CHAPTER 4

TERRESTRIAL HABITATS

 

METHODS

There are almost as many collecting methods as there are collectors. However, there are some well-known and effective methods of capturing terrestrial beetle species. Some of these are active methods, i.e. the collector must find the beetles, while others are passive, such as traps. Below, some of the recommended methods are discussed; many are relatively easy, but some like light trapping and fogging are given more explanation.

 

Searching

Searching is simply the method of using ones eyes to scan the environment for activity and specimens. Visually watching for beetles does require the acquisition of a "search image," that is, an ability to recognize beetles from a distance, in cryptic situations, or identify their behavioral patterns. For example, spotting a leaf beetle on a leaf from several meters distance, or recognizing a fungus beetle on a mushroom does take some practice. With only a little practice many beetles can be recognized, at least to family, by their flight patterns.

 

Netting

Netting is the act of capturing an insect with an aerial or sweep net. When using an aerial net, be sure to rotate and fold the net bag over the rim immediately after capture. This helps keep the beetle in the bag and allows extra time to extract it. Since aerial nets are made of lightweight materials for capturing flying and delicate insects, avoid using the net for extensive sweeping of vegetation, or near fences or branches that may tear the net bag. Nearly all beetles fly and can be captured in flight. Particularly in mid-morning hours or late afternoon, many beetles can be observed flying through and among forest openings or gaps, and along trails and roadways. Commonly collected flying beetles include Lycidae, Lampyridae, Elateridae, Cantharidae, Staphylinidae, Ptiliidae, Leiodidae, Carabidae, Cerambycidae, Buprestidae, and many others.

Sweep nets are made of heavier materials and are designed to be used in vegetation. Like the aerial net, after captures are made, rotate the net so that the bag folds against the rim to slow down the escape of your specimens. Also, avoid barb-wire fencing and other items that might tear the bag. Sweep nets are particularly effective for Chrysomelidae, Bruchidae, Cerambycidae, Buprestidae, Curculionidae, and other leaf and stem feeding beetles.

 
Netting

Beating

Beating, or jarring, of vegetation is a highly productive method of collecting beetles. Almost any microhabitat suspended above the ground will yield beetles when beaten or jarred. The most productive types of materials are dead limbs and branches or clumps of dried, dead leaves. However, even healthy and live foliage will yield many species. A sheet (about 1 square metre, usually made out of rip-stop nylon or canvas) is positioned under the material, which is then struck relatively forcefully. When striking the plant, use of a net handle or stout stick is usually sufficient on leaves and small branches. A thick dowel, such as a wooden broom handle, cut to a comfortable length for the user is excellent. Use a heavier item, such as an axe handle, machete, or mallet when striking thick branches, palm fronds, or other stout plant structures. Striking sharply and repeatedly (1-3 times) in a short sequence is usually adequate. Some beetles will fall with only minimum effort, while others require repeated beating. Experience will teach judgement on intensity and duration of beating in various situations.

When the beetles land on the beating sheet, beetles will either remain motionless, or take flight immediately. Therefore, one must be ready with bottles or aspirators. Some beetles, such as species of Carabidae, Cleridae, or Cerambycidae tend to fly immediately, while others such as Anobiidae or Curculionidae (except Zygopinae!) tend to play dead on the sheet. To be effective at beating, one must take care not to accidentally bump the material to be beaten.

Beating sheet
Aspirator or "Lewinsky"

Beating is particularly effective on densely foliated branches that project from the tree or shrub and overhang, and along trails, roadways, or in forest openings. Different kinds of beetles can be found on the same plant at different times of the day, so sometimes it is useful to visit a productive site at on different days, at different times of the day, and in different weather conditions.

Beating of damaged, dying, or dead plant materials will produce many different beetles than beating live plants. Particularly productive sites are broken branches, dead palm fronds and fungusy branches with loosened bark. Even dead branches of a fallen tree can be worth the effort, especially for Cerambycidae, Curculionidae, Buprestidae, Scolytidae, and others attracted to dying plant material. The use of a heavier beating tool is best in this situation.

When beating, always be cautious of other organisms on the plant, such as climbing snakes, spiders, and scorpions. Also, wasp nests can also be found hanging from branches, particularly on densely foliated clumps.

