Lighting

Light trapping is an efficient method for collecting many species of beetles which are active at night and are attracted to various light spectra. Properly deployed light trap stations will collect beetles of most major families, and over time, may accumulate numerically significant sets of high quality series with marked species diversity. Each parataxonomist should have both ultraviolet (UV) tubes (or blacklight) and mercury vapor (MV) bulbs. Extras are necessary to anticipate accidental breakage or burn-out.

UV tubes are usually rated at 15W and fit standard flourescent fixtures. These bulbs produce a cool light in the blue end of the spectrum and are attractive to many species of beetles and other insects. They can be obtained and used separately, or as part of a commercially marketed trap assemblage. However, most beetle collectors will simply hang a UV tube in front of a large white cloth, such as a bedsheet, that is suspended from a rope or structure. The cloth acts as a reflector of the light, a resting site for the attracted beetles, and hence as a collecting site. Consequently, the tube needs to be set in front of the sheet by about 0.3-0.5 m, to permit good light reflection and provide adequate working room for picking beetles. The use of a second cloth, on the ground below the light provides greater light reflection and collecting surfaces. For ease of use, some collectors will sew two sheets together to form a "T" pattern.

MV bulbs are hotter, brighter, and produce light across the width of the spectrum, including ultraviolet. They are preferred beetle lights because of their relatively greater attractiveness to a wider variety of beetles. However, there are many beetles that can be found at UV lights that will not be attracted to a MV light. MV lights are available as externally or internally-ballasted, 150-175W bulbs. Externally ballasted bulbs are a bit cooler, but still hot(!), and are more energy efficient. Internally ballasted bulbs are hotter in temperature and are less energy-efficient. Both are equally attractive to beetles. Teflon-coated "shock resistant" brands are recommended.

MV bulbs are usually suspended in front of sheets, as described above for UV tubes. When the bulb is suspended in front of a sheet, it is important to keep the it away from the sheet to increase reflectance, to provide working space for the collector, and to avoid burning the sheet from the hot bulbs. Sometimes, an MV bulb can be suspended above a vertical sheet, or one laid on the ground, approximately 1-2 m high. This height will permit illumination to reach both sides of a vertical sheet, or provide a safe zone of movement for the collector beneath the light over a ground sheet.

Both UV and MV bulbs require protection from rain and mist. The MV bulbs, particularly, because of the heat produced, can crack or shatter when moisture hits the hot glass of the bulb.

Lights require power sources. Quiet running and lightweight portable generators need use in remote lighting situations. These generate enough energy to permit deployment of both MV and UV lights. Automobile batteries lack sufficient energy to power a MV light, but are satisfactory for UV tubes. If a constant power supply is available, such as at a biological station, then lights can be operated as desired within the capacity of the station system.

Although MV and UV lights are optimal collecting methods, other light sources can be used. Normal incandescent lights, especially 100 w or greater wattages, are attractive to a wide variety of beetles. Also, kerosene or propane lanterns also provide suffience light for some beetles in restricted areas. Unfortunately, lantern light is usually lacking in intensity to function well for attracting beetles from a long distance.

Mercury vapor (MV) bulb
Ultraviolet (UV) tubes or blacklight
Automobile batteries
Portable generator

Collecting Protocols

Lights should be turned-on prior to sundown, preferably no less than 15 minutes before sunset, and should remain lit at least until approximately 10:00 pm. However, longer periods or second periods of lighting are beneficial as many rarely collected species fly in the early morning hours. Lights on stations with standard power should remain on all night, but require checking before sunrise as many beetles will leave the sheets as the level of natural light increases.

The optimal attraction of nocturnal flying insects is during the dark phases of the moon. The best collecting is for a 12 day period beginning such that the dark of the moon is the 7th night. Collecting cycles may also be adjusted to correspond to particular circumstances, regardless of lunar phases, so that, for example, the sampling period would include the first rainfall following a dry season, when many beetles become active.

Orientation of the light to a breeze is important. Because most insects fly directly upwind to the light and will take refuge on the downwind side of objects, the direction of the prevailing breeze should be considered. The light should be placed such that it is slightly on the downwind side of the sheet. Lighting when the wind reachs or exceeds 15 kph at the lighting site is not sufficiently productive and is not recommended. Under such conditions, the sheets billow and flap excessively. Too, most beetles do not fly extensively under windy conditions.

