When Do Black Flies Hatch In Ontario Canada

FIGURE 23.10 Larval stage (chigger) of the harvest mite, Neotrom-bicula mtitmnalis (Trombiculidae), of Europe. (A) Dorsal view; (B) scutum (dorsal plate), showing characteristic arrangement of setae. (Modified from Baker etal., 1956.)

birds, and mammals, with humans serving only as accidental hosts.

The life history of trombiculid mites includes the following sequence of stages: egg, prelarva, larva, proto-nyrnph, deutonymph, tritonymph, and adult (Fig. 23.2). The eggs are typically laid in soil or ground debris. After about 6 days, the egg shell splits to expose an inactive nonfeeding stage, the prelarva. After another 6 days, the active six-legged larva (i.e., chigger) is produced (Fig. 23.10). After successfully attaching to a suitable host, the larva generally feeds 3-5 days on the host before dropping to the ground to form an inactive transitional stage, the protonymph. This stage in turn develops into the active eight-legged deutonymph. The deutonymph subsequently undergoes development as another quiescent stage, the tritonymph, to produce the eight-legged adult. The deutonymph and adult are free-living predators that feed on small arthropods (e.g., collembolans) and their eggs. The duration of the life cycle requires 2—12 months or longer, depending on the species and environmental conditions. In temperate areas, there may be one to three generations per year, whereas in tropical regions generations may be continuous throughout the year.

Although trombiculid larvae usually cause little or no apparent harm to their normal hosts, they often cause

FIGURE 23.11 Multiple chigger bite lesions on human ankle and foot. (Photo by Elton ). Hansens.)

dermatitis when they attach to and attempt to feed on humans and other atypical hosts. Such an infestation by trombiculid larvae is called chigger dermatitis, or trom-biculosis {trombidiosis of the older literature).

Chiggers are just large enough (150-300 /¿m) to be visible to the unaided eye. They are yellowish, orange, or red and can be seen on close inspection at the center of the skin lesions they induce. Unfortunately, chiggers are often encountered in large numbers, resulting in multiple bites (Fig. 23.11). Given their preference for attaching where clothing fits snugly against the skin, the bites tend to be concentrated about the ankles, lower legs, and waist and along the elastic borders of undergarments.

Contrary to popular belief, chiggers do not burrow into the skin of their hosts. Instead they attach by piercing the epidermis with their chelicerae and feed externally. Because of their small size and tiny mouthparts, chiggers usually attach where the skin is thin or soft. A preferred site is the opening to hair follicles. There they insert their capitulum to feed on the thin epidermal lining. In humans, this results in inflammation at the point of attachment and localized swelling of the skin around the chigger, giving the mistaken impression that it has burrowed into the skin. Their food consists primarily of partially digested skin cells and lymph broken down by saliva introduced at the attachment site. They do not feed on blood. Feeding is facilitated by formation of a feeding tube, or stylostome, produced by the interaction of the saliva with surrounding host tissue.

With the exception of Leptotrombidium species, chiggers often do not survive more than 1—2 days on human hosts, due to the adverse host reaction they cause and injury or removal due to scratching. By then, however, the damage is already done, typically producing a discrete, persistent, itching, reddened papule at each attachment site. The lesions persist for several days but may take several weeks to heal if they become secondarily infected. The recovery time can be significandy shortened by prompt treatment to kill the chiggers when they are first detected, generally within 3—6 hr following attachment; application of a topical medication to alleviate itching and prevent infection; and avoidance of scratching or otherwise excoriating the skin.

More than 50 species of trombiculid mites have been recorded attacking humans. Of this number, about 20 species are considered to be medically important, either due to the dermatitis they cause or due to their role in transmission of disease agents. Four species of particular interest are Eutrombicula alfreddugesi in North America and South America, Neotrombicula autum.na.lis in Europe, and Leptotrombidium akamushi and L. deliense in the Orient.

