A total of 733 bird nests, representing 55 species from 23 habitats, was examined. Forty-nine percent of the nests of 39 bird species were infested with 16 species of Protocalliphora. Infestation of bird nests by Protocalliphora is believed to be related to a number of factors, which are discussed. Loosely constructed nests, nests heavily saturated with feces, and nests occupied early in the season had low rates of infestation. Nests of colonial birds were more frequently infested than those of solitary birds. Nests of some birds were rarely or never infested. Sixteen species of Protocalliphora are differentiated and their host and habitat preferences discussed. Some species appeared to be either host or habitat specific, but infestation by many species appeared to be controlled by a combination of host and habitat specificity. Aspects of the life history of the species of Protocalliphora are discussed. An aggregation of adult Protocalliphora at a Bank Swallow colony was noted. Mortality in nestling birds from the feeding of Protocalliphora was rarely observed, except in nests of Yellow-headed Blackbirds and Cliff Swallows, where other factors may have contributed to high mortality.

The ecology of Protocalliphora parasitism was studied for a two-year period in two species of cavity nesting passerine birds breeding in southwestern Quebec, the eastern bluebird (Sialia sialis Linnaeus) and the tree swallow (Tachycineta bicolor Vieillot). Both species occupied next boxes in open field habitats. Nests were parasitized primarily by Protocalliphora sialia Shannon and Dobroscky. / The relationship between the number of Protocalliphora larvae per nest and selected nesting variables was examine for the two species. The variables included hatching date of the host young, nest material volume, number of fledglings, and percent canopy cover above the nest box. In bluebirds, the number of larvae per nest was significantly correlated with nest material volume in 1989 and number of fledglings in 1990. In tree swallows, the number of larvae per nest was significantly correlated with hatching date and number of fledglings in 1989. / Information on reproduction in Protocalliphora was obtained. Gravid flies were captured in active nests up to the last end of the second week of the nestling period. P. sialia was determined to be at last bivoltine through mark, release, and recapture studies. It was determine that nulliparous P. sialia can complete egg development within 9 or 10 days after eclosion. The practicality of a new Protocalliphora trapping technique and a mark, release, and recapture technique was demonstrated. (Abstract shortened by UMI.)

No description available.