In general, place a light in a position of geographic prominence, such as on a hillside, at a mirador, or along a trail or roadway with extended visibility in several directions. However, for particular circumstances, lights may be placed in the understory, and may be very effective in older-growth habitats with relatively open understory architecture.

Longterm lighting stations will reach a species accumulation asymptote after one or two years, or less, if the habitat sampled is relatively homogeneous. The large beetle fauna, including many Scarabaeidae, Cerambycidae, Elateridae, and others are often well sampled in a relatively short period of time. Because of their size, these groups are often the best studied beetles. Consequently, collecting at lights should focus on the medium and small sized beetles, with discrimination on the large beetles. Use of aspirators is helpful for picking small beetles.

Many beetles attracted to lights, including less commonly collected species, do not necessarily fly to the light itself. Rather, they will land and rest several meters away from the light, often at the edge of the light's aura, where darkness is beginning. Also, many beetles will only fly within a few meters and then walk to the light. Consequently, the collector needs to periodically check areas away from the light and to be cautious about specimens on the ground.

Since portable generators will permit parataxonomists to explore a wide range of habitats and physical situations with lights, we encourage the field person to take advantage of unique and transient sampling opportunities. Use of a light in tree fall gaps, wind gaps, ridge lines, bridges over streams, and other atypical situations will often provide many different beetles.

 

Comments on Some Other Sampling Methods

Fogging is the use of short-life insecticides to sample canopy inhabiting insects. Fogging techniques are complicated and require a team of people for proper operation. Consequently, this is not a method that an individual parataxonomist will use and is not discussed further, here.

Sticky traps are usually commercially made, or otherwise pre-made, colored paper or plastic cards or enclosures that are coated with TanglefootTM or similar substance that entrap and hold insects. Such traps are most frequently used in pest monitoring programs, and are usually baited with a specific pheromone or other attractant. They have a limited use in biodiversity programs because of their tendency to be raided by birds, wasps, and ants that remove specimens, extensive damage to specimens from rain, dust and decay, and the inconvenience of removing and cleaning specimens. For these reasons, we do not recommend their use by INBio parataxonomists.

 

HABITATS

Forests

Canopy

The canopy of a forest is very complex, but for practical purposes it may be divided into two parts with corresponding collecting methods: the part that you can reach by hand, and the part that you cannot reach by hand! Beetles will inhabit all parts of the canopy, but the collecting method used for their capture will depend on their specific location in the canopy. Sweep netting, hand-collecting, and beating are all effective methods for lower canopy beetles. Since sweeping and beating tend to greatly disturb the habitat, hand-collecting should be done first. Many beetles will rest on the undersides of leaves, so be sure to inspect the lower portions of the canopy from all angles. The upper parts of the canopy will be most effectively sampled using insecticidal fogging (discussed above).

Dead Tree Parts (boles)

Stumps, logs, snags, and dead branches are common and should be regularly examined for beetles. Collecting on or in dead wood is one of the most productive methods for obtaining a wide diversity of beetle taxa. This is due to the fact that many beetles and their larvae utilize the wood either directly as a food source, or indirectly by feeding on associated algae, mosses, vascular plants, fungi, slime molds, bacterial colonies, and other insects. Some beetles are associated with the nests of ants, termites, birds, mammals and reptiles that use the dead structure and would be found in the nests and burrows of such animals. Different species can be found on wood of various ages. Freshly cut wood will attract a completely different guild of beetles than will older or decayed wood.

Sampling of such microhabitats can be done with a variety of methods. Typically, a collector will approach the substrate and closely observe for any beetles that may be active on the outer surface. If there are obvious growths of fungi or slime molds, these should be closely examined specifically for families such as Erotylidae, Endomychidae, Ptiliidae, Leiodidae, Staphylinidae, and many others. See the section on fungus beetles for more information on this matter. If the wood is fresh, examine for Cerambycidae, Buprestidae, Scolytidae, and other beetles. Look on all surfaces, including shaded undersides of logs and branches.

