French Broom Project

Lead scientist: RFH Sforza

Presentation & context

French broom, Genista monspessulana (L.) LAS Johnson (Fabaceae) is a perennial woody shrub, native to the Mediterranean region commonly associated with regeneration in fire-prone environments.

 
Blooming French broom (Photo by RFH Sforza)

Introduced as an ornamental plant to many parts of the world, French broom is currently a major invader in several countries including the USA and Australia Introduced in the 19th century as an ornamental plant; it is currently invasive in California and Australia. Foreign exploration in the native range (Spain, France, Italy, Greece) by collecting pods, beating tray samples and threshing of leaves, allowed the identification of two major phytophagous arthropod candidates: Arytinnis hakani (Longinova, 1972, Hemiptera Psyllidae) and Lepidapion argentatum (Gerstaecker, 1854, Col. Brentidae).

  Adult of the French broom psyllid (Photo by RFH Sforza)

Arytinnis hakani is a sap sucking insect that impacts French broom by intense feeding pressure and the production of high levels of honeydew. The honeydew covers the foliage and causes sooty mold growth. This growth may inhibit photosynthesis. Lepidapion argentatum is both a stem gall maker and a seed feeder.

 
Mating couple of Lepidapion argentatum (Photo by RFH Sforza) 

Research components

First, our research is focused on biology and specificity of the weevil Lepidapion argentatum. The development time of L. argentatum in stem galls ranged from 34 to 40 days at mean 23.67 ± 2.43°C. The double ability of L. argentatum to develop in stems and pods appears not to have been recorded in Coleoptera and rare in other phytophagous insects. That makes it a promising candidate. The impact on the reproduction of French broom was studied in Southern France and revealed that it could effectively reduce the number of viable seeds by 18.8%, but also increased the number of aborted seeds by 10% within the attacked pods. To evaluate the specificity of L. argentatum, choice and no-choice tests were performed in 2012 and 2015 on a total of 36 non-target closely related species. Results revealed the presence of galls and larvae in the stems of seven species, including two endemic Californian lupines, i.e. Lupinus arboreus blue and L. chamissonis. In the future, new tests will be conducted to determine if L. argentatum is able to complete its entire development lifecycle on the non-target species where galls have previously been observed.

Second, an important aspect of biocontrol research is to determine the potential of an agent to distribute and not attack native vegetation. Thus, EBCL researchers (Sforza & Desurmont) are conducting an open field test to evaluate the movement and effectiveness of the French broom psyllid Arytinnis hakani under more natural conditions. Two concentric circles with a radius of five and 10 meters were constructed and plant species belonging to the lupine group and French broom control plants randomly placed along the two perimeters in an open field test. At the centre of the two circles, hundreds of psyllids of all life stages were released in spring 2021 & 2022. The spread of individuals on the lupines and the French broom control plants was quantified. The data are currently in the process of being analysed. The overall purpose of studying these two biocontrol candidates is to prepare a petition to release in North America.

Students involved

Tabary (Master1, 2019), E. Kerdellant (Master2, 2015), T. Bernard (Master2, 2012)

Recent publications

Kerdellant et al. 2021 Insects

Kerdellant et al. 2019 Ent. Exp & Applicata