Manipulative field experiments assessing the importance of interspecific competition on the dynamics of parasitoid populations and the impact of multiple parasitoids on host populations are virtually absent from the ecological literature. We report findings from such experiments assessing competitive interactions among three species of parasitoids (Hymenoptera: Aphelinidae) of the silverleaf whitefly Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae), a pestiferous species of worldwide importance. The parasitoids used in the study (Encarsia pergandiella Howard, Eretmocerus mundus Mercet, and Encarsia formosa Gahan) encompass the range of life histories found within Aphelinidae, and they exhibit a high degree of niche overlap. The objectives of our studies were (1) to investigate the occurrence of interspecific competition among the whitefly parasitoids, (2) to quantify shifts in resource utilization patterns as influenced by experimental manipulations of the parasitoid assemblage, and (3) to assess the impact of interspecific competition on the ability of the parasitoids to suppress their host populations.Field cages enclosing cotton plants were inoculated with whitefly by releasing adults at either a high or a low rate followed by releases of all possible combinations of the parasitoid species (including a no-parasitoid release control). The treatments were replicated three and four times each in 1996 and 1997. The presence of interspecific competitors reduced population growth rates of E. formosa and E. pergandiella but not the population growth rate of E. mundus. The spatial distribution of parasitism by E. pergandiella along the vertical axis of cotton plants differed in the multiple species treatments compared to the single species treatments. Changes in parasitoid activity in the presence of competitors may reduce potentially adverse effects of competition and promote species coexistence. Only releases of E. formosa together with E. pergandiella resulted in lower levels of host mortality than would be expected based on observed mortality by individual species. Our results demonstrate competitive interactions among three parasitoids of B. argentifolii under field manipulations but indicate that, in most cases, competitive interactions among parasitoids do not affect host population suppression.

Manipulative field experiments assessing the importance of interspecific competition on the dynamics of parasitoid populations and the impact of multiple parasitoids on host populations are virtually absent from the ecological literature. We report findings from such experiments assessing competitive interactions among three species of parasitoids (Hymenoptera: Aphelinidae) of the silverleaf whitefly Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae), a pestiferous species of worldwide importance. The parasitoids used in the study (Encarsia pergandiella Howard, Eretmocerus mundus Mercet, and Encarsia formosa Gahan) encompass the range of life histories found within Aphelinidae, and they exhibit a high degree of niche overlap. The objectives of our studies were (1) to investigate the occurrence of interspecific competition among the whitefly parasitoids, (2) to quantify shifts in resource utilization patterns as influenced by experimental manipulations of the parasitoid assemblage, and (3) to assess the impact of interspecific competition on the ability of the parasitoids to suppress their host populations. Field cages enclosing cotton plants were inoculated with whitefly by releasing adults at either a high or a low rate followed by releases of all possible combinations of the parasitoid species (including a no‐parasitoid release control). The treatments were replicated three and four times each in 1996 and 1997. The presence of interspecific competitors reduced population growth rates of E. formosa and E. pergandiella but not the population growth rate of E. mundus. The spatial distribution of parasitism by E. pergandiella along the vertical axis of cotton plants differed in the multiple species treatments compared to the single species treatments. Changes in parasitoid activity in the presence of competitors may reduce potentially adverse effects of competition and promote species coexistence. Only releases of E. formosa together with E. pergandiella resulted in lower levels of host mortality than would be expected based on observed mortality by individual species. Our results demonstrate competitive interactions among three parasitoids of B. argentifolii under field manipulations but indicate that, in most cases, competitive interactions among parasitoids do not affect host population suppression.

The pheromone components of many cerambycid beetles appear to be broadly shared among related species, including species native to different regions of the world. This apparent conservation of pheromone structures within the family suggests that field trials of common pheromone components could be used as a means of attracting multiple species, which then could be targeted for full identification of their pheromones. Here, we describe the results of such field trials that were conducted in nine states in the northeastern, midwestern, southern, and western United States. Traps captured 12,742 cerambycid beetles of 153 species and subspecies. Species attracted in significant numbers to a particular treatment (some in multiple regions) included 19 species in the subfamily Cerambycinae, 15 species in the Lamiinae, one species in the Prioninae, and two species in the Spondylidinae. Pheromones or likely pheromones for many of these species, such as 3-hydroxyhexan-2-one and syn- and anti-2,3-hexanediols for cerambycine species, and fuscumol and/or fuscumol acetate for lamiine species, had already been identified. New information about attractants (in most cases likely pheromone components) was found for five cerambycine species (Ancylocera bicolor [Olivier], Elaphidion mucronatum [Say], Knulliana cincta cincta [Drury], Phymatodes aeneus LeConte, and Rusticoclytus annosus emotus [Brown]), and five lamiine species (Ecyrus dasycerus dasycerus [Say], Lepturges symmetricus [Haldeman], Sternidius misellus [LeConte], Styloleptus biustus biustus [LeConte], and Urgleptes signatus [LeConte]). Consistent attraction of some species to the same compounds in independent bioassays demonstrated the utility and reliability of pheromone-based methods for sampling cerambycid populations across broad spatial scales.

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