Biodiversité fonctionnelle en maraîchage biologique : mise en place de bandes florales pour favoriser les punaises prédatrices - compte-rendu d'essai 2010

Summary

Functional biodiversity can be enhanced by in settling, in the crops surroundings, specific vegetal species that will increase the occurrence of beneficial insects, by providing shelters, and alternative preys. This technique, also called biological control by habitat manipulation, was adapted in Southern France to control spider mites (Tetranychus urticae), and white flies (Trialeurodes vaporariorum and Bemisia tabaci) using two predatory mirid bugs Macrolophus melanotoma (form. caliginosus) and Dicyphus errans.
Trials started in 2007, with a first step consisting in selecting adapted host-plants for these two mirids. 22 species of host-plants have been sown in strips between greenhouses at the experimental station of GRAB (Avignon – Provence). Germination rate, competition with weeds have been evaluated. Exhaustive samples of insects on these host-plants have been realised. The ratio [number of predators / number of phytophagous] has been calculated, and the number of predatory mirid bugs evaluated.
Dittrichia viscosa and Calendula officinalis appeared to be the most promising species, considering their rusticity, their high ratio [predators/phytophagous] and their ability to shelter Macrolophus and Dicyphus. These 2 species were sown in 2009 in 3 different production sites around Avignon. Mixtures of seeds of the 2 species were compared to “pure” plots of Dittrichia and Calendula. Dittrichia, which germination is poor and late, has suffered from competition with Calendula in the mixtures. Sowing at 3g/m² for Dittrichia and 2,5g/m² for Calendula has given the best results in terms of ground occupation. As noticed in 2007 and 2008 at the experimental station at GRAB, Dittrichia and Calendula have sheltered many more predatory bugs than the control (spontaneous flora) did.
In 2010, new strips were sown, in order to check the capacity of beneficials to migrate into the greenhouses, and to decrease the targeted pest populations (spider mites and white flies).