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.

No abstract

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.