stem of trees during late May and June. This coincides with the period when adults are most active in ascending trees to feed. This method of treatment was also suggested for control of H. radicis (Wilson and Millers 1983). ForestManagementGuideZine7: Use of chemical insecticides for control of H. warreni should not be attempted except as a last resort, and only when justified by analyses of economics, environmental hazard, and overall effectiveness. For the most recent information on chemicals available for management of this insect, contact Agriculture Canada's Pesticide Directorate in Ottawa. New Management Strategies Requiring Research Ree Genetic Selection. Numerous field plantings of genetically selected conifer stock exist in Canada but little or no attention has been given to evaluate planted material for resistance and susceptibility to H. warreni. Some differences in host species susceptibility have been suggested in plantations of exotic species but the host characters that might be involved have not been examined (Warren 1956c; Finnegan 1962b; Warren and Pmott 1965; Warren and Singh 1970). Provenance test plantations of jack, lodgepole, and Scots pines (including six varieties of the latter species) in Ontario were surveyed for H. warreni injury but no varietal preference was established (Foster et al. 1968; Foster and Hook 1972). Survey results of lodgepole pine plantations in Alberta with genetically selected stock, although not analyzed for provenance preference, have not suggested any genotypic selectivity. The possibility of detecting a provenance preference in mature natural stands of lodgepole pine, jack pine, and Volume 126 THE CANADIAN ENT~M~LM~IST 1435 white spruce seems remote, however, because of the high incidence of weevil wounding (80-100%) sustained in these stands (Warren 1956a, 1960c; Stark 1959a; Cerezke 1969, 1970b, 1970c). Resistance characteristics are more likely to be detected in young stands during the period of early weevil invasion and establishment. A provenance test plantation of Scots pine grown in Michigan from seed collected in 108 natural stands in Europe and Asia was assessed for genetic differences among varieties showing resistance to H. radicis damage (Wright and Wilson 1972). Three varieties native to southern Europe showed the highest degree of resistance and were recommended as best choice for Christmas tree plantings (Wilson and Millers 1983). The mode of resistance was not identified. Selander and Kalo (1979) investigated the possible association of monoterpenes in Scots pine seedlings and resistance to feeding by adult H. abietis. Their studies suggested that small quantitative and qualitative changes in monoterpene composition likely affect the olfactory preference of adults in the field, leading to the conclusion that selection of resistance characters may be possible in the future. Research Guideline I: Existing and new plantations of genetically selected provenances of jack pine, lodgepole pine, and white spruce (as well as susceptable exotic hosts) should be evaluated for potential resistance and relative susceptibility to H. warreni, especially where these sites have already been invaded by this weevil. Forest Fertilization Effects. The effects of fertilization, applied to increase growth and productivity of conifer trees, on the survival and damage of H. warreni have not been investigated. There may, however, be two areas of concern: the first is in the planting of nursery-grown seedlings that are maintained in a nutrient-rich environment to maximize early growth and development, and subsequently field-planted; the second concern is the application of fertilizers around established trees, whether young or mature. Adult feeding behavior on such trees, compared with naturally grown, unfertilized seedlings and trees is entirely unknown. Studies in Finland of 2-year-old container-grown Scots pine seedlings subjected to feeding preference tests with the adult pine weevil, Hylobius abietis, showed that water stress alone increased seedling susceptibility to weevil feeding and that the nitrogen component in fertilizers increased weevil feeding preference over fertilizer regimes without nitrogen (Selander and Irnmonen 1992). It was speculated that the nitrogen fer- tilization increased the relative quantity and concentration of terpenes in the seedlings, thus influencing their attractiveness. In Wisconsin, young jack pine plantations infested with the root weevil Hylobius rhizophagus Millers, and subjected to various nitrogen levels in fertilizer treatments, were shown to decrease the rate of larval feeding and increased the time of larval and pupal development (Goyer and Benjamin 1972). The mode of action of increased nitrogen level effects was not determined but may have caused increased tissue moisture in the tree and decreased sugar content; these factors in turn affected feeding behavior. In contrast, Hunt et al. (1993) showed that both H. radicis and H. pales, when reared on diets containing pine phloem that had received various amounts of nitrogenous fertilizer, preferred increased levels of nitrogen, developed more rapidly on it, and weighed more as adults than adults reared on untreated phloem. They suggested that fertilizer treatments of pine stands may increase problems especially with H. radicis. Because of its analogous feeding behavior with H. radicis, H. warreni is likely to respond similarly to fertilized trees. The feeding response by larvae and adult H. warreni to fertilized seedlings and trees may be quite different from that of H. abietis and H. rhizophagus. Additional changes resulting from fertilizer applications include increased radial root and stem growth and possibly increased growth of ground floral species. The implications of these changes on H. warreni survival and abundance need to be assessed. 