BIOLOGY AND CONTROL OF NON-BITING AQUATIC MIDGES
By: Charles Apperson, Michael Waldvogel and Stephen Bambara, Extension Entomology
Insect Note - ENT/rsc-15
|Non-biting midge flies or chironomids commonly
occur in inland and coastal natural and man-made bodies of water. These
midges are commonly known as “blind mosquitoes” because they are mosquito-like
but do not bite. Midges are also called “fuzzy bills” because of the male’s
bushy antennae. These aquatic insects are tolerant of a wide range of environmental
conditions. Chironomid midges are found in swift moving streams, deep slow
moving rivers, stagnant ditches, and in lakes and ponds that are rich in
decomposing organic matter. The presence of certain chironomid midges is
often used as an indicator of water quality.
Bodies of water in urban and suburban areas are subjected to intensive human use through residential, recreational and agricultural activities. Through runoff, these ponds and lakes often become exceedingly rich in nutrients. Consequently, the variety of organisms in such habitats is usually low with just a few pollution tolerant species developing large populations. Some species of chironomid midges that are tolerant of low dissolved oxygen conditions often are a major component of the bottom invertebrate organisms of urban and suburban lakes, ponds and storm water retention ponds.
During summer, the entire life cycle from egg to adult can be completed in 2 to 3 weeks. In the fall, larvae do not pupate, but they suspend development and pass through the winter months as mature larvae. Pupation and emergence of adults occurs the following spring in late March or early April. Several more generations of midges will be produced throughout summer, resulting in mass emergences of adults. In each generation, adults will typically emerge in large numbers for several weeks.
Physical and Cultural
Nutrient reduction. Dense larval populations usually occur in nutrient rich habitats. Fertilizer run-off from residential lawns and garden, golf courses and agricultural fields are sometimes responsible for the development of nuisance populations of midges. Community awareness and education about proper use of fertilizers can avoid
excess run-off into lakes, ponds and streams and can help reduce midge populations.
Lighting Issues. If you live in a near a pond or in a lakeside community, you might try getting advice from your local government or from a lighting consultant concerning the type of public lighting in your neighborhood. It may be possible to reduce lighting or switch from the typical metal halide streetlight to one that is less attractive to midges, such as the use of high-pressure sodium lamps. There might be a situation where you would use brighter lights in an non-occupied area to attract them away from houses or where people are active outdoors. On the personal front, reduce or eliminate exterior lighting at night around your house. Close window shades. Use subdued walkway/landscape type lighting if you wish. Don’t burn lampposts or floodlights except when needed.
BiologicalMidges are fed upon by a large variety of aquatic organisms, such as dragon fly nymphs, predaceous diving beetles and a variety of fish species. Where the diversity of predaceous animals is high, the density of midge larvae is usually held below nuisance population levels. Shallow, organically rich lakes and heavily polluted habitats such as sewage waste lagoons are inhabited by few predaceous species compared to bodies of water that receive less nutrient-rich input.
Predatory fish. Chironomid midges are a major component of the
diet of many fish species. In particular, bottom-feeding fishes, such
as catfish and carp, consume large numbers of midge larvae. However, the
feeding of these fishes has, generally, not been shown to reduce adult
midge populations below nuisance levels adjacent to habitats where there
were large larval populations. You might want to contact your local NC Wildlife Resources Commission office
for advice on stocking ponds.
Larvicides. Granular temephos (Abate ®) is
registered by the U.S. EPA for control of aquatic midge larvae in standing
water habitats . Application of temephos to control chironomid midge larvae
should be regarded as a temporary, “stopgap” method. Although application
of temephos is an effective treatment for control of chironomid midges,
repeated and prolonged use of the chemical may lead to the development
of resistance in midge larvae. Currently, residue tolerances for temephos
in fish have not been established. Consequently, it is illegal to consume
fish that are caught in bodies of water that have been treated with temephos.
The biological larvicide, Bacillus thuringiensis var. israelensis (Bti), is registered for use against chironomid midge larvae. Unlike temephos which exerts contact toxicity, Bti is toxic after being consumed by the larvae. Consequently, in waters of high organic content (which present a competing food source for the midges), Bti is only effective at high rates of application (at least 10 times the rates needed for mosquitoes), which limits the economic use of Bti to small habitats. To maximize the effectiveness of larvicides, applications should be properly timed. Accordingly, dredge samples of bottom mud should be collected, sieved, and the chironomid larvae recovered and counted. Chemical treatments should be made when the number of larvae found equals or exceeds 200 per 6 inch square bottom sample. This treatment threshold is completely arbitrary. It is based on insecticide treatments made for the control of midge larvae in Florida and California. Without monitoring a midge population for one season, the rela-tionship between numbers of immature midges in the bottom mud and consequent numbers of nuisance adults can not be established.
The insect growth regulator methoprene (Strike®) is registered for use in municipal wastewater treatment facilties to control midges and filter flies.
Adulticides. Many insecticides that are registered for the control of adult mosquitoes are also registered for application against non-biting midge adults. These products are listed in the NC Agricultural Chemicals Manual . Adulticides can be applied in the air as ultra low volume sprays or to wall surfaces or vegetation where midge adults rest. The use of insecticides against adults should be expected to achieve temporary control during heavy emergence periods, because treated areas are rapidly repopulated by midges flying in from outside the treatment zone. Application of residual insecticides to porch alcoves, carports, under the eaves of house and other similar areas should help to discourage the establishment of spiders that are associated with outbreaks of chironomid midge adults.
References used in preparing this publication:Ali, A. and C. D. Morris. 1992. Management of non-biting aquatic midges. IFAS, Univ. of Florida Medical Entomology Laboratory Technical Bulletin no. 4. 16 p.
Koehler, P. 1980. Extension Entomology Report #62. IFAS, Univ. of Florida,
Florida Cooperative Extension Service Plant Protection Pointers. 6 p.
[Blind mosquito life cycle taken from Koehler (1980)].
Pest information and control recommendations presented here were developed for North Carolina and may not be appropriate for other states or regions. Any recommendations for the use of chemicals are included solely as a convenience to the reader and do not imply that insecticides are necessarily the sole or most appropriate method of control. Any mention of brand names or listing of commercial products or services in the publication does not imply endorsements by North Carolina Cooperative Extension nor discrimination against similar products or services. All recommendations for pesticide use were legal at the time of publication, but the status of pesticide registrations and use patterns are subject to change by actions of state and federal regulatory agencies. Individuals who use chemicals are responsible for using these products according to the regulations in their state and to the guidelines on the product label. Before applying any chemical, always obtain current information about its use and read the product label carefully. For assistance, contact the Cooperative Extension Center in your county.
Distributed in furtherance of the acts of Congress of May 8 and June 30, 1914. North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, or disability. In addition, the two Universities welcome all persons without regard to sexual orientation. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.