No-see-ums

During no-see-um season, many Carsonites don’t venture outside without full protection!

At the recent Carson Spring Bling Fling, some attendees had to flee the event early when they found themselves mercilessly bitten by tiny biting insects commonly referred to as biting midges or no-see-ums in North America. The no-see-um season generally lasts about two weeks in Carson, usually during the later half of June according to long-time Carsonites. However, with the unusually heavy amount of winter precipitation, Carson saw a longer no-see-um season and a much heavier population than in previous years.

No-see-ums are flies in the order Diptera, family Ceratopogonidae that includes >4000 species in 78 genera worldwide, with >600 species in 36 genera in North America. The vast majority feed on other insects or other non-human animals, with species in only four genera feeding on the blood of mammals. Biting midges are not known to transmit disease agents to humans in the USA but they are vectors of the Blue Tongue virus, a major cause of disease in livestock. The most important genera are Culicoides, Leptoconops, and Forcipomyia. They go through the usual life cycle (egg, larva, pupa, and adult) which can last 2–6 weeks depending on species and environmental conditions. They may complete two or more generations per calendar year, and last-stage larvae overwinter and pupate the following spring through early summer.

Biology

ADULTS are 1–3 mm long (1/16th to 1/8th inch). Pigmentation patterns that vary by species result from dense hairs on the two wings and give them a grayish appearance. The adults are abundant near breeding sites but disperse to feed and mate, with females generally flying up to 2 km and males half the distance. Females of Leptoconops kertszi, an important biting pest in the semiarid southwest, can disperse up to about 10 miles. In contrast, most Culicoides spp. females typically disperse no more than ½  to 1 mile from the site of larval development. Biting midges are generally weak fliers, and flight is greatly reduced or curtailed in windy conditions. Females typically fly into swarms of males to mate in flight. Adults can live 2–7 weeks in the laboratory but their lifespan may be shorter in the wild. 

Adults have well-developed mouthparts with cutting teeth on elongated mandibles in the proboscis, adapted for blood-sucking in females. The four minute cutting blades lacerate the skin, inflicting sharp, burning pain. Both males and females feed on plant sap and nectar which are the primary energy sources for flight and for increased longevity of females. Males are not attracted to vertebrates but egg production in females requires a protein source. This is obtained  from the body fluids of small insects or vertebrate blood primarily from mammals but also birds, reptiles, and amphibians. 

While some species are host specific, others are opportunistic on vertebrates they encounter, usually in response to carbon dioxide emitted by the host. Generally, females primarily search for blood meals around dawn and dusk. However, feeding periods peak at different times of the day for different species. Leptoconops spp. females feed during daylight while Culicoides spp. typically begin to feed at dusk and continue at night. Culicoides spp. that are major biting pests of humans are attracted to light and readily enter dwellings to feed.

EGGS are cigar-shaped, about 0.25 mm, and initially white turning to brown or black later. They are laid in a mass on moist soil and cannot withstand drying. Number of eggs laid depends on species and size of bloodmeal: some species can lay up to 450 eggs per batch, and up to seven batches per lifespan. Eggs hatch in 2–10 days depending on species and temperature.

LARVAE are worm-like, 2–5 mm long, and creamy white. They require moisture and develop in aquatic or semi-aquatic habitat through four instars. Some Culicoides spp. larvae are truly aquatic and develop in streams and ponds but most species occur in semi-aquatic organically rich areas such as marshes, bogs, edges of ponds and streams, tree holes, and saturated rotting wood. They can also be found in plants that trap moisture, and water-logged / wet compost, and garden soil. Larvae of livestock-biting Culicoides spp. are found in saturated manure-enriched soil around wastewater ponds and watering troughs. Human-biting Leptoconops spp. develop in moist soil fissures in many parts of the arid west. Forcipomyia spp. larvae develop in mosses, algae, rotting logs, and moist soil beneath cow-pats. The larvae feed on small organisms and the larval stage can last from two weeks to a year, depending on species, temperature, geographic area, and food supply.

PUPAE are 2–5 mm long, with color varying from pale yellow to to light or dark brown. The pupal stage lasts 2–3 days.

Mitigation

The most effective way to reduce the chances of being bitten is to adopt a combination of the following measures: 

  • Scheduling outdoor activities to avoid daily peaks of biting midges. This requires getting to know when those peaks occur.
  • Installing window and door screens with mesh size smaller than normal window screen to prevent midges from entering dwellings.
  • Having fans on at high speeds to exclude midges from limited areas.
  • Covering up exposed skin by wearing long pants, long-sleeved shirts, head net, hat, and shoes, if planning to be outdoors for extended periods. Be aware that midges can fly up hems and cuffs that are not tucked in or buttoned up tight.
  • Spraying a bug repellent on exposed skin or clothing.*

*Repellents containing DEET (diethytoluamide) and clothing impregnated with DEET or permethrin have been found to offer limited protection or be ineffective for many people. In Taos County, some people swear by Avon Skin So Soft, others by Old Spice, and yet others botanicals such as picaridine or lemon eucalyptus, or a whole suite of essential oils including eucalyptus, tea tree, peppermint, lemongrass. Others recommend producing a kind of ‘internal bug repellent’ through eating a clove of garlic a day and/or increasing turmeric intake and avoiding sugary foods during bug season. Some people claim success in reducing their midge population by spraying neem oil around moist planting areas in their gardens.

Disclaimer: We have not tested the suggested repellents / measures and cannot speak to their effectiveness or potential side effects.

References

https://extension.entm.purdue.edu/publichealth/insects/bitingmidge.html

http://entnemdept.ufl.edu/creatures/aquatic/biting_midges.htm

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=10473

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