Figure 1. A field collecting kit
1.1 Basic Equipment
Collecting methods may be divided into two broad categories. In the first the collector actively searches out the insects, using nets, aspirators, beating sheets, or whatever apparatus suits his or her particular needs. In the second, the collector participates passively and permits traps to do the work. Both approaches may be used simultaneously, and both are discussed in the following pages. Using a variety of collecting methods will help to maximize the number of specimens taken, especially when briefly visiting an interesting area.
While picking up insects by hand is simple and sometimes effective, their size, mobility, and the possibility of being bitten or stung usually dictates that various kinds of equipment and special methods are needed. Those described here have general application; it is expected that the collector will make some adaptations to fit his or her own purposes and resources. In fact, as experience collecing increases, or the target group becomes more focussed, the use of specialized techniques increases. For additional information, especially concerning the use of specialized techniques, consult the list of references.
References (general): Arnett, 1985; Balogh 1958; Banks 1909; Banks et al. 1981; Bland & Jacques 1978; Borror et al.; British Museum 1974; Cantrall 1939-40; Cantrall 1941; Chu 1949; Edmunds & McCafferty 1978; Foote 1948; Klots 1932; Knudsen 1966; Knudsen 1972; Kogan & Herzog 1980; Lehker & Deay 1969; Lincoln & Sheals 1979; McNutt 1976; Martin 1977; Nicholls 1970; Norris 1966; Oldroyd 1958; Peterson 1964; Service 1976; Southwood 1979; Stein 1976; Upton, 1991; USDA 1970; USDA 1966-70; Urquhart 1965; Wagstaffe & Fidler 1955.
The equipment used to assemble a general insect or mite collection need not be elaborate or expensive. In many instances, a collecting net (see below) and several killing bottles (see p. 5) will suffice; however, additional items will permit more effective sampling of a particular fauna. Many collectors carry a bag (fig. 1) or wear a vest in which they store equipment. The following items usually are included in the general collector's bag:
(1) Forceps. Fine, lightweight forceps are recommended; if sharp-pointed forceps are used, care must be taken not to puncture specimens. If possible, grasp specimens with the part of the forceps slightly behind the points.
(2) Vials containing alcohol or other preservatives (see p. 21).
(3) Killing bottles of various sizes.
(4) Small boxes or containers for storing specimens after their removal from killing bottles. These may be made of cardboard, plastic, or metal and should be partly filled with soft tissue or cloth to keep specimens from rolling about. Do not use cotton because specimens become entangled in the fibers and may become virtually impossible to extricate without damage.
(5) Small envelopes for temporary storage of delicate specimens and/or gelcaps for tiny specimens.
(6) One or more aspirators (see p. 7-8).
(7) Absorbent tissue for use in killing bottles and aspirators.
(8) Notebook and writing equipment for jotting down notes and label data.
(9) A strong knife for opening galls, seed pods, twigs, etc and a pair of scissors for cutting labels.
(10) A small, fine brush (camel's hair is best) for picking up minute specimens. Moisten the tip; tiny specimens will adhere to it and may be transferred to a killing bottle or vial.
(11) Bags for storing plant material, rearing material, or Berlese samples. For collecting much plant material, a botanist's vasculum or tin box is advisable.
(12) A hand lens.
This list may be modified according to the special kinds of insects or mites to be collected. A small digging tool or trowel may be useful for collecting insects from soil or for gathering Berlese samples and a heavy knife or small hatchet for searching under bark or in decaying logs. A plant press should be available to prepare plant specimens for determination or as voucher specimens, especially when leaf-mining insects are being studied. When collecting at night, have a flashlight or headlamp; the latter is especially useful because it leaves the hands free.
Much of the equipment listed above may be obtained from around the home or from ordinary sources like a drug store, but equipment especially designed for insect collecting often must be bought from special supply houses. If there is a local company, their address may usually be found in the yellow pages of telephone directories under "Biological Laboratory Supplies" or "Laboratory Equipment and Supplies." The faculty members of a local university's biology or entomology department or curators at a nearby museum are usually willing to help and in the best position to recommend a supplier in the area. Professional journals also sometimes carry advertisements for equipment suppliers.
