The invasive bramble Rubus alceifolius is not called a "plant pest" for nothing. Originally from South-East Asia and accidentally introduced to Reunion in the 19th century, its development at the expense of local species is comparable to that of an infection spreading in an organism. In the absence of a predator, its progression knows no limit. Until now, the control methods put in place, mainly mechanical or chemical, have been expensive and inefficient ...
Finally, a little bee from Sumatra has proved to be the right remedy. Cibdela janthina, known as "the blue fly", has, after a whole battery of tests conducted by CIRAD since 1997, been declared able to restore the biodiversity of Reunion. This little hymenopter has the peculiarity of exclusively attacking the genus Rubus, to which the invasive bramble belongs. Following its introduction on the island in 2007, the results were not long coming; 700 hectares formerly colonized have now been returned to nature! The invasive bramble now only thrives above 1200m above sea level in areas the bluefly finds difficult to reach.
Larvae of Cibdela janthina / Adult Cibdela janthina - © Antoine Franck – CIRAD
Biological control of an invasive population is similar to testing a new treatment. It must be studied, adapted and specific. Sometimes it's a success, as was the case for the invasive bramble with the blue fly. In other cases, the treatment acts in the desired way but has disastrous side effects.
Being able to restore biodiversity without playing the mad scientist is one of the ambitions of the project COREIDS, developed at CESAB and led by ecological researchers François Massol and Patrice David. They analysed the functioning of ecosystems in detail; what are the different species that contribute to their balance? How do they interact? What could be the effects of a disruptor as was the case with the invasive bramble? All of these elements will ultimately help to better understand and anticipate threats to biodiversity ... prevention is better than cure!