Collecting and Rearing

From Bugwoodwiki

Maier, C.T., C.R. Lemmon, J.M. Fengler, D.F. Schweitzer, and R.C. Reardon. 2004. Caterpillars on the Foliage of Conifers in the Northeastern United States. FHTET-2004-1. Morgantown, WV: USDA Forest Service, Forest Health Technology Enterprise Team; 151 p.

Learning about the biology and the identity of moths and butterflies can be an exciting and rewarding educational activity for the amateur or the professional. Collecting and rearing can contribute much new information about lepidopteran species because the food plants, feeding period, variation in appearance, and other biological attributes of many species are poorly known. Furthermore, new species await discovery. By rearing caterpillars to adults and by preserving specimens, even amateurs can make worthwhile contributions to entomological science. A careful observer, however, should record the locality, food plant, date of collection, rearing method, and other details for specimens raised to adults.

Caterpillars can be collected by striking or "beating" the trunk or the limbs of woody plants with a stick or baseball bat, causing them to drop onto a light-colored cloth or plastic sheet placed beneath the foliage (Figure 6). After collection, caterpillars can be enclosed singly in clear plastic cups or other suitable containers, along with the foliage of their food plant (Figure 7). Preventing desiccation, supplying fresh foliage every few days, and avoiding temperature extremes will improve the success of rearing.

Figure 6. "Beating" the foliage of eastern hemlock to dislodge caterpillars.

Figure 7. Plastic cups used to rear caterpillars in the laboratory. The cup on the far right contains a pupa that has been prepared for overwintering by placing it in sphagnum moss.

Valuable information about the developmental time and number of generations per year can be obtained by rearing caterpillars outdoors under natural light. One widespread method of raising caterpillars outdoors is to confine one or more in a mesh or muslin bag or sleeve placed over the branch of a food plant (Figure 8). The position of the rearing cage should be changed whenever the food supply dwindles.

Figure 8. Fine-mesh nylon bags used to rear caterpillars on eastern hemlock.

Another technique to obtain caterpillars is to let them hatch from eggs laid by captive adults. At night, many species of moths are attracted to lights, especially ultraviolet or mercury vapor lights. Others come to bait (a fermenting mix of sugar, rotting fruit, beer, and sometimes other material) that is applied to tree trunks. After adult females are collected, they can be put into a container with the foliage of a known or suspected food plant. If they were mated and fed, they soon should lay eggs. An excellent adult food for most species is a solution of tap water (2 parts) and honey or maple syrup (1 part) soaked into cotton. Butterflies confined with their food plant should be exposed to bright light to stimulate the laying of eggs. Once caterpillars have hatched from eggs, they can be reared as described earlier. Rearing in bags or sleeves significantly reduces mortality from parasites and predators and usually produces larger, more normal adults.

Caterpillars that eat the needles of conifers often will form their pupae on or beneath the foliage in rearing containers, although in nature most normally change to pupae in soil or debris. Larger caterpillars may need to be supplied with moist sand, potting soil, sterile peat, or fresh sphagnum moss for pupation. When full-grown caterpillars begin to wander about their enclosures, they probably are seeking a site for pupation. At this time, they may show some color change or shrinkage. Most caterpillars will burrow into the soil or other material and quickly form their pupae. Some full-grown cutworms (Family Noctuidae) construct a chamber in the soil or the moss where they remain for a month or more before they transform to pupae. After caterpillars find a pupation site but before they actually form pupae, they continue to change color and to shrink in size.

In the fall or winter, the pupae or the caterpillars of most northern species must be exposed to low temperature before they will finish their development and produce adults. In the fall, the pupae of most species can be placed in moist, but not wet, soil, peat, or sphagnum (Figure 7, far right). If the rearing containers are then stored in a refrigerator or in an unheated garage for 3 to 5 months, the pupae (or caterpillars) usually will resume development after they are returned to room temperature or after they warm in the spring. After adults emerge, they should be allowed to age for several hours to one day before they are killed for study or released. Many books explain how to prepare adult moths and butterflies for a collection. Several books with procedures for rearing are cited at the end of this manual.

We recommend that several caterpillars of any one type be reared because similar caterpillars may well yield more than one species of adult and because some immatures are likely to be killed by handling, diseases, parasites, or predators. Data on parasites are valuable, especially if the stage (including the instar of the caterpillar) killed can be recorded. Parasitic flies and wasps that emerge also should be preserved for identification. Consult general entomology textbooks for proper techniques of preservation, but remember that the recording of data is the most crucial step.