1.2 Collecting Nets
Collecting nets come in three basic forms: Aerial, sweeping, and aquatic. The first is designed especially for collecting butterflies and other flying insects. Both the bag and handle are relatively lightweight. The sweeping net is similar to the aerial net but is stronger and has a more durable bag to withstand being dragged through dense vegetation. Aquatic nets are used for gathering insects from water and are usually made of metal screening or heavy scrim with a canvas band affixed to a metal rim. A metal handle is advisable because wooden ones may deteriorate after repeated wetting. The net you choose depends on the kind of insects or mites you wish to collect.
Figure 2. Construction of a sweeping net: A, Steet wire loop; B, pattern for cutting net bag; C, top of net sewed to canvas band that is fitted over wire loop; D, end of net handle showing grooves and holes into which arms of wire loop fit; E, completed net with wooden handle.
Several kinds of nets, including collapsible models with interchangeable bags, are available from biological supply houses, but anyone with a little mechanical ability can make a useful net. The advantage of a homemade net is that the size and shape can be adapted to the needs of the user, to the kind of collecting intended, and to the material available, which need not be expensive. These materials include-
(1) Piece of heavy (8-gage) steel wire for the rim, bent to form a ring 30-38 cm in diameter (fig. 2, A). Small nets 15 cm or so in diameter sometimes are useful, but nets larger than 38 cm are too cumbersome for most collecting.
(2) Dacron or other strong, light fabric through which air can flow freely. Brussels netting is best but may be difficult to obtain; otherwise nylon netting, marquisette, organdy, or good quality cheesecloth can be used, but the last snags easily and is not durable. The material should be folded double and should be 1.5-1.75 times the rim diameter in length (fig. 2, B). The edges should be double-stitched (French seams).
(3) Strip of muslin, light canvas, or other tightly woven cloth long enough to encircle the rim. The open top of the net bag is sewn between the folded edges of this band to form a tube through which the wire rim is inserted (fig. 2, C).
(4) Straight hardwood dowel about 19 mm in diameter and 105-140 cm long (to suit the collector). For attachment of the rim to the handle, a pair of holes of the same diameter as the wire are drilled opposite each other to receive the bent tips of the wire, and a pair of grooves as deep and as wide as the wire are cut from each hole to the end of the dowel to receive the straight part of the wire (fig. 2, D).
(5) Tape or wire to lash the ends of the rims tightly into the grooves in the end of the handle. This may be electrician's plastic tape or fiber strapping tape commonly used for packaging. If wire is used, the ends should be bound with tape to secure them and to keep them from snagging. A close-fitting metal sleeve (ferrule) may be slipped over the rim ends and held in place with a small roundheaded screw instead of tape or wire lashing.
After the net has been placed on the rim, the ends of the band should be sewn together and the rim ends fastened to the handle. The other end of the handle should be filed to remove sharp edges. The net is then ready for use (fig. 2, E).
Efficient use of a net is gained only with experience. Collection of specimens in flight calls for the basic stroke-swing the net rapidly to capture the specimen, then follow through to force the insect into the very bottom of the bag. Twist the wrist as you follow through so the bottom of the bag hangs over the rim; this will entrap the specimen. If the insect alights on the ground or other surface, it may be easier to use a downward stroke, quickly swinging down on top of the insect. With the rim of the net in contact with the ground to prevent the specimen from escaping, hold the tip of the bag up with one hand. Most insects will fly or crawl upward into the tip of the bag, which can then be flipped over the rim to entrap the specimen.
Sweeping the net through vegetation, along the sand and seaweed on beaches, or up and down tree trunks will catch many kinds of insects and mites. The aerial net may be used in this way, but the more durable sweeping net is recommended for such rough usage. After sweeping with the net, a strong swing will bring anything in the bag to the bottom, and then by immediately grasping the middle of the net with the free hand, the catch will be confined to a small part of the bag. Only the most rugged sweeping net may be used through thistles or brambles. Even some kinds of grasses, such as sawgrass, can quickly ruin a net. Burs and sticky seeds are also a serious problem.