Barking

Barking is the removal of bark from a tree, log, snag, or stump, in order to find the beetles and larvae that live in or under the bark, or within the wood. Usually, only bark from dead or dying tree materials are removed. Although the loose bark of dead trees is easier to remove, recently dead trees with tight bark are also productive. Remember that as a tree dies and decays, different kinds of beetles will be found on the same kind of tree at different post-mortem stages. Also, the position, exposure, and contact with soil and moisture all help to determine the decay rate, and use by decay organisms, including beetles. For example, a large tree that falls across a trail may have at least the following microhabitats that need collecting assessment: upturned roots; cracked, split, or broken trunk; tight bark; sloughing or peeling bark; sun exposed surfaces; shaded surfaces; partially soil embedded surfaces; internal decay; or fungal sprouts.

When assessing a dead tree part many microhabitats need assessment. For example, if the bole of the tree broke low to the ground, or was cut, the stump may have different beetles than the prostrate trunk. Removing bark below the soil surface and from large roots will permit discovery of many beetles and larvae not otherwise readily found, or rarely found in above ground portions. Many beetles and larvae can be found within the layers of decaying bark, itself. A tall stump or snag will often have different beetles at different heights. Also, exposed and protected sides of a stump or trunk will have different kinds of beetles because of the differing temperatures and moisture levels.

When examing the upper portion of a fallen tree, beating residual leaves and clusters of small branches is necessary. Since different species of Scolytidae, Curculionidae, Cerambycidae, Elateridae, Buprestidae, Anthribidae, and other beetles occur in different sized portions of the tree and in different exposures, be sure to break or cut into the diversity of branches and bark thicknesses. Branch crotches with loose bark are always worth examination. Collecting small and medium sized branches for subsequent close examination or rearing of many beetles is an excellent way to assure host records and different life stages.

Removing bark from trees is a very effective way of collecting beetles that very rarely are collected by using more traditional (i.e. sweeping or aerial netting) methods. It is also an excellent way of collecting larvae, either with or without an association with adults of the same species. It takes some practice and much trial and error to be able to discern which tree-type habitats will lend themselves to good barking. Generally, the tree must be dead for a few years (this will vary, depending on the local climatic and other conditions), and have its outer bark loosened from the inner tree material. While freshly fallen trees are excellent for collecting Buprestidae, Cerambycidae, and Brentidae, for example, they are usually poor for barking. Live trees with deciduous outer bark may be barked also, as many beetles will use this habitat for temporary hiding places.

There is no single best tool for use in barking. This is left up to the tastes of the collector. The tool must be relatively sharp, be very sturdy, and effectively carried in a collecting bag. Effective and popular tools include large and flat-bladed screwdrivers, hatchets, machetes, large pocket knives, prybars, or a beekeeper's hive tool.

Dead trees come in a variety of shapes and sizes. They may remain standing as snags, they may fall over and come in contact with the ground, or a part (or all) of the tree may be suspended above the ground. Or, there may be only a stump if the tree was wind-broken near its base or was harvested. In all these situations, the method is relatively similar. Bark is loosened, in small pieces if possible, with a beating sheet or a net placed under the worked area to capture any insects that fall. Take care to examine the underside of the removed bark, as well as the actual tree surface. Many subcortical (under bark) beetles are small, brown, and slow-moving. An aspirator is a useful tool, in combination with the barking implement.

 
Barking

Sifting and Berlese

Sifting

Sifting is the act of using a screen, usually of metallic hardware cloth, for separating beetles and other organisms from leaf litter, moss, soil, or other materials. Sifting of living and decaying accumulations of organic material provides many small beetles. Sampling of leaf litter, humus, wood debris, and other materials and the separation of the beetles from them reveals an assemblage of taxa not generally collected in other ways. For many beetle taxa, species diversity in this assemblage is generally high and species distributions are often restricted (sometimes to single mountains), likely because dispersal powers are often limited by loss of wings and/or eyes. General forest floor leaf litter usually yields many species, but attempts should also be made to specialize on other focal substrates such as flower and fruit falls, concentrations of fungi or twigs, or similar concentrations of any kind of organic material. Sifting should be also carried out at varying elevations. Higher montane, wet sites with deep litter usually yield more taxa and individuals, but specialized habitats in all areas should yield valuable and perhaps unique collections. Sifting followed by use of extraction funnels (see below) is particularly effective.

Field sampling should first consist of selection of site and focal substrates. The selected material should then be sifted with ca.1 cm2 hardware cloth as a screen. Litter should be scraped into the sifter to the level of the soil only. Approximately 6 liters of sifted litter should be collected as one sample. This unit of material is placed and shaken horizontally and vertically over the screen to cause separation of the material, with the beetle and fine materials falling through the screen and onto a light colored sheet from which the specimens can be hand picked. into a container or bag. However, the screened beetles and materials are best gathered into a bag for transport back to your lab for extraction in a Berlese funnel (see below). If the latter option is chosen, then the sifted litter is placed in a cotton pillowcase (or similar receptacle), labelled and tied. Four such samples should be attempted when possible for each selected habitat or microhabitat.

