Sex interacts with age-dependent change in the abundance of lice-infesting Amur Falcons (Falco amurensis).

Sex-biassed and age-biassed parasite infections are common in nature, including ectoparasites-vertebrate host systems. We investigated the effect of Amur Falcons' sex, age and body size on the abundance of their lice at a migratory stopover site, where the falcons' habitat use and behaviour are more homogeneous across sex and age categories than during the breeding season. We sampled Amur Falcons in Nagaland, India at major roosting sites in 2016. We applied generalized linear models (with negative binomial distribution and log-link) to model the abundance of their two most numerous lice (Colpocephalum subzerafae and Degeeriella rufa) using the host age category (juvenile or adult) and wing length, both in interaction with sex, as explanatory variables. The abundance of C. subzerafae was only affected by host age, being nearly four times higher on juveniles than on adults. Juveniles were also more infested with D. rufa than the adults. Additionally, the abundance of the latter species was lower on adult male Falcons as compared to adult females. A juvenile bias in ectoparasite infestations is common in nature, probably due to juveniles being immunologically naïve, more resource-limited and may be inexperienced in body maintenance behaviours like preening and grooming. On the other hand, female-biassed infestations are much rarer than male-biassed infestations. We briefly discuss the possible causes of female-biassed infestations on Amur Falcons reported here, and in the closely related Red-footed Falcon and Lesser Kestrel as reported in the literature.

Sex-dependent changes in the louse abundance of red-footed falcons (Falco vespertinus).

Permanent ectoparasites live in stable environments; thus, their population dynamics are mostly adapted to changes in the host life cycle. We aimed to investigate how static and dynamic traits of red-footed falcons interplay with the dynamics of their louse subpopulations during breeding and how they affect the colonisation of new hosts by lice. We sampled red-footed falcon (Falco vespertinus) nestlings (two breeding seasons) and adults (one breeding season) in southern Hungary. The mean abundance of Colpocephalum subzerafae and Degeeriella rufa lice on the nestlings was modelled with generalized linear mixed models using clutch size and host sex in interaction with wing length. For adults, we used wing length and the number of days after laying the first egg, both in interaction with sex. D. rufa abundances increased with the nestlings' wing length. In one year, this trend was steeper on females. In adult birds, both louse species exhibited higher abundances on females at the beginning, but it decreased subsequently through the breeding season. Contrarily, abundances were constantly low on adult males. Apparently, D. rufa postpones transmission until nestlings develop juvenile plumage and choose the more feathered individual among siblings. The sexual difference in the observed abundance could either be caused by the different plumage, or by the females' preference for less parasitized males. Moreover, females likely have more time to preen during the incubation period, lowering their louse burdens. Thus, sex-biased infestation levels likely arise due to parasite preferences in the nestlings and host behavioural processes in the adult falcons.

Tachinid Fly Parasitism and Phenology of the Neotropical Red-Shouldered Stink Bug, Thyanta perditor (F.) (Heteroptera: Pentatomidae), on the Wild Host Plant, Bidens pilosa L. (Asteraceae).

Field and laboratory studies were conducted with the Neotropical red-shouldered stink bug Thyanta perditor (F.) (Heteroptera: Pentatomidae) aiming to evaluate parasitism incidence on adults by tachinid flies (Diptera: Tachinidae), which were raised in the laboratory for identification. Egg deposition by flies on adult body surface was mapped. In addition, nymph and adult incidence on the wild host plant black jack, Bidens pilosa L. (Asteraceae), during the vegetative and the reproductive periods of plant development was studied. Seven species of tachinid flies were obtained: Euthera barbiellini Bezzi (73% of the total) and Trichopoda cf. pictipennis Bigot (16.7%) were the most abundant; the remaining five species, Gymnoclytia sp.; Phasia sp.; Strongygaster sp.; Cylindromyia cf. dorsalis (Wiedemann); and Ectophasiopsis ypiranga Dios & Nihei added 10.3% of the total. Tachinid flies parasitism on T. perditor adults was significantly greater on the dorsal compared to the ventral body surface. On the dorsal surface, the pronotum was significantly preferred and the wings the least preferred site. No differences were observed on the number of tachinid fly eggs deposited on wings, considering the "under" and "above" sites. Results indicated a significantly greater number of nymphs on mature compared to immature seeds. Adults significantly preferred immature compared to mature seeds; both were less abundant on leaves/stems and inflorescences.

The role of parasite dispersal in shaping a host-parasite system at multiple evolutionary scales.