1436 THE CANADIAN ENTOMOLOGIST NovernberDecernber 1994 Research Guideline 2: Observations and assessment of H. warreni response to fertilized trees are required over several years to evaluate feeding behavior and the potential risks. Biological Control. The natural biological agents and their influence on the survival of H. warreni are not fully known and require additional study. Excess moisture in the pupal chamber was identified as the most important mortality factor affecting mature larvae, pupae, and teneral adults, and additional losses to early-instar larvae may result from water trapped in galleries (Cerezke 1973~).Studies of biological control of other Hylobius species, however, offer some potential for application to H. warreni. The virulence of the entomopathogenic fungus Beauveria bassiana (Bals.) Vuill. found on dead adult and immature forms of H. warreni needs to be confirmed as the cause of death (Cerezke 1973~).This fungus was identified as a natural mortality factor of H. rhizophagus (Goyer and Benjamin 1972), and mortality of H.pales adults was shown to be related directly to the concentration of spores of B. bassiana and another entomogenous fungus, Metarrhizum anisopliae (Metschnikoff) Sorokin (Walstad and Anderson 1971). Very large dosages, however, are required to infect and cause mortality, and more so for adults than for larvae (Schabel 1976). In a sample of adult H. pales, the natural infection rate of B. bassiana was as high as 17.43% (Taylor and Franklin 1973). Spores of B. bassiana have also been added to a sub-lethal solution of insecticide (Trichlorfon) and some control of H. abietis was achieved (SamSinikovB and Nov& 1967). More recently, Wegensteiner and Fiihrer (1988) examined the efficacy of B. bassiana on adult H. abietis under laboratory and field conditions and at various temperatures and feeding conditions. Up to 100% mortality was obtained and was correlated with conidia concentration at 13 and 23°C. Under field conditions, bark traps with B. bassiana spores were effective in attracting adults and caused a low level of mortality. There thus appears to be a potential for use of fungal pathogens for control of adult H. warreni within the moist environment around tree bases. Certain entomopathogenic nematodes (e.g. Steinernema spp., Heterorhabditis sp.) known to infect many soil-inhabiting insects may have potential for control of Hylobius species. These parasitic nematodes carry within their bodies associated entomopathogenic bacteria that assist in infecting and killing the host insect and provide food for the nematodes (Moms 1985). Schmiege (1963) tested a nematode, Neoplectana sp. (= Steinernema sp.), for control of a number of forest insect pests including H. radicis; adults of this species were rated moderately susceptible. Some success was obtained in Sweden in the treatment of logs infested with H. abietis larvae and in protecting seedlings from adult feeding (Burman et al. 1979; Pye and Pye 1985), and in Canada, experiments have been underway to examine use of nematodes to control the adult seedling debarking weevil, H. congener (Eidt and Weaver 1993; Eidt and Thurston 1994). Research Guideline3: Because of its preference for a moist environment within the forest litter and soil, entomopathogenic fungi and nematodes appear to have con- siderable potential for future application in the control of H. warreni, but no studies have been undertaken to explore this. Treatments aimed at the adult stage have greater potential for success than do treatments aimed at other life stages. Semiochemical-mediated Monitoring and Control. Recent research of the semio- chemistry of Hylobius species has indicated that both kairomone and pheromone com- ponents are likely involved in the chemical communication of these species. Species such as H.pales, H. abietis, H.pinastri, and probably H. congener all respond strongly to fresh-cut host stumps and killed trees as they utilize these as breeding sites (Tilles, Norlander et al. 1986; Tilles, Sjoden et al. 1986; Norlander 1987, 1991; Magasi 1988; Raffa and Hunt 1988; Hunt and Raffa 1989; Pendrel 1990; Rieske and Raffa 1991, 1993). Hunt and Raffa (1989) suggested also that for H. radicis the stimulus to oviposit may be partly mediated by Volume 126 THE CANADIAN EXTVMOLOGIST 1437 kairomones such as host-produced volatiles and ethanol. It is likely that H. warreni responds similarly in its selection of oviposition sites but evidence is lacking. The monoterpene a-pinene, when added to ethanol, provides a strong attractant bait for H. abietis and H. pinastri in Europe (Norlander 1987; Zumr and Starj 1992), and in North America, ethanol with turpentine is now used successfully as a bait to trap H. pales and H. radicis (Rieske and Raffa 1993), and seems effective for H. congener as well (Pendrel 1990). Field trials to monitor the response of H. warreni in lodgepole pine stands in Alberta and British Columbia to a variety of monoterpene mixtures with ethanol and turpentine components were inconclusive in identifying attractant kairomones because of low catch results (MacKenzie et al. 1989). Factors that likely influenced the low rate of capture included low populations, difficulties in the trap design (pitfall traps), and establishment of appropriate release rates. Preliminary results of electroantennogram bioassays of H. warreni adults, however, indicated they responded positively to a-pinene, turpentine, lodgepole pine resin, and adult frass extracts (MacKenzie et al. 1989). These results suggest that the identification of attractant baits for H. warreni is possible, with potential use in both pitfall and in tree-stem-attached trap designs. Because of its long-lived, flightless condition, low population level, and pedestrian dispersal behavior, the use of attractants has potential application in monitoring and control strategies, especially in young stands. Recent studies with H. abietis and H. pinastri have also identified several plant extracts that are strongly repellent to adults of these species (Norlander 1990; Miiller and Haufe 1991). The discovery of similar compounds repellent to H. warreni could also have application in the management of this weevil. Resemh Guideline 4: The potential for uses of baits that are attractive or repellent to H.warreni adults is quite high, especially for detection and monitoring of populations, for retarding dispersion into young high-value stands, and for direct population reduction by trapping out. Several major unknowns need to be resolved, however, before the commercial application of semiochemicals can be realized; these include the identification and testing of appropriate baits, establishment of optimum release rates, design or modification of a suitable collection trap, and the development of baited-trap deployment strategies.

ACKNOWLEDGMENTS I extend my sincere appreciation and thanks to the many students and technical staff who assisted in collecting and analyzing field data, in particular R. Gordey; to D. Lee for preparing graphs; to J. Simunkovic for arranging the text and tables; to W.J.A. Volney for reviewing an earlier draft of the manuscript; to J.R. Spence for his numerous helpful comments; and to an anonymous reviewer who provided valuable comments on the manuscript. I also thank J.A. Muir for providing permission to quote from three unpublished reports of the British Columbia Ministry of Forests, to E.A. Dixon for permission to quote from an unpublished report of the University of Calgary, Alberta, and to N. Dhir, Alberta Environ- mental Protection, Forest Management Division, Edmonton, for permission to quote results of a cultural treatment trial.

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