Responses of Ornithonyssus sylviarum (Acari: Macronyssidae) and Menacanthus stramineus (Phthiraptera: Menoponidae) to gradients of temperature, light, and humidity, with comments on microhabitat selection on chickens

Varroa destructor relies on physical cues to feed in artificial conditions

Olfaction is a major sense in Varroa destructor. In natural conditions, it is known that this honey bee parasite relies on kairomones to detect its host or to reproduce. Yet, in artificial conditions, the parasite is able to feed and survive for a few days even though most honey bee pheromones are lacking. Other key cues are thus probably involved in V. destructor perception of its close environment. Here, we used several artificial feeding designs to explore the feeding behaviour of the parasite when it is deprived of olfactory cues. We found that V. destructor is still able to feed only guided by physical cues. The detection of the food source seems to be shape-related as a 3D membrane triggers arrestment and exploration more than a 2D membrane. The tactile sense of V. destructor could thus be essential to detect a feeding site, although further studies are needed to assess the importance of this sense combined with olfaction in natural conditions.

Factors associated with prevalence and intensity of the northern fowl mite (Ornithonyssus sylviarum) in commercial poultry farms of Argentina

The haematophagous mite Ornithonyssus sylviarum may cause important economic losses in commercial poultry farms whilst also potentially affecting the health of farm workers. The dynamics of this ectoparasite has been linked to several factors, including wild birds, fomites, farm workers, management of hen houses, and host traits. Along two consecutive years, we carried out systematic sampling at three laying hen farms located in Santa Fe province, Argentina, with the aim of identifying factors that may influence O. sylviarum prevalence and intensity. We found that the density of feathers around the hen vent area and the presence of Menoponidae lice were negatively associated with mite abundance. We also found that the density of hens in the cages was negatively associated with mite prevalence, suggesting a possible dilution effect, whereas prior reports found a positive association with hen density. In addition, summer was the season with minimum mite prevalences and intensities, contrary to previous studies in northern farms where warm weather appeared to prompt an increase in mite populations. Another factor associated with mite intensity was age, but this effect varied depending on the season, which hints that the association between hen's age and mites is complex. Basic epidemiological knowledge on O. sylviarum in poultry farms from South America may aid in a more efficient and integrative approach to its control.

Evidence for idiothetic and allothetic control of thermo-orientation in feather-feeding lice

Thermal cues are widely used by ectoparasites to find and exploit hosts. Recently, the wing louse Columbicola columbae (Phthiraptera: Ischnocera) was shown to use thermo-orientation when migrating between host microhabitats. Here, we study the control systems governing thermo-orientation by motion tracking wing lice on spatial and temporal heat gradients. As previously demonstrated, lice placed on spatial heat gradients successfully located nearby heat targets. Unilateral antennectomies were then used to remove spatial aspects of the thermal cue. These lice were still capable of locating heat targets, suggesting their response relied on tracking changes in the cue over time (idiothetic control). Course control was accomplished via angular corrections after louse body-angles deviated from the heat target. Louse behavior on temporal heat gradients provided additional evidence for idiothetic control- lice altered turn size and velocity after temperatures uniformly shifted without any spatial reference. We also show that lice are likely capable of responding to spatial aspects of the cue, consistent with allothetic control. On the spatial heat gradient, lice with two antennae were more efficient at locating heat targets as compared to those with unilateral antennectomies. Additionally, when traveling along temperature isoclines (where lice can detect spatial but not temporal aspects of the cue), lice with two antennae consistently turned towards the heat target, while those with unilateral antennectomies showed no preference. In all, we find evidence that lice can use both idiothetic and allothetic control during thermo-orientation, and likely integrate information from these two systems to guide movements on hosts.

Microclimate and host body condition influence mite population growth in a wild bird-ectoparasite system

Parasite populations are never evenly distributed among the hosts they infect. Avian nest ectoparasites, such as mites, are no exception, as their distribution across the landscape is highly aggregated. It remains unclear if this pattern is driven by differences in transmission events alone, or if the environment that parasites inhabit after transmission also plays a role. Here, we experimentally examined the influence of the post-transmission microclimate, nest characteristics, and host condition on ectoparasite population growth in a bird-ectoparasite system. We infested barn swallow (Hirundo rustica erythrogaster) nests with a standardized number of Northern Fowl Mites (Ornithonyssus sylvarium) and analyzed both biotic (nestling mass, wing length, number of other arthropods present in the nest, and brood size) and abiotic (temperature, humidity, nest lining, nest dimensions, and substrate upon which the nest was built) predictors of mite population growth. Our results suggest that mite populations were most successful, in terms of growth, in nests with higher temperatures, lower humidity, few other arthropods, and hosts in good condition. We also found that nests built on wooden substrates support larger populations of mites than those constructed on metal or concrete. These findings lend insight into the factors that drive large-scale patterns of ectoparasite distributions.

