Since a trap is defined as anything that impedes or stops the progress of an organism, this subject is extensive, including devices used with or without baits, lures, or other attractants. Besides its construction, the performance of a trap depends on such factors as its location, time of year or day, weather, temperature, and kind of attractant used, if any. A little ingenuity coupled with knowledge of the habits of the insects or mites sought will suggest modifications or improvements in nearly any trap or may even suggest new traps.
Only a few of the most useful traps are discussed here, but the following references describe many more, especially Martin 1977; Peterson 1964; Southwood 1979.
References: A'Brook 1973; Banks 1959; Banks et al. 1981; Barber 1931; Bidlingmayer 1967; Broadbent 1949; Broadbent et al. 1948; Dunn & Reeves 1980; Evans 1975; Flaschka & Floyd 1969; Ford 1973; Glasgow & Duffy 1961; Golmeric & Davenport 1971; Granger 1970; Hafraoui et al. 1980; Hanec & Bracken 1964; Hansens et al. 1971; Hargrove 1977; Hartstack et al. 1968; Hathaway 1981; Heathcote et al. 1969; Hienton 1974; Hollingsworth et al. 1963; Howell 1980; Kimerle & Anderson 1967; Klein et al. 1973; Martin 1977; Meyerdirk et al. 1979; Morris 1961; Peterson 1964; Pickens et al. 1972; Southwood 1979; Sparks et al. 1980; Taylor 1962b; Thorsteinson et al. 1965; Weseloh 1974; Whittaker 1952; Williams 1951; Woke 1955.
1.10.1 Effects of Elevation
One of the external factors affecting the performance of traps, especially light traps, has been specially studied, namely the effect of the elevation (above sea or ground level) at which the trap is placed when in use. The subject is complex, with many variables related to kinds of insects, locality, and so forth, which are discussed in the following references.
References: Blakeslee et al. 1959; Callahan et al. 1972; Cooke 1969; Frost 1957; Glick 1939; Glick 1957; Goma 1965; Meyers 1959; Roling & Kearby 1975; Stewart & Lam 1968.
1.10.2 Windowpane Traps
One of the simplest and cheapest traps is a barrier consisting of a windowpane held upright by stakes in the ground or suspended by a line from a tree or from a horizontal line. A trough filled with a liquid killing agent is so placed that insects flying into the pane drop into the trough and drown. They are removed from the liquid, washed with alcohol or other solvent, then preserved in alcohol or dried and pinned. The trap is not recommended for adult Lepidoptera or other insects that may be ruined if collected in fluid.
A modification of this trap uses the central "pane" of a malaise trap instead of a pane of glass. The malaise trap pane covers more space than glass, is easier to transport, and, of course, is not breakable. Various mesh sizes if cloth can also be used depending on the insects targeted. These traps may also be referred to as flight intercept traps.
References: Chapman & Kinghorn 1955; Corbet 1965; Kato et al. 1966; Lehker & Deay 1969; Masner and Goulet 1981; Nijholt & Chapman 1968; Peck and Davies 1980; Roling & Kearby 1975; Wilson 1969.
1.10.3 Interceptions Nets and Barriers
A piece of netting, 1.8 meters or more in height, can be stretched between three trees or poles to form a V-shaped trap with the wide end of the V open. A triangular roof should be adjusted to slope gently downward to the broad open side of the V. A device of this type will intercept many kinds of flying insects, particularly if the trap is situated with the point of the V toward the side of maximum light and in the direction of air movement. A pair of such nets set in opposite directions, or a single net in a zigzag shape, will intercept specimens from two directions. Since insects flying into such a net tend to gather at the pyramidal apex, they are easy to collect. In one variant of this trap the cloth is sprayed with a sythetic pyrethroid insecticide and the insects which are killed by contact with the cloth then fall into a long pan trap at the bottom. The so-called 'funnel' or 'ramp' traps are interception devices that direct insects to a central point, where a retaining device or killing jar may be placed. More complex arrangements have been described in the literature, primarily for migrating butterflies.
References: Gillies 1969; Graham et al. 1961; Hocking & Hudson 1974; Jonasson 1954; Leech 1955; Masner and Goulet 1981; Merrill & Skelly 1968; Nielsen 1960; Parman 1931, 1932; Steyskal 1981; Walker and Lenczewski 1989; Walker and Whitesell 1993, 1994.
