Host Head Research Articles

Deterministic approaches for head lice infestations and treatments

Pediculus humanus capitis are human ectoparasites which cause infestations, mostly in children, worldwide. Understanding the life cycle of head lice is an important step in knowing how to treat lice infestations, as the parasite behavior depends considerably on its age and gender. In this work we propose a mathematical model for head lice population dynamics in hosts who could be or not quarantined and treated. Considering a lice population structured by age and gender we formulate the model as a system of hyperbolic PDEs, which can be reduced to compartmental systems of delay or ordinary differential equations. Besides studying fundamental properties of the model, such as existence, uniqueness and nonnegativity of solutions, we show the existence of (in certain cases multiple) equilibria at which the infestation persists on the host’s head. Aiming to assess the performance of treatments against head lice infestations, by mean of computer experiments and numerical simulations we investigate four possible treatment strategies. Our main results can be summarized as follows: (i) early detection is crucial for quick and efficient eradication of lice infestations; (ii) dimeticone-based products applied every 4 days effectively remove lice in at most three applications even in case of severe infestations and (iii) minimization of the reinfection risk, e.g. by mean of synchronized treatments in families/classrooms is recommended.

Experimental study of micro-habitat selection by ixodid ticks feeding on avian hosts

Mechanisms of on-host habitat selection of parasites are important to the understanding of host-parasite interactions and evolution. To this end, it is important to separate the factors driving parasite micro-habitat selection from those resulting from host anti-parasite behaviour. We experimentally investigated whether tick infestation patterns on songbirds are the result of an active choice by the ticks themselves, or the outcome of songbird grooming behaviour. Attachment patterns of three ixodid tick species with different ecologies and host specificities were studied on avian hosts. Ixodes arboricola, Ixodes ricinus and Ixodes frontalis were put on the head, belly and back of adult great tits (Parus major) and adult domestic canaries (Serinus canaria domestica) which were either restricted or not in their grooming capabilities. Without exception, ticks were eventually found on a bird’s head. When we gave ticks full opportunities to attach on other body parts – in the absence of host grooming – they showed lower attachment success. Moreover, ticks moved from these other body parts to the host's head when given the opportunity. This study provides evidence that the commonly observed pattern of ticks feeding on songbirds’ heads is the result of an adaptive behavioural strategy. Experimental data on a novel host species, the domestic canary, and a consistent number of published field observations, strongly support this hypothesis. We address some proximate and ultimate causes that may explain parasite preference for this body part in songbirds. The link found between parasite micro-habitat preference and host anti-parasite behaviour provides further insight into the mechanisms driving ectoparasite aggregation, which is important for the population dynamics of hosts, ectoparasites and the micro-pathogens for which they are vectors.

Morphology and Development of a Termite Endoparasitoid Misotermes mindeni (Diptera: Phoridae)

Abstract The morphology and developmental stages of Misotermes mindeni Disney & Neoh (Diptera: Phoridae), a newly described endoparasitoid of the fungus-growing termite Macrotermes gilvus (Hagen) (Termitidae: Macrotermitinae) were studied, and biometric descriptors of eggs, larvae, and pupae were recorded. The larvae of M. mindeni exhibit three larval stages. Larvae complete their first instar development in fourth larval instars and major presoldiers, whereas the second and third instars develop entirely in major soldiers' head capsule and abdomen, respectively. The second instar can be readily differentiated from the first by the presence of a posterior spiracular base and more defined body segments, and the third instar can be discriminated from the second by the presence of respiratory horns and a well-developed posterior spiracular base. Differentiation of the larval instars is further supported by morphometric measurements. The first instar moves freely within the host's body cavity and head capsule, whereas the last two instars remain in the host's head capsule and abdomen, respectively. Termite developmental stages were used as a model to determine the developmental time of M. mindeni larvae. Duration between the first and second instars was 19.00 ± 2.28 d and between second and third instars was 36.88 ± 5.17 d. It took the third instar, 0.53 ± 0.08 d to reach pupation. The pupal stage lasted for an average of 13.51 ± 0.74 d. Mean adult longevity was 1.47 ± 0.57 d and 3.00 ± 0.98 d for females and males, respectively. Longevity of males was significantly longer than that of females.

Visual control of host pursuit in the parasitoid fly Exorista japonica.