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Experimental manipulations of nest mites controls for initial transmission.

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Tested the role of microclimate and host factors on mite population growth.

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Mite populations grow larger in warmer, drier nests with high body condition hosts.

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Nests on wooden substrates had more stable microclimate and larger mite populations.

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Presence of other arthropods was negatively correlated with mite population growth.

A review of the biology, ecology, and control of the northern fowl mite, Ornithonyssus sylviarum (Acari: Macronyssidae)

The northern fowl mite, Ornithonyssus sylviarum (Canestrini & Fanzago, 1877), is found on several continents and has been a major pest of poultry in the United States for nearly a century. Lack of earlier USA reports in the United States suggests an introduction or change to pest status in domestic poultry systems occurred in the early 1900s. Though predominantly a nest-parasite of wild birds, this obligate hematophagous mite is a permanent ectoparasite on domestic birds, especially egg-laying chickens. Economic damage is incurred by direct blood feeding and activation of the of host's immune responses. This in turn causes decreased egg production and feed conversion efficiency, and severe infestations can cause anemia or death to birds. Here we review the biology, ecology, and recent control measures for the northern fowl mite. Photomicrographs are included of adult males and females, protonymphs, and larvae with key characters indicated. Special emphasis is placed on current knowledge gaps of basic and applied science importance.

Northern fowl mite (Ornithonyssus sylviarum) effects on metabolism, body temperatures, skin condition, and egg production as a function of hen MHC haplotype

The northern fowl mite, Ornithonyssus sylviarum, is the most damaging ectoparasite on egg-laying hens in the United States. One potential strategy for management is breeding for mite resistance. Genes of white leghorn chickens linked to the major histocompatibility complex (MHC) were previously identified as conferring more (B21 haplotype) or less (B15 haplotype) mite resistance. However, immune responses can be energetically costly to the host and affect the economic damage incurred from mite infestations. We tested energy costs (resting metabolic rate) of mite infestations on egg-laying birds of both MHC B-haplotypes. Resting metabolic rates were documented before (pre-) mite infestation, during (mid-) infestation, and after peak (late) mite infestation. Mite scores, economic parameters (egg production, feed consumption), and physiological aspects such as skin inflammation and skin temperature were recorded weekly. Across experiments and different infestation time points, resting metabolic rates generally were not affected by mite infestation or haplotype, although there were instances of lower metabolic rates in infested versus control hens. Skin temperatures were recorded both at the site of mite feeding damage (vent) and under the wing (no mites), which possibly would reflect a systemic fever response. Ambient temperatures modified skin surface temperature, which generally was not affected by mites or haplotype. Feed conversion efficiency was significantly worse (4.9 to 17.0% depending on trial) in birds infested with mites. Overall egg production and average egg weight were not affected significantly, although there was a trend toward reduced egg production (2 to 8%) by infested hens. The MHC haplotype significantly affected vent skin inflammation. Birds with the mite-resistant B21 haplotype showed earlier onset of inflammation, but a reduced overall area of inflammation compared to mite-susceptible B15 birds. No significant differences in resting energy expenditure related to mite infestation or immune responses were detected. Potential breeding for resistance to mite infestation using these two haplotypes appears to be neutral in terms of impact on hen energy costs or production efficiency, and may be an attractive option for future mite control.

