Patterns in food-web structure have frequently been examined in static food webs, but few studies have attempted to delineate patterns that materialize in food webs under nonequilibrium conditions. Here, using one of nature's classical nonequilibrium systems as the food-web database, we test the major assumptions of recent advances in food-web theory. We show that a complex web of interactions between insect herbivores and their natural enemies displays significant architectural flexibility over a large fluctuation in the natural abundance of the major herbivore, the spruce budworm ( Choristoneura fumiferana ). Importantly, this flexibility operates precisely in the manner predicted by recent foraging-based food-web theories: higher-order mobile generalists respond rapidly in time and space by converging on areas of increasing prey abundance. This “birdfeeder effect” operates such that increasing budworm densities correspond to a cascade of increasing diversity and food-web complexity. Thus, by integrating foraging theory with food-web ecology and analyzing a long-term, natural data set coupled with manipulative field experiments, we are able to show that food-web structure varies in a predictable manner. Furthermore, both recent food-web theory and longstanding foraging theory suggest that this very same food-web flexibility ought to be a potent stabilizing mechanism. Interestingly, we find that this food-web flexibility tends to be greater in heterogeneous than in homogeneous forest plots. Because our results provide a plausible mechanism for boreal forest effects on populations of forest insect pests, they have implications for forest and pest management practices.

The efficient and effective monitoring of individuals and populations is critically dependent on correct species identification. While this point may seem obvious, identifying the majority of the more than 100 natural enemies involved in the spruce budworm (Choristoneura fumiferana – SBW) food web remains a non-trivial endeavor. Insect parasitoids play a major role in the processes governing the population dynamics of SBW throughout eastern North America. However, these species are at the leading edge of the taxonomic impediment and integrating standardized identification capacity into existing field programs would provide clear benefits. We asked to what extent DNA barcoding the SBW food web would alter our understanding of the diversity and connectence of the food web and the frequency of generalists vs. specialists in different forest habitats. We DNA barcoded over 10% of the insects collected from the SBW food web in three New Brunswick forest plots from 1983 to 1993. For 30% of these specimens, we amplified at least one additional nuclear region. When the nodes of the food web were estimated based on barcode divergences (using molecular operational taxonomic units (MOTU) or phylogenetic diversity (PD) – the food web became much more diverse and connectence was reduced. We tested one measure of food web structure (the “bird feeder effect”) and found no difference compared to the morphologically based predictions. Many, but not all, of the presumably polyphagous parasitoids now appear to be morphologically-cryptic host-specialists. To our knowledge, this project is the first to barcode a food web in which interactions have already been well-documented and described in space, time and abundance. It is poised to be a system in which field-based methods permit the identification capacity required by forestry scientists. Food web barcoding provided an effective tool for the accurate identification of all species involved in the cascading effects of future budworm outbreaks. Integrating standardized barcodes within food webs may ultimately change the face of community ecology. This will be most poignantly felt in food webs that have not yet been quantified. Here, more accurate and precise connections will be within the grasp of any researcher for the first time.

We conducted a 14‐yr intensive study of spruce budworm (Choristoneura fumiferana (Clem.)) survivorship at three study plots in largely balsam fir (Abies balsamea (L.) Mill.) stands in New Brunswick, Canada, to elucidate certain key mechanisms underlying spruce budworm outbreak cycles. The study covered a peak‐to‐declining phase (from 1981 and 1994) of the budworm outbreak cycle that had started in the early 1960s. Frequent sampling was carried out in each plot‐year to construct a practically continuous survivorship curve, and the annual variation in population density was estimated. We found a high level of correlation between the studied phase of the outbreak cycle and annual variations in the survivorship over the postdiapause period, suggesting that postdiapause survivorship was the chief determinant of the cycle. We found the annual changes in population density in the present study to be closely similar in pattern to those from the provincial budworm surveys conducted in much larger areas. This implies that the mechanism underlying the population process found in the few study plots in largely balsam fir stands also applies to the process in much larger areas of diverse stand types. The main source of postdiapause mortality is found to be natural enemies. The impacts of parasitoids and disease are evaluated by rearing budworm samples in the laboratory. Hymenopteran and dipteran parasitoids are by far the major sources of mortality, and microsporidians are the most prevalent pathogen. Occurrences of other entomopathogenic fungi and viruses were insignificant throughout the study. Seasonal changes in laboratory survivorship are compared with the corresponding field survivorship to estimate the effect of predation. No major mortality factor is found to singly play a predominant role in determining the outbreak cycle. Conversely, some minor factors are shown to have played significant roles. Thus, the importance of recognizing the action of natural enemies as a complex is emphasized for understanding the budworm outbreak cycle. Finally, centered on the roles played by the chronological succession of natural enemies in the present study, the results of budworm research in New Brunswick since the mid‐1940s are synthesized to outline basic mechanisms underlying the outbreak processes as a guide for further studies.

