AN AMATEUR NATURALIST’S GUIDE TO NON-BITING MIDGES IN SASKATCHEWAN P. G. MASON, Agriculture Canada, Research Station, 107 Science Place, Saskatoon, Saskatchewan. S7N 0X2; D. W. PARKER and P. MORRILL, Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan. S7N 0W0 Non-biting midges (chironomids) ing other aquatic insects and mol- belong to the insect order Diptera (true luscs.1 14,15.41 flies). Their life cycle consists of four stages: egg, larva, pupa and adult. Chironomid larvae form an important part of many aquatic ecosystems. In The larvae and pupae of chironomids Tobin Lake and nearby parts of the Sas¬ inhabit almost every aquatic habitat in katchewan River, two-thirds of the the world. Some species can withstand aquatic insect species are chironomids.27 temperatures in excess of 50°C in Chironomids also form the bulk of the Australian rockpools, while others in¬ aquatic insect species in marshes and habit glacial meltwaters at 0.5°C.18,19 In ponds.17,50 Larvae in some nutrient-rich Canada, chironomids have been found habitats occur in densities of more than living in petroleum pools and one 100,000/m2.20 species, Cricotopus ornatus Meigen, oc¬ curs abundantly in Waldsea Lake, Sas¬ The larvae of most species feed on katchewan, where salinity exceeds algae and decaying plant material and 200,000 ppm (ten times the salinity of therefore provide primary links in ocean water).38,42 Many species, par¬ aquatic food webs. They are also impor¬ ticularly in the genera Chironomus and tant indicators of pollution at sublethal Cryptochironomus, have a characteristic and lethal levels.29, 5,46 red colour because their blood (hemolymph) contains the oxygen carry¬ Chironomids are economically impor¬ ing pigment haemoglobin. These so- tant in many parts of the world. Larvae called “blood worms” live in the mud of one semi-terrestrial species, Bryo- where oxygen levels are very low, such phaenocladius fur cat us (Kieffer) are 36 as at the bottom of Waskesiu Lake. known to cause damage to seedling tomato and lettuce crops in England.9 In Some chironomid species form close certain parts of Florida and California, relationships with other organisms. For large emergences of adult chironomids example, certain species of Cricotopus cause reduced use of recreational live within colonies of the blue-green areas.2,7,22 In many areas people suffer alga Nostoc.6 Species of the genus from allergenic responses to either body Metriocnemus live in pitcher plants.34 hairs or haemoglobin of chironomid Many other species exhibit phoresy, a adults.10 In Saskatchewan, summer mass type of relationship in which one or¬ emergences of adult Chironomus ganism is carried on the body of a larger plumosus (Linnaeus) at Tobin Lake have organism but does not feed on the latter, resulted in many complaints by local or parasitize other invertebrates, includ- residents. 174 Blue Jay The objectives of this article are to ing of their larval case or burrow and fil¬ provide the reader with some back¬ ter particles such as bacteria, detritus and ground information on these ecologically algae from the water. important insects and to list the species which have been recorded in Sas¬ Species of the subfamily Tanypodinae katchewan. and a few species from other subfamilies are predators. The mouthparts of these Life History larvae are modified to grasp prey. Small prey are engulfed whole; larger prey are During the spring or summer the held while the body fluids are sucked female deposits a mass of eggs em¬ out.28 A few species are parasitic on bedded in a gelatinous matrix. When the larger aquatic insects and molluscs.41 egg matrix comes in contact with water, it expands and floats on the surface until The length of time required to com¬ it contacts a rock, vegetation or other plete the life cycle depends on environ¬ solid surface, to which it adheres. The mental conditions, especially tempera¬ duration of the egg stage depends on the ture.30 In warm regions, life cycles can temperature.31 be as short as two weeks.43 In temperate regions, such as Saskatchewan, there are The larval stage is the longest of the usually only one or two generations per life cycle and is essentially the only year because development is interrupted feeding stage. The larva sheds its skin 31 during winter. In these regions the lar¬ (moults) four times. The first instar larva vae are the usual overwintering stage.11 (the larva from the time of hatching until the first moult) is free-swimming which Just before pupation the anterior part is important for dispersal in lakes and of the larva becomes enlarged and the ponds. In rivers and streams, dispersal adult leg, wing and antennae can be ob¬ is accomplished by drifting with the cur¬ served through the sheath during this rent or by upstream movement by the stage. Pupation of burrow-dwelling larvae. First instar larvae obtain chironomids usually occurs within the nourishment from the remaining yolk burrow. In free-living species the pupa is and by feeding on suspended particles in also free-living. The pupal stage typical- the water. 