If you are examining an older piece of wood, such as a log, begin careful removal of the bark, starting at one end where the bark is broken or cut. If there are large cracks or areas of removed bark along the length of the log, check these or start at such sites. If the bark is loose and is easily removed, carefully remove small portions and search closely on both the log and bark surfaces for specimens of adults and immatures. There will usually be interstitial material that will be a combination of frass, decomposing wood tissues, fungal mycelia, slime molds, dead insects, and other accumulated materials. If there is an abundance of small beetles, it may be advisable to use your machete or knife to scrape a volume of interstitial material from the log or bark into a bag or other container and return it to your lab for closer examination.

Litter and Soil

Forest litter and other ground substrate can be a very productive material for collecting beetles, as discussed above in the section on sifting and Berlese extraction. Logs, rocks, and other material should be carefully lifted (turning the item towards you so that if there are any dangerous animals, the item will act as a shield), inspected, and then lowered back into position. Often, the same log or rock may be sampled repeatedly in this manner, with different beetles collected each time. Samples of leaf litter should be taken from different forest microhabitats, and either sifted or Berlesed back in the laboratory.

Soil

 Successful sampling of the soil beetle fauna is usually directly affected by moisture of the soil. Sandy soil sites have different species of beetles than do clay-soil sites. A careful assessment of general habitat conditions must be made. General moisture retention of the soil, seasonality, and vegetative cover affect the beetle fauna in the soil.

Savannas and Pastures

In Costa Rica, savannas are human and livestock created environments, thus artificial, but many species of beetles use them as habitat. Many of the beetles that frequent savannas are highly active on plant boles and leaves. Sweeping and beating is effective in savanna and pasture environments. Lighting is extremely effective because of the open structure of savannas. Many species of difficult to collect litter and soil inhabiting beetles can be attracted to lights. Because savannas and pastures typically are used for livestock grazing, many species of dung associated or even introduced species may be attracted to the lights.

Canopy

The canopy of savannas and pastures is more open and less complex than that of forests, with fewer species of plants. However, the collecting methods are generally the same as that listed above in 4.2.1.1. In savanna habitats, special consideration should be given to the outermost clusters of leaves, where many beetles will aggregate when they fly into the trees.

Dead tree portions should be closely examined as in forested habitats. Consideration should be given to the exposure of any logs, stumps, or snags. Generally, the more exposure to direct sun of a habitat the lower the diversity of beetles that will be found. Many hours of direct sun exposure will dry the wood and create higher temperatures that drive-away or kill beetles. Although a number of beetles prefer hot and dry microhabitats and such exposed sites can be good collecting for such species, the diversity is much lower than that of more protected microhabitats.

As with dead tree portions, the ground and litter beetle fauna of exposed sites differs from more protected sites. If sampling sites are subject to extreme season fluctuations in available moisture, sampling for ground and litter inhabiting beetles may be best done during periods shortly after the initiation of the rainy season.

Soil

Successful sampling of the soil beetle fauna is usually directly affected by moisture of the soil. Sandy soil sites have different species of beetles than do clay-soil sites. A careful assessment of general habitat conditions must be made. General moisture retention of the soil, seasonality, and vegetative cover affect the beetle fauna in the soil.

 

Paramo

Shrubs and grasses dominate the vegetation of paramo. The relative height and community composition of paramo various with elevation, with shorter and sparser communities found at higher elevations. Typically, paramo communities are cooler, with higher winds, and frequently foggy or with drizzel. This means that sampling of paramo in good weather conditions is a rare event.

Because of the less favorable weather conditions in paramo, many beetles only fly at the best times. Sweeping and beating of the shrubbery is essential for obtaining many species of beetle. Lighting is rarely effective, but is valuable on the rare evenings when good weather is available.

Paramo ground, litter and soil habitats are usually always moist. Because of the frequent inclement weather, most beetles will be found in protected sites, such as in leaf litter, under ground plants and stones, or among grass tussocks. Sifting and berlese would be good options for sampling paramo beetles.

 

Playa

In Costa Rica, playas are usually associated with ocean shorelines. Vegetation can be sparse or non-existent on open sand or mud areas below the usual storm tide mark on the beach. Nevertheless, specialized species of beetles can be found on playas.

Generally, there is no vegetational canopy on playas, unless shrubs or small trees are present and scattered. The ground, litter 4.2.4.1 ground and litter , and soil microhabitats will be sparse or specialized. As with other environments, a greater diversity of beetles will be found where moisture is available. Other than tiger beetles and ground beetles active on the playa during the heat of the day, most collecting will be under logs and other wood drifted onto the beach. Turning this debris will reveal both adult and immature beetles in the sand and soil beneath the wood.