The catch may be transferred from the bag to a killing jar in one of several ways. Single specimens are transferred most easily by lightly holding them in a fold of the net with one hand while inserting the open killing jar into the net with the other. While the jar is still in the net, cover the opening until the specimen is stupefied; otherwise, it may escape before the jar can be removed from the net and closed. To prevent a butterfly from damaging its wings by fluttering in the net, squeeze the thorax gently through the netting when the butterfly's wings are closed. Experience will teach you how much pressure to exert; obviously, pinching small specimens of any kind is not recommended. When numerous specimens are in the net after prolonged sweeping, it may be desirable to put the entire tip of the bag into a large killing jar for a few minutes to stun the insects. They may then be removed and desired specimens placed separately into a killing jar, or the entire mass may be dumped into a killing jar for later sorting. These methods of mass collecting are especially adapted to obtaining small insects not readily recognizable until the catch is sorted under a microscope.
Removal of stinging insects from a net may be a problem. They will often crawl toward the rim of the bag and may be made to enter a killing jar held at the point where they crawl over the rim. However, many insects will fly as soon as they reach the rim, and a desired specimen may be lost. A useful method is to trap the insect in a fold of the net, carefully keeping a sufficient amount of netting between fingers and insect to avoid being stung. This fold of the net can then be inserted into the killing jar to stun the insect. After a few moments, it should be safe to remove the insect from the net and transfer it to a killing jar. If the stunned insect clings to the net and does not fall readily into the jar, use forceps or pry the insect loose with the jar lid or a small stick-not with your fingers.
Aerial nets made of dacron or nylon may be used to sweep insects from water if an aquatic net is not at hand. The netting will dry quickly if swept strongly through the air a few times; however, it should not be used again until thoroughly dry, or other specimens, especially butterflies, may be ruined. A number of special modifications are necessary to adapt a net for aquatic collecting.
Figure 3. A truck equipped with a large net
For specialized collecting, nets can be attached to the ends of beams that are rotated about their midlength by a motor drive. Nets also can be adapted to be towed by or mounted on vehicles (fig. 3) (Peck and Cook, 1992).
References: Dresner 1970; Johnson 1950; Rogers & Smith 1977; Rudd & Jensen 1977; Takeda et al. 1962; Williams & Miine 1935; vehicle-mounted net: Almand et al. 1974; Barnard 1979; Grigarick 1959; Harwood 1961; Hill 1971; Holzapfel et al. 1978; Kronblad & Lundberg 1978; Landin 1976; McNutt 1976; Noyes, 1982; Rudd & Jensen 1977; Torre-Bueno 1937; Traver 1940.
1.3 Killing Jars or Bottles
Effective collecting of insects and related groups usually requires that the specimens be killed so that they may be properly mounted and studied. The most widely employed method for killing collected specimens is the killing jar (bottle). Any heavy, wide-mouthed glass jar or bottle with a tight-fitting stopper or metal screw top may be used. Tops that may be removed with only a quarter turn often are preferred but may not be obtained readily. The killing agent used may be any of various liquids or solids. Liquid killing agents generally are considered to be slower acting but safer to use than solids such as cyanide, but some of them are known to accumulate in human tissue after repeated or prolonged exposure. Despite its extreme toxicity, cyanide is a noncumulative poison, and brief exposure to the fumes, as inevitably occurs when opening jars to insert or remove specimens, is not believed to reault in any permanent harm. Never deliberately inhale the fumes, even momentarily. All killing agents are to some extent hazardous to human health. All killing jars or bottles should be clearly labeled "POISON" and should be kept away from children or persons who may be unaware of their potential danger.
When not in use, killing jars should be stored in a safe place away from children and pets where they are not liable to accidental breakage. Cyanide jars should not be stored in an area such as a bedroom where any accidental leakage could expose someone to fumes. Remember that killing agents can be as effective against humans as they are against insects and that care and caution in their construction and use are essential.
