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Destructive outbreaks of forest pests are classified as gradient, cyclical or eruptive. The first of two types of outbreaks (gradient, cyclical) are generated by stand and site conditions conducive to the reproduction and survival of the pest or stressfull for the host plant(s). In these cases, outbreak probability, or risk, can be assessed with unidimensional risk equations. Outbreaks of the third type, the eruptive pests, are more difficult to predict because the density of the pest plays a critical role in initiating outbreaks in particular stands. Risk assessment models for these pests require a two-dimensional structure that integrates stand, site and insect numbers. We discuss methods for developing risk assessment models for eruptive pests using, as an example, mountain pine beetle populations infesting lodgepole pine stands. Zusammenfassung Beurteilung des Risikos bei Forstinsekten-Kalamitaten Schadliche Massenvermehrungen von Forstinsekten werden eingeteilt in gradierende, zyklische und eruptive. Die ersten beiden Typen werden durch Bestandes- oder Lagebedingungen hervorgerufen, die fur die Reproduktion und das Uberleben des Schadlings gunstig oder fur die Wirtspflanze ungunstig sind. In solchen Fallen kann die Kalamitatswahrscheinlichkeit bzw. das Risiko mit eindimensionalen Gleichungen beurteilt werden. Kalamitaten des eruptiven Typs sind schwieriger zu prognostizieren, weil die Schadlingsdichte eine ausschlaggebende Rolle bei der Auslosung der Vermehrung in einzelnen Bestanden spielt. Modelle zur Risiko-Beurteilung erfordern hier eine zweidimensionale Struktur, in welcher Bestand, Lage und Insektendichte integriert sind. Es werden am Beispiel eines Befalls von Lodgepole-Kiefern durch den Mountain Pine Beetle Erorterungen uber die Entwicklung von Risikobeurteilungs-Modellen fur eruptive Schudlinge angestellt.

The magnetic field dependence in the amplitude of de Haas-van Alphen or magnetoresistance oscillations introduces magnetic field dependent phase shifts which are not included in the standard formation of the Lifshitz-Kosevich theory. It is found that the magnetic field dependence of the oscillatory amplitude introduces an additional signal which is pi /2 out of phase in 1/H with respect to the signal which would be observed if the amplitude of the oscillation is strictly independent of magnetic field strength. A number of examples are presented which illustrate the magnitude of this magnetic field dependent amplitude effect when the large amplitude modulation field technique is employed to measure the frequency of the quantum oscillations.

The normal-state shear-wave attenuation has been calculated for propagation along the three principal symmetry directions in magnesium, zinc, and cadmium. The real metal theory of Pippard employing Fermi surfaces of these metals based on band structure calculations was used to calculate the attenuation. The attenuation was calculated for five shear modes for ql values between 0.1 and 60. The shear deformation parameter was assumed to equal zero in these calculations. The calculations are compared with experimental data for the fast shear modes for propagation along the [11–20] and [10–10] directions.

The ultrasonic attenuation due to conduction electrons has been calculated for the hexagonal metals magnesium, cadmium, and zinc using the real metal theory of Pippard and Fermi surfaces of these metals based on band structure calculations. For most cases when the calculations are compared with experimental data excellent agreement is obtained. Since the calculations assume isotropic deformation parameters, the ultrasonic attenuation is determined principally by strictly geometrical features of the Fermi surface.

The results of an experiment at 4.2 K using the magnetoresistance oscillations caused by the interferometer trajectories in magnesium are reported. The magnesium crystal used in this experiment is believed to have an impurity concentration of ∼1 ppm. The quantum state lifetime of electron states traversing the interferometer was determined to be .01±.002 nsec. In addition, the values of the three magnetic breakdown parameters needed to describe the size of the spin orbit energy gaps occurring near the AHL zone plane in magnesium were found to be:H1=2.90±.1KG,H2=12.5±.5KG,H3=4.25±.25KG. The presence of higher harmonics was also observed in the magnetoresistance oscillations and the higher harmonics were used to allow an experimentally meaningful value ofH3 to be determined. It is presently believed that the sensitivity of the interferometer to quantum state lifetimes can be extended by using the higher harmonics and hence information about electron-phonon and possibly electron-electron interactions will be obtained.

Root systems of western white pine, Pinus monticola Douglas, were excavated with explosives and examined for pathogens. Data were also recorded on portions of the crown killed by blister rust caused by Cronartium ribicola Fisch. Statistical tests revealed a significant association between the bark beetles Dendroctonus ponderosae Hopkins and Pityogenes fossifrons (LeConte), and the root pathogen Armillariella mellea. (Vahl. ex Fr.) Karst and between beetles and all root diseases. Ninety-two percent of the trees attacked by bark beetles had root diseases, and 97% had either root diseasesor blister rust. A discriminant analysis correctly classified 88% of the sample trees into two categories, trees infested with D. ponderosae or trees not infested with D. ponderosae, using the variables age (stump), diameter at 1.3 m in height, and percentage of the primary roots infected with pathogens. Major pathogenic organisms isolated from the roots included A. mellea, Phaeolus schweinitzii (Fr.) Pat., Resinicium bicolor (Fr.) Parm., Verticicladiella spp., and a Europhium strain. A hypothetical sequence of host tree invasion by blister rust, followed by infection by root diseases, and finally attacks by bark beetles, is postulated.

The “on-axis” and “off-axis” regimes of quantum transport discussed theoretically in the preceding paper in this journal have been observed experimentally. The observation of the “on-axis” regime required magnetic field alignment to within an accuracy of ±0.002° of the basal plane. The data for the “off-axis” regime indicate that the electron quantum state lifetime for this crystal is about 5×10−10 sec at 4.2 K. A comparison between the predictions of first principles theory and the experimental results in these two regimes shows that the theory not only predicts the qualitative behavior correctly but also provides a quantitatively accurate description for the transverse magnetoresistance.

Studies of the de Haas---van Alphen spectra arising from the two-dimensional lattice of magnetic-breakdown---coupled orbits in magnesium contain spectral features which disagree qualitatively with the accepted theory of Falicov and Stachowiak. Their theory, which was thought to be equivalent to Pippard's theory for the magnetic band structure, is shown to be inequivalent.

The lodgepole terminal weevil, Pissodes terminalis Hopping (Coleoptera: Curculionidae), is widely distributed in western North America on three races of lodgepole pine (Pinus contorta Dougl.), as well as jack pine (P. banksiana Lamb.), Bishop pine (P. muricata D. Don.), and Monterey pine (P. radiata D. Don.).Three types of life cycle, one with three subtypes, are identified. In the univoltine type 1 cycle, adults emerge from attacked leaders in the fall, overwinter probably in the ground, and re-emerge in the spring to lay eggs in elongating leaders. Larval and pupal development is completed by early fall. The univoltine type 2 life cycle is similar, except that overwintering takes place in leaders; fourth-instar larvae overwinter in type 2A, pupae in type 2B, and adults in type 2C. The type 3 life cycle takes 2 years to complete, with the first winter being passed as a third-instar larva in the leader and the second as an adult, probably in the ground. The type 1 life cycle is most common at altitudes < 2000 m and the type 3 life cycle at altitudes over ca. 2500 m; all types may be found at altitudes of 2000–2500 m.

The effect of changes in the lattice parameters on the Fermi surface of zinc is calculated. The results of the calculations are in reasonably good agreement with experimental data.

The magnetoresistance of extremely pure, strain-free magnesium is dominated by the transport properties of a narrow slab of coupled orbits in the geometry in whichJ ∥ [11\(\bar 2\)0] andH lies in the (11\(\bar 2\)0) plane. In samples whose quantum state lifetimeτs exceeds 10−10 sec the conductivity of the coupled orbit system is controlled byτs as well as the large-angle scattering lifetimeτ1. The magnetoresistance then exhibits complicated behavior, oscillating with |H| and varying rapidly with field orientation. The behavior withH aligned to within about 0.001° of [10\(\bar 1\)0] is due to manifold multiply connected open orbits, whereas forH tilted away from [10\(\bar 1\)0] by more than this the behavior is due to extended, multiply connected closed orbits. Detailed models for both these regimes are developed, taking into account the interference effects resulting from the feedback paths. Within these models the transport properties are calculated exactly, taking into account to all orders the amplitude propagation of wave packets within the network. Results are compared to experimental data and previous calculations, and the limitations of the model are discussed.

A new quantitative theory is developed to calculate from first principles the transverse magnetoresistance of Mg for the special case in whichH is parallel to a [10 $$\bar 1$$ 0]-type axis andJ is parallel to a [11 $$\bar 2$$ 0]-type axis. For this case, magnetic breakdown produces a multiply coupled network of interfering electron trajectories which generate large-amplitude quantum oscillations in the transverse magnetoresistance. It is shown that two distinct regimes of quantum transport exist for these oscillations and that this theory can be used to derive the electron quantum state lifetime τ from experimental data. The sensitivity of this effect to τ extends the experimentally accessible range by four orders of magnitude from about 10 −12 to 10 −8 sec. In addition, since the quantum interference oscillations are essentially insensitive to the temperature dependence of the Fermi-Dirac distribution function, this effect is ideally suited to study the quantum state lifetime dependence on electron-electron scattering.

We report here the results of an extensive investigation of the de Haas-van Alphen effect in white tin. These results agree qualitatively with the predictions of Weisz's pseudopotential model for the tin Fermi surface; for every case in which Weisz's model differs qualitatively from the single-orthogonalized-plane-wave model, our data agree with the former. Quantitative agreement, however, has not been obtained. The experimentally determined cross-sectional areas of the Fermi surface typically differ by about 30% from those calculated by Weisz. Area branches are also reported that are due to coupled orbits generated by magnetic breakdown of the spin-orbit-coupling-induced energy gap between the third and fourth bands near the $\mathrm{XL}$ and $\mathrm{XP}$ zone lines.

Recent theoretical work suggests that magnesium and lithium should be superconducting in the m°K temperature range. We have cooled samples of each of these metals to a temperature of 4 m°K, measured by a gamma-ray anisotropy thermometer. Although the magnetic field was less than 10−2 Oe, no superconducting transitions were observed. The use of a nuclear orientation thermometer employing60Co in single crystal (hcp) cobalt is described.

The Fermi surface of beryllium has been throughly investigated by means of the de Haas-van Alphen effect, and the frequencies, though substantially in agreement with earlier measurements, have been obtained to greater accuracy. This has made it possible to construct a nonlocal pseudopotential model for the Fermi surface, in which the Fourier coefficients of the crystal potential are treated as parameters to be evaluated by fitting to the experimental data. In this way, all the principal cross sections of the surface have been fitted to within 1%, using only five adjustable parameters. Comparison of calculated cyclotron masses for these cross sections with the masses determined from the temperature dependence of the dHvA amplitudes indicates that the mass is enhanced about 20% by many-body interactions neglected in the model. Finally, the pressure dependence of the Fermi surface has been calculated and compared with some available experimental measurements.

Using a very pure single crystal of magnesium we have observed large-amplitude oscillations in the transverse magnetoresistance which result from the direct interference of normal-state electron waves. The amplitudes of these interference oscillations appear to be independent of the $\mathrm{kT}$ broadening of the Fermi distribution. The primary result of our experiment shows that these waves are phase coherent at 1.2\ifmmode^\circ\else\textdegree\fi{}K over macroscopic distances of at least 0.01 mm; this corresponds to a quasiparticle lifetime of at least 2 \ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}11}$ sec.

Measurements of the magnetoresistance of high-purity single crystals of magnesium were made in order to determine the magnetic field directions for which open trajectories exist on the magnesium Fermi surface. Nine distinct series of open trajectories with net directions parallel to the basal plane of reciprocal space were observed. These trajectories have basic periodicities extending up to nine Brillouin zones and result from magnetic breakdown between the monster and cigar. The magnetic field directions for which these trajectories exist are shown to be in excellent agreement with the predictions of the Fermi-surface model proposed by Kimball, Stark, and Mueller. Measurements for the open trajectory parallel to the hexagonal axis in reciprocal space are also reported; these show a clear indication of the onset of magnetic breakdown across the spin-orbit gap separating the monster and the cap.

Certain aspects of insect-disease relationships, especially those concerning transmission of pathogens, have been studied extensively and their significance has been well established. However, the role of diseases as factors predisposing coniferous trees to bark beetle infestation has received only minor attention. There has been little effort to determine the extent of the association between disease and bark beetle infestation, the significance of predisposing diseases in the ecology of the beetles, or the effects of disease upon the host that may increase susceptibility to beetle attack. The series of papers in this issue presents the results of studies to determine (a) the degree of association between photochemical atmospheric pollution injury to ponderosa pine and infestation by bark beetles (paper I), and (b) the changes in the physiology of diseased trees which might influence host susceptibility to bark beetles (papers II and III). The results show that oxidant injury does, in fact, predispose ponderosa pine to beetle infestation, and that the injury leads to physiological changes in the host which may be related to increased bark beetle susceptibility. The significance of these results in relation to the present knowledge on bark beetle ecology and host susceptibility is discussed in paper IV.

Certain aspects of insect-disease relationships, especially those concerning transmission of pathogens, have been studied extensively and their significance has been well established. However, the role of diseases as factors predisposing coniferous trees to bark beetle infestation has received only minor attention. There has been little effort to determine the extent of the association between disease and bark beetle infestation, the significance of predisposing diseases in the ecology of the beetles, or the effects of disease upon the host that may increase susceptibility to beetle attack. The series of papers in this issue presents the results of studies to determine (a) the degree of association between photochemical atmospheric pollution injury to ponderosa pine and infestation by bark beetles (paper I), and (b) the changes in the physiology of diseased trees which might influence host susceptibility to bark beetles (papers II and III). The results show that oxidant injury does, in fact, predispose ponderosa pine to beetle infestation, and that the injury leads to physiological changes in the host which may be related to increased bark beetle susceptibility. The significance of these results in relation to the present knowledge on bark beetle ecology and host susceptibility is discussed in paper IV.

The Neodiprion sawfly studied in this investigation is an undetermined species which attacks sugar pine, Pinus lambertiana Dougl., in California. The conditions of the infested area were particularly suitable for an investigation of some of the basic factors affecting distribution of cocoons on the ground. The efforts of previous workers (Prebble, 1943; Ives and Turnock, 1959) were complicated by dense stand conditions and deep, variable pound cover. The sawfly discussed here was found in considerable numbers on an isolated, young sugar pine at Grass Valley, California. The tree was 19 feet high, 16 vears old, with s diameter of 5.5 inches. The infestation was presumed to be recent as no effect on diameter growth was found, even though the tree possessed only the current year's foliage. The ground cover was extremely sparse and the soil was a compacted, sandy-clay, typical of many foothill areas in California.

The current results of our de Haas‐van Alphen investigation of ferromagnetic nickel yield complete data for the [111] directed neck which is assumed to be associated with L2′ of the spin ↑ s band and for a set of X‐centered pockets which have been assigned to the X5 spin ↓ d‐band holes. The negative results of the experiment indicate that the X2 spin ↓ level is below the Fermi level and that the ordering of the L32 ↓ and L2′ ↓ levels is that recently proposed by Krinchik and Canshina.