Parasite dispersal can shape host-parasite interactions at both deep and shallow timescales. One approach to understanding the effects of dispersal is to study parasite lineages that differ in dispersal capability but are from the same group of hosts. In this study, we compared phylogenetic and population genetic patterns of wing and body lice from ground-doves. Wing lice are more capable of dispersal than body lice. We sequenced full genomes of individual lice for multiple representatives of several wing and body louse species. From these data, we assembled genes for phylogenetic analysis and called SNPs for population genetic analysis. At the phylogenetic level, body lice showed more codivergence with their hosts than did wing lice. However, both wing and body lice exhibited some phylogenetic congruence with their hosts. Within species, body lice showed more population genetic structure than wing lice, although both types of lice showed some structure according to biogeography. Body lice also had significantly lower heterozygosity than wing lice, suggesting more inbreeding. Our results demonstrate that dispersal can shape a host-parasite system across evolutionary time, but also that other factors (e.g., host association and biogeography) can have varying degrees of influence on different groups of parasites and at different evolutionary scales.

Comparative cophylogenetics of Australian phabine pigeons and doves (Aves: Columbidae) and their feather lice (Insecta: Phthiraptera).

Host-parasite coevolutionary histories can differ among multiple groups of parasites associated with the same group of hosts. For example, parasitic wing and body lice (Insecta: Phthiraptera) of New World pigeons and doves (Aves: Columbidae) differ in their cophylogenetic patterns, with body lice exhibiting higher phylogenetic congruence with their hosts than wing lice. In this study, we focus on the wing and body lice of Australian phabine pigeons and doves to determine whether the patterns in New World pigeons and doves are consistent with those of pigeons and doves from other regions. Using molecular sequence data for most phabine species and their lice, we estimated phylogenetic trees for all three groups (pigeons and doves, wing lice and body lice), and compared the phabine (host) tree with both parasite trees using multiple cophylogenetic methods. We found a pattern opposite to that found for New World pigeons and doves, with Australian wing lice showing congruence with their hosts, and body lice exhibiting a lack of congruence. There are no documented records of hippoboscid flies associated with Australian phabines, thus these lice may lack the opportunity to disperse among host species by attaching to hippoboscid flies (phoresis), which could explain these patterns. However, additional sampling for flies is needed to confirm this hypothesis. Large differences in body size among phabine pigeons and doves may also help to explain the congruence of the wing lice with their hosts. It may be more difficult for wing lice than body lice to switch among hosts that vary more dramatically in size. The results from this study highlight how host-parasite coevolutionary histories can vary by region, and how local factors can shape the relationship.

The Strategy to Survive Primary Malaria Infection: An Experimental Study on Behavioural Changes in Parasitized Birds.

Avian malaria parasites (Haemosporida, Plasmodium) are of cosmopolitan distribution, and they have a significant impact on vertebrate host fitness. Experimental studies show that high parasitemia often develops during primary malaria infections. However, field studies only occasionally reveal high parasitemia in free-living birds sampled using the traditional methods of mist-netting or trapping, and light chronic infections predominate. The reason for this discrepancy between field observation and experimental data remains insufficiently understood. Since mist-netting is a passive capture method, two main parameters determine its success in sampling infected birds in wildlife, i. e. the presence of parasitized birds at a study site and their mobility. In other words, the trapping probability depends on the survival rate of birds and their locomotor activity during infection. Here we test (1) the mortality rate of wild birds infected with Plasmodium relictum (the lineage pSGS1), (2) the changes in their behaviour during presence of an aerial predator, and (3) the changes in their locomotor activity at the stage of high primary parasitemia.We show that some behavioural features which might affect a bird's survival during a predator attack (time of reaction, speed of flush flight and take off angle) did not change significantly during primary infection. However, the locomotor activity of infected birds was almost halved compared to control (non-infected) birds during the peak of parasitemia. We report (1) the markedly reduced mobility and (2) the 20% mortality rate caused by P. relictum and conclude that these factors are responsible for the underrepresentation of birds in mist nets and traps during the stage of high primary parasitemia in wildlife. This study indicates that the widespread parasite, P. relictum (pSGS1) influences the behaviour of birds during primary parasitemia. Experimental studies combined with field observations are needed to better understand the mechanisms of pathogenicity of avian malaria parasites and their influence on bird populations.

Ectoparasites may serve as vectors for the white-nose syndrome fungus.

