Naomi Cappuccino

Population dynamics : new approaches and synthesis

Introduction. N. Cappuccino, Novel Approaches to the Study of Population Dynamics. Observation and Comparative Approaches: P. Turchin, Population Regulation: Old Arguments and a New Synthesis. A.F. Hunter, Ecology, Life History and Phylogeny of Outbreak and Nonoutbreak Species. N. Cappuccino, H. Damman, and J.-F. Dubuc, Spatial Behavior and Temporal Dynamics of Outbreak and Nonoutbreak Species. M.J. Auerbach, E.F. Connor, and S. Mopper, Minor Miners and Major Miners: Population Dynamics of Leaf-Mining Insects. Mechanisms and Processes of Population Dynamics: R.F. Denno and M.A. Peterson, Density-Dependent Dispersal and its Consequences for Population Dynamics. S. Harrison and N. Cappuccino, Using Density-Manipulation Experiments to Study Population Regulation. I. Hanski and M. Kuussaari, Butterfly Metapopulation Dynamics. S.J. Walde, Internal Dynamics and Metapopulations: Experimental Tests with Predator-Prey Systems. J. Roland and P.D. Taylor, Herbivore-Natural Enemy Interactions in Fragmented and Continuous Forests. G. Dwyer, Simple Models and Complex Interactions. J.H. Myers and L. Rothman, Field Experiments to Study Regulation of Fluctuating Populations. M.C. Rossiter, Impact of Life History Evolution on Population Dynamics: Predicting the Presence of Maternal Effects. Case Studies: C. Solbreck, Long-Term Population Dynamics of a Seed-Feeding Insect in a Landscape Perspective. T. Ohgushi, Adaptive Behavior Produces Stability in Herbivorous Lady Beetle Populations. P.W. Price, T.P. Craig, and H. Roininen, Working Toward Theory on Galling Sawfly Population Dynamics. J.D. Reeve, M.P. Ayres, and P.L. Lorio, Host Suitability, Predation, and Bark Beetle Population Dynamics. G.E. Belovsky and A. Joern, The Dominance of Different Regulating Factors for Rangeland Grasshoppers. Conclusion: P.W. Price and M.D. Hunter, Novelty and Synthesis in the Development of Population Dynamics. Subject Index.

Novel chemistry of invasive exotic plants

Of the many exotic plants that have become naturalized in North America, only a small proportion are pests capable of invading and dominating intact natural communities. In the present study, we tested the hypothesis that the most invasive plants are phytochemically unique in their new habitats. A comparison of exotic plant species that are highly invasive in North America with exotics that are widespread, but non-invasive revealed that the invasive plants were more likely to have potent secondary compounds that have not been reported from North American native plants. On average, the compounds found in the invasive plants were reported from fewer species, fewer genera and fewer families than those from non-invasive plants. Many of the unique phytochemicals from invasive plants have been reported to have multiple activities, including antiherbivore, antifungal, antimicrobial and allelopathic (phytotoxic) effects, which may provide the plants with several advantages in their new environments.

Invasive exotic plants suffer less herbivory than non-invasive exotic plants

We surveyed naturally occurring leaf herbivory in nine invasive and nine non-invasive exotic plant species sampled in natural areas in Ontario, New York and Massachusetts, and found that invasive plants experienced, on average, 96% less leaf damage than non-invasive species. Invasive plants were also more taxonomically isolated than non-invasive plants, belonging to families with 75% fewer native North American genera. However, the relationship between taxonomic isolation at the family level and herbivory was weak. We suggest that invasive plants may possess novel phytochemicals with anti-herbivore properties in addition to allelopathic and anti-microbial characteristics. Herbivory could be employed as an easily measured predictor of the likelihood that recently introduced exotic plants may become invasive.

