Ground cover vegetation composition predicts the abundance of Sphaerophoria scripta (Linnaeus, 1758) (Diptera: Syrphidae) in olive groves from Trás-os-Montes region (Portugal)

Abstract: The spontaneous ground cover vegetation provides shelter and vital floral resources for the hoverflies (Diptera: Syrphidae). Such resources can contribute to the growth, development, reproduction, and survival of syrphids, allowing them to maximize their function as natural pest enemies, pollinators, and decomposers of organic matter. So, identifying the plant families driving the abundance of Sphaerophoria scripta (Linnaeus, 1758), one of the main syrphids species present in the olive groves in the Mediterranean region, is essential to promote its presence and abundance. Here, we investigate how the percentage of plants in the flowering stage presents in the ground cover vegetation within two olive groves, under integrated production management located in Mirandela (Portugal), shapes the abundance of S. scripta. For that in 2018, weekly, from April to August, in both olive groves, ground cover vegetation was identified. Thirty sample units randomly distributed over a transect covering 1 ha were selected per sampling date and sampling site. In each sample unit was recorded the vegetative stage of the plants and the percentage of ground cover by each plant family. On the same dates, syrphids were also collected using an entomological net, nevertheless, only S. scripta was considered. The effect of the percentage of the plant families in the flowering stage in the abundance of S. scripta was studied through a Generalized Linear Model. The results showed that the abundance of the S. scripta is positively associated with the proportion of plants in the flowering stage of the families Asteraceae and Orobanchaceae and negatively with the plants of the families Boraginaceae and Polygonaceae. According to the developed model, the families Poaceae, Euphorbiaceae and Plantaginaceae did not influence the abundance of S. scripta in the olive grove. Our results suggest that the increase of the percentage of certain plant families and the decrease of others can promote the abundance of S. scripta in the olive groves in Trás-os-Montes.