Finding a natural balance: fireweed biocontrol on Kohala is supported by local ranchers

Fireweed biocontrolKWP partners and staff gathered recently to welcome the newest residents in the pastures of Kohala:  a bunch of furry black caterpillars. These larvae of the Madagascan fireweed moth, Secusio extensa, are from the home range of a damaging invasive weed known locally as “fireweed.” This daisy relative has invaded pastures across the Big Island, and not only reduces edible forage for cattle, but is also toxic to livestock.

Three KWP ranching partners (Kahua Ranch, Ponoholo Ranch, and Parker Ranch) are working with the State Department of Agriculture to rear these insects in cages, hoping to raise a population in the millions to deal with the 850,000 acre infestation of fireweed on the Big Island.

The public often expresses to me great skepticism about the intentional importation of a new insect to our islands, and their concern is appreciated! In the past, there was little knowledge or understanding of the importance of controlling the spread of new weeds, new insects, or new animals to our islands, and some of our worst invaders were accidentally introduced.

The idea behind biocontrol is to find the “perfect” natural balance for an invasive species. This means sending explorers to places like Madagascar to learn about the natural predators, parasites and diseases that keep a species’ population under control in its home range. The core reason that a non-native species becomes invasive is that it moved to a new location where it had no natural controls on its population. So our goal is to find something like that natural balance here in its new home.

This is the case with this great little caterpillar. It has been undergoing tests for over a decade to make sure it won’t eat anything useful or native to Hawaii. In quarantine, it was offered all kinds of plants as food, and in every case, this little bug won’t touch anything but fireweed and a couple other weeds.

The greatest story I heard about this process is the descriptions of fireweed in its home range in Madagascar.  On that island, you can’t find fields yellow with fireweed like you do here, because the native insects keep its population to a couple yellow clumps in every field – which is the goal for Hawaii, too.

Read more here: http://westhawaiitoday.com/sections/news/local-news/moths-versus-fireweed-state-uses-biological-control-help-protect-pastures

Photo: KWP partners and staff observe the rearing cages for the fireweed biocontrol, a moth named Secusio extensa.