1.10.4 Malaise Traps
One of the most widely used insect traps was developed by the Swedish entomologist René Malaise and that now bears his name. Several modifications of his original design have been published, and at least one is available commercially. The trap, as originally designed, consists of a vertical net serving as a baffle, end nets, and a sloping canopy leading up to a collecting device (fig. 9). The collecting device may be a jar with either a solid or evaporating killing agent or a liquid in which the insects drown. The original design is unidirectional or bidirectional with the baffle in the middle, but more recent types include a nondirectional type with cross baffles and with the collecting device in the center. Malaise traps have been phenomenally successful, sometimes collecting large numbers of species that could not be obtained otherwise. Attractants may be used to increase the efficiency of the traps for special purposes.
Figure 9. Malaise trap
References: Butler 1966; Townes 1972; Steyskal 1981 (bibliography).
1.10.5 Pitfall and Dish Traps
Another simple but very effective and useful type of interception trap consists of a jar, can, or dish sunk in the earth (fig. 10). A cover must be placed over the open top of the jar to exclude rain and small vertebrates while allowing insects and mites to enter. A piece of bark, wood, or flat stone will serve this purpose. Pitfall traps may be baited with various substances, depending on the kind of insects or mites the collector hopes to capture. Although most that fall into the trap will remain there, it should be inspected daily, if possible, and desired specimens removed and placed in alcohol or in a killing bottle while they are in their best condition.
Also in the pitfall category is the cereal dish trap, which is a simple but effective device for obtaining insects attracted to dung. It consists of a small dish, preferably with a rim, set in the earth (fig. 11) and partly filled with 70 percent ethanol, or, if available, with ethylene glycol, which does not evaporate. A piece of stout wire, such as a coathanger, is bent as shown, with a loop at one end to hold the bait receptacle. A few zigzag bends in the other end of the wire will keep the looped end from swinging after the wire is pushed into the earth. The bait receptacle may be a small plastic or metal cup such as is often used for medicine doses, or a coffee creamer, or a cup formed from aluminum foil. When baited with animal or human feces, this trap attracts beetles, mostly of the families Scarabaeidae and Staphylinidae, springtails, ants, earwigs, some parasitic Hymenoptera, and, rather surprisingly, several families of flies, especially Phoridae, Sepsidae, and Muscidae. The larger, strong-flying calliphorid and sarcophagid flies seldom fall into the liquid, although they are attracted to the bait. The alcohol fumes probably cause the smaller flies to drop into it. The trap is made of easily obtained materials, is easily transported, and provides excellent results. It deserves wide use.
Figure 10. Simple pitfall trap covered with screening and provided with hanging bait.
Figure 11. Cereal dish trap.
References: Adlerz 1971; Barber 1931; Beaudry 1954; Briggs 1971; Clark and Blom 1992; Dethier 1955; Fichter 1941; Gist & Crossley 1973; Golding 1941; Greenslade 1973; Greenslade & Greenslade 1971; Greenslade 1964; Gressitt et al. 1961; Grigarick 1959; Heathcote 1957; Houseweart et al. 1979; Joosse 1975; Loschiavo 1974; Luff 1968, 1975; Masner & Huggert 1979; Morrill 1975 (bibliography); Muma 1975; Newton & Peck 1975; Reeves 1980; Schmid et al. 1973; Shubeck 1976; Smith 1976; Smith et al. 1977; Thomas & Sleeper 1977; Tretzel 1955; Van den Berghe 1992; Welch 1964.
1.10.6 Moericke Traps and Other Color Traps
Moericke traps or yellow pan traps are used extensively by some collectors. An aluminum or plastic pan is painted yellow and placed on the ground (or a depression may be dug and the pan set in the depression) and filled about 1/3 full with salt water, or some other non-toxic fluid. A few drops of detergent of some other surfactant is added to the water to break the surface tension. Insects attracted to the pan fall into the fluid and perish. The trap is then strained periodically (one favorite strainer is a small aquarium fish net). Pan traps such as this, are often placed under malaise traps and flight interception traps to catch insects that may hit the trap and fall to the ground.
Yellow seems to be the best color for traps, but various kinds of insects react differently to different colors. Some recent research indicates that certain parasitic wasps respond most strongly to blue.
Colored sticky traps are also used to sample insects in various habitats. One of these, the Manitoba trap (fig. 15) has a black sphere to attract horse flies (family Tabanidae), which are then captured in a canopy-type trap.