 

Extraction funnels

Extraction funnels are used in a wide variety of designs. The most commonly used designs are modifications of the Berlese or Tullgren funnels. These devices are extremely valuable for extracting beetles and other organisms from forest leaf litter, humus, soil, mosses, fungal mats, and other organic materials. Many of the beetles collected with extraction funnels are rarely, or never, collected otherwise because of the difficulty of finding the insects.

The funnels are usually made of light metal sheets, and have a matching cone that rests on top of the funnel that contains an electrical fixture with a 60-100W light bulb. The bottom of the funnel directs specimens into a container of ethanol. The primary elements are a funnel with a hardware cloth screen to prevent plugging by litter and promote rapid drying, a heat source within a reflector, and a capture jar with ethanol. The following drawings show the basic design and elements.

Samples taken from the field as described above for sifting can be kept in the pillowcases in the laboratory for up to 4-5 days as long as they are turned frequently and not exposed to excess moisture or extreme temperatures. Processing in the laboratory consists of placement of 2 liters of litter in each funnel and heating for 6 hours. Extracted insects should fall into 80% ethanol. The insects can then be poured into whirlpak bags for temporary storage, or immediately sorted and prepared for the inventory collection. The specimens extracted from three funnels represent a sample. Aside from beetles, other taxa sampled will include ants, small flightless Hymenoptera and Diptera, spiders, mites, millipedes, and centipedes. These taxa should be routed to the appropriate TWIG.

 

Malaise Traps

Malaise traps are designed to capture insects that fly or crawl upwards after striking mesh panels, which makes them different from flight intercept traps (FIT's) discussed below. Because of its design, the malaise trap is used most effectively for Hymenoptera, Diptera, and other flying insects that typically travel upwards when an object is encountered. However, many beetles will also climb the mesh panels and be captured. Scirtidae, Lycidae, Lampyridae, Elateridae, Cerambycidae, Lathridiidae, and many other beetles are frequently sampled with malaise traps. Some beetles, such as Cerophytidae, are only known from Costa Rica by malaise trap samples.

A malaise trap has mesh panels that for a rooflike structure on the trap. It is these roof panels that direct the insects into an upper corner of the trap where a collection bottle is located. The bottle typically contains 80% ethanol or an ethanol and propylene glycol solution. A malaise trap is often set for longterm sampling and only the collecting bottle is exchanged or decanted on a scheduled basis. Thus, for beetle collecting, a malaise trap should be viewed as a supplemental tool generally used on a longterm basis, rather than in a shortterm sampling effort. However, this consideration does make malaise traps essential for placement and use where opportunity allows for undisturbed and regular sampling, such as at stations. Also, a malaise trap can function to a limited degree as a FIT by placing pans beneath the central panel to capture beetles that fall when striking the mesh, particularly in a denser forested habitat. Unfortunately, beetles readily collected by FIT's are only occasionally collected by malaise in open areas, possibly because the extra mesh paneling to form the side and roof panels affects air current movement and light relectance that redirect the beetles around the trap.

Malaise traps are best set in a relatively open area. Some of the best sites are along sides of infrequently traveled roads, trails, stream channels, and in forest openings. The primary considerations for placement are the travel lanes of insects and avoidance of potential vandalism. Avoid the placement of malaise traps in frequently used pastures, as cattle and other animals will destroy the traps by their curiosity or clumsiness. As a killing agent/preservative, 70-80% ethanol may be used. Traps should be inspected and sampled every week, depending on the killing agent used and the amount of insect activity.

Malaise traps usually have several guy ropes that are used to anchor the trap to surrounding trees, or if in open areas, to the ground. Plastic tent pegs are the best for anchoring into the ground, although sturdy tree branches can be shaped with a knife or small ax and used as tent pegs. It is quite important to ensure that the collecting head (where the preservative is) is well secured, hopefully to a tree trunk.

The most important factor in determining size of catch in a Malaise trap is its location. Since this trap has no attracting power of its own, it is critical that it be placed in areas with maximum flight of insects. The best areas tend to be on or near natural openings in forests (paths, streams or clearings), or perpendicular to forest edges. Unfortunately, Malaise traps are very large, and conspicuous, and often attract unwanted attention, from both humans and cattle and other large animals. This should be kept in mind when choosing a site for placement. Also, it has been shown that it is better to leave a single trap in a one location for a prolonged time, rather than moving it every week.

