Close up of C. odorata. Note the three prominent “pitchfork” shaped veins in leaves, giving it the name devil weed.

  • Chromolaena odorata, also known as devil weed, siam weed or bitter bush, is one of the most notorious tropical weeds in the world. Emerging as a shrub that quickly forms dense thickets, it can thrive in all environments except deep shade, flourishing in newly disturbed areas. Each plant can grow up to 12 feet tall and produce 800,000 small seeds in a year, which readily disperse via the wind or burrow into clothing, gear, or fur.
  • The plant suppresses the growth of other plants (it’s “allelopathic”), allowing it to grow in dense fire-prone thickets in both native forest remnants and agricultural fields choking out all other plant life. If allowed to spread unchecked, it could easily become ubiquitous across dry to mesic-wet environments in Hawai‘i.
  • Distribution: C. odorata was first detected in Hawai‘i at the Kahuku Training Area on the north shore of O‘ahu in January 2011.  The only known infestations in the state are on the island of O‘ahu, centered around the northern Ko‘olau range. C. odorata is native to Central and South America and is a well-documented pan-global pest in the tropics worldwide.

THE CANDIDATE: Cecidochares connexa

  • Adult female Cecidochares connexa, proposed biocontrol agent.

    A small fly, Cecidochares connexa, is proposed as a means to contain devil weed in Hawai‘i. It is a gall-forming fly that mates on C. odorata, ovipositing eggs in the buds of the plant. This gall slows the growth of the stem and plant, reducing flower and seed production. It has been successfully introduced in several countries in Asia, Africa & the Pacific with positive test results.  In Papua New Guinea, where devil weed is a major agricultural pest, crop yields went up by as much as 50% after the introduction of C. connexa (Day et al. 2013).

  • Native range: Americas (Columbia) where C. odorata originated.

Timeline of project progress:

  • Permits to bring the agent into testing sites in Hawaii are underway. Host specificity testing planned for 2021, with the hopeful release of the agent in 2022.

Further Information:

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