1.4 Liquid Killing Agents
Jars for use with liquid killing agents are prepared in one of two ways. One way (fig. 4, A) is to pour about 2.5 cm of plaster of paris mixed with water into the bottom of the jar and allow the plaster to dry. Enough of the killing agent is then added to saturate the plaster; any excess should be poured off. This kind of jar can be recharged merely by adding more killing agent. The second method is to place a wad of cotton or other absorbent material in the bottom of a jar, pour enough liquid killing agent into the jar to nearly saturate the absorbent material, and then press a piece of stiff paper on it or a cardboard cut to fit the inside of the jar tightly. The paper or cardboard acts as a barrier between the insect and the killing agent, keeping the latter from evaporating too rapidly and also preventing the specimen from becoming entangled in loose fibers.
Figure 4. Killing jars; A, for use with liquid kiling agent; B, for use with solid killing agent.
Among the liquid killing agents are ethyl acetate (CH3CO2 · C2H5), ether (diethyl ether, C2H5 · O · C2H5), chloroform (CHCI3), and ammonia water (NH4OH solution). Ethyl acetate is most widely used. All of these chemicals are extremely volatile and flammable and should never be used near fire. Children should only use them under adult supervision.
Ethyl acetate is regarded by many as the most satisfactory liquid killing agent. Its fumes are less toxic to humans than those of the other substances. Although it usually stuns insects quickly, it kills them slowly. Specimens that appear dead may revive if removed from the killing jar too soon, but a compensating advantage is that most specimens may be left in an ethyl acetate killing jar for several days and still be limp. If the ethyl acetate is allowed to evaporate from the specimens, they will harden. Killing jars with ethyl acetate are preferred by many entomologists, especially for infrequent use.
Ether and chloroform are both extremely volatile and flammable and should not be used near an open flame or lighted cigarette. Their high volatility makes them serviceable in a killing jar for only a short time. Perhaps the greatest hazard with chloroform is that even when stored in a dark-colored jar, it eventually forms the extremely toxic gas phosgene (carbonyl chloride, COCI2). Chloroform, however, is useful when other substances cannot be obtained. It stuns and kills quickly but has the disadvantage of stiffening specimens.
Ethyl Alcohol (ethanol or ETOH) is widely used to kill small Coleoptera adults, small Hymenoptera, and many immature insects and soft-bodied insects. It is most commonly used at 70-80% concentration and many workers add 5% glacial acetic acid ("acetic alcohol") which helps penetration of the alcohol into the specimen and leaves specimens more relaxed. Isopropyl alcohol (rubbing alcohol) may also be used, and may be easier to find and purchase than Ethanol. However, Ethanol is preferred for most applications. Ethanol is used commonly in Berlese funnels and similar traps.
Liquid ammonia is irritating to humans, and in general is not a particularly effective killing agent for most insects. However, it is highly recommended for use in small vials for dispatching microlepidoptera, and it has been used with variable success in blacklight traps, again for Lepidoptera. Specimens killed in ammonia tend to stay in a relaxed condition much longer than those killed by cyanide, allowing greater ease of spreading. Ammonia is readily available from many sources. Ammonium carbonate, a solid but volatile substance, also can be used.
1.5 Solid Killing Agents
The solid killing agents most often used in killing jars are the cyanides-potassium cyanide (KCN), sodium cyanide (NaCN), or calcium cyanide [Ca(CN)2]. Handle all cyanides with extreme care. They are dangerous, rapid-acting poisons with no known antidote. If even a single grain touches the skin, wash immediately with water. To avoid handling the cyanide and having to find a safe place to store or dispose of surplus crystals, you may be able to find a chemist, pharmacist, or professional entomologist to make the killing jar for you. If this is not feasible, use utmost care in following the instructions given here.
To make a cyanide killing jar or bottle, place a layer (about 15 mm) of cyanide crystals in the bottom (fig. 4, B). Potassium cyanide is best; sodium cyanide is as effective but is hygroscopic, that is, it absorbs water and makes the jar wet; and calcium cyanide is seldom available. Cover the crystals with about 10 mm of sawdust and then add about 7 mm of plaster of paris mixed with water to form a thick paste, working quickly before the plaster solidifies. Then add crumpled absorbent paper to prevent water condensation on the inside glass surface. Instead of the plaster of paris, a plug of paper or cardboard may be pressed on top of the sawdust. Be sure that it fits tightly. When ready to use after a few hours, place several drops of water on the plaster or paper plug. In an hour or so, enough fumes of hydrocyanic acid will have been produced to make the jar operative. Do not test this by sniffing the open jar.
