On the contrary, if physical contact were not managed or if the host were not close enough for them to drop on it, chiggers would invariably and promptly return to the cluster and would continue waiting. Chiggers would temporarily disperse if a host approached. A possible explanation for this focalization may be that chiggers apparently do not move more than a few meters from where they hatched. Mite islands are quite clearly defined, and larvae could not be detected in their immediate vicinity. Therefore, chiggers have a patchy distribution on the vegetation. Trombiculid mites often form localized “mite islands” (or “mite focus”, “larvae focus”) in suitable areas inhabited by potential hosts. The optimum activity of chiggers occurs at temperatures of 25–30☌.
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In general, optimal living conditions require a relative air humidity of 80% (what explains that chiggers are not typically found on vegetation higher than 30 cm off the ground) and neutral to slightly alkaline soil. Trombiculid mites live in moist soil covered with vegetation such as grassy and weedy areas. Once engorged (development to subsequent stage cannot take place unless larvae have fed on the host), larvae fall to the ground and develop to the nymphal stages and subsequently to adults (900–1,200 µm). In humans, bites occur mainly in body exposed areas and at sites where the clothing constricts. Ears, head, armpits, abdomen, genitalia, and the area around the tail are preferred in animals.
#PAULA TSUI 92 SKIN#
On the host, chiggers mainly move to areas where the skin is especially thin and feed on lymph and tissue fluids of the dermal layer (but not blood). These tiny larvae (about 200 µm) climb onto low vegetation, where they aggregate into clusters to wait for a suitable host. Chiggers are usually reddish but can vary between yellow and orange. The general term “chigger” refers to the parasitic larval stage, and this is the name commonly given to trombiculid mites due to the importance of this instar. (Adapted from Takahashi et al., 2003 with the permission of the author.)ĭuring their life cycle, eggs are laid in well-drained soil, and six-legged larvae emerge from them. Schematic description of the trombiculids’ life cycle. Most likely, trombiculids are associated with specific habitats and attack and feed on the first available animal within their favorite habitat, although they can have preference for a particular host among the available ones. However, the question of the host specificity of trombiculids still arises. There are just a few reports of chiggers feeding on invertebrates. Larvae parasitize all groups of vertebrates, except fishes, whereas the small mammals and birds are the main hosts. Sexual dimorphism is not apparently evident. Both present eight legs, but deutonymphs are slightly smaller. Deutonymphs look almost identical to adult mites. Active postlarval stages are soil dwellers that prey on various arthropods and their eggs. This cycle is characterized by alternating active and inactive instars, being the larva, deutonymph, and adult the active ones. Trombiculid mites undergo seven stages in their life cycle: egg, deutovum, larva, protonymph, deutonymph, tritonymph, and adult ( Figure 1). Southeast Asia, Australia, and the Pacific Islands Spain, Czech Republic, England, Austria, Germany, Bulgaria, France, states of former Yugoslavia, Ukraine, Russia, Romania, Hungary, Slovakia, and Poland Japan, northern China, Korea, Thailand, and MalaysiaĮurope (including British Isles, excluding Norway, Sweden, Finland, and northern Russia), Turkey, and Turkmenistan Japan, Korea, and Primorye region of Russia
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Southeast Asia, Malaysia, New Guinea, Philippines, Indonesia, and Melanesia Japan, China, Southeast Asia, Indonesia, Philippines, and New GuineaĬhina, Taiwan, Sri Lanka, Nepal, Bangladesh, India, Myanmar, Vietnam, Cambodia, Thailand, Singapore, Brunei, Malaysia, Indonesia, Philippines, New Guinea, southwestern Pacific Islands, northern Australia, Pakistan, Kazakhstan, Uzbekistan, and Afghanistan Japan, Southeast Asia, Australia, and Pacific Islands Southeast Asia, Australia and the Pacific IslandsĮastern United States (from the Gulf Coast North to Massachusetts, Minnesota) and Ontario United States: from Alabama and Tennessee West to Arkansas, Oklahoma and Kansas Hungary, Spain, Moldova, Ukraine, Russia, Sumatra, Malaysia, and AfricaĬanada, South of United States (except for the southwest), South and Central America (including West Indies)īolivia, Mexico, Central and South America, southwestern and southeastern United States