The effect of an invasive alien vine, Vincetoxicum rossicum (Asclepiadaceae), on arthropod populations in Ontario old fields

Vincetoxicum rossicum is an invasive alien vine introduced from Europe in the late 1800s that is now an emerging pest in upstate New York and eastern Ontario. The plant can form dense, monotypic stands in woodlots and old fields, and may be displacing native vegetation. As a consequence, V. rossicum may be displacing arthropod fauna associated with native vegetation. In June and August 2002, we sampled V. rossicum and three other old field plants (Asclepias syriaca, Solidago altissima, and mixed graminoids) for arthropods using pitfall traps and by sampling individual plants. A total of 7868 arthropods were counted on plants and 18,195 individuals were trapped; these were sorted by feeding guild. Overall, stands of V. rossicum supported the lowest abundance of both stem- and ground-dwelling individuals, as well as the lowest number of arthropods in most phytophagous guilds. Some feeding guilds are entirely absent: V. rossicum stands are completely devoid of gall-makers and miners, and support few pollinators. This study suggests that arthropod diversity will decline if V. rossicum displaces native old-field plants.

Coping with a Capricious Environment: A Population Study of a Rare Pierid Butterfly

Found in small, scattered colonies, the West Virginia white butterfly (Pieris virginiensis) is absent from many areas where its food plant, Dentaria diphylla, is common. To better understand the demographic processes contributing to this butterflys rarity, we studied the natural history and population ecology of a colony of Pieris virginiensis in Connecticut. Survival to instar IV for P. virginiensis is comparable to that observed for its superabundant congener, P. rapae. However, for P. virginiensis problems begin with instar IV and V larvae, which appear to be victimized by unpredictable host phenology. In 1982, early senescence of Dentaria stranded most fourth and fifth instar caterpillars; stranded caterpillars were unsuccessful at locating secondary host plants. P. virginiensis adults also encounter difficulties because they attempt to oviposit in the spring, when weather conditions are rarely suitable for flight or oviposition. Furthermore, when the females do fly, they are not very effective at laying eggs rapidly. Buildup of granulosis virus through soil contamination may also contribute to the butterflys rarity. By coating Dentaria plants with water-and-soil slurries from wood- land areas with and without P. virginiensis populations, we documented significant vertical transmis- sion of granulosis virus through the soil (i.e., higher virus mortality on plants coated by slurries from P. virginiensis locales). Finally, because P. virginiensis appears reluctant to fly across open fields, recolonization of extinct colonies is an unlikely event. We speculate that P. virginiensis may have been more abundant in the past, when butterflies would have had less trouble dispersing among Dentaria stands because fewer woodlands were dissected by open habitats.

Herbivory on invasive exotic plants and their non-invasive relatives

The Enemy Release Hypothesis links exotic plant success to escape from enemies such as herbivores and pathogens. Recent work has shown that exotic plants that more fully escape herbivores and pathogens are more likely to become highly invasive, compared to plants with higher enemy loads in their novel ranges. We predicted that highly invasive plants from the Asteraceae and the Brassicaceae would be less acceptable, in laboratory no-choice feeding trials, to the generalist herbivore the American grasshopper, Schistocerca americana. We also compared herbivory on invasive and non-invasive plants from the genus Centaurea in no-choice feeding trials using the red-legged grasshopper Melanoplus femurrubrum and in a common garden in the field. In accordance with our predictions, highly invasive plants were fed on less by grasshoppers in the laboratory. They also received less damage in the field, suggesting that they contain feeding deterrents that render them less acceptable to generalist herbivores than non-invasive plants.

Forest composition, host-population density, and parasitism of spruce budworm Choristoneura fumiferana eggs by Trichogramma minutum

