Collecting insects (part 1)
Where and How to Collect Insects
Insects feed on the leaves, stems, roots, flowers and fruit of many horticultural plants, producing directly visible damage or symptoms. Examine plants closely. Look for holes in leaves or ragged leaves near the ends of branches. Turn leaves over to see for sure, especially if you spot any leaf discoloration or stippling patterns. Also check for ant activity – they often tend aphids or scale insects whose honeydew (sugary excrement) they love. Look for holes in stems – evidence of boring insect activity and insect frass (excrement). Plants damaged by soil insects or stem-borers may wilt in the heat of day and recover somewhat in the evening when the sun goes down. Pull damaged plants and closely examine root systems for signs of insect attack.
The best insect collecting is often in diverse habitats. A vegetable or flower garden or landscaped facility such as a park, arboretum or zoo will usually have multiple plantings of many different types of plants. But make sure that you have permission to collect first. Note that it is illegal to collect in a federally sponsored facility or national park without a collecting permit. Always be careful not to damage plants when collecting. You shouldn’t cause more damage to the plantings than do the pests themselves. Be reasonable and don’t hack off side branches, limbs of trees or entire shrubs or flowers unless they are not salvageable (dead or dying). When collecting insects, don’t forget to dig in soil. Most plants have a characteristic group of “specialist” insects which feed on them. Other insects may be more general feeders, attacking a large group of plants. Chop into a dying tree or rotting log to discover some interesting specimens.
Insect Collecting Equipment
The basic equipment necessary for field collecting is an insect net, one or more storage boxes, insect nets, pins, pinning blocks, spreading boards, light and pitfall traps, killing jars, killing and preserving chemicals, several vials of assorted sizes, plastic bags and assorted containers. A collecting bag (roughly 14" x 18") made of canvas, muslin or other strong material is helpful to carry equipment, plant cuttings and insects when out in the field. These supplies can be obtained by direct order from one or more biological supply houses such as BioQuip (310-324-0620 or e-mail: bioquip@aol.com).
The Killing Jar
Insects must be killed before pinning and mounting. Killing jars are used as a sort of “small scale fumigation” to kill collected insects as rapidly as possible, using a liquid fumigant or killing agent (ethyl acetate/nail polish remover) that produces a toxic atmosphere that the insect cannot breath.
When placed in the killing jar, insects often close their spiracles, but eventually they must open them. The process may take several minutes for smaller insects or up to a half hour or more for larger specimens. Because large, hard-bodied insects such as beetles die slowly and may damage other insects placed in the same killing jar, you will need more than one jar. Also, you may break or lose one of your jars.
It is possible to make suitable killing jars with nearly any jar used for jam or jelly and baby food jars are especially handy. Do not use plastic containers, because the chemical killing agent may damage them. At least one large (i.e. pint or quart size) jar would be helpful for larger specimens.
In the bottom of each jar, place about 1 to 1 1/2 inches of absorbent material, such as cotton, shredded newspaper, Plaster of Paris or wood fiber (sawdust). If Plaster of Paris is used, pour it about 1 inch deep and allow it to dry for at least 48 hours before use. With paper-or fiber-filled jars, cut a cardboard circle just slightly larger than the inside diameter of the jar and push it into the opening against the plaster in the bottom. Wrap the outside
bottom third of each jar with masking tape to prevent cuts in case the jar is broken. Attach a label that says POISON to each jar and store the jars out of reach of children (or irresponsible adults) until you are ready to go collecting.
The killing jar is now ready to charge with a killing agent. Pour enough ethyl acetate (a tablespoon or so) into the killing jar to thoroughly wet the dry, absorbent plaster. Use a bit more if the plaster will absorb it. Pour off any excess into the original container. Do not use too much or you may “wet” and damage insects that you collect. Turn the lid on tightly to prevent loss of fumes. As the killing jar is used, it will lose its strength so the killing agent must be replenished from time to time. Tear up some strips of paper, crumple them slightly and place them in each jar. This will help to prevent insects from damaging one another.
Pinching the thorax of large butterflies or moths before placing them in the killing jar will prevent them from flopping around and damaging the wings. Squeeze them for 20-30 seconds between thumb and index finger and put them in the killing jar. This procedure stuns the insects so they do not flutter once inside the jar. Remove butterflies and moths from the killing jar fairly soon so their wings do not become soaked with killing agent.
If a killing jar is not available, freezing is another way to kill insects. Simply place your specimens in a plastic bag (the Zip-Lock kind is nice) or small jar and put them in the freezer for an hour or two. Do not handle them again until they are thawed or legs and antennae may break. And don’t forget them in the freezer. Insects, like food, left too long in the freezer for several days or weeks will desiccate and
remain dry and stiff, even when thawed. If pinned when dry, these insects will break during handling and wings, especially of Lepidoptera, will be impossible to spread. Remember that specimen quality is an important consideration in grading insect collections.
Using the Relaxing Jar
We recognize that while insects should be pinned on the same day they were collected, this is not always possible. So before pinning these specimens left in the killing jar or freezer too long, to restore their flexibility, it is necessary to “relax” them. By placing them in a relaxing jar at high humidity for a few days we can restore their flexibility enough to allow pinning without damage to the specimens.
