In our lab we often rear hundreds of monarchs for our research on OE (pictured below). Through the years, we've learned what to do to maintain healthy (non-infected) populations. Here are some tips for maintaining parasite-free monarchs.
Tip # 1: Sterilize all materials that contacted larval and adult monarchs, including rearing containers, flight cages, and countertops, with 20% bleach solution. Soak plastic ware and fabric for a minimum of 4 hrs in a basin filled with bleach solution, and allow to soak overnight if possible. Bleach surfaces that contacted monarchs several times daily. Sterilize butterfly nets that may have contacted infected adults.
Tip # 2: Always wear disposable gloves when handling milkweed, tubs, larvae and adults. Change your gloves frequently while working! This will prevent spreading infected spores to healthy monarchs.
Tip # 3: Use only fresh milkweed to rear larvae. If you have a greenhouse, keep the plants indoors or away from potentially infected adults. Soak wild milkweed cuttings in 10% bleach solution for 20 minutes, then rinse thoroughly with tap water before giving it to the larvae.
Tip # 4: Rear larvae in washable (and bleachable) tubs, at the lowest densities possible (ideally, 1 larva per container, or no more than 10 per container). When finished, bleach all tubs before using again.
Tip # 5: If any pupae turn brown, black or grey before the adults eclose, they're probably infected with OE (or another pathogen) and must be removed (and frozen) before they eclose and spread spores to the other individuals. Click here to see other possible signs of OE.
Tip # 6: When the adults eclose, they should be removed from the container as soon as their wings have hardened (within 8 hrs), placed in individual glassine envelopes, and checked for OE (see instructions here). Freeze any infected individuals. Everything that touched that infected adult must then be sterilized (bleached) thoroughly.
It is important to remember that OE spores can persist for many years and tolerate a wide range of temperatures and external conditions. Therefore, careful examination of monarchs and surface sterilization with bleach is necessary to prevent continued transmission.