BACKGROUND: Vertebrate ectoparasites frequently play a role in transmission of infectious agents. Pseudogymnoascus destructans is a psychrophilic fungus known to cause white-nose syndrome (WNS), an emerging infectious disease of bats. It is transmitted with direct contact between bats or with contaminated environment. The aim of this study was to examine wing mites from the family Spinturnicidae parasitizing hibernating bats for the presence of P. destructans propagules as another possible transmission route. METHODS: Wing mites collected from 33 bats at four hibernation sites in the Czech Republic were inspected for the presence and load of pathogen's DNA using quantitative PCR. Simultaneously, wing damage of inspected bats caused by WNS was quantified using ultraviolet light (UV) transillumination and the relationship between fungal load on wing mites and intensity of infection was subjected to correlation analysis. RESULTS: All samples of wing mites were positive for the presence of DNA of P. destructans, indicating a high probability of their role in the transmission of the pathogen's propagules between bats. CONCLUSIONS: Mechanical transport of adhesive P. destructans spores and mycelium fragments on the body of spinturnicid mites is highly feasible. The specialised lifestyle of mites, i.e., living on bat wing membranes, the sites most typically affected by fungal growth, enables pathogen transport. Moreover, P. destructans metabolic traits suggest an ability to grow and sporulate on a range of organic substrates, including insects, which supports the possibility of growth on bat ectoparasites, at least in periods when bats roost in cold environments and enter torpor. In addition to transport of fungal propagules, mites may facilitate entry of fungal hyphae into the epidermis through injuries caused by biting.

Anatomical location of Periglischrus iheringi(Acari: Spinturnicidae) associated with the great fruit-eating bat (Chiroptera: Phyllostomidae).

Spinturnicid mites are ectoparasites that infest the wings of bats, and species of the genus Periglischrus Kolenati, 1857 are associated exclusively with bats of the family Phyllostomidae. We tested the hypothesis that a long-term evolutionary association led P. iheringi to choose very specific wing locations to infest the great fruit-eating bats, Artibeus lituratus. Seven anatomical wing regions and the uropatagium from 140 bats were analyzed and a total of 78 parasites were collected. Periglischrus iheringi had a significant preference for the plagiopatagium and dactylopatgium major wing regions (i.e., large, proximal regions) and infestation was directly correlated to area (r=0.9744). However, other factors may also influence mite choice, such as higher and more stable temperature and humidity, vascularization and lower risk of displacement.

Climate-driven variation in the intensity of a host-symbiont animal interaction along a broad elevation gradient.

Gradients of environmental stress may affect biotic interactions in unpredictable ways responding to climate variation, depending on the abiotic stress tolerance of interacting partners. Here, we study the effect of local climate on the intensity of feather mites in six mountain passerines along a 1400 m elevational gradient characterized by shifting temperature and rainfall. Although obligatory symbionts of warm-blooded organisms are assumed to live in mild and homeothermic environments, those inhabiting external, non-blood-irrigated body portions of the host organism, such as feather mites, are expected to endure exposure to the direct influence of a fluctuating climate. As expected, feather mite intensity declined with elevation in all bird species, a pattern that was also found in cold-adapted passerines that have typical alpine habits. The elevation cline was mainly explained by a positive effect of the average temperature upon mite intensity in five of the six species studied. Precipitation explained less variance in mite intensity than average temperature, and showed a negative correlation in half of the studied species. We found no climate-driven migration of mites along the wings of birds, no replacement of mite species along elevation gradients and no association with available food resources for mites (estimated by the size of the uropygial gland). This study suggests that ectosymbionts of warm-blooded animals may be highly sensitive to climatic variation and become less abundant under stressful environmental conditions, providing empirical evidence of the decline of specialized biotic interactions among animal species at high elevations.

Thermo-orientation and the movement of feather-feeding lice on hosts.

Temperature variation on the host is known to influence ectoparasite distributions. Ectoparasites may also use temperature gradients between host regions when moving on the host; however, tests are rare. Feather-feeding wing lice (Phthiraptera: Ischnocera) spend the majority of their time on the flight feathers of their avian hosts where they insert their bodies between feather barbs to escape host preening. However, because wing lice feed on downy abdominal feathers, they must repeatedly migrate between the flight feathers and body regions of their hosts. We performed a series of experiments that tested thermo-orientation in wing lice and evaluated its potential use during louse migrations between host regions. We found that wing lice can rapidly and accurately locate nearby heat targets that approximate host temperatures (37 C), demonstrating a capacity for directed thermo-orientation. We next tested the preference of wing lice for temperatures found along migration routes between bird flight feathers and their body regions. Wing lice could distinguish between temperatures found within distinct bird regions, and lice that had recently fed preferred the cooler temperatures (32 C), similar to those within bird flight feathers where they typically reside. However, when starved for 18-20 hr, wing lice shifted their preferences toward temperatures typical of bird body regions where they feed (36 C), demonstrating an ability to use thermal cues when moving between bird regions. We discuss the use of thermal cues during louse migration and microhabitat selection, as well as other potential impacts of thermo-orientation on host-parasite interactions.

