Dittrichia viscosa as a reservoir of Bactrocera oleae parasitoids

Abstract: The false yellowhead Dittrichia viscosa (L.) W. Greuter (Asteraceae) is a widespread plant species in the Mediterranean region. Several studies have reported its role as an alternative host plant of certain olive fruit fly parasitoids. These parasitoids parasitize the larvae or pupae of Myopites stylatus (Fabricius) (Diptera: Tephritidae) that causes galls on the flowers of this plant. However, relatively little effort has been devoted to investigating the number of larvae or pupae present per gall, the parasitism level of M. stylatus and the period that each parasitoid species emerges from the galls. In the current work, D. viscosa plants bearing galls of M. stylatus were located in the area of Chalkis, central Greece. On 14 February 2018 and on 23 November 2019, 20 galls were collected and were dissected under the stereomicroscope to record alive and parasitized larvae or pupae of M. stylatus per gall. In the first and second sampling, in average, each gall had 2.55 or 1.95 chambers, 62 or 71 % of them were occupied by alive larva or nymph of M. stylatus and nymphs consisted of 48 and 9 % of the population, respectively. Larvae but mainly pupae of parasitoids were recorded in the galls. The parasitism level was 32 % and 33 %, respectively. On 14 February 2018 galls were enclosed in cages and transferred in the laboratory where were kept under room conditions to monitor the emergence of parasitoids. Parasitoids firstly emerged on 20 February and their emergence continued till September 2018. In the samples Eupelmus urozonus, Eupelmus sp., Eurytoma martelli, Eurytoma sp., Ormyrus sp., Torymidae, Pteromallidae and Eurytomidae were recorded. Among them, E. urozonus and E. martelli are important parasitoids of the olive fruit fly. Eupelmus urozonus emerged from 20 February to April 3, 2018. Therefore, this work shed light on aspects of the role of D. viscosa and M. stylatus in the conservation of olive fruit fly parasitoids and further research should focus on more detailed evaluation of their importance in olive fly parasitization.