Establishment of Parasitoids of the Lily Leaf Beetle (Coleoptera: Chrysomelidae) in North America.

Three larval parasitoids were imported from Europe to control the lily leaf beetle, Lilioceris lilii Scopoli (Coleoptera: Chrysomelidae), an accidentally introduced herbivore of native and cultivated lilies in North America. Tetrastichus setifer Thomson (Hymenoptera: Eulophidae) was introduced in Massachusetts in 1999, and was found to be established there in 2002. Subsequent releases of T. setifer were made and two additional parasitoids, Lemophagus errabundus Szepligeti (Hymenoptera: Ichneumonidae) and Diaparsis jucunda (Holmgren) (Hymenoptera: Ichneumonidae), were introduced. The establishment and distribution of the three parasitoids was evaluated through 2016. Tetrastichus setifer is now established in Massachusetts, Rhode Island, New Hampshire, Maine, Connecticut, and Ontario, Canada. Lemophagus errabundus is established in Massachusetts and Rhode Island, and D. jucunda is established in Massachusetts, Rhode Island, Connecticut, and Maine. All three parasitoids have spread at least 10 km from release sites. The establishment of T. setifer is associated with a substantial reduction of L. lilii. In time it is likely that the parasitoids will spread throughout the North American range of L. lilii. This process can be accelerated to protect ornamental and native lilies by collecting and redistributing parasitoids to new infestations of L. lilii.

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.

Spruce budworm impact, abundance and parasitism rate in a patchy landscape.

The hypothesis that vegetational diversity may lessen the impact of forest insect pests by favoring natural enemies is appealing to those who seek ecologically sound solutions to pest problems. We investigated the effect of forest diversity on the impact of the spruce budworm Choristoneurafumiferana following the last outbreak, as well as the budworm's current abundance and parasitism rate, in the boreal forest of northwestern Québec. Mortality of balsam fir caused by the budworm was greater in extensive conifer stands than either in "habitat islands" of fir surrounded by deciduous forest or on true islands in the middle of a lake. Adult spruce budworm abundance, assessed by pheromone traps, did not differ significantly between the three types of sites. Larval and pupal parasitism rates were examined by transferring cohorts of laboratory-reared larvae and pupae to trees in the three site types and later collecting and rearing them. The tachinid Actiainterrupta, a parasitoid of fifth and sixth instar larvae, as well as the ichneumonid pupal parasitoids Itoplectesconquisitor, Ephialtesontario and Phaeogenesmaculicornis, caused higher mortality in the habitat islands than on true islands or in extensive stands. Exochusnigripalpistectulum, an ichneumonid that attacks the larvae and emerges from the pupae, caused greater mortality in the extensive stands of conifers.

Comparative Population Dynamics of Two Goldenrod Aphids: Spatial Patterns and Temporal Constancy.

Two aphid species, Uroleucon nigrotuberculatum and U. caligatum, that feed on the goldenrod Solidago altissima, are similar in life histories and feeding habits, but differ markedly in their spatial distribution and temporal variability. In this study, U. caligatum typically occurred in small colonies scattered throughout goldenrod fields, and its numbers remained relatively constant through time, whereas U. nigrotuberculatum occurred in dense colonies and exhibited greater fluctuations in population size. The aggregated spatial pattern of U. nigrotuberculatum resulted from both active aggregation of alates and lack of dispersal by apterae and nymphs. Field experiments in which colony size was held constant revealed that U. nigrotuberculatum enjoyed no clear reproductive advantage that might explain its greater tendency to outbreak. In addition, U. nigrotubercultatum was more susceptible to generalist predators (such as cantharid beetles, mirid bugs, and mites) than U. Caligatum. Aphid dispersion was then manipulated in the field to determine how the different spatial patterns of the two species influenced reproduction and mortality, and hence the relative tendencies of their populations to irrupt. Feeding in large colonies provided no reproductive advantage to either species. Aggregation did, however, enhance aphid survivorship when generalist predators were the main mortality agents. The advantage was reversed later in the season when the aphids' fungal pathogen was present; aggregation then led to a decrease in survivorship. Thus, aggregation allowed a numerical escape from generalist predators but also promoted fungal epidemics, so that the temporal variability in U. nigrotuberculatum populations was largely a consequence of its spatial distribution.