 

Fungi and Slime Molds

Fungi present an amazing array of sizes, shapes, and colors and are found in many different habitats. There are many families of beetles that spend their entire life cycles associated with various fungi, including many Staphylinoidea, Cucujoidea, and Tenebrionoidea. Often, on suitable fungal substrates, relatively large numbers of beetles may be collected. Each type or species of fungus will be host to a number of specialized mycophagous beetles, or beetles that are preying on mycophagous beetles. The age of the fungus will also influence the associated beetle fauna. This is especially true for short-lived, fleshy gilled mushrooms as opposed to the more durable, persistent bracket fungi or polypores. Some beetle species are attracted by very fresh mushrooms, while others prefer older, rotting fungi. Generally speaking, fungi are a valuable food resource (especially in forest habitats) and almost every species will be host to at least one species of beetle. Therefore, the beetle collector must include fungus collecting in their usual collecting activities.

When encountering some fungi in the field, the first thing to do is to visually inspect the fungus without removing it. During the day, many fruiting bodies will appear devoid of beetles. However, if one returns to the same fungi at night, often there are many beetles which are visible externally, crawling on the surface of the fungi. Remove as many adult beetles as possible, using an aspirator, without disturbing the host. It is useful to hold a small net or beating sheet under the fungus if possible, as many fungus beetles drop or run actively when disturbed. One can return to the same fungus repeatedly and collect a variety of species over a week or two, depending on the persistence of the fungus. If there are a large number of fungi in an area, some may be removed for more detailed examination. It is useful to shake the fungi over a beating sheet and collect the adults or larvae with an aspirator; then, the fungi may be cut open to look for larvae. (See section on larval beetles below for details). If possible, a specimen of the fungus should be returned to the lab for identification.

Many fungus beetles will be brightly colored, but there are many that are rather nondescript. Also, remember that many fungivorous beetles are very small! For example, the nanoseline Ptiliidae are among the smallest insects known.

 

Carrion and Dung

In most habitats, carrion is a very important source of protein for insects and other invertebrates. Carcasses are colonized almost immediately after death, primarily by flies (Calliphoridae), but they also have a specialized beetle fauna. The factors which will influence the species of beetles on carrion are: size of the dead animal, the length of time it has been dead, and the general habitat type in which the carrion is found. Some of the more important families of beetles that have been shown to be attracted to carrion include Staphylinidae and Silphidae, Scarabaeidae (especially scarabaeines), Trogidae, Dermestidae, Nitidulidae, and Cleridae. Some species are specialists on smaller carrion, while others are generalists.

When encountering a dead animal in the field (usually you will smell it before you see it), it may be inspected for beetles. If the carrion is very fresh, the vast number of maggots of Calliphoridae can often obscure anything else; most of the beetles will be on the underside of the carrion, just above the ground. Some species will construct burrows immediately under the carrion and drag bits of the carrion underground. Many species of Staphylinidae will be found on fresh carrion, as they prey on fly eggs and larvae.

Good results may be obtained by hanging a small amount of carrion (e.g. chicken parts) in a cheesecloth or mesh bag from a pitfall trap cover, over the actual pitfall trap. This type of bait often attracts the unwanted attention of various vertebrate scavengers, so the pitfall traps should be well-anchored into the ground.

The vertebrate production of dung in the majority of habitats is very constant and abundant. Because the dung is a rich source of nutrients, in most part derivated from microorganisms like bacteriae, fungus and yeast, that grow in it, many insects, including some larvae or adults Coleoptera use it as its only or almost only food source. Other insects, like predators, indirectly use it as microhabitat where they find preys. Almost immediately after the dung deposition, that is visited by some kinds of flies and beetles. They are attracted by smell. The Scarabaeidae, Leiodidae, Hydrophilidae, and other less common Families of beetles, have members that come to dung and use it as food. Histeridae, Staphylinidae, and Carabidae normally visit dung in search of preys like adults, eggs and larvae of other insects.