The tachinid fly Exorista japonica is a parasitoid of many kinds of lepidopterous larvae. After encountering a suitable host, the fly pursues the crawling larva on foot using visual cues to guide it. To investigate the visual control of host pursuit, we observed and videotaped pursuits of a host, the common armyworm Mythimna separata, for frame-by-frame analysis. Observation was performed in sunlight and under illumination from a fluorescent lamp. The fly pursued hosts discontinuously with a repeated stop-and-run motion. During a run, its movements consisted of rotation, forward translation and sideways translation. Rotation during a run was positively correlated with the angular position of the host's head. The direction of translation depended on the angular position of the host's head. Forward translation was negatively correlated with the visual angle subtended by the host. These results suggest that the fly orients and walks towards the leading edge of a moving target. There was little difference in the results between sunlight and illumination from a fluorescent lamp.

A New Host Record for Pseudacteon crawfordi (Diptera: Phoridae)

The biology of the phorid fly Pseudacteon was reviewed by Porter (1998). The female fly oviposits into the thorax of its ant host. After hatching, the larva works its way into the host's head capsule where it continues to grow and ultimately decapitates the host. The fully grown larva then uses the head capsule of the host as a pupal case. Because of their parasitic lifestyle, flies of this genus are of great interest as potential biocontrol agents against the imported fire ants, Solenopsis invicta Buren and Solenopsis richteri Forel, in North America. Four species of Solenopsis fire ants are native to North America: S. amblychila Wheeler, S. aurea Wheeler, S. geminata (Fab.) and S, xyloni (MacCook). All four of these species overlap in their ranges in the southwestern United States, mainly in Arizona and Texas (Trager 1991). Pseudacteon crawfordi was described by Coquillett in 1907 and is known to be parasitic on S. geminata (Disney 1994) and S. xyloni (Feener 1987). Here we report that P. crawfordi attacks S. aurea. Solenopsis aurea is a species of fire ant that occurs in xeric conditions in the southwestern United States and is found mainly in Texas and Arizona (Trager 1991). Collection: Near dusk, on August 3, 1999, a nest of S. aurea was excavated. The nest was located close to mile marker 13 north of Portal, Arizona on Speed Road. Foragers from the colony were initially found under a pile of semi-moist cow manure. The nest was located close to a pool of water created by a leaking irrigation line. Shortly after the cow manure was disturbed and the ants were uncovered, six female phorid flies were seen hovering around and attacking intermediate-sized workers. A series of the phorid flies was collected with the ants. Solenopsis aurea workers were also collected the next day from 0800-1200 h, but no phorid flies were seen. The phorid flies were identified as Pseudacteon crawfordi by Sanford Porter (Medical and Veterinary Entomology Research Laboratory, USDA-ARS, Gainesville, Florida) and the fire ants were identified as S. aurea by senior author (JPP). This represents a new host record for Pseudacteon crawfordi. Voucher specimens of both the ants and flies are deposited in the University of Georgia, Collection of Arthropods, Athens, Georgia, USA.

Stimuli inducing detachment of larvalArrenurus danbyensis (Hydrachnidia: Arrenuridae) from adultCoquillettidia perturbans (Diptera: Culicidae)

In this study, potential cues for detachment of parasitic larvalArrenurus danbyensis Mullen mites fromCoquillettidia perturbans (Walker) mosquitoes were investigated. Contact with water did not induce a dramatic rate of dissociation. Crushing the host's abdomen was not as effective as crushing the head or thorax; although general body trauma has an effect, it is not sufficient to explain these results. Crushing the host's head following application of a ligature slowed the rate of mite detachment. We infer that haemolymph-borne cues, possibly hormones, are released by crushing the head or thorax of the host and induce rapid mite detachment. External application of Ringers solution or body fluids from mosquitoes significantly increased rate of mite detachment. It is possible that two separate mechanisms stimulate detachment of mites: external haemolymph reception signifying damage to the host and internal reception of haemolymph-borne cues associated with oviposition behavior.

Temporal Synchronization of Emergence of Hyposoter exiguae and H. fugitivus (Hymenoptera: Ichneumonidae) with Apolysis Preceding Larval Molting in Manduca sexta (Lepidoptera: Sphingidae)

Hyposoter exiguae (Viereck) is an ichneumon wasp parasite of many species of lepidopteran larvae including the tobacco hornworm. After parasitization of first-instar Manduca sexta (L.), wasp larvae developed inside the host and emerged during the host's second or third instar, after it had undergone apolysis in preparation for larval molting. When the host was parasitized as late as the third instar, emergence was delayed until onset of host apolysis preceding the fourth or fifth instar. Fourth-instar M. sexta larvae were not successfully parasitized by H. exiguae , due to parasite encapsulation and developmental disruption of the host. In hosts with emerging wasps, size of the emerging parasite was correlated with size of the host's head capsule, indicating that larger parasites emerged from larger hosts. Experiments with H. fugitivus (Say) demonstrated that it also emerged from tobacco hornworm larvae undergoing apolysis preceding larval molting, suggesting that other species of Hyposoter may show a similar developmental interaction with their host.