Eutrombicula alfreddugesi This is the most common and widespread trombiculid mite in the Western Hemisphere, occurring from Canada to Argentina and in the West Indies. In North America, it and related species that attack humans are known as red bugs, especially in the southeastern United States. In Mexico it is called tlalzahuatl, and in Mexico and other parts of Latin America it is called coloradilla and bicho Colorado. E. alfreddugesi is parasitic as larvae on a variety of amphibians, reptiles, birds, and mammals. It is particularly common in areas of secondary growth, such as shrub and brush thickets and blackberry and bramble (Rubus spp.) patches, along margins of swamps, and ecotones between woodlands and open fields or grasslands. The larvae are present in late summer and early fall in the more temperate parts of its range and throughout the year in the tropics and subtropics, including southern Florida. Although it is the most common cause of chigger dermatitis in the New World, it is not involved in the natural transmission of any human disease agent.

Neotrombicula autumnalis Known as the harvest mite, this is the most common chigger that attacks humans in Europe and the British Isles (Fig. 23.10). Other names include aoutat and lepte automnal. As both its common and scientific names suggest, N. autumnalis is particularly annoying during harvest time in late summer and fall. The larvae are present from July to the onset of winter, usually reaching peak populations in early September. They tend to be most active on warm, sunny days in grasslands, cultivated grain fields, brush lands, and thickets. The widespread occurrence of this mite reflects its wide variety of natural hosts, especially mammals and certain ground-dwelling birds. Rabbits are a particularly common host. Other hosts include voles, wood mice, hedgehogs, squirrels, catde, sheep, goats, horses, dogs, cats, pheasants, partridges, chickens, and other domestic fowl.

Eutrombicula spp. E. splendens occurs in the eastern United States from the Gulf Coast north to Massachusetts, Minnesota, and Ontario, Canada. It is especially common in the southeastern United States, where it is second only to E. alfreddugesi as the cause of trombiculosis in humans. Although it occurs in drier habitats with E. alfreddugesi, it is especially abundant in moist habitats such as swamps, bogs, and low-lying areas with rotting stumps and fallen trees. The larva is parasitic on amphibians, reptiles, birds, and mammals but seems to prefer snakes and turtles as natural hosts. The seasonal occurrence of E. splendens is similar to that of E. alfreddugesi. Another Eutrombicula. species that causes chigger dermatitis of humans in the United States is E. lipovskyi. It is restricted to moist areas, generally characterized by an abundance of decaying logs and stumps bordering swamps and streams. It occurs from Alabama and Tennessee west to Arkansas, Oklahoma, and Kansas. Reptiles, rodents, and birds serve as hosts.

Leptotrombidium spp. Several members of the genus Leptotrombidium serve as vectors of Orientia tsutsugamushi, the causative agent of tsutsugamushi disease. They occur widely throughout Southeast Asia and the southwestern Pacific islands. As a group, the larvae of medically important Leptotrombidium species are parasitic primarily on ground-dwelling rodents (e.g., Rattus, Microtus, and Apodemus spp.). Other hosts include insectivores, marsupials, cattle, dogs, and cats. They occur in forests, second-growth areas along the margins of woodlands, in river valleys, and in abandoned agricultural fields where populations of rodents flourish. The principal vectors of the tsutsugamushi disease agent are L. deliense in Southeast Asia, the southwestern Pacific islands, and northern Australia; L. akamushi in Japan; L. arenicola and L. fletcheri in the Pacific islands; and L. pallidum, L. pavlovskyi, and L. scutellare in more restricted regions of the Asian mainland, Japan, and Malaysia (see Table III).

Members of several families of mites that infest unprocessed and processed plant materials can cause human dermatitis and other health-related problems. Most cases involve people handling infested materials such as grains, flour, hay, straw, dried fruits, and vegetables. Others involve processed materials of animal origin such as meats,

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  • emppu
    When do black flies hatch in Ontario Canada?
    6 years ago
  • Mirren
    How many black flys hatch in ontario each year?
    6 years ago
  • darren
    When do bugs hatch in southweat ontario?
    5 years ago
  • ermias
    Do black flies hatch on ontario lake?
    4 years ago
  • stacy
    When do the black flys hatch in Missannabee Ontario Canada?
    4 years ago

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