Epidemiological aspects of lice (Menacanthus species) infections in laying hen flocks from the State of Minas Gerais, Brazil

The epidemiology of chicken lice species such as Menacanthus stramineus, M. cornutus and M. pallidulus were studied during an observational, analytical and sectional survey, to determine predisposing factors for their occurrence in laying hen farms in the State of Minas Gerais, Brazil. A total of 431 houses on 43 farms were visited in 2012. M. cornutus, M. stramineus and M. pallidulus occurred in 20.9%, 11.6% and 11.6% of farms, respectively. The frequencies of occurrence of M. cornutus, M. stramineus and M.pallidulus in poultry houses were 10.4%, 8.8% and 3.7%, respectively. The epidemiological determinants for the occurrence of these species were investigated using Poisson or logistic regression models. The region of the farm, the recent use of acaricides and the presence of birds, such as saffron finch (Sicalis flaveola), feral pigeon (Columba livia) and Guira cuckoo (Guira guira) around the farms were related to the epidemiology of M. cornutus. Infestation by M. stramineus was associated with age of birds, number of birds per cage and the presence of Guira cuckoo and Chopi blackbird (Gnorimopsar chopi) near the poultry houses. The occurrence of M. pallidulus was influenced by the type of facilities, presence of cattle egret (Bubulcus ibis) and free-range domestic hens around the farm. The use of wire mesh nets in the houses and of forced moulting did not influence lice infestation.

Temperature governs on-host distribution of the northern fowl mite, Ornithonyssus sylviarum (Acari: Macronyssidae)

The northern fowl mite, Ornithonyssus sylviarum (Canestri & Fanzago), is an ectoparasite of more than 70 species of North American wild birds, but it has a particularly significant impact on chickens, where it is a permanent resident of vent feathers. Improved control practices depend on a better understanding of host-mite relationships. ISA Brown hens were inoculated experimentally with northern fowl mite adults, and northern fowl mite populations developed naturally. Using a fast-response microprobe, temperatures of individual vent feathers (n = 15) were recorded at 5-mm increments along the length of the feather shaft. Immediately after temperatures were recorded, the individual feathers were quickly clipped at the skin surface and then flash-frozen between 2 small blocks of dry ice, freezing all northern fowl mite stages in situ. The feathers then were cut into 5-mm sections for careful mite enumeration by life stage. There were no overall differences among life stages in the distributions on the feather. Mite positions on feathers (distance from skin) varied distinctly with feather zone temperatures, as well as with ambient and average temperatures over the prior 24 hr. Ambient temperature at time of sampling affected the positions of the 2 mobile categories, adults and larvae/nymphs, but showed no statistical relationship with egg distribution. In contrast, ambient 24-hr temperature influenced the positions of all life stages. On-host feather temperatures reflected ambient temperatures. Feathers collected on hot days (ambient temperatures of 23-33 C) provided a narrow and quite warm range of temperature conditions for mites (often >30-36 C). Temperatures on cool days (ambient temperatures of <23 C) provided much wider on-host temperature ranges for mites to occupy (13-35 C). Mites were farther from the skin on warmer days. When mites had a broad range of temperatures, the feather temperature zone occupied by all life stages averaged 28-29 C. Mites move to occupy favorable temperature conditions on-host. When further out on feathers in warm weather, and under thermal stress, northern fowl mites either move off host or are dislodged. They then become a human pest, are noticed by farmers, and are more likely to disperse.

Beak condition drives abundance and grooming-mediated competitive asymmetry in a poultry ectoparasite community

OBJECTIVE

Ornithonyssus sylviarum (northern fowl mite) and Menacanthus stramineus (chicken body louse) are key poultry pests currently controlled by exclusion or pesticide application. We studied how host beak condition affected their populations over time and how the lice and mites might interact on a host.

METHODS

Beak-trimmed or beak-intact white leghorn hens were infested initially with either mites or lice and subsequently challenged using the alternate ectoparasite species (reciprocal transfer), while other hens harboured only the initial ectoparasite species.

RESULTS

Beak-trimmed hens had far higher ectoparasite numbers relative to beak-intact hens, and the 2 ectoparasites showed evidence of grooming-mediated competitive asymmetry. On beak-trimmed hens, larger numbers of lice quickly nearly completely excluded mites in competition for enemy-free space (lower abdomen), while in the reciprocal transfer mites did not affect louse numbers on beak-trimmed hosts. The 2 ectoparasites co-existed on beak-intact hens, which were better able to defend the lower abdomen habitat by grooming.

CONCLUSION

Lice are somewhat less damaging and much easier to control relative to mites, and might be used to eliminate mites in commercial, beak-trimmed flocks. Beak trimming impairs host grooming and contributes greatly to the high ectoparasite populations seen in commercial flocks. The study adds incentives for poultry breeders to develop more docile hen strains that can be held without beak trimming. This has advantages both to welfare advocates and producers who may no longer need to use insecticides for pest control or be concerned about worker exposure to pesticides.