References: Beroza 1972; Granger 1970; Gurney et al. 1964; Hottes 1951; Kieckhefer et al. 1976; Kring 1970; Marshall, 1994; Moericke 1951, 1955 (in german); Prokopy 1973; Weseloh, 1986.
1.10.7 Emergence and Rearing Traps
An emergence trap is any device that prevents adult insects from dispersing when they emerge from their immature stages in any substrate, such as soil, plant tissue, or water. A simple canopy over an area of soil, over a plant infested with larvae, or over a section of stream or other water area containing immature stages of midges, mayflies, and other arthropods will secure the emerging adults. If it is equipped with a retaining device, as in the Malaise trap, the adults can be killed and preserved shortly after emergence. It must be remembered, however, that many insects should not be killed too soon after emergence because the adults are often teneral or soft bodied and incompletely pigmented and must be kept alive until the body and wings completely harden and colors develop fully. Emergence traps and rearing cages (fig. 12) enable the insects to develop naturally while insuring their capture when they mature or when larvae emerge to pupate.
References: Adkins 1972; Akar and Osgood 1987; Banks et al. 1981; Barber & Mathews 1979; Butler 1966; Catts 1970; Cheng 1975; Coon & Pepper 1968; Davidson & Swan 1933; Debolt et al. 1975; Doane 1961; Gerking 1957; Glen 1976; Harwood & Areekul 1957; Hollis 1980; Kimerle & Anderson 1967; Krombein 1967; LaGasa & Smith 1978; Lammers 1977; Langford & Daffern 1975; Levin 1957; Lindeberg 1958; Macan 1964; McCauley 1976; Masteller 1977; Merritt & Poorbaugh 1975; Morgan et al. 1963; Morrill & Whitcomb 1972; Mundie 1956, 1964, 1966, 1971; Murray & Charles 1975; Needham 1937; Nielson 1974; Smith et al. 1977; Thompson & Gregg 1974; Turnock 1957; Yates 1974.
Fig. 12. Emergence traps and rearing cages
1.10.8 Lobster or Eel Trap
This category includes any container that has its open end fitted with a truncated cone directed inward, as in a lobster or eel trap, known as a 'Reuse' in German. An ordinary killing jar with a funnel fastened into its open end is an example. When the funnel is placed over an insect, the specimen will usually crawl or fly toward the light and enter the jar through the funnel. Modified traps of this type include the Steiner and McPhail traps, which are used primarily in fruit fly surveys but are suitable for many other purposes. The inside of the Steiner trap usually has a sticky material containing a pheromone or other lure. Both traps, as well as similar devices, may be used with different attractants to collect diverse kinds of insects.
References: Bellamy & Reeves 1952; Broce et al. 1977; Brockway et al. 1962; Doane 1961; Hollis 1980; Jacobson & Beroza 1964; Morrill & Whitcomb 1972; Nakagawa et al. 1975; Nicholls 1960; Nielson 1974; Reierson & Wagner 1975; Steyskal 1977.
1.10.9 Light Traps
With light traps, advantage is taken of the attraction of many insects to a light source. Using various wavelengths as the attractant, a great variety of traps can be devised, a few of which are described here.
Many traps can be constructed easily from materials generally available around the home. All wiring and electrical connections should be approved for outdoor use. Funnels can be made of metal, plastic, or heavy paper. Traps can be used with or without a cover, but if they are to be operated for several nights, covers should be installed to keep out rain.
The New Jersey trap (fig. 13) includes a motorized fan to force insects attracted to the light into a killing jar. It has been especially useful for collecting small, non-scaly insects such as midges and gnats. This type of light trap, in which the insects fall directly into a killing jar, is not recommended for use with moths because such delicate specimens may be badly rubbed or torn. If only small insects are desired, they may be protected from damage by larger insects by placing a screen with the proper sized mesh over the entrance. The Minnesota trap is very similar to the New Jersey trap, but it does not include a fan or any motorized method of draft induction.
Figure 13. New Jersey Trap
The Wilkinson trap (fig. 14) requires somewhat more effort to construct than the preceding traps, but it has the advantage of confining, not killing, the trapped insects. Moths, therefore, can be collected in good condition if the trap is inspected frequently and desirable specimens are removed quickly through the hinged top and placed in a killing jar.