Relaxing is always a risky process and, if carelessly done, the specimens may be ruined.
A relaxing jar is easy to make. Simply use another baby food or larger jar as the relaxer. Place some absorbent material such as newspaper, sand or cotton in the bottom and cut a blotting paper disk to fit tightly inside. Moisten the material with water and add a drop or two of ethyl acetate, phenol, Lysol or laundry beach (Hi-Lex, Purex, Clorox) to prevent mold. Place insects on the paper, close the jar tightly and let it sit for about 2-3 days. Check the jar. If the insects are flexible, mount them immediately. If the specimens are still too stiff, keep them in the relaxer for a few more days, but watch them carefully. Insects will mold and decompose if held
in the relaxer too long.
Using a Collecting Net
Aerial nets for collecting flying insects can be ordered or made at home from a 4-foot length of doweling, about 4 feet of heavy wire and a half yard or so of sheer nylon or orlon netting. Grooves are cut across one end of the handle, then a one-half inch deep hole is bored on one side of the handle (in the groove) three inches from the end. A second hole is bored one-half inch deep in the opposite groove four inches from the end. A four foot length of heavy wire is bent into a hoop and attached to the handle by a 4-inch aluminum slip collar, which holds the wire hoop in place.
The bag, once hemmed and attached to the hoop, is about one foot in diameter, two to three feet long and tapered to a point. The bag is slipped onto the wire hoop before it is attached to the handle. A muslin or denim band is usually sewn over the hoop end of the bag to make the net last longer. Sweeping or beating nets are made like aerial nets. However, the net bag is constructed of strong muslin material instead of the lighter netting. These heavier duty nets are used to collect insects from grass, trees and shrubs by swinging the net through heavy
foliage. Thus, these nets are sometimes referred to as “beating” or “sweeping” nets. The sweeping net is widely used to sample insect populations in standing field crops such as alfalfa, wheat and soybeans. As the surveyor walks through the crop, the net is swung in an arc a specified number of times – e.g. 10, 20, 50, 100, etc. Done at several locations over time in a field, and the results totaled, a reasonable assessment of the pest population can be made, compared with economic thresholds and management/control decisions made.
Other Collecting Equipment and How To Use It
Aspirator. The aspirator is a suction device for collecting small insects which are difficult (or hazardous) to capture with the fingers or with an insect net. Basically, it consists of a large glass or plastic vial, a length of flexible rubber tubing, some rigid plastic or metal tubing and a rubber stopper with 2 holes cut in it to receiving the tubing. A small piece of cheesecloth or fine metal screen serves to seal the suction tube on the inside so that insects are not sucked into the mouth. Bear in mind that if you collect ants, you may not suck the ants through the fine mesh, but their defensive secretion (formic acid) can give you a nasty mouthful, especially if the ants are large and numerous. This experience is guaranteed to clear your sinuses.
To make an aspirator, bend the two lengths of rigid tubing and fit the tubes into a rubber stopper. The long tube should extend down to within about one inch of the bottom of the vial when it is in proper position. Attach the small piece of cheesecloth or metal screen to the short piece of tubing with solder, glue or a rubber band. (This is to prevent you from sucking several bugs or bits of dirt into your
mouth when you are using the aspirator.) Now attach the rubber tube to the short piece of rigid tubing.
To use the device, just place the long tube beside a small insect, put the rubber tube into your mouth and suck sharply. With a bit of practice, you will find that this is an excellent way to collect smaller insects with ease.
Light traps. Many types of insects are attracted to light and can be captured there by hand. A light trap offers the advantage that it will continue to trap specimens without being constantly watched by the collector. Insects are quite sensitive to different types of light; therefore, more of certain types can be captured with “black” (or ultraviolet) light as opposed to the regular “white” light given off by most standard light bulbs. The difference in attractiveness of the two types of light is due to the wave lengths produced by the two kinds of bulbs. Black light consists mainly of the shorter wave lengths which are more attractive to night-flying moths, flies and beetles. White light bulbs (producing mostly longer wave lengths) attract some moths and other insects, but not as many as a black light. Simply turning your home entry lights on or standing under a street light or in your car headlights often produces many specimens, including many horticultural pest insects. Many of the night-flying cutworm moths can be captured when feeding on various flowers during evening hours.
All that is needed to make a simple light trap is a battery-operated lantern or an automobile trouble light with a 100-watt or larger bulb, a large metal funnel (you can also make one of plastic sheeting, but remember this is flammable) and a wide mouth jar or a large tin fruit juice can. Hang the light outdoors away from the buildings, in a sheltered place, near a power source, if needed and no more than 4 feet off the ground. Construct a wire framework to support the lantern or suspended bulb, funnel and trap can. Make sure that the end of the collecting funnel is large enough to allow larger insects to pass through. Place some crumpled newspaper in the bottom of the can (about 2 inches deep) and lightly wet it with killing solution. Start the trap at dusk and empty it in the morning. A simpler trap setup is to prop up a white sheet to serve as a reflecting surface, then to sit a lantern in front of it on a chair or stool. Collect the insects attracted to the sheet as they land on the surface. Blacklights are made in the same form as
regular fluorescent tube lights and can be operated in similar types of fixtures. Do not look directly at the blacklight bulb, because ultraviolet light can damage eyes. Night-flying insects seem to be more often attracted to light traps placed in sheltered areas (i.e. protected from wind by trees) than those in more open areas.