Every killing jar or bottle should be clearly and prominently labeled "POISON". The bottom must be covered with tape, preferably cloth, plastic, or clinical adhesive tape, to cushion the glass against breakage and to keep its dangerous contents from being scattered if the container breaks.
Killing jars or bottles will last longer and give better results if the following simple rules are observed:
(1) Place a few narrow strips of absorbent paper in each jar or bottle to keep it dry and to prevent specimens from mutilating or soiling each other. Replace the strips when they become moist or dirty. This method is useful for most insects except Lepidoptera, which are too difficult to disentangle without damage.
(2) Do not leave killing jars in direct sunlight as they will sweat and rapidly lose their killing power.
(3) If moisture condenses in a jar, wipe it dry with absorbent tissue.
(4) Keep delicate specimens in separate jars so that larger specimens will not damage them.
(5) Do not allow a large number of specimens to accumulate in a jar unless it is to be used specifically for temporary storage.
(6) Do not leave insects in cyanide jars for more than a few hours. The fumes will change the colors of some insects, especially yellows to red, and specimens will generally become brittle and difficult to handle.
(7) If it is necessary to keep insects in killing jars for more than several hours, place the specimens in another container and store them in a refrigerator.
(8) Keep butterflies and moths in jars by themselves so that their hairs and scales will not ruin other kinds of insects.
(9) Never test a killing jar by smelling its contents.
(10) Old jars that no longer kill quickly should be recharged or disposed of by burning or burying. A cyanide jar that has become dry may be reactivated by adding a few drops of water.
Spray-dispensed insecticides may be used, if not to kill specimens, to at least 'knock them down' into a container from which they may be picked up. If they are directed into a container topped with a funnel, they may be allowed to revive and treated further as desired (see Clark & Blom 1979).
References: Banks et al. 1981; Clark & Blom 1979; Frost 1958; Lindroth 1957; Pennington 1967; Preiss et al.; White 1964.
1.6 Aspirators and Suction Devices
Figure 5. Aspirators; A, sucking-type; B, blowing-type
The aspirator (fig. 5, A), known in England as a 'pooter,' is a convenient and effective device for collecting small insects and mites. The following materials are needed to construct an aspirator:
(1) Vial 2.5-5 cm in diameter and about 12 cm long.
(2) Two pieces of glass or copper tubing about 7 mm in diameter, one piece about 8 cm long and the other about 13 cm long.
(3) Rubber stopper with two holes in which the tubing will fit snugly.
(4) Piece of flexible rubber or plastic tubing about 1 meter long, with diameter just large enough to fit snugly over one end of shorter piece of stiff tubing.
(5) Small piece of cloth mesh, such as cheesecloth, and rubberband.
To make an aspirator, bend the glass or copper tubes as in figure 5, A. In bending or cutting glass tubes, always protect your fingers by holding the glass between several layers of cloth. Obtain the advice of a chemist or laboratory technician for cutting and bending glass. Moisten one end of the longer tube and insert it through one of the holes in the rubber stopper. Moisten one end of the shorter tube, insert it through the other hole in the stopper, and using a rubberband fasten the cloth mesh over the end that was inserted through the stopper; this will prevent specimens from being sucked into the collector's mouth when the aspirator is used. Attach one end of the flexible tubing to the free end of this tube. The length, size, and amount of bend in the tubing will vary according to the user's needs. To complete the assembly, insert the rubber stopper into the vial. To use the aspirator, place the free end of the flexible tubing in the mouth, move the end of the longer glass tube close to a small specimen, and suck sharply. The specimen will be pulled into the vial.
Instead of using a vial, some workers prefer a tube (fig. 5, B). In either method, it is well to keep small pieces of absorbent tissue in the vial or tube at all times to prevent moisture from accumulating. Be cautioned that there is some danger of inhaling harmful substances or organisms when using a suction-type aspirator (see Hurd 1954).
