Insect attractivenness of five weeds

Abstract

The number of pollinators in agro-ecosystems worldwide has declined alarmingly in recent decades due to the mismanagement of the habitat and intensive agricultural practices. Increases in agricultural land area have restricted natural flora to small patches, reducing food sources for most insects. Thus, knowledge of the role that surviving weeds can play in maintaining insect biodiversity in these systems is crucial. Field studies of cereal margins located in central Catalonia, carried out by Morrison et al. in 2015, revealed that several weed species were highly attractive to insects. To further estimate the level of attraction of these weed species, a trial was carried out at the Agropolis experimental farm located near Barcelona. The trial consisted of three repetitions of six, 2.5 x 2.5 m2 plots sown with: Sonchus oleraceus L., Papaver rhoeas L., Daucus carota L., Malva sylvestris L., Convolvulus arvensis L. and a mixture of these species. When flowers were in bloom, visual counts of insects visiting flowers were performed in each plot for 5 minutes, twice a week. Insect sampling was also carried out with pan traps (yellow, blue and white dishes with soapy water), set for 24 h each week. Collected insects were classified to family level. Visual counts showed that pollinators, such as honeybees and wild bees, were highly attracted to P. rhoeas, D. carota and the mixture. Sirfidae were highly attracted to D. carota. Heteroptera were mainly attracted to M. sylvestris and D. carota, although the number of individuals was very low. Coleoptera were mainly attracted to D. carota. Insects collected in the traps belonged to three orders: Hymenoptera (Apidae, Halictidae, Ichneumonidae, Megachilidae, Sphecidae), Coleoptera (Cantharidae, Cerambycidae, Chrysomelidae, Meloidae, Mordellidae) and Heteroptera (Lygaeidae, Pentatomidae). According to these results, weeds like P. rhoeas and D. carota can not only contribute to maintain the ecosystem biodiversity but also they can contribute to increase crop production, because they attract beneficial insects such as different Himenoptera species (pollinators) and also Syrfidae (predators). This study shows the role that weeds can have also in maintaining the ecosystem services, rather threatened by agricultural intensification.