The genus Philornis (Diptera: Muscidae) comprises Neotropical parasitic flies that parasitize bird nestlings while in their larval stage. The ecology of most species of these parasitic flies is largely unknown. Here, we contribute with data that shed some light on the environmental factors that are associated with variations in parasitism intensity of Philornis torquans, and examine whether increased intensity is followed by greater probability of mortality or reduced nestling growth. Intensive examination of nestlings of the bird community present in a 30 ha area was carried out weekly along two breeding seasons in Santa Fe, Argentina. Some nestlings of the most frequently parasitized bird species were followed twice a week, from hatching to fledging, to assess the impact of the parasites. High average maximum temperature and increased rainfall were significantly positively correlated with mean Philornis intensity. In turn, heavily parasitized nestlings were more likely to die: 10 larvae doubled the chances of mortality, and growth was affected in those that survived. The greater precipitation and warmer weather predicted for some areas of South America pose a potential impact on nestlings via this parasitism, and consequently on the population dynamics of native birds.

The study of myiasis is important because they may cause problems to the livestock industry, public health, or wildlife conservation. The ecology of parasitic dipterans that cause myiasis is singular, as they actively seek their hosts over relatively long distances. However, studies that address the determinants of myiasis dynamics are very scarce. The genus Philornis include species that may be excellent models to study myiasis ecology, as they exclusively parasitize bird nestlings, which stay in their nests until they are fully fledged, and larvae remain at the point of entry until the parasitic stage is over, thus allowing the collection of sequential individual-level infection data from virtually all the hosts present at a particular area. Here we offer a stratified multi-level analysis of longitudinal data of Philornis torquans parasitism in replicated forest bird communities of central Argentina. Using Generalized Linear Models and Generalized Linear Mixed Models and an information theory approach for model selection, we conducted four groups of analyses, each with a different study unit, the individual, the brood, the community at a given week, and the community at a given year. The response variable was larval abundance per nestling or mean abundance per nestling. At each level, models included the variables of interest of that particular level, and also potential confounders and effect modifiers of higher levels. We found associations of large magnitude at all levels, but only few variables truly governed the dynamics of this parasite. At the individual level, the infection was determined by the species and the age of the host. The main driver of parasite abundance at the microhabitat level was the average height of the forest, and at the community level, the density of hosts and prior rainfall. This multi-level approach contributed to a better understanding of the ecology of myiasis.

Philornis Meinert, 1890 (Diptera: Muscidae) is a genus of Neotropical dipterans that parasitise birds. The currently used external morphological characters to distinguish between species within this genus present some limitations. We used the second internal transcribed spacer region (ITS2) of the rRNA gene as a molecular marker to differentiate adult specimens of Philornis identified morphologically as Philornis torquans and Philornis seguyi from different localities. Specimens identified as P. seguyi from Magdalena (Buenos Aires Province) showed an ITS2 sequence different from that for P. torquans, whereas all other specimens of P. seguyi had sequences identical to those for P. torquans. These findings do not necessarily confirm that specimens from Magdalena indeed belong to P. seguyi, nor that P. seguyi is a valid species. Instead, they alert us about the potential for species misidentification when using morphological characters alone. The use of molecular approaches to aid the identification of Philornis spp. will shed light on the systematics of this group. P. torquans is reported for the first time in Mendoza Province and Uruguay.

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The tropical fowl mite, Ornithonyssus bursa, is a common avian parasite found on diverse bird species worldwide. In the Neotropical region, O. bursa is present in wild birds, but it may also infect poultry and bite humans. Little is known about the ecology and epidemiology of this parasite. We conducted a thorough longitudinal study in passerine assemblages from central Argentina, gathering data from six reproductive seasons, with the aim of identifying factors that have a role in driving the occurrence and distribution of O. bursa in its natural hosts. We focused on the brood and microhabitat levels, accounting for potential confounders of higher levels. The results hereby presented contribute to our knowledge on the eco-epidemiology of O. bursa in natural hosts of the Neotropical region. Among the many variables assessed, nest material and host species appeared to be the most important correlates of O. bursa prevalence. Nonetheless, supplementary analyses showed that host species is a stronger predictor than nest material. Moreover, mite burden (parasite intensity) was found to depend on host species, but not on nest material. The association with species depended on nestling age, suggesting that resistance builds up as the nestling develop, but at a different pace depending on the bird species. Brood size was inversely correlated with intensity of parasitism, suggesting a dilution of the parasite burden on each nestling.

The life cycle of the avian parasitic fliesPhilornisMeinert (Diptera: Muscidae) is poorly known, limiting the understanding of the ecology of these flies, including interactions with their hosts. We provide data on length and survival of pupal and adult stages and the duration of the pre-oviposition period ofPhilornis torquansNielsen. Specimens were collected at larval and pupal stages from infested broods. The pupal stage lasted on average 10.5 days and adults lived up to 100 days in the laboratory. At least 90.2% of larvae pupated and 85.7% of the latter emerged as adults. For individuals collected as larvae, pupal mortality was 3.5 times higher than for those collected as pupae. Females laid from 1–8 clutches in their lifetime and deposited, on average, 41 eggs per female (range: 1–148). Females collected as pupae were larger and had shorter pre-oviposition periods and lifespans than females collected as larvae, but there were no differences in the total eggs laid by these females. This is the first information on reproductive parameters of a subcutaneous species ofPhilornis, and forms the basis for studies on conditions required for reproduction of this species in captivity.

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