Simple guide to collecting and rearing caterpillars and their parasitoids

- Record in a field notebook the collecting date, detailed location, type of habitat (e.g., forest, garden), time spent searching, and number of caterpillars found. If possible, take pictures of the collected larvae.

- Avoid touching caterpillars with your bare hands (it might harm the larva, and in some cases irritate your skin). Better to use a soft forceps, or a piece of paper to catch it and place it inside of a container. Use small (~250 ml) glass or plastic containers with good lids. Ideally, place only one caterpillar per container –larvae of many species are cannibal and the largest tend to eat the smallest. If you must place more than one caterpillar per container, try to group them by species and similar sizes. While collecting, if the day is too hot, make sure to keep the containers already filled with larvae in a shady and cool area, while you continue searching for more caterpillars.

- Collect leaves of the plants where the caterpillars were found, they will be used later to feed the larvae. Leaves can be kept in separate plastic bags (one per plant species). If you are collecting different caterpillars on different host plants the same day, make sure to clearly identify the caterpillar containers and associated plastic bags containing leaves, to avoid confusions later. A simple way is to number every container and bag (using a permanent marker or paper labels), and record them all in your notebook.

- Keep the caterpillars in a cool shed or an indoor room with temperatures not too different from outside. Feed the larvae using the leaves brought from the field (leaves can last for several days if kept in a plastic bag inside a fridge, close to the vegetable section). Every other day remove any debris and supply fresh leaves. It helps to place a small piece of paper towel inside of the containers to prevent high humidity.

- Continue to feed the caterpillars until they pupate (i.e., become chrysalides or spin a cocoon). If the caterpillar used some leaves to build a shelter for its pupation keep them, otherwise remove all leaves that were not used at that point. Pupae can stay that way from several days to several months, depending on the species and the time of the year the caterpillar was collected.

- Sometimes caterpillars will die from pathogens (virus, bacteria, fungi). In those cases, make sure to clean well the container before using it again for another larva.

- Some caterpillars, if parasitized, would never pupate, but instead will die as a larva and the parasitoid larvae (wasps or flies) will come outside of the caterpillar skin and will spin their own cocoons on top or near the dead caterpillar. In cases the parasitoids spin their cocoons on top of the caterpillar, it will look as if it has several white/yellowish “things” over its skin (see picture in the back). Remove unused leaves, clean the container and wait (several days/weeks) until parasitoids emerge from their cocoons.

- Parasitoids can be safely killed by leaving the container in a domestic freezer for a few hours. Once dead, the parasitoids can be transferred to a small tube, either dry (for flies) or preferably immersed in alcohol at 70% or higher % (for parasitoid wasps). A collection of reference specimens (=vouchers) of both the reared butterflies/moths and their parasitoids is very important, in order they can be correctly identified later by specialists on those groups. Any additional information recorded (e.g., % of adult butterflies/moths emerged from the collected larvae, % of caterpillars that were parasitized, etc.), as well as photos illustrating different stages of the rearing process will also be very useful.

[Prepared by José Fernández-Triana, Canadian National Collection of Insects, Ottawa, Canada. May, 2014].

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith