Populations of the fir engraver reached epidemic proportions and then declined to a very low level over the study period (1964–71). However, population density within infested trees showed an inverse relationship to overall population trend. The population trend over the past 40 years was associated to some degree with rainfall deficits and with Douglas-fir tussock moth outbreaks.

The major contribution to total mortality in each generation occurred in the larval, pupal and pre-emergent adult stages, next was adult mortality and infecundity, while egg mortality was of least significance. Mortality and infertility of parent females was mainly caused by nematode parasites although host resistance resulted in a significant number of attack failures. Parasitism by a phorid fly was of minor importance. Nematode parasitism appeared to be density-dependent in relation to overall population size.

Most egg mortality resulted from host resistance which was inversely related to egg density within trees. Other egg mortality occurred in a density-independent manner.

Mortality between larva and brood adult stages was mainly attributed to intra- and interspecific competition. The impact of these factors was directly related to within-tree larval density. Nematode parasitism was related to overall fir engraver population size and to per cent infection of attacking females. Predator activity was weakly density-dependent and mortality caused by resinosis was inversely related to fir engraver density. Parasitism and other mortality factors appeared to be independent of host density.

An hypothesis is presented for the population behavior of the fir engraver; population fluctuations being determined by the quantity of susceptible trees and ultimately regulated by intraspecific competition. Nematode parasitism and interspecific competition were regarded as modifying, and perhaps sometimes regulating, abundance. Areas needing additional study, particularly host-tree physiology are discussed.

Animals are capable of multiplying their numbers by some form of reproduction; but they are hindered by natural means from multiplying to the point of committing collective suicide by exhausting the resources of this planet. Animals are also subject to having their numbers decreased; but, likewise, their decrease to extinction is hindered by natural means. The question of these natural means of limiting increase and decrease of numbers is a fundamental problem of Ecology: the problem of the mechanism of natural control of populations. The solution of this problem has, of course, great practical interest because man suffers from some animals being too few (beneficial species) and others too numerous (pests).

Emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a non-native, wood-boring beetle that has caused widespread mortality of ash (Fraxinus Linnaeus (Oleaceae)) in eastern North America. During 2004–2007, we determined whether forest community composition and structure of black (F. nigra Marshall), green (F. pennsylvanica Marshall), and white (F. americana Linnaeus) ash stands influenced their susceptibility to EAB invasion in southeast Michigan, United States of America. There was no relationship between EAB-induced ash decline or percentage mortality and any measure of community composition (tree species diversity, stand/ash density, total basal area, or relative dominance of ash). There was also no relationship between measures of EAB impact (density of EAB signs, ash decline rating, percentage ash mortality, or percentage infested ash) and forest attributes (ash/total stand density, basal area, ash importance, or stand diversity). Decline and mortality of black ash advanced more rapidly than that of white and green ash. Percentage mortality of ash increased from 51% to 93% during 2004–2007. Distance from the epicentre of the invasion was negatively correlated with ash mortality, but this relationship dissipated over time. Stand composition data suggests that ash will be replaced by Quercus Linnaeus (Fagaceae), Acer Linnaeus (Sapindaceae), and Tilia Linnaeus (Malvaceae); such vegetation changes will irreversibly alter the structure and function of these forests.

Adult ♀.—Length, 5 mm.; width, 3 mm.; many are smaller than this, but this seems to be the average size of the adult containing eggs. Colour yellowish-gray, although they appear light gray, from the mealy secretion which covers the body.

Shape, ellipsoidal, dorsal surface quite convex, ventral surface flat, extremities rather pointed. segmentation quite distinct to naked eye. Extremely short lateral appendages, little projections just visible; caudal appendages a little longer.

The photoperiodic reaction in North American codling moth populations displayed clinal-type variation similar to populations in Europe. A latitudinal shift of 10° to the north corresponded to an increase of 1.25 h in the critical photoperiod. Intrapopulation variance in diapause response appeared to be similar in populations of different origin. The critical photoperiod was not constant for a geographic population but varied between years probably due to the modifying effect of prediapause temperatures. In Michigan and other areas in the northeastern United States with similar climate the codling moth is essentially bivoltine with considerable yearly variability in second generation emergence. A graphic model is presented which gives an estimate of voltinism and the proportion of diapausing first-generation larvae based on the seasonal heat unit total at the time of diapause initiation. From an analysis of original data and historical phenological records an algorithm was developed which describes the relationship between effective temperatures and the variance of second generation emergence and which can predict population curves for climatically different years. Use of this predictive method in conjunction with monitoring information provided by a pheromone trap is discussed.