Several highly effective but more elaborate devices have been made for collecting moths and other fragile insects in good condition. Basically, they all use the principle of a funnel with a central light source above it and vanes or baffles to intercept the approaching insects that are dropped through the funnel into the container beneath, which may or may not hold a killing agent. The nature of the container and the type of killing agent affect the quality of the specimens obtained. Some traps catch the insects alive in a large collection chamber, such as a garbage can, which is filled or nearly filled with loosely arranged egg cartons. Most moths will come to rest in the cavities between the egg cartons and will remain there until removed in the morning.
Other traps are designed to kill the insects by means of high concentrations of fumes from a liquid killing agent, such as tetrachloroethane or calcium cyanide. A heaping tablespoon or more of calcium cyanide is placed in each of four to six brown paper bags, which are hung in a large garbage can or other large container. A dampened cloth, such as a washcloth, is also hung inside the can to humidify the air and activate the cyanide. This is especially necessary in dry weather. The concentration of the gas inside the can is so great that insects are inactivated almost instantly on entering, and even the most delicate specimens are damaged very little. The bags containing the calcium cyanide powder should be replaced as needed. If two of the oldest bags are replaced with two fresh ones each successive night, the trap can be run as long as the collector desires.
Figure 14. Wilkinson Trap
Handle cyanide outdoors, facing downwind, and with extreme caution. During the day, when the trap is not in use, store the cyanide bags in an airtight container. All forms of cyanide used as killing agents react and break down quickly when exposed to air and moisture; nevertheless dispose of the residue carefully.
To prevent rainwater from accumulating in the trap, place a screen-covered funnel inside the collection chamber to drain the water out through a hole in the bottom of the trap. Sometimes a system of separators is added to guide beetles and other heavy, hard-bodied insects into a different part of the container than the moths and other delicate specimens.
The most efficient light traps use lamps rich in their output of ultraviolet light. The British-made Robinson trap employs an intense, blue-white, 125-watt mercury vapor lamp of a type used for street lighting. This, the most effective insect attractant commercially marketed, is widely used in many kinds of light traps because it has some special advantages over other kinds of attractants. For example, this type of lamp is the only one that emits the kind of light that attracts large numbers of Catocala (underwing) moths, a colorful group popular with many collectors.
Many traps are equipped with 15-watt ultraviolet fluorescent tubes, which emit a highly visible bluish-white light, although blacklight tubes emitting deep purple light are similarly effective. Ultraviolet tubes of lower or higher wattage also may be used and are all highly effective. A 15-watt ultraviolet tube has been estimated to attract about 10 times as many insects as a 500 candlepower gasoline lantern or incandescent lamp. The advantage of the fluorescent tube over the mercury vapor lamp is that it is less expensive and much more portable. A 15-watt tube is easily powered by an ordinary automobile battery by using an inverter to change 6- or 12-volt direct current to 120-volt alternating current. Also, its ultraviolet output is not strong enough to cause any significant eye damage. The safety factor of the mercury vapor lamp at close range is less certain, although entomologists who have used the Robinson trap for many years seem to have suffered no ill effects.
A new, lightweight, spillproof 12-volt battery, in which the acid electrolyte is a gel rather than a liquid, is far superior to the standard automotive battery for powering light traps, but it is fairly expensive and requires a special charger. Special lightweight, nickel-cadmium battery packs, used to power blacklights for collecting, are marketed by some dealers of entomological equipment.
1.10.10 Light Sheets
Another highly effective method of using light to attract moths and other nocturnal insects is with a light sheet (fig. 15). This is simply a cloth sheet, usually a white bedsheet, hung outdoors at night with an appropriate light source or combination of sources such as ultraviolet fluorescent tubes, gasoline lanterns, or automobile headlights placed a few feet in front of it. As insects are attracted and alight on the sheet, they are easily captured in cyanide bottles or jars by the collector who stands in attendance or at least checks the sheet frequently. The sheet may be pinned to a rope tied between two trees or fastened to the side of a building, with the bottom edge spread out on the ground beneath the light. Some collectors use supports to hold the bottom edge of the sheet several centimeters above the ground so that no specimens can crawl into the vegetation under the sheet and be overlooked. Other collectors turn up the edge to form a trough into which insects may fall as they strike the sheet.
The light sheet remains unsurpassed as a method of collecting moths in flawless condition or of obtaining live females for rearing purposes. Its main disadvantage is that species that fly very late or those that are active only in the early morning hours may be missed unless one is prepared to spend most of the night at the sheet. Many other insects besides moths are attracted to the sheet, and collectors of beetles, flies and other kinds of insects would do well to collect with this method.
