Statement About Butterfly Releases
By Dr. Orley Taylor, Monarch Watch Organization
University of Kansas Entomology Program
Butterfly releases are fairly well regulated and should be. At present, only 9 species can be released. In practice, only two species, the monarch (Danaus plexippus) and the painted lady (Vanessa cardui) are commonly released. These species probably constitute 99% of the releases. The latter is the most widely distributed butterfly in the world and it is probably the most abundant. It is a highly "migratory" species and apparently lacks the genetic differentiation seen in species with well defined subpopulations. Similarly, the monarch can be characterized a migratory species with a panmictic breeding system.
There is no evidence of genetic differentiation within North America with the possible exception of monarchs west of the Rockies. The likelihood that western monarchs are different genetically from those in the east is low and nothing has been found that convincingly establishes such a difference. Nevertheless, regulations prohibit shipping monarchs across the Rockies - just in case - a prudent policy, in the event that further research reveals genetic differences.
The disease argument sounds frightening but it is misdirected and reflects a lack of knowledge of how diseases operate in natural populations. In practice, the breeders, who would be presumably be the source of contamination, could not stay in business if such diseases sweep through their stocks. Although it is likely that some diseased butterflies are released from time to time, the numbers are probably low. The diseases that occur in stocks are those commonly found in the wild and, in the wild, conditions seldom support dissemination of microbes such that they would decimate populations. The real threat of diseases would be the transfer of a novel microbe from one species to another while multiple species, particularly species from different continents, are being reared in a common environment. The release of such novel microbes into populations that have no resistance could have severe consequences. This possibility is not specifically addressed in the regulations. however, I know of only a few cases where exotics are reared in the same facility with natives and even this shouldn't be a problem if the exotics are quarantined before being reared in a common facility. Even so, in practice, it is not diseases that are the biggest threat to native populations but the introduction of novel parasites, parasitoids, and predators from outside North America. The current regulations require that pupae of introduced species used in display facilities be isolated so that any emerging parasitoids can be trapped and killed before they escape. Let's hope this system continues to be effective.
We already have an abundance of introduced species, various parasites, parasitoids and predators such as Polistes dominulus, Vespula germanica, Comsilura (tachinid fly) and other parasitoids, lady bird beetles, fire ants, etc., that feed on the larvae, and sometimes the adults, of our native butterflies. These are real concerns. Releases, in the present form, are a minor issue but they sure generate a lot of heat.