Either the vial- or tubing-type aspirator (fig. 5, B) may be converted into a blow-type aspirator by removing the 13-cm glass tube (see fig. 5, A) and substituting a T-shaped attachment (fig. 5, B). The flexible tubing is attached to one arm of the 'T,' the opposite arm is left open, and the stem of the 'T' is inserted into the vial and covered with mesh. Upon blowing through the flexible tubing, a current of air passes across the 'T' and creates a partial vacuum in the vial, which produces the suction needed to draw specimens into the vial. This kind of aspirator eliminates the danger of inhaling small particles, fungus spores, or noxious fumes.
Aspirators with a squeeze bulb may sometimes be purchased, or if a valved bulb can be obtained, they may be constructed for use with either pressure or suction. Collection traps also have been devised with the suction feature applied on a much larger scale than with the usual aspirator. Suction produced by a fan has been employed in traps in conjunction with light or other attractants. Some of these traps are described in the following references and in the section on Traps. Suction is created by a piston in a 'slurp-gun' described for aquatic collecting. This principle could be adapted for use in air to gather insects and to deposit them in a vial attached to the side of the piston.
References: Azrang 1976; Barnard & Mulla 1977; Bradbury & Morrison 1975; Clifford et al. 1977; Evans et al. 1964; Galtsoff et al. 1937; Hurd 1954; Johnson 1950; Johnson & Taylor 1955; Johnson et al. 1957; Lumsden 1958; Minter 1961; Mulhern 1942; Scholdt & Neri 1974; Taylor 1962a; Turnbull & Nicholls 1966; White 1964; Weins & Burgess 1972; Williams 1973; Woke 1955.
1.7 Beating Sheets
A beating sheet should be made of durable cloth, preferably white, attached to a frame about 1 meter square, with two pieces of doweling or other light wood crossing each other and fitted into pockets at each corner of the cloth. An ordinary light-colored umbrella also may be used as a beating sheet. Place the beating sheet or umbrella under a tree or shrub and sharply beat the branches or foliage with a club or stick. Specimens will fall onto the sheet and may be removed from the light-colored material by hand or with forceps, a moistened brush, or an aspirator. Locating specimens on the sheet is sometimes a problem because of leaves or other unwanted material dropping onto the sheet. Watching for movement will help locate specimens, as well as tilting the sheet so that the debris is displaced or even allowed to fall off, with the insects and mites left clinging to the cloth.
Beating sheets are especially useful in collecting beetles, true bugs, and larval Lepidoptera. Beating may be the best collecting technique when the weather has turned cold, or early and late in the day, when normally active insects seek shelter in vegetation and are otherwise difficult to detect.
A 'ground cloth' also is used in sampling crop fields (see Rudd & Jensen 1977).
Sifters are used to collect insects and mites that live in ground litter, leaf mold, rotting wood, mammal and bird nests, fungi, shore detritus, lichens, mosses, and similar material. Sifters are especially useful for winter collecting to pick up hibernating specimens. Almost any container with a wire-mesh screen bottom will serve as a sifter. The size of the mesh depends on the size of the specimens sought. For general purposes, screening with 2.5-3 meshes per centimeter is satisfactory. To use the sifter, place the material to be sifted into the container and shake it gently over a white pan or piece of white cloth. As the insects and mites fall onto the cloth, they may be collected with forceps, a brush, or an aspirator.
A similar method is used chiefly to collect mites from foliage. Using a sifter of 20-mesh screen (about 8 per centimeter) with a funnel underneath that leads to a small vial, beat pieces of vegetation against the screen to dislodge the mites, which will fall through the screen and into the vial below.
Another type of sifter employs two hoops of heavy metal, each with a handle. A long (3-4 ft.) canvas bag is sewn to the top hoop. The bag is left open at the end and secured with a cord or twist-tie. About 1 foot down in the bag, the second hoop is sewn to the canvas and to this is attached a metal screen. Coarse debris is loaded into the top and sifted down to the end of the canvas bag. Sifted debris is then ready to be processed by one of the following separators or extractors.