 

Flight Intercept Traps (FITs)

Flight intercept traps (FIT) are a mass collecting insect trap that takes advantage of the fact that many flying insects fall whenever they strike an obstacle. FITs are one of the most effective ways to sample the flying beetle fauna of the forest understory, and they allow sampling of the canopy fauna over the entire range of seasonal and diel activity. A FIT is essentially a piece of mosquito netting suspended perpendicularly to the ground. A set of collecting pans filled with a non-evaporative collecting fluid (salt water or propylene glycol are frequently used) are arranged along the bottom. A plastic rain hood is added to keep rain and debris out of the pans below. Insects that hit the netting fall into the fluid in the collecting pans. The insects can be removed with a very fine-meshed aquarium fishnet and transferred to alcohol for storage.

Traps should be run for at least one week a month in each habitat, but they can also be run continuously. Because the diversity of flying insects changes most rapidly during the transitional periods between the rainy and dry seasons, this is an important time for the operation of FIT's, and malaise traps.

Supplies for flight intercept trap: flight intercept traps with rain hoods, plastic or aluminum pans, 1.5 liters of propylene glycol per trap per visit, 5 liters of 75-80% ethanol, fine-meshed aquarium fishnets, and repair materials.

FIT's should be used with discretion and frequently maintained. Experience shows that with relatively non-toxic fluids such as propylene glycol or a saline solution in the capture trays, birds will extract insects and mammals will drink the liquid. Specimen loss can be minimized by frequent trap visitation and the use of repellants around the trap, or chemicals to help make the liquid unpalatable. Urine from cats is useful for short periods of time and will repel many mammals, but rain and fog drip will demand frequent reapplications. Small amounts of liquid soap will help dissuade many animals from drinking the fluids.

 

Multiple Funnel (Lindgren) Traps

These traps are a set of dark colored plastic funnels with wide openings that are nested within each other, have a raincover on top, and a capture container at the bottom. The capture container can be used dry for live captures, or partially filled with an ethanol-propylene glycol solution, or saturated saltwater with a drop of detergent, depending on length of service intervals.

The traps are hung from branches or other supports that allow the trap to be free-hanging and in a canopy or forest opening. Multiple funnel traps are highly effective collectors of beetles that are attracted to dark vertical objects, such as tree trunks. These traps are also excellent for capturing beetles that are attracted to ethanol. Other baits, such as fruit, can be attached to the traps to attract certain other beetles.

A logistical problem with multiple funnel traps is their bulk. Thus a large number of traps requires extra space for trap storage and transportation.

 

Pitfall Traps

Pitfall traps are one of the most widely used passive collecting techniques for terrestrial insects. These traps are relatively cheap, easily constructed, and require a minimum of maintenance through the collecting season. A jar, can, plastic cup, or other container is sunk into the ground so that the rim of the container is level with the substrate. Gates or guides can be used that will direct the beetles to the pitfall trap. These enlarge the effective collecting radius of the pitfall substantially and usually result in much larger catches, and are typically set in a cross-like pattern centered on the trap. It is desirable to place a slightly elevated piece of wood or flat stone over the trap opening to keep out rainwater and to provide a small space between the ground and the cover to allow for insect movement.

Saturated saltwater solutions with a small amount of soap as a wetting agent. With this preservative, however, traps will have to be sampled at least once a week, or the contents will begin to deteriorate. Propylene glycol solutions should be used for longer sampling intervals. Ethylene glycol (automotive radiator fluid) can be used in emergency situations, but should not be used regularly due to its high level of attractiveness to many animals and environmental toxicity. Pitfall traps can be combined with baits for specific target taxa (e.g. carrion for Silphidae and Scarabaeinae).

 

Baiting

Many beetles will fly to and congregate at suitable food sources, either for themselves, or for their larvae. These tendencies can be exploited by placing natural or artificial baits in convenient situations or in traps. Examples of baits that can be used to attract insects are: flowers, honeydew, fermenting tree sap, rotting or overripe fruit, carrion, dung, and rotting fungi. Each of these materials will attract a unique assemblage of beetles, with some overlap of course. Human dung is particularly attractive to certain rare beetles. Generally, one's imagination is the only limiting factor when it comes to baiting!

Baits can be spread on the ground, on logs, hung from branches in bowls, or used in combinations with other traps mentioned above.

Pitfall trap baited with human dung


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