Male Ips paraconfusus selected a host, ponderosa pine (Pinus ponderosa), over a non-host, white fir (Abies concolor), only after the beetles had bored through the outer bark and into the phloem. Males, when given a choice between bark discs of these tree species in petri dishes, bored readily through the outer bark of either species. However, the beetles penetrated no more than 1 mm into the phloem of white fir, but they bored extensively in the phloem of ponderosa pine. The beetle’s preference for the pine over fir phloem was apparent with intact samples of phloem with the outer bark removed and with ground phloem. No preferences were apparent for the ground or intact pine or fir outer bark, with the phloem removed. The beetles bored preferentially in fissured as opposed to smooth outer bark of either tree. Beetles did not feed in the outer bark but did feed in the phloem of either species. In field experiments beetles attracted to logs of pine and fir bored through the outer bark of each species in nearly equal numbers. In white fir they re-emerged and departed soon after penetration of the phloem, whereas in ponderosa pine they continued excavation of tunnels in the phloem. In contrast, few beetles penetrated even the outer back of incense cedar (Calocedrus decurrens), another non-host species.

It is universally recognized that the spatial distribution or pattern of animals and plants in nature is neither uniform nor truly random. In order to study a biological community quantitatively, or to assess the densities of living organisms in their habitats, ecologists have found it profitable to sample the space in which the organisms occur. The distribution of the number of individuals per sample is of fundamental importance.

In 1996, damage symptoms typical of the swede midge, Contarinia nasturtii (Keiffer), were observed on broccoli, Brassica oleracea L. var. italica (Brassicaceae), crops east of Toronto, Ontario. Early attempts to identify an associated insect larva were unsuccessful, and damage symptoms became mistakenly attributed to nutrient deficiencies (T Clarke, personal communication). Between 1996 and 1999, damaged plants were seen by growers regularly, and resulted in up to 85% loss of marketable yield (T Clarke, personal communication). In June 2000, we initiated investigations at two sites 12 km apart to determine the causal organism of this damage. Both sites were located at farms where cole crops are primarily -gown and from where the first damage reports originated.

The age at which Pseudaletia unipuncta females initiated calling varied with temperatures experienced during pupal and adult stages. Entrainment was induced by temperatures during pupal development if similar to or lower than temperatures during adult life. However, adult temperatures were of major importance if lower than those experienced during pupal development. These observations were generally supported by data from field experiments repeated at different periods of the summer. The possibility that entrainment occurs at a specific period of development is proposed to explain certain field observations.

Changes in mean onset time of calling and the time spent calling also varied, although generally not in the same manner as reported for other species. Differences in the life cycles, particularly the site of pupation, are proposed to explain these discrepancies.

Many soil-inhabiting insects are susceptible to entomopathogenic nematodes but the degree of susceptibility ranges widely. Much is understood about the habitat of insect pests in relation to their susceptibility but little attention has been paid to the influence of physical deterrents. "Physical deterrents" is used here to include morphological barriers (passive deterrents) and behavioural responses to attack (active deterrents). The roles of both are reviewed and discussed, in particular with reference to wireworms (Elateridae), a group of insects generally resistant to the nematodes. Knowledge of insect morphology and behaviour as well as habitat is important in predicting susceptibility to entomopathogenic nematodes.

An absolute requirement for sugar could not be shown but laboratory rearing experiments using artificial diets have demonstrated a definite increase in weight of adult spruce budworm (Choristoneura fumiferana (Clem.) Freeman) with increasing dietary levels of certain sugars. Males exhibit a threshold of 0.9% soluble sugars above which higher sugar levels produce no further increases in size. Females respond with an increase in size up to 4.0%, the highest level tested. Generally, faster development rates accompany greater mature weights on diets with higher nutrient levels.

Maltose, raffinose, glucose, sorbitol, sucrose, and fructose are all good sugar sources. Galactose and trehalose are only slightly inferior. Lactose, ribose, melibiose, xylose, mannose, arabinose, and melezitose in the diet are little different from the sugarless control. Sorbose is somewhat inhibitory.

Results of transfer experiments confirm the importance of sugar particularly during late larval development. They also indicate that a high protein diet during early instars has a significant effect on development rates. These results suggest that departure from the normal synchrony of development in the insect and its host can affect both rate of development and mature size of the insect.

The mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), is a destructive insect pest in western Nearctic conifer forests. Currently, British Columbia, Canada, is experiencing the largest recorded outbreak of this insect, including areas that historically have had low climatic suitability for it. We analyzed 26 constitutive resin terpenes in phloem samples from British Columbia lodgepole pine (Pinus contorta) populations to test for differential resistance to mountain pine beetle attack, based upon the likelihood of previous exposure to mountain pine beetle. We assessed sampled trees for number of mountain pine beetle attacks, number of pupal chambers, and tree survival the following spring. Significant differences were found when levels of certain terpenes in lodgepole pine populations that had likely experienced substantial mountain pine beetle infestations in the past were compared with those in populations that likely had not experienced large outbreaks of mountain pine beetle. Although we expected southern pine populations to contain more total terpenes than northern populations, owing to higher historical exposure to the beetle, the converse was found. Northern populations generally had higher levels of constitutive terpenes and beetle attack than southern populations. Because several terpenes are kairomones to the mountain pine beetle and also serve as precursors for the synthesis of pheromones, the lower levels of terpenes expressed by lodgepole pines from the historical range of the mountain pine beetle may render them less chemically perceptible to foraging beetles.

Fourteen new records of introduced leafhoppers are added to the 157 leafhoppers previously recorded as occurring in both the Old and New worlds. Of these, 62 were erroneously recorded previously although 12 of the European species subsequently have been found in North America. Two North American species have been introduced into Europe, and one European species has been found in South America; North America has received 61 species from Europe, 3 from Asia, and 1 from Africa. One pan-tropical species is probably a recent introduction into the Caribbean from the Old World. There are 30 transboreal leafhoppers, 5 transarctic species inhabiting the tundra and alpine meadows, and 9 inhabiting temperate regions of both Eurasia and North America.

The Aster leafhopper (Macrosteles quadrilineatus Forbes) is removed from synonymy with the transboreal sedge-feeding M. fascifrons (Stål) and 25 other confused species are distinguished in the genera Aphrodes, Euscelis, Evacanthus, Limotettix, Macrosteles, and Typhlocyba. These include 11 new species: Evacanthus bellaustralis, E. chlamidatus, E. grandipes, E. lacunar, E. nigramericanus, E. ustanucha, Macrosteles lagus, M. severini, M. tesselatus, M. vilbastei, and Typhlocyba frigida, all from North America, Balclutha punctata confluens Rey and Limotettix striola ferganensis Dubovsky are elevated to species status. One new generic synonymy, 23 new specific synonymies, and 3 new combinations are created.

Cortical blister and wound reaction resin vapors from Abies grandis, and some of their monoterpene fractions, were quantitatively bioassayed for attractiveness and repellency to the fir engraver beetle, Scolytus ventralis. All were found to be repellent.

Quantitative differences between liquid resins and vapors were examined. Wound reaction resin vapors contained higher percentages of the more repellent monoterpenes than cortical blister resin vapors. It is hypothesized that α-pinene is the most important monoterpene in the insects’ perception of a resistant host.

Continuous trapping on the bark surface of Dendroctonus brevicomis LeConte infested trees in the central Sierra Nevada mountains was undertaken with the objective of determining the spatial and temporal arrival patterns of the natural enemies and other insect associates of the western pine beetle. Over 100 species of D. brevicomis associates were collected and patterns of arrival were described for many of these. The main bark beetle predators were trapped during D. brevicomis mass arrival and shortly thereafter. Enoclerus lecontei, Temnochila chlorodia, and Aulonium longum, all predaceous beetles on D. brevicomis adults and larvae, were among the first species to arrive, as was Medetera aldrichii (Diptera), a larval predator. The bark beetle parasites Roptrocerus xylophagorum and Dinotiscus (=Cecidostiba) burkei (Hymenoptera) were well synchronized with the beetles’ life cycle as they arrived late in the beetles’ larval stages when suitable hosts were available.

Approximately twice as many associates were trapped in the first (spring) beetle generation as in the second (fall). Differences between species with regard to height distribution were common, and these often varied with seasonal beetle generation.

Calculations of changes in species diversity through time, of the associate complex trapped at the bark surface, were made for both the first and second beetle generation. Linear correlation analysis indicated a highly significant increase in species diversity occurred from the time of the beetles’ mass arrival until brood emergence. This increase may correspond to an increase in diversity of the structure of the subcortical community, as more insect species arrived and progressively modified the habitat of the newly killed tree.

An energy-flow multitrophic-level model incorporating acquisition (functional response) and assimilation (metabolic pool model) functions and stochastic development is proposed and put into historical perspective. The model is general for each trophic level and for all subcomponents. Prey demand drives the functional response model, while food supply–demand determines all intrinsic rates in the model. The model is used to explore the theoretical properties of a multitrophic system comprising alfalfa, blue aphids, pea aphids, a host-specific parasitoid, and two predators (lady beetles, green lacewings). The model shows:

(1) the importance of the resource base on higher trophic level dynamics and vice versa

(2) the stability properties of different combinations of species

(3) the role of parasitoids and predators in population regulation in this system

(4) how food acquisition and respiration as functions of temperature and per capita resource interact to determine the rate of population growth

(5) that extreme caution must be used in extrapolating theoretical results to field situations.

Investigations in 1959 (Dyer and Kinghorn, 1961) revealed a large overwintering population of the ambrosia beetle, Trypodendron lineatum (Oliv.), in a level accessible stand of timber. It was decided to use this location for field studies on attack behaviour of this insect, with three general objectives in mind: 1) direct observation of beetles as they searched for and found suitable log material; 2) experimental verification by means of various ‘hidden log’ situations, with controls, of the importance of smell in the beetles' search, and 3) observation and measurement of differences in attractiveness between logs during the flight period.

Loblolly pine trees struck by lightning offer a favorable attack and brood environment for the southern pine and Ips beetles. In central Louisiana lightning strikes reduced oleoresin exudation pressure, oleoresin flow, and relative water content of inner-bark tissue and resulted in a decrease in sucrose and an increase in reducing-sugar content of inner bark. Interspecific competition was much greater in struck trees than nonstruck trees. Among struck trees, those with highest carbohydrate levels produced the most numerous broods of the southern pine beetle.

The life history of the Sitka spruce weevil, Pissodes sitchensis Hopk., is described. Adults overwinter in duff at the base of trees and emerge in April or early May. Oviposition begins in late April on leaders. The larvae hatch and mine downward, eventually girdling and killing the leader. Larvae pupate in chip cocoons under the bark. Newly developed adults start emerging in August and, prior to hibernation, feed on leaders of young trees. Adults have been observed in the field as late as December.

Predators caused heavy mortality but the weevil population maintained itself and increased in some years. Parasitism was light. Natural control factors reduced the population level but were incapable of controlling a population. Satisfactory control was obtained by applying DDT and phosphamidon to leaders with a hand-sprayer early in the spring, but repeated applications would be necessary to protect a plantation through the critical years.

Damage to Sitka spruce regeneration and plantations in British Columbia is severe. At present, protection of Sitka spruce plantations would require considerable expense.

Prepupae of Neodiprion sertifer (Geoff.) held in darkness at 21 °C undergo a short normal diapause if exposed as feeding larvae to long photoperiods, but have no diapause if reared in the larval stage under short photoperiods. If cocoons from short-day rearings are exposed to 10 °C instead of 21 °C, a small proportion of the prepupal larvae undergo the normal or short diapause, but the majority enter an intense or prolonged type of diapause which results in three clearly defined periods of adult emergence within the range of 160 to 800 days after cocoon spinning. Mortality increases directly with the prolonged cocoon periods associated with intense diapause at 10 °C and there is a progressive decrease in reproductive potential of the survivors. If cocoons are held at 29 °C normal diapause and morphogenesis are prolonged but there is no evidence that a state of intense diapause is induced. Mortality is extreme, however, and the reproductive potential of the survivors is greatly reduced.

The implication of these findings is discussed in relation to prolonged diapause in nature, a factor critical to the assessment of the seasonal history and population dynamics of the insect.