Flyway homogenisation or differentiation? Insights from the phylogeny of the sandpiper (Charadriiformes: Scolopacidae: Calidrinae) wing louse genus Lunaceps (Phthiraptera: Ischnocera).

The wing louse genus Lunaceps, is the most speciose chewing louse (Phthiraptera) genus inhabiting sandpipers (Charadriiformes: Calidrinae) and is known from almost all sandpiper species. The hosts follow specific flyways from the Arctic breeding grounds to wintering locations in the southern hemisphere, and often form large mixed-species flocks during migration and wintering. We estimated a phylogeny of Lunaceps based on three mitochondrial loci, supporting monophyly of the genus but revealing extensive paraphyly at the species level. We also evaluated the relative importance of flyway differentiation (same host species having different lice along different flyways) and flyway homogenisation (different host species having the same lice along the same flyway). We found that while the lice of smaller sandpipers and stints show some evidence of flyway homogenisation, those of larger sandpipers do not. No investigated host species migrating along more than one flyway showed any evidence of flyway differentiation. The host-parasite associations within Lunaceps are in no case monophyletic, rejecting strict cospeciation.

Different scales of spatial segregation of two species of feather mites on the wings of a passerine bird.

The "condition-specific competition hypothesis" proposes that coexistence of 2 species is possible when spatial or temporal variations in environmental conditions exist and each species responds differently to those conditions. The distribution of different species of feather mites on their hosts is known to be affected by intrinsic host factors such as structure of feathers and friction among feathers during flight, but there is also evidence that external factors such as humidity and temperature can affect mite distribution. Some feather mites have the capacity to move through the plumage rather rapidly, and within-host variation in intensity of sunlight could be one of the cues involved in these active displacements. We analyzed both the within- and between-feather spatial distribution of 2 mite species, Trouessartia bifurcata and Dolichodectes edwardsi , that coexist in flight feathers of the moustached warbler Acrocephalus melanopogon. A complex spatial segregation between the 2 species was observed at 3 spatial levels, i.e., "feather surfaces," "between feathers," and "within feathers." Despite certain overlapping distribution among feathers, T. bifurcata dominated proximal and medial regions on dorsal faces, while D. edwardsi preferred disto-ventral feather areas. An experiment to check the behavioral response of T. bifurcata to sunlight showed that mites responded to light exposure by approaching the feather bases and even leaving its dorsal face. Spatial heterogeneity across the 3 analyzed levels, together with response to light and other particular species adaptations, may have played a role in the coexistence and segregation of feather mites competing for space and food in passerine birds.

The evolution of host specificity in dove body lice.

OBJECTIVE: Conventional wisdom suggests that parasites evolve increased host specialization over time. Host specificity, which describes the number of host species parasitized, is one aspect of host specialization. Recent studies of vertebrate parasites indicate that highly host-specific parasite lineages are not, in fact, evolutionary dead ends; host generalists can evolve from host specialists. METHODS: Using phylogenetic reconstruction methods, we evaluate these patterns in the body lice (Insecta: Phthiraptera) of pigeons and doves, which are permanent ectoparasites that complete their entire life cycle on the body of the host. RESULTS: We find that species of body lice that parasitize more than one species of host (generalists) are invariably derived from lice parasitizing only one species of host (specialists). A previous study of the wing lice of pigeons and doves also found that generalists were derived from specialists, and that these changes were correlated with the presence of a potentially competing species of wing louse on the same host. For body lice we did not find such a correlation with competition. Instead, the evolution of host generalists in body lice was correlated with host ecology. When we compared body lice that parasitize terrestrial versus arboreal hosts, we found that the evolution of host generalists was associated with terrestrial hosts. In contrast, wing lice showed no correlation between the evolution of generalists and host ecology. CONCLUSION: The correlation in body lice suggests that dispersal between host species may occur via the ground. This, in turn, suggests that body lice may fall to the ground more often than wing lice. To test this hypothesis, we conducted an experiment to compare the rate at which body and wing lice are dislodged from the bodies of preening pigeons. Interestingly, our results showed that body lice are dislodged four times more often than wing lice. Therefore, species of terrestrial doves are far more likely to encounter body lice than wing lice on the ground.