The frequency of egg parasitism in the spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae) by Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae) was recorded in several host populations during the rising phase of an outbreak in the Gatineau Valley (Quebec, Canada) in 1999 and 2000. Some of the observed spruce budworm populations were subjected to experimental aerial applications of Bacillus thuringiensis var. kurstaki during the course of the study. Untreated spruce budworm population densities at the onset of the study were directly related to stand composition (the proportion of non‐host basal area) but unrelated to plant species diversity. Much of the variation in budworm egg mass parasitism rates was accounted for (77.1% of total variance) by three variables: year, spruce budworm egg population density, and proportion of non‐host basal area in the stand. The exploitation of eggs within parasitised egg masses was related to year, B. thuringiensis treatment, egg mass size, and the proportion of egg masses parasitised in the host population (76.9% of variance). The yearly variation in parasitism rate was considerable, and was consistent with climatic conditions, namely heat accumulation and precipitation during the spruce budworm oviposition period. Parasitism by T. minutum on eggs of C. fumiferana was recorded in 16 additional sites in 2000, to confirm the general form of the inverse density dependence of parasitism. Observations recorded by Neilson in the Green River area of New Brunswick (Canada) between 1948 and 1957 are discussed in the context of the present analysis. These results indicate that parasitism by T. minutum may be more predictable than previously believed and may be an important and consistent source of mortality in the several years preceding an outbreak of C. fumiferana, especially in mixed‐wood stands and in warmer, drier portions of the spruce budworms range.

Potential novel hosts for the lily leaf beetle Lilioceris lilii Scopoli (Coleoptera: Chrysomelidae) in eastern North America

Abstract 1. Introduced insects often incorporate native plants into their diets and might be expected to show a predilection for novel hosts that are phylogenetically related to their normal hosts. The lily leaf beetle, Lilioceris lilii (Coleoptera: Chrysomelidae), is an introduced pest of cultivated lilies. Oviposition behaviour, larval behaviour, and development of L. lilii was examined on a range of potential host plants, as well as on the normal host, Asiatic hybrid lilies Lilium sp.

Comparative life tables of leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae), in its native range

Leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae), is an invasive alien species in eastern Canada, the larvae of which mine the green tissues of Allium spp. This study was designed to construct and analyse life tables for leek moth within its native range. Stage-specific mortality rates were estimated for the third leek moth generation at three sites in Switzerland from 2004 to 2006 to identify some of the principle factors that inhibit leek moth population growth in areas of low pest density. The contribution of natural enemies to leek moth mortality was measured by comparing mortality on caged and uncaged leeks. Total pre-imaginal mortality on uncaged plants was 99.6%, 99.1% and 96.4% in 2004, 2005 and 2006, respectively. Variation in mortality was greater among years than among sites. Total larval mortality was greater than that in the eggs and pupae. This was due largely to the high mortality (up to 83.3%) of neonates during the brief period between egg hatch and establishment of the feeding mine. Leek moth pupal mortality was significantly greater on uncaged than on caged leeks, indicating an impact by natural enemies, and this pattern was consistent over all three years of study. In contrast, the other life stages did not show consistently higher mortality rates on uncaged plants. This observation suggests that the pupal stage may be particularly vulnerable to natural enemies and, therefore, may be the best target for classical biological control in Canada.

Native range assessment of classical biological control agents: impact of inundative releases as pre-introduction evaluation

Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae) is a pupal parasitoid under consideration for introduction into Canada for the control of the invasive leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae). Since study of the parasitoid outside of quarantine was not permitted in Canada at the time of this project, we assessed its efficacy via field trials in its native range in central Europe. This was done by simulating introductory releases that would eventually take place in Canada when a permit for release is obtained. In 2007 and 2008, experimental leek plots were artificially infested with pest larvae to mimic the higher pest densities common in Canada. Based on a preliminary experiment showing that leek moth pupae were suitable for parasitism up to 5-6 days after pupation, D. pulchellus adults were mass-released into the field plots when the first host cocoons were observed. The laboratory-reared agents reproduced successfully in all trials and radically reduced leek moth survival. Taking into account background parasitism caused by naturally occurring D. pulchellus, the released agents parasitized at least 15.8%, 43.9%, 48.1% and 58.8% of the available hosts in the four release trials. When this significant contribution to leek moth mortality is added to previously published life tables, in which pupal parasitism was absent, the total pupal mortality increases from 60.1% to 76.7%. This study demonstrates how field trials involving environmental manipulation in an agents native range can yield predictions of the agents field efficacy once introduced into a novel area.