The insect attractivity of dung is determinated by some factors like size of dung (normally larger dung attract larger insects and viceversa), exposition time (the attractivity is larger when the dung is just deposited, then it diminish gradually), climatic conditions of the habitat (rain, temperature, humidity, etc), exposition to wind, food habits of producer organism (in general terms omnivore's or hervibore's dung is more attractive than carnivore's one).

The localization of dung by the insects is mostly realized using their antennae as specialized smell organs. They can search flying or waiting in the vegetation. The smell column produced by the wind is perceived and followed by the insect until the source.

Beetles can be found on, in or under dung. Many of coprophagous beetles cut and put apart pieces, or construct burrows under the dung where they deposit pieces for its larvae or self feeding. If you find dung, then very probably you will find beetles associated.

 

Sloth carrion

 

Flowers and Fruits

Some of the best-known and most obvious components of the beetle fauna occur repeatedly at flowers, e.g. Cleridae, Buprestidae, Scarabaeidae, Cerambycidae, Chrysomelidae, etc. Flower pollen is an important protein source for many beetles, and this may be exploited by the collector. Flowers may be inspected and hand-collected, or they may be shaken over a net or beating sheet. The collector must be quick and agile for good flower collecting, as almost all beetles coming to flowers will be very fast and wary.

Floral structures of many plant species are attractive to a wide variety of beetles. Many of these beetles are feeding on nectar, pollen, or the floral structures themselves. Also, flowers of different species of plants are attractive to different kinds of beetles. Consequently, no flowers should be ignored and each species should be checked at different stages of development.

Whenever possible, keep beetles from different flowers separated for proper labelling. Accurate floral records are important for understanding beetle feeding habits. Common families found on flowers include Curculionidae, Bruchidae, Mordellidae, Cerambycidae, Buprestidae, Chrysomelidae, Nitidulidae, Dermestidae, and many more.

Fruits, especially those that are rotting or fermenting, can be an excellent source for beetles. Often, if the fruit is quite advanced in it stage of decay, species otherwise usually collected at carrion may be attracted. Species of Nitidulidae are quite common at rotting fruit. Fruit may be used as bait in traps, as described above.

 

Vascular Epiphytes

Plants in this category include primarily orchids, bromeliads, mosses, liverworts, and ferns. Each of these kinds of plants have insects that specialize on various parts of the plants as hosts. However, these plants also provide specialized microhabitats for beetles.

Particular attention should be given to the root masses that attach these plants to trees. Usually, the root areas also include organic matter and a mixture of plants and fungi. As such, these masses provide small homes for numerous species of beetles and their larvae, some of which are very rare and poorly studied.

Bromeliads, especially the large water-holding species, are particularly interesting. There is some discussion of this for aquatic beetles in previous sections, but many beetles also occupy the tight spaces between the leaves. Examples include Cucujidae, Elateridae, Carabidae, and Tenebrionidae. If sampling can be done without destruction of rare plants, opportunities should be taken to examine these plants for rare beetles and their larvae.

 

Algae, Mosses, and Lichens

Terrestrial algal mats, mosses, and lichens are specialized microhabitats that often include beetles that feed only on these hosts. Beetle occupants of algae, mosses, and lichens on trees are usually using them as home, particularly when combined with the roots of vascular epiphytes (see above).

Ground living species of these plants are hosts and homes to different kinds of beetles. For example, the only species of Costa Rican Byrrhidae is probably in thin algal or moss growths on silt accumulations along rivers, and many weevils and ground beetles live in mosses and lichens.

 

Additional and Alternative Collecting Methods and Habitats

Mountain tops

The peaks and summits of mountains are excellent places to find beetles. Most of the species found at these locations flew to or were blown to the site by winds coming from the valleys and mountain sides. Buildings, large rocks, and trees and shrubs should be examined for a wide variety of beetles. If winds are calm and buildings have lights, these should be visited for beetles. If a mountain top is occupied by a military or commercial site with restricted access, such as radio or television towers, permission can usually be obtained from local commanders or managers.

Street Lights and Windows

Street lights and windows are often good places for finding many beetles. However, these should be regarded as passing opportunities rather than explicit sampling sites. Yet, isolated security lights, storefronts, or home windows in rural areas will be effectively similar to a light trap or sheet.

Garbage

Household garbage seems like an unusual source for beetles. However, typical household garbage typically contains portions, leftovers, and spoils of meat, vegetables, and fruits. All of which can attract beetles.


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