References: Martin 1977.
1.9 Separators and Extractors
Somewhat similar to the sifter are various devices designed to separate or extract live specimens from substances in which they may be found, such as leaf mold and other kinds of vegetable matter, shore detritus, dung, even net sweepings that include so much foreign matter that it is difficult to pick out the insects. These devices usually depend on some physical aid such as light, heat, or dryness to impel the insects to leave the foreign matter.
One of the simplest such devices is the sweeping separator (fig. 7). This is simply a carton or wooden box with a tight-fitting lid. Near the top of the box on one side is inserted a glass jar. If the jar is made with a screw top, a hole of proper diameter cut in the side of the carton will permit the jar to be screwed onto it. The cover ring, without the lid, from a home-canning jar may be nailed to the periphery of a hole in a wooden box and the jar then screwed onto the ring.
Figure 6. Separation bag
The sweepings are dumped into the box and the cover is quickly closed. The insects in the darkened box soon will be attracted to the lighted glass jar. When all the insects appear to have entered the jar, it can be removed and its contents put into a killing jar. Alternatively, a jar cover containing a piece of blotting paper soaked with xylene may be placed over the jar for awhile to stun the insects, which may then be sorted.
A more sophisiticated version of this separator is made of alumnium with a clear plastic top and cloth collecting bag (fig. 6). Sitting on three legs, this separator allow the collector to dump the catch into the bag, place the lid, which is lined with a magnet, on top and insert an aspirator through a small hole in the side of the bag. As insects are attracted to the top and collect on the plastic, the aspirator can be moved about to suck up the insects of interest.
Nets can also be modified to help keep plant material contacted during sweeping away from the insects. In most cases, hardware cloth or some other screening material with fairly large holes (ca. 1cm in diameter) is placed across the net opening and fastened to the net ring. This works well to keep out larger pieces of plant debris but will not be effective in excluding seeds and other small plant parts (Noyes 1988; Zolnerowich et al. 1990).
Insects collected into alcohol can also be separated from plant debris by the use of screens. In this method, a screen of 1/4 inch diameter galvanized hardware cloth is fastened over a frame. Below this is another screen made from a very fine mesh material such as organdy or a small section of panty hose. The insect/plant material collection is poured over the coarser screen and alcohol is added. When agitated, the insect will sink through the larger screen while plant material will float or be stopped by the screen mesh. A similar method uses a set of three stacked screens of decreasing diameter and specimens are washed from one layer to another using a gentle spray of water. Care must be taken so that the washing does not damage the specimens.
Figure 7. Sweeping separator
The Berlese or Tullgren funnel (Upton 1991) (fig. 8) and its modifications are cleaner and more efficient than sifting to separate insects and mites from leaf mold and similar materials. The sample (usually presifted to remove large debris) is placed on a screen near the top of a funnel. A light bulb can be placed above the sample to produce heat and light, which drive the insects downward into the funnel, or heated coils or a jacket around the funnel can be used to dry the sample and make it inhospitable. The insects and mites are directed by the funnel into a container, sometimes containing alcohol at the bottom of the funnel. Care should be taken not to dry the sample so rapidly that slow-moving specimens are immobilized before they can leave the sample. To prevent large amounts of debris from falling into the container, place the sample on the screen before the container is put in place.
Figure 8. Berlese or Tullgren Funnel
A similar separator is the photoeclector or Winkler/Moczarski Elector. This device is similar to the Berlese funnel except that no light bulb or other heat source is used to drive the insect to the bottom. Instead, an open jar, with a most cloth or tissue inside, is attached to the bottom of the funnel or canvas bag and insects are attracted to the light and humidity. An added advantage of this device is that it requires no electricity and so may be more readily used in the field.
References: Besuchet et al. 1987; Brown 1973; Everett & Lancaster 1968; Finch & Skinner 1974; Gui et al. 1942; Kempson et al. 1962; Kevan 1955; Kevan 1962; Lane & Anderson 1976; Martin 1977; Masner & Gibson 1979; Murphy 1962; Newell 1955; Norton and Kethley 1988; Salmon 1946.