Pattern Formation inHydraHead Regeneration

SYNOPSIS. I have reinvestigated the “classical” Hydra transplantation phenomena, using experiments of simple design and large sample sizes. All experiments involved transplanting small tissue fragments from a donor hydra to a host. Both of the effects which are considered to demonstrate “head inhibition” in hydra (removing the head of the host, and placing transplants at different distances from the host's head) can be explained by assuming a diffusible inhibitory substance produced in the head; the apparent half-life of the substance is 2 hr and the apparent diffusion constant 2 × 10−6cm2/sec. In contrast, the two effects which are considered to demonstrate the “head activation” probably have different mechanisms. The “head activation gradient” is controlled by a factor with a half-life of 36 hr or more; the “activation increase” of head regeneration has an apparent half-life of about 12 hr. Further new findings are (i) that the head inhibition is restored quite late in head regeneration, (ii) that some head inhibitor appears to be produced in hydra's body, and (iii) that injury produces a local increase in the head activation. All these results can be rationalized by a new version of the Gierer-Meinhardt model; this model also accounts quantitatively for the changes in transplantation properties during head regeneration and for the proportioning of hydra's body and head. In simulations the model has 9 independent parameters but predicts 17 seemingly independent results. The model is thus more than trivially successful, and seems suitable as a guiding hypothesis for further work.

Influence of the olfactory placode on the development of the brain in Xenopus laevis (Daudin) : I. Axonal growth and connections of the transplanted olfactory placode

The olfactory placode of Xenopus laevis larvae at different stages of development has been removed and transplanted onto the head of host larvae to determine the effect of the donor/host age on the viability of the transplant. Viability of the transplant (defined as penetration of the nerve of the transplanted placode in the host's CNS) has been found to be maximal when both donor and host were at about stage29/30. Using stage 29/30 larvae, three distinct zones have been mapped on the host's head from which the transplanted olfactory placode consistently sent its nerve to three different regions of the brain, namely to the telencephalon, the diencephalon and to the myelencephalon, respectively. The additional olfactory input induced a hypertrophy where it penetrated the telencephalon. When the olfactory input penetrated the diencephalon a marked hyperplasia of the neuronal elements and formation of glomeruli was observed in the dorsal thalamus. There was no overall change in the organization of the myelencephalon when the input reached this region. Donors up to and including stage 41 remade the placode. Removal of the placode after this stage resulted in permanent loss of the organ and hypoplasia of the olfactory bulb and telencephalon. The results illustrate the unique property of the olfactory sensory neurons to induce hyperplasia in anomalous regions of the host's CNS and to determine, in these regions, the characteristic terminal structures which are commonly described as glomeruli.

Autökologische Untersuchungen an Populationen der gemeinen Kiefern‐Buschhornblattwespe Diprion pini (L.) (Hym.: Diprionidae)

AbstractStudies on the autecology of the common pine sawfly Diprion pini (L.) V. Investigations on the larvae parasitic Tachinids, particularly Drino gilva Htg.Drino gilva (Htg.) and D. inconspicua (Meig.) (Tachinidae) are important larval parasites of the common pine sawfly Diprion pini (L.) (Diprionidae). Another species, Diplostichus janithrix (Htg.) is constant, but much less abundant, than the two Drino‐species. A fourth, Blondelia inclusa (Htg.), is rare. The sex ratio of the first two species is 1:1.The biology of D. gilva is described with special reference to egg‐laying behaviour and development periods. It has two generations a year in the lowlands and one in the mountains. Up to 12% of the sawfly larvae succeed in encapsulating the larvae of D. gilva. The first two larval stages develop within the host's head capsule, causing malformations apparent in the adult stage. In three samples, superparasitism ranged between 68% and over 90% with 2.5 to 3.5 parasites per host.Multiparasitism and interspecific competition are pronounced at high rates of parasitism. Twenty eight different combinations of multiparasitism were found by dissection.Two aspects of synchronisation (seasonal‐ and prolonged diapause‐), between Tachinids and the common pine sawfly, are discussed.

A collection device for Leptoconops kerteszi (Diptera: Ceratopogonidae) biting gnats.

A portable, gasoline-powered D-Vac® insect suction sampler was modified by replacing the flexible suction tube with a sheet metal funnel. Large numbers of Leptoconops Kerteszi gnats flying about a human host's head are drawn into a fine mesh net held in the mouth of the funnel. More gnats were captured by a man wearing the device than by the device standing alone, in a study conducted near the Salton Sea. The device can be carried into areas inaccessible to wheeled vehicles, it enables the standardization of collections, and it provides statistically analyzable estimates of adult gnat populations in ecological and control studies.