L’intensification des pratiques agricoles a été identifiée comme cause majeure du déclin de la biodiversité. Plusieurs études ont documenté l’impact de la fragmentation du paysage naturel et de l’agriculture intensive sur la diversité des espèces, mais très peu ont quantifié le lien entre la structure du paysage et les interactions trophiques, ainsi que les mécanismes d’adaptation des organismes. J’ai étudié un modèle biologique à trois niveaux trophiques composé d’un oiseau hôte, l’hirondelle bicolore Tachycineta bicolor, de mouches ectoparasites du genre Protocalliphora et de guêpes parasitoïdes du genre Nasonia, au travers d’un gradient d’intensification agricole dans le sud du Québec. Le premier objectif était de déterminer l’abondance des espèces de mouches ectoparasites et de leurs guêpes parasitoïdes qui colonisent les nids d’hirondelles dans la zone d’étude. La prévalence de nids infectés par Protocalliphora spp. était de 70,8% en 2008 et 34,6% en 2009. Le pourcentage de nids comprenant des pupes de Protocalliphora parasitées par Nasonia spp. était de 85,3% en 2008 et 67,2% en 2009. Trois espèces de Protocalliphora ont été observées (P. sialia, P. bennetti et P. metallica) ainsi que deux espèces de Nasonia (N. vitripennis et N. giraulti). Il s’agit d’une première mention de P. bennetti et de N. giraulti dans la province de Québec. Mon deuxième objectif était d’évaluer l’impact de l’intensification agricole et de la structure du paysage sur les relations tri-trophiques entre les organismes à l’étude. Les résultats révèlent que les réponses à la structure du paysage de l’hirondelle, de l’ectoparasite et de l’hyperparasite dépendantent de l’échelle spatiale. L’échelle spatiale fonctionnelle à laquelle les espèces répondent le plus varie selon le paramètre du paysage modélisé. Les analyses démontrent que l’intensification des pratiques agricoles entraîne une diminution des populations d’oiseaux, d’ectoparasites et d’hyperparasites. De plus, les populations de Protocalliphora et de Nasonia sont menacées en paysage intensif puisque la dégradation du paysage associée à l’intensification des pratiques agricoles agit directement sur leurs populations et indirectement sur les populations de leurs hôtes. Mon troisième objectif était de caractériser les mécanismes comportementaux permettant aux guêpes de composer avec la variabilité de la structure du paysage et de la qualité des hôtes. Nos résultats révèlent que les femelles Nasonia ajustent la taille de leur ponte en fonction de la taille de la pupe hôte et de l’incidence d’hyperparasitisme. Le seul facteur ayant une influence déterminante sur le ratio sexuel est la proportion de paysage dédié à l’agriculture intensive. Aucune relation n’a été observée entre la structure du paysage et la taille des filles et des fils produits par les femelles Nasonia fondatrices. Ce phénomène est attribué aux comportements d’ajustement de la taille de la ponte et du ratio sexuel. En ajustant ces derniers, minimisant ainsi la compétition entre les membres de leur progéniture, les femelles fondatrices sont capables de maximiser la relation entre la disponibilité des ressources et la valeur sélective de leur progéniture. En conclusion, ce travail souligne l’importance de considérer le contexte spatial des interactions trophiques, puisqu’elles influencent la biodiversité locale et le fonctionnement de l’écosystème. / Landscape fragmentation and homogenization are considered to be the main causes of the worldwide decline in biological diversity. The degradation of habitat quality is mainly caused by the expansion and intensification of human land-use activities, primarily for agricultural purposes. Many studies documented the impact of landscape fragmentation and agricultural intensification on the overall fitness of animals across various taxa, but few works have studied this phenomenon in relation to trophic interactions. Here, we investigated the effects of landscape structure on the tri-trophic interactions between a bird host (the Tree Swallow Tachycineta bicolor (Vieillot)), its blowfly ectoparasites (Protocalliphora Hough), and their parasitoid wasps (Nasonia Walker) along a gradient of agricultural intensification covering 10, 200 km2 in southern Québec, Canada. The first objective was to describe the assemblages of Protocalliphora and Nasonia species found in Tree Swallow nests within our system. The prevalence of nest infestation by Protocalliphora was of 70.8% in 2008 and 34.6% in 2009. The percentage of nests containing Protocalliphora pupae parasitized by Nasonia spp. was of 85.3 % in 2008 and 67.2% in 2009. Three species of Protocalliphora were collected (P. sialia, P. bennetti and P. metallica) and two species of Nasonia (N. vitripennis and N. giraulti). Secondly, I evaluated the impact of landscape structure and agricultural intensification on the number of Tree Swallow fledglings, number of Protocalliphora per nest and the level of hyperparasitism by Nasonia. Our results revealed that organisms from different trophic levels perceived the landscape at distinctive spatial extents. This perception, however, differed based on whether the proportions of intensive or extensive culture in the landscape were considered. Furthermore, the number of Tree Swallow fledglings, the abundance of P. sialia and the level of hyperparasitism by N. vitripennis all decreased with an increase in the proportion of intensive culture in the landscape. Protocalliphora and Nasonia were more susceptible to extinction within highly intensive landscapes as they are confronted with both the direct effect of habitat degradation on their populations and the indirect effect of habitat degradation on their host populations. The last objective was to investigate how parasitoid wasps respond to environmental variability. We showed that the size of the P. sialia pupae hosts decreased in more intensive landscapes. Wasps clutch size was shown to increase within increasing host size and the sex ratio of offspring produced by N. vitripennis became more male biased as the proportion of intensive culture increased in the landscape. In addition, both female and male size was influenced by resource availability (size of host and number of competitors). Our data indicate that by producing smaller male biased clutches in the smaller hosts within intensive landscapes, females were able to respond to poor environments and maximize the size of their offspring. To conclude, this work highlights the importance of considering the landscape context of trophic interactions, as these interactions dictate local biodiversity and ecosystem function.

No description available.