A hitchhiker's guide to parasite transmission: The phoretic behaviour of feather lice.

Transmission to new hosts is a fundamental challenge for parasites. Some species meet this challenge by hitchhiking on other, more mobile parasite species, a behaviour known as phoresis. For example, feather-feeding lice that parasitise birds disperse to new hosts by hitchhiking on parasitic louse flies, which fly between individual birds. Oddly, however, some species of feather lice do not engage in phoresis. For example, although Rock Pigeon (Columba livia) "wing" lice (Columbicola columbae) frequently move to new hosts phoretically on louse flies (Pseudolynchia canariensis), Rock Pigeon "body" lice (Campanulotes compar) do not. This difference in phoretic behaviour is puzzling because the two species of lice have very similar life cycles and are equally dependent on transmission to new hosts. We conducted a series of experiments designed to compare the orientation, locomotion and attachment capabilities of these two species of lice, in relation to louse flies. We show that wing lice use fly activity as a cue in orientation and locomotion, whereas body lice do not. We also show that wing lice are more capable of remaining attached to active flies that are walking, grooming or flying. The superior phoretic ability of wing lice may be related to morphological adaptations for life on wing feathers, compared to body feathers.

Correlated evolution of host and parasite body size: tests of Harrison's rule using birds and lice.

Large-bodied species of hosts often harbor large-bodied parasites, a pattern known as Harrison's rule. Harrison's rule has been documented for a variety of animal parasites and herbivorous insects, yet the adaptive basis of the body-size correlation is poorly understood. We used phylogenetically independent methods to test for Harrison's rule across a large assemblage of bird lice (Insecta: Phthiraptera). The analysis revealed a significant relationship between louse and host size, despite considerable variation among taxa. We explored factors underlying this variation by testing Harrison's rule within two groups of feather-specialist lice that share hosts (pigeons and doves). The two groups, wing lice (Columbicola spp.) and body lice (Physconelloidinae spp.), have similar life histories, despite spending much of their time on different feather tracts. Wing lice showed strong support for Harrison's rule, whereas body lice showed no significant correlation with host size. Wing louse size was correlated with wing feather size, which was in turn correlated with overall host size. In contrast, body louse size showed no correlation with body feather size, which also was not correlated with overall host size. The reason why body lice did not fit Harrison's rule may be related to the fact that different species of body lice use different microhabitats within body feathers. More detailed measurements of body feathers may be needed to explore the precise relationship of body louse size to relevant components of feather size. Whatever the reason, Harrison's rule does not hold in body lice, possibly because selection on body size is mediated by community-level interactions between body lice.

Recapture of male and female dragonflies in relation to parasitism by mites, time of season, wing length and wing cell symmetry.

For aquatic mites parasitic on dragonflies, completion of their life cycle depends on their being returned to appropriate water bodies by their hosts, after completion of engorgement. We examined whether differences among hosts in timing of emergence or phenotypic attributes might affect their probability of return to an emergence pond, and hence success of mites. Parasitized males and females of the dragonfly Sympetrum obtrusum (Hagen) did not differ in overall recapture rates. Females that had wing cell symmetry and emerged early were more likely to be recaptured than females that emerged later or had wing cell asymmetry, but there were no consistent relations between these variables and parasitism by mites. No such relations between wing cell asymmetry, emergence date, and recapture likelihood were found for males. Using randomization tests, we found that mean intensities of Arrenurus planus (Marshall) mites at host emergence were the same for recaptured females and females not recaptured; however, males that were recaptured had lower mean intensities of mites at emergence than males not recaptured. Further, mature females carried more mites than mature males, and the latter had fewer mites than newlyemerged males not recaptured. Biases in detachment of engorging mites do not explain the differences in parasitism between mature males and females, nor the differences in mite numbers between mature males and newly emerged males that were not recaptured. Rather, heavily parasitized males appear to disperse or die and are not recaptured, which should have implications for dispersal of mites and fitness of male hosts.

Three new species of larval Charletonia Oudemans, 1910 (Acari: Prostigmata: Erythraeidae) and the first record of Charletonia krendowskyi (Feider, 1954) from Rhodes, Greece.