the classic population dynamics studies on the spruce budworm reviewed by Morris (75), the newly recognized importance and application of behavioral differ­ ences in population dynamics studies (131), and new application of computer techniques (75, 127, 128) were based on forest entomological work, and forest entomologists have had considerable influence on their development. The wid ening scope of forest entomology is also reflected in other recent reviews and major publications. The fields of ecology (35, 94), sampling (74), biological control (5, 61), chemical control (7, 30), systematics (46, 47, 137), physiology and behavior (31, 132), and various forestry techniques such as photogrammetry (39, 40, 129), mensuration, and tree growth studies (76), have all been advanced through the efforts of scientists working on forest insect problems. One of the most monumental surveys of pests of a particular crop is moving into its third volume-The Forest Lepidoptera of CanadaL-which, hopefully, wi11 lead to comparable lists for all forest insects. These various studies indicate a strong trend toward specialization and as pointed out by Balch (6) this emphasizes the need for more integrated studies. There are many such programs now in existence in forest entomo­ logical work and the need for the synecological approach is being recognized. The sheer volume of literature on forest entomology is, at times, positively frightening. However, it is of great interest to see the new names and locations now appearing in our abstracting journals. Not too long ago, the bulk of the literature on forest insects was confined to North America and Germany. Articles appearing from Israel, South America, and Africa were written largely by the "perambul ating professors." Now, however, a casual survey of Forestry ·Abstracts yields references to workers from Argen­

The life history of a tortricid cone moth Choristoneura lambertiana subretiniana Obraztsov in California is described. The larvae feed primarily on staminatc flowers and cones of lodgepole pine although some needle- and tip-mining occurs. The only other recorded host is ponderosa pine.Eggs are deposited in late July to early August; first-instar larvae migrate from the needles to protected locations on the branches and spin hibernacula. The larvae overwinter predominantly as second-instar larvae in the hibernaculum. They emerge from the hibernacula in April, and mature in four to six weeks. There are six larval instars. The pupal period lasts approximately two weeks; adult emergence begins in mid-July and extends through the end of August.

Pissodes terminalis Hopping attacks the terminal leaders of jack pine and at least two of the four geographic subspecies of lodgepole pine. The development on Pinus contorta murrayana in central California is described and compared with the development on jack pine in Canada. The oviposition period is synchronized with leader elongation, early spring to mid-summer. Feeding of the first three instars is in the phloem-cambial region and the fourth (last) instar is found in the pith. Part of the population completes development in late summer; adults emerge and presumably overwinter in the ground. The balance overwinter usually as mature larvae and occasionally as pupae, completing their development in the spring.Mortality is high and is caused by feeding of associated insects, possibly resin flow, high parasitism and other unknown factors. Seven parasite species from five families were reared.

General.—The purpose of this paper is to analyse a sampling method devised to assess larval populations in an outbreak of the lodgepole needle miner, Recurvaria milleri Busck (Busck 1914, Hopping 1945).The problem of developing an adequate sampling method is intimately concerned with the life-history of the insect, the region of the outbreak and the nature of the forest stand in which the outbreak occurs. In sampling most defoliator populations the problem is made more difficult by external feeding and wandering habits, hence it is usually done in some relatively inactive stage at a fixed time. de Gryse (1934) describes the problems inherent in sampling these insects. The needle miner, however, is fixed in its location for most of its life-cycle and is therefore readily obtainable for study. The problem here is reduced to a statistical one, that of obtaining an acceptable sample i.e. within suitable error limits with due regard for existing variables.

Certain aspects of insect-disease relationships, especially those concerning transmission of pathogens, have been studied extensively and their significance has been well established. However, the role of diseases as factors predisposing coniferous trees to bark beetle infestation has received only minor attention. There has been little effort to determine the extent of the association between disease and bark beetle infestation, the significance of predisposing diseases in the ecology of the beetles, or the effects of disease upon the host that may increase susceptibility to beetle attack. The series of papers in this issue presents the results of studies to determine (a) the degree of association between photochemical atmospheric pollution injury to ponderosa pine and infestation by bark beetles (paper I), and (b) the changes in the physiology of diseased trees which might influence host susceptibility to bark beetles (papers II and III). The results show that oxidant injury does, in fact, predispose ponderosa pine to beetle infestation, and that the injury leads to physiological changes in the host which may be related to increased bark beetle susceptibility. The significance of these results in relation to the present knowledge on bark beetle ecology and host susceptibility is discussed in paper IV.

