Neotrombicula autumnalis

Geographic Range

The taxonomy of Neotrombicula autumnalis is complicated with a number of closely related species described ranging from western Europe to Southwestern Asia. Neotrombicula autumnalis is best known for its distribution in Europe and is the most abundant trombiculid species in central Europe and the British Isles. Populations have been found in Austria, Belgium, Denmark, Eire, England, France, Germany, Italy, Netherlands, Spain, Switzerland, Czechoslovakia, and Yugoslavia. Isolated populations have also been found in areas of Western Russia and Turkey.

• Biogeographic Regions
• palearctic palearctic
  • native native

Habitat

Little is known about the ecology of N. autumnalis and no propensity for any characteristic habitat has been found. Mites have been found both inside the soil or on the surface in both pre-larval and adult stages, and several studies have found the mites' distribution to be extremely patchy. Neotrombiculus autumnalis has been described as having tremendous “ecological potency”, occupying regions within a wide variety of temperature, vegetation, and pH of the soil. In an experimental study, the type and layers of vegetation or organic matter, morphological surface of the soil, and the amount of moisture and solar radiation had no significant affect on the distribution of N. autumnalis . On a larger scale, these mites have been found in city areas, forests, creeks, grasslands, cultivated grain fields, brush lands and thickets.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• forest forest

• Other Habitat Features
• urban urban
• suburban suburban
• agricultural agricultural

Physical Description

Neotrombicula autumnalis larvae appear red or orange in color and range from 0.2-0.4 mm in length. Covering the three pairs of elongated legs are an outer pair and medial claws, which are covered with setae. A tiny pentagonal sclerotized shield houses a pair of eyes, a pair of sensilla, five ciliated setae, and flagella. Paired chelicerae and palps lie laterally to the gnathostoma. The palpal tibia contains a claw with three forks, and ciliated setae cover the palpal tarsus; movable digits permit host attachment.

Adults of N. autumnalis are among the largest of the mites and can be up to 2 mm in length. They have a wide back plate and two double eyes, and are not sexually dimorphic.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Development

The lifecycle of Neotrombiculus autumnalis is complicated and not completely understood in full. The number of lifecycles per year varies in the field; however, complete life cycles in vitro have taken in place in the time span of 4-5 months.

As is common within trombiculid mites, N. autumnalis has a sequence of life stages that include egg, larva, protonymph, deutonymph, tritonymph, and adult. In May, eggs are laid by an adult female in upper parts of a soil layer, or in ground debris. The eggs hatch in ten days and six-legged larvae emerge. To further develop, the larvae must seek a liquefied skin tissue meal from a vertebrate, and becomes ectoparasitic. Physically climbing onto bird or mammal hosts, the larvae feed for 2-10 days. Following this period on the host, larvae return to the soil and develop into eight-legged nymphae in 5-6 weeks. While the protonymph, as a transitional stage, shows no active movement or feeding activity, the deutonymph actively moves about in the soil, feeding upon arthropods, their eggs, or plant fluids. The tritonymph resumes a resting stage, and adults feed in a similar fashion as the deutonymphs. Neotrombicula autumnalis has indeterminate growth; larave grow up to 0.4 mm and adult forms can grow up to as large as 2 mm.

• Development - Life Cycle
• indeterminate growth indeterminate growth

Reproduction

Although the mating system of Neotrombicula autumnalis has not been extensively studied, behaviors of related species within the order Trombidioidea have been described. Both sexes tap each other with their front legs and commence a circular dance. The male ceases the dance, and spermatophore deposition occurs shortly after, with jerking upward and downward behaviors seen in the male, accompanying spermatophore deposition. Throughout this process, the female continues to encircle the male, while maintaining contact by leg tapping. The female will attempt to capture the sperm from the stalk by sucking it into her vagina. If this fails, the sperm is desiccated; this seems to be a mechanism to prevent the female from collecting old sperm.

Signals that have indicated subsequent spermatophore deposition include circular fields of threads that are deposited on the ground throughout the time course of the circular dance. In some species within the Trombidioidea , the circular field of threads corresponds precisely with the median axis of the spermatophore, known commonly as the “zig zag track”. These threads can mark mating territories and are defended against male invaders. Attraction to mating fields is chemotactics; pheromones contribute to the recognition of these territories by other males and females. Mating commences when a female enters the marked territory.

• Mating System
• monogamous monogamous

The reproductive system consists of two sac shaped gonads, represented by the testes in the male, and the ovaries in the female. These gonads are located in the middle of the body near coxae IV. Fertilization occurs externally via spermatophore deposition, and sperm are taken up by the female into the vagina. Although the sexes are separate in this species, adults of Neotrombicula autumnalis are not sexually dimorphic. Development is oviparous and larvae emerge in early May. However, exact months during which breeding occurs is uncertain.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

The extent of parental investment along with parental care is not known.

Lifespan/Longevity

The mobility of mammalian and bird hosts that have direct contact with the soil, rather than activity of the larvae, determines successes and levels of parasitism. Although the the exact lifespan of Neotrombicula autumnalis is not known, other species within the genus Neotrombicula can live up to a year.

