Fireweed

Fireweed [Senecio madagascariensis Poiret].  The colonies of the two very promising, potential biocontrol agents of fireweed, Secusio extensa (Butler), an arctiid moth, and Sphenella austrina Munro, a tephritid fly, have died out in the HDOA Insect Quarantine Facility. The probable cause of the demise of both colonies was a decline in host plant suitability as a result of heavy aphid infestations and severe damage. A third highly promising agent, Nyctemera apicalis, an arctiid moth, is being reared successfully and is undergoing host range testing. The first two species had been collected in Madagascar and South Africa, respectively, during an exploration for fireweed natural enemies in 1999. The third species was collected more recently in South Africa during a second fireweed exploration in 2005.

The loss of the colonies of the first two agents was very unfortunate because host specificity studies were completed for the first species and nearing completion for the second. Both species are believed to be highly suitable for release in the Hawaiian Islands to suppress fireweed infestations, which are mainly found in pastures and wayside areas on Hawaii and Maui. Although this setback will delay the anticipated releases of S. extensa and S. austrina, which are eagerly being awaited by the cattle industry, it may have been a blessing in disguise because those insects were originally collected in 1999 and seven years of rearing in quarantine has very likely resulted in inbreeding. Plans are being made for new collections in Africa.