The known parasites of the lodgepole needle miner, Evagora (Recurvaria) starki Freeman, 27 in all, are listed and notes on the biologies of the most common species are presented. Data are given to show fluctuations in parasite populations from 1944 to 1958. The probable reasons for the ineffectiveness of the parasites to control the needle miner are discussed briefly.

A detailed analysis is presented of the large-amplitude temperature-insensitive oscillations in the transverse magnetoresistivity of ultrapure Mg single crystals resulting from the direct interference of electron quantum states. A calculation of the relative harmonic content of these interference signals based on the transmission characteristics of a magnetic breakdown-generated interferometer is used to quantitatively study certain aspects of the electron states in Mg as well as details of magnetic breakdown. In particular, values of magnetic breakdown parametersH 0are determined without invoking the complexities of transport theory. An absolute lower limit for the electron quantum state lifetime of τ ≳ 0.5 nsec is obtained (forT=1.5° K), although a best fit to the data gives a value an order of magnitude larger, τ∼5 nsec, which corresponds to quantum phase coherence extending over a distance of 3 mm in these crystals. In addition, this work provides direct experimental verification of the π/2 phase difference between transmitted and reflected electron states at a magnetic breakdown junction. Comparison of the results of this experiment with previous work via an existing semiempirical band structure calculation demonstrates the complete consistency of these measurements with previous Fermi surface data.

The virtual crystal approximation is used to formulate the Schrodinger equation for the electronic band structure of a dilute substitutional alloy and to analyze the effect of coherent scattering on the lifetime τk of an electron quantum state. Both coherent and incoherent scattering theory yield essentially the same functional and numerical relationship connecting τk,C, and |VO|, whereC is the impurity concentration and |VO| is the typical Fourier transform of the impurity perturbation potential. Electron quantum interference data for Mg-Zn and Mg-Cd alloys are interpreted using this formulation. A consistent picture of these alloys results which contains the following features. (1) The impurity atoms in both types of alloys are partially ordered in the Mg lattice. (2) The perturbation potentials for both Zn and Cd are somewhat larger than predicted by simple pseudopotential theories, with the perturbation for Zn being about 6.5 times larger than for Cd. (3) A standing charge density wave commensurate with the lattice and having aC-dependent amplitude is present in these alloys.

The use of radiography in the study of cryptic insects was investigated for several kinds of forest insect damage. Longwave or “soft” X-rays (5-35 kilovolts) were found most suitable for the detection and study of insects infesting plant material. A portable industrial X-ray unit was used which had an output of up to 35 kilovolts, 10 milliamperes, and variable exposure time. Excellent results were achieved in radiographs of western pine beetle larvae and pupae in ponderosa pine bark; adult gallery construction and larval development of Ips confusus (LeConte) ; red turpentine beetle in situ in sugar pine; buprestids, cerambycids, siricids, and lyctids infesting various thicknesses and kinds of timber; weevils infesting lodgepole pine tips and seed-infesting insects. Less satisfactory was the detection of insects in whole cones, although their galleries could be detected.

Ips calligraphus (Germar) is distributed continentally throughout North America, including Guatemala and British Honduras. It has been collected on only rare occasions in California, primarily in the central Sierra Nevada Mountains. Four generations were observed during 1961 and 1962, and average summer development required about 40 days. All stages except the egg were observed in the winter. The unique gallery system exhibits four to six egg galleries, which range in length from 25.4 to 38.1 cm, and radiate characteristically from a large, irregular, nuptial chamber excavated by the male. At Grass Valley, Cal., this bark beetle was observed breeding predominantly in the thick-barked portions of the lower bole. Its galleries are often intermixed with those of Dendroctonus brevicomis LeConte, I. confusus LeConte, I. latidens LeConte, and Melanophila californica Van Dyke in ponderosa pine. I. confusus was the most abundant species of Ips in all localities where I. calligraphus was found.

The galvanomagnetic properties of several single-crystal specimens of high-purity zinc have been investigated. The results of this investigation are presented and a Fermi-surface topology consistent with the data is discussed. Many of the detailed features of the galvanomagnetic properties are found to result from the effects of magnetic breakdown. The open orbit parallel to the hexagonal axis is modified but not eliminated by magnetic breakdown at fields of about 17.5 kG. A "giant orbit" of the type previously observed in magnesium is found in zinc. This orbit results from magnetic breakdown across the energy gap near $K$ which separates the second-band hole sheet from portions of the third-band electron sheets. Magnetic breakdown across this same energy gap gives rise to discrete bands of open trajectories in the basal plane when the direction of the magnetic field is tilted away from the hexagonal axis in the ($10\overline{1}0$) and ($11\overline{2}0$) crystallographic planes. The transition region of the magnetic breakdown which gives rise to the giant orbit is investigated in detail, and the large quantum oscillations which have been previously observed in the transport properties of zinc are shown to be a transition-region phenomenon. The oscillations appear to result from an oscillatory breakdown probability which, in turn, arises from oscillations in the density of states associated with the Landau levels of the needle-shaped portion of the Fermi surface of zinc. An analysis of the detailed shape of the oscillations indicates that the Landau levels of the needle are split into discrete spin levels with a very large effective $g$ factor. The three values of the effective $g$ factor which are compatible with the present data are ${g}^{*}=90$, ${g}^{*}=180$, and ${g}^{*}=360$, but an investigation with higher magnetic-field strengths will allow a unique choice to be made. No evidence has yet been obtained that yields a direct confirmation of the quasi-particle states predicted by Pippard.

We report here the results of a detailed investigation of the de Haas---van Alphen effect in magnesium. The data were taken for the three major crystallographic planes in magnetic fields extending to 52 kG and at temperatures down to 0.31\ifmmode^\circ\else\textdegree\fi{}K. The results yield cross-sectional area branches for every sheet of the single-OPW-model Fermi surface (OPW=orthogonalized plane wave). Coupled orbits generated by magnetic breakdown are shown to be responsible for many of the observed area branches. The results are in good qualitative agreement with existing models for the magnesium Fermi surface.

In economic entomology, particularly forest entomology, the Description of insect numbers in absolute terms may be misleading. The effect of an individual on its host varies tremendously between species and this gives rise to unwarranted comparisons within current systems. The insect-host relationship between Recurvaria starki Freeman and Pinus contorta Dougl. is reviewed lind used as an example in the erection of a three-class system for the description of insect numbers based on the effect of the insect on its host.

The lodgepole needle miner, Recurvaria starki Freeman, has been studied intensively since 1948. Life tables, survival, and death-rate curves show clearly that there are five periods in the 2-year life cycle of the needle miner during which extensive mortality may occur: (1) between egg formation and oviposition; (2) between oviposition and larval establishment; (3) during the first larval hibernation; (4) during the second larval hibernation; (5) during the spring of moth emergence. Population success is also undoubtedly affected by conditions during the adult life.Population sampling has shown that the outbreak has declined since 1948. Defoliation and increment studies have shown that the period of greatest defoliation occurred from 1940 to 1944 and that the outbreak probably began in the late 1930's. The major cause of the decline was severe winter temperatures, probably during the coldest month. Parasitism was not an important factor in the outbreak decline, apparently because it was controlled in the same manner as the host, by winter temperatures. Other natural control factors are discussed as well as the possible effects of climatic factors on oviposition and fecundity.A detailed survey of weather records since 1920 and yearly averages since 1885 suggest that release of the needle miner population was due to a warming trend in the climate of western Canada. This trend began in the late 1930's, reached a peak in the mid-1940's, and has declined since that time. The warming trend in northern latitudes has been noted by other authors and is substantiated by weather records of this region. It is further postulated that the climate of the Canadian Rocky Mountains is generally too severe for an outbreak of the lodgepole needle miner to be prolonged.