It should be emphasized that the phases of the moon may influence the attraction of insects to artificial light. A bright moon may compete with the light source resulting in a reduced catch. The best collecting period each month extends from the fifth night after the full moon until about a week before the next full moon.
References (light traps and sheets): Andreyev et al. 1970; Apperson & Yows 1976; Barr et al. 1963; Barrett et al. 1971; Bartnett & Stephenson 1968; Belton & Kempster 1963; Belton & Pucat 1967; Blakeslee et al. 1959; Breyev 1963; Burbutis & Stewart 1979; Carlson 1971; Carlson 1972; Clark & Curtis 1973; Davis & Landis 1949; DeFoliart 1972; Freeman 1972; Frost 1952, 1964; Graham et al. 1961; Gurney et al. 1964; Hardwick 1968; Hathaway 1981; Hollingsworth & Hartstack 1972; Hollingsworth et al.; Howell 1980; Kovrov & Monchadskii 1963; Lowe & Putnam 1964; McDonald 1970; Meyers 1959; Miller et al. 1970; Morgan & Uebel 1974; Mulhern 1942; Nantung Institute of Agriculture 1975; Onsager 1976; Powers 1969; Pratt 1944; Smith et al. 1974; Stanley & Dominick 1970; Stewart & Payne 1971; Stewart & Lam 1968; Tedders & Edwards 1972; USDA 1961; White 1964; Wilkinson 1969; Williams 1948; Zimmerman 1978.
1.10.11 Sticky Traps
In this type of trap, a board, piece of tape, pane of glass, piece of wire net, cylinder, or other object, often painted yellow, is coated with a sticky substance and suspended from a tree branch or other convenient object. Insects landing on the sticky surface are unable to extricate themselves. The sticky material is later dissolved with a suitable solvent, usually toluene, xylene, ethylacetate, or various combinations of these, and the insects are washed first in Cellosolve and then in xylene. This type of trap should not be used to collect certain specimens, such as Lepidoptera, which are ruined by the sticky substance and cannot be removed without being destroyed.
Various sticky-trap materials are available commercially, some with added attractants. However, use caution in selecting a sticky substance because some are difficult to dissolve.
References: Buriff 1973; Chiang 1973; Dominick 1972; Edmunds et al. 1976; Evans 1975; Gillies & Snow 1967; Golding 1941, 1946; Goodenough & Snow 1973; Harris et al. 1971; Harris & McCafferty 1977; Heathcote 1957; Johnson 1950; Lambert & Franklin 1967; Mason & Sublette 1971; Maxwell 1965; Moreland 1955; Murphy 1962 (pp.226-227), 1985; Prokopy 1968; Still 1960; Taylor 1962b; Williams 1973.
1.10.12 Snap Traps
Two kinds of traps designed for quantitative sampling may be termed "snap traps." One of them (see Menzies & Hagley 1977) consists of a pair of wooden or plastic discs, slotted to the center so as to fit on a tree branch and connected to each other by a pair of rods. A cloth cylinder is affixed at one end to one of the discs and at the other end to a ring sliding on the rods. After the cloth cylinder has been pulled to one end and has been secured in place, the ring is held by a pair of latches. When insects have settled on the branch, its leaves, or flowers, the latches are released by pulling on a string from a distance, and the trap is snapped shut by a pair of springs on the rods, capturing any insects present. One of the canopy traps (see Turnbull & Nichols 1966) operates in a similar fashion. When a remotely controlled latch is pulled, a spring-loaded canopy is snapped over an area of soil, and insects within the canopy are collected by suction or a vacuum device. This trap was designed for use in grasslands.
1.10.13 Artificial Refuges
Many insects, especially beetles, are successfully found under stones, planks, or rotten logs. Providing such refuges, as pieces of wood, card board, or even complex traps, is also a form of trapping. Lepidoptera larvae, for example, will congregate under burlap tied in a band around the trunks of trees. This technique has even been used to help control some pest species such as the gypsy moth.
References: Campion 1972; Shubeck 1976.
1.10.14 Electrical Grid Traps
In recent years, electrocuting pest insects has been used extensively in control work. The insects are attracted to a device by a pheromone or other lure placed in a chamber protected by a strongly charged electrical grid. The method deserves study for other purposes, such as surveying the arthropod fauna of an area.
References: Goodenough & Snow 1973; Hartstack et al. 1968; Mitchell et al. 1972, 1973, 1974; Rogers & Smith 1977; Stanley et al. 1977.