Behavior

Neotrombiculus autumnalis is parasitic only in its larval stages. In summer months, hatched larvae move upwards from the soil to parts of vegetation within their immediate reach. Larvae congregate and form clusters on particular pieces of vegetation. Larvae clusters are sedentary for weeks on a site at a particular height above the soil surface. Such heights are favorable to increase the likelihood of contacting foraging hosts. Upon the approach of a potential host, several of the mites’ legs will stick out such to increase their chances of retrieval by fur or feathers. This colonial behavior has been described as the entire larval cluster moving as “one organism” onto a field investigator upon contact with the skin. Larvae exist as clusters on the host that result in multiple bites at a particular location on hosts.

In vitro, larval clusters have displayed questing behavior upon exposure to heat, without any directional movement towards or away from the heat source. The larvae approach the outer surface of either fur and feathers, and commence external feeding on the first part of bare skin that is encountered, often attaching to areas of the skin where the texture is thin, such as the opening of hair follicles. On humans, infections have been found in high abundance in areas where clothing is tightly fit, such as under armpits, around the neck, and waist. In birds, preferred areas are nearby feather follicles.

After direct contact with a host, the immobile cluster assumes a parasitic lifestyle. Feeding commences when the gnathosoma penetrates the host's epidermis. Outside of interactions with the host, N. autumnalis demonstrates little mobility and stays within the same general area throughout its lifetime.

• Key Behaviors
• terricolous
• parasite parasite
• motile motile
• sedentary sedentary
• colonial colonial

Communication and Perception

In vitro, larval clusters of Neotrombicula autumnalis have displayed questing behavior upon exposure to heat, without any directional movement towards or away from the heat source. Males and females in related species of the order Trombidioidea use pheromones to recognize mating territories marked by thread deposition. Potential mates communicate by tapping one another with their front legs, and commence a circular dance.

• Communication Channels
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• infrared/heat infrared/heat
• tactile tactile

Food Habits

Neotrombiculus autumnalis does not feed on blood, but on liquefied epidermal and cutaneous tissue of terrestrial mammals and birds, including humans. Interaction of the lytic enzymes within the parasites' saliva with host tissue induces formation of a stylostome by host lymphocytes, which acts as a feeding tube and facilitates feeding. The larvae then suck the host's macerated tissue.

Throughout the deuto-nymphal and adult stages of the Neotrombiculus life cycle, they dwell on soil and feed on plant fluids, other arthropods and their eggs.

• Primary Diet
• carnivore carnivore
  • eats terrestrial vertebrates
  • eats eggs
  • eats non-insect arthropods
• herbivore herbivore
  • eats sap or other plant foods

• Animal Foods
• eggs
• terrestrial non-insect arthropods

• Plant Foods
• sap or other plant fluids

Predation

While no predators of Neotrombiculus autumnalis have been recognized in the literature thus far, strategies to reduce the number of pests in the field have involved the use of gamasid species Amblyseius cumcumeris and A. agrestis .

Ecosystem Roles

In its larval stages, Neotrombiculus autumnalis is parasitic; this species demonstrates little host specificity and has parasitized a wide variety of mammal and bird taxa. Mammalian taxa include but are not limited to: humans, rodents, shrews, dogs, cats, voles, mice, horses, hedgehogs, rabbits, bat, and weasels.

Neotrombicula autumnalis is predatory on other arthropods and their eggs throughout the deuto-nymphal and adult stages of the life cycle.

• Ecosystem Impact
• parasite parasite

Economic Importance for Humans: Positive

Neotrombicula autumnalis has no known positive impact on humans.

Economic Importance for Humans: Negative

Though they cause little damage to their normal host, when attaching to and attempting to feed on an irregular host, they cause dermatitis, referred to trombiculosis; salivary enzymes cause severe itching and skin inflammation. If untreated, itching sensations can remain for several weeks. In animals, this can cause violent scratching, biting, neurological impacts, paresis of the posterior limbs, asthenia, limping, and continual head shaking. Precautions include using repellants either on animals, clothes or limbs, before exposing oneself to areas that are considerably “at risk” for larvae infestation, or during the peak of the larval cycle.

Neotrombicula autumnalis vectors a number of pathogens that originiate either from present or prior hosts, and are trasmitted transovarially. These include the bacteria Rickettsia tsutsugamushi , Borrelia genospecies , Anaplasma phagocytophilium , and Ehrlichia phagocitophila .

• Negative Impacts
• injures humans
  • bites or stings
  • carries human disease

Conservation Status

Neotrombicula autumnalis is widespread throughout its natural habitats and is not considered to be an endangered species.

Additional Links

Encyclopedia of Life

Contributors

Nicole Lederman (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.

References

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Durden, L. 2002. Medical and veterinary entomology (3rd ed.) . San Diego, California: Academic Press.

Fernandez-Soto, P., R. Perez-Sanchez, A. Encinas-Grandes. 2001. Molecular detection of Ehrlichia phagocytophila genogroup organisms in larvae of Neotrombicula autumnalis (Acari: Trombiculidae) Captured in Spain. Journal of Parasitology , 87: 1482-1483.

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