Pitfall trap.
A pitfall trap will catch many ground beetles and other insects that live on or in the soil.
It consists of a trap can that is buried in the soil, level with the rim so that insects attracted to it will fall in. Once inside, it is difficult for them to get out. An attractive bait in the bottom will increase the drawing power of the trap. Use pieces of spoiled fruit, vegetables, excrement or meat. Cover the trap with a board placed on small stones so insects can crawl under it and into the can. This arrangement will protect the trap from wind and rain, but allow access to the insects you want to catch. It will also help to hold insects inside the trap once they are caught.
Remove the insects that you catch each morning.
PRESERVING INSECTS
Hard-Bodied Insects
Since insects have a hard shell or exoskeleton and all of the soft parts are on the inside, they tend to keep rather well after drying, even for long periods of time. Only a small amount of maintenance is necessary to keep them in good condition. Many specimens in museums today are over one hundred years old and look just as they did on the day they were collected. Certain types of insects may fade, but others hold their colors indefinitely. If you want to study insects in the winter, you must work with collections of dead insects or with living laboratory-reared material. Remember that dead, pinned insects are very brittle and delicate. They must be handled very carefully and never jarred, dropped or touched directly. Specimens whose legs, antennae and wings are broken and lost are essentially worthless. Also, damaged specimens will not be graded as highly in your insect collection.
Soft-Bodied Insects
Many types of insects, including aphids, springtails, thrips, mayflies or silverfish, are soft- bodied and cannot be pinned successfully. The same is true of many immature insects such as caterpillars, beetle and wasp larvae and others. If placed on pins, most soft-bodied insects will shrivel or decompose. Such insects must be preserved in liquids in rubber-stoppered glass vials. However, prior to preserving soft-bodied specimens for the long term, their color must be “fixed” or they may fade in some cases or blacken in others. The “fixing” process prevents, reduces or delays color change.
For the long term, insects are preserved in ethyl alcohol, usually of about 70 percent concentration (70% alcohol, 30% water). Isopropyl alcohol can also be used, but with less success. Over time, alcohol at lesser dilutions, i.e. stronger solutions can cause colors of specimens to darken and bodies to shrivel. Remember that alcohol is a dehydrator -- it removes water. These problems can be largely prevented in either of two ways. The best way is to “fix” the insect tissues and color by killing the specimens in boiling water. For smaller specimens, simply dip them in boiling water for about 30 seconds and then transfer them to 70 percent alcohol. Use more extended periods for large-bodied insects.
The most preferred method, often used for caterpillars and other soft-bodied larvae, is to kill the insects in a special fixing solution called K.A.A.D. mixture. This solution is made by mixing one part of refined kerosene, two parts of glacial acetic acid (a weak acid), ten parts of 95 percent alcohol and one part of dioxane. A good feature of the K.A.A.D. solution is that it causes soft-bodied larvae to uncurl, distend and swell, expanding the tissues and making them easier to examine and study. Leaving specimens in the solution too long can cause the bodies to burst, however, so watch them carefully. Small insects should not remain in the solution for more than 30 minutes while larger ones, such as a medium-sized caterpillar, might require 2 to 3 hours. After they are fixed in the solution, they should be transferred to 70 percent alcohol in tightly closed vials, with rubber stoppers.
Chemicals can be purchased directly from biological supply houses. Also, grain (ethyl) alcohol is sold in liquor stores in many states as “Everclear”, a product that is 95% pure . Price will vary depending on the level of state and federal taxes. Vodka is another option, but it is usually sold at 40% strength. The 95% pure alcohol, or ethanol can be easily diluted to 70% strength by working in units to get the amount you need. To dilute 95% alcohol to 70%, use “about” (slightly less than/actually 2.8) 3 parts of 95% alcohol to 1 part distilled water.
Note that collection and specimen identification labels must accompany insect specimens in each vial (labeling will be discussed in detail later). With the insects in the solution, top off the liquid to within 1/4" of the top of the vial. Wipe off the excess alcohol, then place an insect pin against the interior of the vial, and push a rubber stopper deep into the vial opening as the pin is simultaneously withdrawn. This procedure “burps” the bottle, forcing surplus air out of the vial as a stream of tiny bubbles, thus helping to ensure an airtight fit. Otherwise, the stopper may pop out -- especially if the stopper or inside vial rim were wetted by the alcohol.
Because the body contents of a large specimen may dilute the preservative, it is best to replace or top off the original alcohol with fresh alcohol after a day or two. After this special treatment, colors should not fade much. Over time, the alcohol may evaporate, so it may be necessary to add a bit more from time to time.