5 31 ly lasts two to three days. ' When a suitable microhabitat is found, When mature, the pupa rises to the the larvae establish either a sedentary or water surface; the skin, which is also an free-living mode of life, which continues exoskeleton, splits lengthwise long the throughout the rest of larval develop¬ upper surface of the thorax; the adult ment. Many sedentary species construct emerges through this split. The adult is cases composed of particles of silt or able to fly almost immediately. The adult sand cemented together with silk-like stage may last for several weeks; its secretions from their salivary glands. primary functions are dispersal and Some species attach their cases to plants reproduction. The adults have reduced or animals while others make burrows a mouth parts and most do not feed, al¬ few centimetres into the substrate. Free- though adult females of some species living larvae move over the bottom and imbibe nectar.16 skim plants in search of food. Many lar¬ vae feed be scraping algae, bacteria and Most chironomid species form mating organic debris from rocks or wood, or by swarms comprised of adult males. On a engulfing quantities of sediment.44,51 The warm, calm summer evening, larvae of other species construct a net of chironomid swarms commonly appear silk-like salivary strands over the open- just before sunset at the edge of lakes. 49(4). December 1991 175 The mass of hundreds of individuals adults emerge, can be collected using a gently moves up and down, similar to fine mesh net. In running water, the net smoke rising from a smokestack. The is held in the current for a few minutes swarms occur over a marker, such as a with half the opening below the water post or rock. Females are attracted to the surface; in lakes or ponds the net is swarm and fly into it in search of a mate. skimmed over the surface. The accumu¬ Mating can take place in midair or the lated individuals are washed to the bot¬ pair may fly to the ground. Male tom of the net and the contents placed in chironomids identified by their long, a jar containing 80% alcohol. Foam plumose (feathery) antennae are at¬ along the shore of streams, lakes or tracted to the sound of females in ponds can also yield specimens. flight.35 Dusk is a particularly good time to After mating the females fly to collect adult specimens using an aerial oviposition sites where the egg masses sweep net. Males are attracted also to are laid on the water surface at dawn or lights at night. Specimens are aspirated dusk. Adults may live for up to two into a vial and preserved in 70% alcohol. weeks and the females of some species lay two egg masses. A few species can A label with the location, habitat type, lay eggs without mating.30 approximate water depth, date and name of the collector should be placed on each Collection and Preservation sample. Labels should always be written of Specimens in pencil. Egg masses may be collected from Rearing floating sticks or vegetation. A trap can be made by passing a string through a For many species of chironomids the series of corks, arranged perpendicular larval, pupal and adult stages are known to the prevailing winds or current to col¬ independently of each other and have yet lect floating egg masses. to be associated. Rearing larvae to the adult stage is the best means to fill this Larval and pupal specimens can be important gap in our knowledge. Larvae collected by several methods. A simple can be reared with little or no specialized method involves scooping substrate from equipment. Prepupal individuals, iden¬ the bottom of a water body with a net or tified by the enlarged area just behind kitchen screen and washing the contents the head, are placed in small vials half using a sweeping motion to remove fine full of dechlorinated water (this is done silt particles from the sample. The con¬ using an aquarium dechlorinator or by tents are placed in a white pan partially letting the water stand for 24 h). The filled with water. Live specimens are vials are placed in a tray of water out of removed with a wire loop, dropper or direct sunlight. Tap water (15°C) can forceps and either placed in jars for then be circulated through the tray using transport to the laboratory for rearing or rubber hoses to keep the larvae cool if preserved in 80% alcohol.