Native parasitic nest fly impacts reproductive success of an island‐endemic host

Genetic diversity and geographic distribution of parasitic flies of the Philornis torquans complex in Argentina

Philornis Meinert 1890 (Diptera: Muscidae) is a genus of flies that parasitize birds in the Neotropical region. The characteristics of the host-parasite interactions and its consequences may depend on the Philornis species involved, and thus precise identification of these parasites is crucial for the interpretation of ecological and epidemiological studies. However, morphological identification of Argentine Philornis species is elusive while molecular evidence points towards the existence of a complex of cryptic species or lineages undergoing a speciation process, which were named the 'Philornis torquans complex'. Herein the authors extended the current knowledge on the systematics and biogeography of parasitic Philornis flies from Argentina, analysing samples collected in several ecoregions, including the Atlantic Forest, Iberá Wetlands, Open Fields and Grasslands, Espinal, Pampa, Dry Chaco, Humid Chaco, Delta and Paraná River Islands, Monte of Plains and Plateaus. The results of the present study strengthen the evidence on previously described Philornis genotypes using four genetic markers (ITS2, COI, ND6, 12S rRNA). The authors report new patterns of occurrence and describe the presence of a novel genotype of subcutaneous Philornis. In addition, the present study unveils ecological niche differences among genotypes of the Philornis torquans complex in southern South America.

Survey of Philornis (Diptera: Muscidae) larvae in adult birds from central Argentina

The majority of known Philornis species (Diptera: Muscidae) cause subcutaneous myiasis in Neotropical altricial and semi-altricial nestlings. Generating information about these parasites is of relevance as they are a threat for the conservation of some wild bird species and also because they are an excellent model to study the ecology of host-parasite interactions. Although there are records of this parasitism in adult birds, the parasitic larvae are primarily associated with nestlings. However, systematic surveys including active search for larvae in older birds have been very scarce. Here we present results from a survey conducted along 6 years and encompassing a sample of 3029 subadult and adult birds in Santa Fe province, Argentina, where broods are frequently parasitised by the Philornis torquans complex. We found only one dipteran larva parasitising a greater thornbird. This larva was morphologically compatible with Philornis. Given the extremely low estimated prevalence (1/3029 = 0.03%), we conclude that the presence of larvae in subadult and adult birds is an extremely rare event in the studied bird community and that the species belonging to the P. torquans complex present in central Argentina are almost exclusively parasites of nestlings.

Is the grass always greener on the other side? Weak relationships between vegetation cover and parasitic fly infestations

Understanding parasite-host ecology is increasingly important for conservation efforts in a changing world. Parasitic nest flies in the genus Philornis (Diptera: Muscidae) have been implicated in the decline of endemic island species and are also known to negatively impact breeding success of the critically endangered Ridgway's hawk (B. ridgwayi) on the island of Hispaniola. Despite the importance of these effects on hosts, and extensive research of Philornis downsi in the Galápagos, the ecology of most species of philornid nest flies is poorly understood. We examined biotic factors related to Philornis pici infestations of nestling Ridgway's hawks in the Dominican Republic, where both fly and hawk are native. We found grass-cover was negatively associated with P. pici infestations, while coverage and height of other vegetation classes (tree, shrub, herbaceous, and bare ground) had no association, which is interesting considering recent landscape-level changes to Ridgway's hawk habitat. Anthropogenic activities in Los Haitises National Park, the last strong-hold of Ridgway's hawk, have shifted the landscape from primary forest to a fragmented secondary forest with smallholder or subsistence farms and grassy patches. New information on the ecology of nest flies in their native habitat can inform conservation efforts and allow us to make recommendations for future research.