Four major air masses, tropical maritime (mT), polar maritime (mP), arctic maritime (mA), and arctic continental (cA) may be used in describing the winter climate of a lodgepole needle miner (Recurvaria starki Free.) outbreak area. The main circulation is from the north and west which results in a predominance of mP and cA air. Local topography and its effect on winter climate is described for four areas now sampled on a life-table basis. Variations in winter mortality from year to year and between sampling areas are related to climate. Extensive invasions of cA air, particularly of long duration, cause lethal winter temperatures. Winter mortality usually occurs during the coldest month, January, and may be exceptionally high when extreme minima of −30° F to −40° F persist long enough to depress the monthly mean temperature close to O° F. However, less extreme temperatures in other months may result in similar high mortalities if these are unseasonably low. The climatic conditions causing high mortality generally occur at the tops of slopes and at valley bottoms, allowing the middle slopes to serve as "refuge areas" for surviving needle miner populations.

Geometric resonances in the ultrasonic attenuation have been studied in magnesium for sound propagated in the three principle crystallographic directions. A total of twenty different geometric resonance branches have been obtained. The assignment of these branches to Fermi-surface calipers shows that the magnesium Fermi surface is much more free-electron-like than currently thought. Three of the first four local pseudopotential Fourier expansion coefficients are estimated from data to be 5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ 1.0 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}2}$, and 1.7 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}2}$ Ry for the absolute value of the [$10\overline{1}0$], [0002], and [$10\overline{1}1$] coefficients, respectively. A two orthogonalized-plane-wave model is given for the lens-shaped piece of the Fermi surface in the third Brillouin zone, and various physical properties of this model are calculated and compared with experimental data.

General. The life history of the lodgepole needle miner in Yosemite National Park, California, has been described (24). The Canadian outbreak was discovered in 1942 but intensive investigations were not commenced until 1948. Many differences have been noted between the Canadian and Californian life histories since the discovery of the outbreak.It is the purpose of this paper to bring together all information collected by the author and staff of the Laboratory of Forest Zoology at Calgary, Alberta, concerning the life history of the lodgepole needle miner in the Canadian Rocky mountains.

In the Canadian Rocky Mountain National Parks, the lodgepole needle miner has a two-year life cycle, so that larvae of each generation are exposed to two successive winters. Although there is no doubt that mortality of these over­ wintering larvae is directly attributable to a period of low temperature, there has been some doubt as to whether the bulk of the mortality occurs during the coldest part of the winter, or whether it occurs during periods of low temperature during the late autumn or early spring. Although spring and autumn mortality undoubtedly take place, estimation of the relative importance of mortality during the various seasons must await successive sampling throughout the three seasons. Nevertheless, in the absence of such data, we wish to present evidence that points to the major importance of the weather of the coldest month of the winter to not only the amount but also the vertical distribution of larval mortality. Evaluation of this evidence requires some knowledge of the migratory weather systems that affect the eastern slopes of the Rockies. Consequently, a brief outline of this necessary meteorological background is presented before the mortality data are discussed. The winters of 1948-49 and 1949-50 are used as examples, because records of vertical variations in mortality along different slopes are more complete for these than for previous years. The discussion is restricted to the part of the Bow Valley that lies within Banff National Park, Alberta.

Sterilization of male and female Ips confusus (Coleoptera: Scolytidae) exposed to gamma radiation (Co60) as newly emerged adults was almost complete at levels exceeding 7500 r and 10,000 r, respectively. Mating behavior of males as expressed by sperm transfer was unaffected by dosages up to 60,000 r. The capacity of beetles of either sex to establish galleries was not affected significantly below this dosage, but female gallery pattern was altered above 15,000 r. Longevity was reduced at levels greater than 5000 r. LD50 for males occurred at 11.5 days at 7500 r and 29 days in the controls. Mortality of progeny resulting from males irradiated at substerilization levels was higher than in the controls. The dosage to achieve significant population reduction with minimum effect on longevity and other biological activity is estimated to lie between 6000 and 7500 r.These studies indicate that this sterilization technique may have promise in the control of bark beetles. The necessity for rearing large numbers on artificial media could be circumvented by mass trapping utilizing their natural sex attractant and by mass rearing in cut host material in the laboratory.