Outbreak and declining populations of spruce budworm (Choristoneura fumiferana (Clem.)) were sampled extensively at three locations in New Brunswick, Canada, between 1982 and 1992 and were examined for the prevalence of granulosis and nuclear polyhedrosis viruses (Baculoviridae). Larvae, pupae, and adults were collected using a variety of methods. Spruce budworm nuclear polyhedrosis virus (CfMNPV) genomic DNA probes and wet-mount light microscopy were used to determine CfMNPV prevalence in 50 274 juvenile spruce budworms. Spruce budworm granulosis virus (ChfuGV) genomic DNA probes were used to determine the prevalence of ChfuGV in 25 703 of these same samples. The prevalence of both viruses was low, with ChfuGV and CfMNPV not found in more than 15% and 2%, respectively, of samples in any collection in a given year. Prevalence of ChfuGV was greatest in mid-to late June in sixth-instar larvae. Each virus was detected in only two of 2177 female moths and in none of the 420 male moths examined. In the entire collection, cytoplasmic polyhedrosis virus (Reoviridae) was detected in only two budworm larvae and entomopoxvirus (Poxviridae) was not detected in any. Lucarotti CJ, Eveleigh ES, Royama T, Morin B, McCarthy P, Ebling PM, Kaupp WJ, Guertin C, Arella M. 2004. Prévalence des baculovirus dans des populations de tordeuse des bourgeons de l'épinette (Lepidoptera : Tortricidae) au Nouveau-Brunswick. The Canadian Entomologist 136 : 255-264. 255 1 Corresponding author (e-mail: clucarot@nrcan.gc.ca). mêmes échantillons. La prévalence des deux virus était faible, ne dépassant pas 15% pour ChfuGV et pas plus de 2% pour le CfMNPV, pour chaque méthode d'échantillonage, pour chaque année d'étude. La prévalence du ChfuGV atteint son maximum entre le milieu et la fin de juin, au sixième stade de développement larvaire. Chaque virus n'a été détecté que chez deux des 2177 adultes femelles et chez aucun des 420 adultes mâles examinés. Parmis tous les specimens recueillis, le virus de la polyhèdrose cytoplasmique (Reoviridae) n'a été détecté que dans deux larves de la TBE alors que l'entomopoxvirus (Poxviridae) ne l'a été dans aucun.

An illustrated key is given to 28 genera, representing 10 families of at least 50 chalcidoid parasitoids and hyperparasitoids recorded from Choristoneura species (Tortricidae), or their primary parasitoids, in America north of Mexico. We include species reared throughout a 12-year study of the parasitoids and hyperparasitoids associated with the spruce budworm, Choristoneura fumiferana (Clemens), in New Brunswick, Canada, as well as those listed in various catalogs. Notes are provided for all the chalcidoid species, whether or not they are recorded in the literature. Nine species doubtfully or incorrectly recorded from Choristoneura species are also discussed.Primary parasitoids belonging to the Ichneumonidae, Braconidae, and Tachinidae have been recorded from 10 of the 16 Nearctic Choristoneura species but chalcidoid parasitoids are recorded, usually as hyperparasitoids, from only four of the 16 species. The species of primary parasitoids of Choristoneura checked for records of parasitism by Chalcidoidea are tabulated by host species. Also listed are species of primary parasitoids serving as hosts for each of the chalcidoid species. We report 51 new host records of primary parasitoids and hyperparasitoids from C. fumiferana and its parasitoids collected in New Brunswick.A new generic combination is given: Mesopolobus tortricis (Brues) comb.nov. from Psychophagus (proposed by Z. Boucek).

1 Nosema fumiferanae infections in populations of both sexes of spruce budworm Choristoneura fumiferana moths, collected live above the forest canopy (canopy moths), within the tree crown (crown moths) and in drop trays (dead moths), were examined over a 5-year period in New Brunswick, Canada. 2 The incidence of infection and of moderate -heavy infections in canopy and crown moths of both sexes increased concomitantly with moth eclosion, indicating that N. fumiferanae retards larval/pupal development, with infected moths, particularly those having higher disease loads, emerging later in the season. 3 Infection rates differed among canopy, crown, and dead female, but not male, moths. Canopy (i.e. emigrating) females had a lower incidence of infection, lower incidence of moderate -heavy infections, and had longer forewings and higher dry weights, than crown females. These results suggest that N. fumiferanae infections negatively affect aspects of female, but not male, flight performance. Regardless of infection, forewing length and dry weight of both canopy and crown females declined over the moth flight period, but infected females in both moth types were smaller than their uninfected counterparts. Forewing lengths and dry weights of moderately -heavily infected females were most severely affected. 4 Despite high annual infection rates in parents, only a small percentage of offspring (second-instar larvae) that established feeding sites each spring were infected, indicating that high rates of horizontal transmission occurred annually throughout the larval period. 5 The present study indicates that whether N. fumiferanae infections are a debilitating sublethal factor in spruce budworm populations depends more on the disease load than on the overall incidence of infection. The potential importance of N. fumiferanae infections on various fitness parameters related to host dispersal is discussed.

1 Although the successful management of the Colorado potato beetle Leptinotarsa decemlineata (Say) depends on the prevention of its dispersal, its walking pattern in the landscape remains poorly understood. In the present study, post-diapause, early summer, late summer and colony adult beetles, both fed and unfed before release, were tracked with a harmonic radar to establish their walking movement pattern in a bare-ground field. 2 The random walk model successfully described the dispersal of all beetle types, whether fed or unfed. 3 The diverse life history of this species was manifested by an increased distance travelled and deviations of individual paths from the random model. Starved postdiapause beetles travelled furthest and individual paths deviating from random were both local and directed, probably aiming to maximize opportunities for host colonization. Starved early summer beetles also travelled further than fed beetles but relied more on random movement to disperse in the habitat. Starving had little impact on the distance travelled or the path deviations of late summer beetles that are searching for overwintering site rather than hosts. 4 The increased displacement of starving beetles over fed beetles corresponded with an increased walking step and index of straightness. 5 The impact of starvation on travel distance was greater than expected from laboratory tests. 6 In conclusion, the results obtained in the present study suggest a random walking pattern to search arable land until host volatile or visual impulses trigger a more directed walk or flight.

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