Environmental variables determining the distribution of an avian parasite: the case of the Philornis torquans complex in South America

Philornis flies are the major cause of myiasis in nestlings of Neotropical birds, being of major concern in geographically-restricted and endangered bird species. Despite its relevance for the conservation of birds, there is little information about the environmental dimensions determining Philornis spp. geographical range. By using maximum entropy, we identified for the first time the macro-environmental variables constraining the abiotic niche of the P. torquans complex in South America, and provided a model map of its potential distribution based on environmental suitability. We identified the minimum temperature of the coldest month as the most relevant variable, associated with the largest decrease in habitat suitability in Brazil and northern South America. Furthermore, the mean temperature of the warmest quarter limited suitability mostly along with the Andean range. In addition, humidity and moisture are influential factors in most of Argentina, northern Chile, and coastal Peru. The geographical projection suggests that environments in most of central-eastern Argentina, and in a broad area in central Chile, are suitable for the presence of the P. torquans complex. Besides providing information about the ecology of Philornis spp., this study represents a tool for bird conservation and a reference for future work on the distribution of this genus.

Sub-lethal effects of permethrin exposure on a passerine: implications for managing ectoparasites in wild bird nests

Permethrin is increasingly used for parasite control in bird nests, including nests of threatened passerines. We present the first formal evaluation of the effects of continued permethrin exposure on the reproductive success and liver function of a passerine, the zebra finch (Taeniopygia guttata), for two generations. We experimentally treated all nest material with a 1% permethrin solution or a water control and provided the material to breeding finches for nest building. The success of two consecutive clutches produced by the parental generation and one clutch produced by first-generation birds were tracked. Finches in the first generation were able to reproduce and fledge offspring after permethrin exposure, ruling out infertility. Permethrin treatment had no statistically significant effect on the number of eggs laid, number of days from clutch initiation to hatching, egg hatch rate, fledgling mass or nestling sex ratio in either generation. However, treating nest material with permethrin significantly increased the number of hatchlings in the first generation and decreased fledgling success in the second generation. Body mass for hatchlings exposed to permethrin was lower than for control hatchlings in both generations, but only statistically significant for the second generation. For both generations, an interaction between permethrin treatment and age significantly affected nestling growth. Permethrin treatment had no effect on liver function for any generation. Permethrin was detected inside 6 of 21 exposed, non-embryonated eggs (28.5% incidence; range: 693-4781 ng of permethrin per gram of dry egg mass). Overall, results from exposing adults, eggs and nestlings across generations to permethrin-treated nest material suggest negative effects on finch breeding success, but not on liver function. For threatened bird conservation, the judicious application of this insecticide to control parasites in nests can result in lower nestling mortality compared to when no treatment is applied. Thus, permethrin treatment benefits may outweigh its sub-lethal effects.

More than just nestlings: incidence of subcutaneous Philornis (Diptera: Muscidae) nest flies in adult birds

Philornis flies Meinert (Diptera: Muscidae) have been documented parasitizing over 250 bird species, some of which are endemic species threatened with extinction. Philornis parasitism is hypothesized to affect nestlings disproportionately more than adult birds because limited mobility and exposed skin of nestlings increase their vulnerability to parasitism. We used a comprehensive literature review and our recent fieldwork in the Dominican Republic, Puerto Rico, and Grenada to challenge the idea that parasitism by subcutaneous Philornis species is a phenomenon primarily found in nestlings, a fact that has not been quantified to date. Of the 265 reviewed publications, 125 (49%) reported incidences of parasitism by subcutaneous Philornis, but only 12 included the sampling of adult breeding birds. Nine of these publications (75%) reported Philornis parasitism in adults of ten bird species. During fieldwork in the Dominican Republic, Puerto Rico, and Grenada, we documented 14 instances of parasitism of adult birds of seven avian species. From literature review and fieldwork, adults of at least fifteen bird species across 12 families and four orders of birds were parasitized by at least five Philornis species. In both the published literature and fieldwork, incidences of parasitism of adult birds occurred predominantly in females and was frequently associated with incubation. Although our findings indicate that Philornis parasitism of adult birds is more common than widely presumed, parasite prevalence is still greater in nestlings. In the future, we recommend surveys of adult birds to better understand host-Philornis relationships across life stages. This information may be essential for the development of effective control measures of Philornis to ensure the long-term protection of bird species of conservation concern.