Three new species of larval Charletonia Oudemans, 1910 from Rhodes, Greece are described: C. dalegori from an undetermined orthopteran, C. glifadaensis from Oedipoda sp. (Orthoptera: Acrididae: Oedipodinae) and C. kaliksti from Aiolopus sp. (Orthoptera: Acrididae: Oedipodinae). C. krendowskyi is recorded for the first time from Greece. A key to the European species of larval Charletonia is provided.

Traumatic myiasis of geese in Hungary.

Five geese flocks were surveyed to gather data on the prevalence and clinical manifestation of traumatic myiasis and the fly species involved. Myiasis was recorded in all the flocks and the total number of infested geese was 26 (ca. 0.1% of the total numbers). The first cases were observed at the end of May, the last ones in August. Most birds (16/26) were infested in August. Each affected goose had only one lesion, which was located more frequently on the wings (14/26) than on any other body. In seven geese, Wohlfahrtia magnifica (Diptera: Sarcophagidae) was the only myiasis-causing species. In these cases the detransformed mean number of larvae per wound was 18.1 (range 5-40). Lucilia sericata (Diptera: Calliphoridae) was found to be solely responsible for the lesions of 12 birds, with detransformed mean of 94.0 (range 2-893) larvae per goose. The larvae of this species appeared to be generally less invasive than those of W. magnifica, but in three cases they were also deeply embedded in the wounds. In seven geese larvae of both fly species developed together in and around the wounds. With the exception of one lesion, there were more larvae of W. magnifica (detransformed mean of 21.8 with a range of 1-55) than that of L. sericata (detransformed mean of 11.2 with a range of 2-61) in these mixed infections. Predisposing conditions for development of traumatic myiasis in geese included plucking of feathers, other injuries and bacterial infections (e.g. inflammation of the phallus).

Trichobius joblingi, Aspidoptera falcata, and Megistopoda proxima (Diptera : Streblidae) parasitic on Carollia perspicallata and Sturnia lillium (Chiroptera : Phyllostomidae) in southeastern Brazil: sex ratios, seasonality, host site preference, and effect of parasitism on the host.

This note examines the effect of parasitism on host size, the preference of the parasite for a specific host body area, and the seasonal abundance for the 3 most abundant bat flies (i.e., Trichobius joblingi Wenzel, a parasite of the bat Carollia perspicillata [Linnaeus], and Aspidoptera falcata Wenzel and Megistopoda proxima [Séguy], parasites on Sturnira lilium [Geoffroy]). Trichobius joblingi and A. falcata are moderately dorsoventrally flattened and were collected on the wing membranes of their hosts, and M. proxima is moderately laterally compressed, has long, thin hind legs, and was collected in the body fur of the host. These 3 parasites also showed distinct seasonal patterns. There was a significant negative correlation between the simultaneous occurrence of A. falcata and M. proxima on the host. Parasitism by M. proxima was correlated with a significant weight loss in male S. lilium, which may reflect the large size, high activity, and constant feeding of this parasite, thereby causing a significant negative effect on the host. Sex ratios favoring male flies could be explained by the tendency of female flies to leave the host immediately before the bat leaves the shelter in search for food or immediately after bats are collected but could also be a consequence of higher mortality among females, especially gravid ones. Finally, collecting may have influenced the skewed sex ratio because male flies, being more active, were more evident to the collector.

Mechanical transport of rotavirus by the legs and wings of Musca domestica (Diptera: Muscidae).

Factors affecting the mechanical transmission of rotavirus by the legs and wings of the housefly, Musca domestica L., were examined in a laboratory study. Rotavirus was picked up when houseflies walked on thin smears of clarified rotavirus suspensions. The addition of glycerol, which increased viscosity of the virus suspension, and particulate human feces slightly increased the proportion of flies contaminated with virus. However, the addition of glycerol greatly reduced the average number of virus particles picked up per fly, whereas feces greatly increased the number of particles. The proportion of flies with virus-contaminated legs, which transferred virus to > 1 contact surface, was increased by longer contact time with the surface and when the contact surface was agar instead of glass. Most virus particles were deposited on 1st contact with the surface. Most flies dislodged virus particles inoculated on the underside of their wings soon after the start of simulated flight. Our data indicated that the nature of the virus-suspending medium has a greater effect on the level of virus contamination than on the ability to become contaminated. The importance of walking as a mode of virus transport depends on the nature of the contact surface, the risk of the contaminated fly settling first on a surface likely to come into contact with humans, and fly numbers.