EFFECTS OF NECTAR-INHABITING BACTERIA AND MEDITERRANEAN FLOWERING PLANTS ON INSECT PARASITOIDS

As a source of nectar for parasitoids of economically important insect pests, angiosperm flowering plants are well-documented as important components of plant diversity for integration in agroecosystems. Even though nectar provisioning has proven to increase performance of adult hymenopteran parasitoids, flower establishment does not necessarily translate into pest suppression. This discrepancy may be attributed to the hidden role of nectar microbiome, which can alter the overall quality of nectar either through alterations in nectar chemistry and/ or through the intrinsic value of microbial cells. Furthermore, with the growing interest in wild flowering plants for biological control, we need to identify suitable species that are adapted to the local conditions (i.e., Mediterranean basin) and can effectively attract and retain parasitoids within agroecosystems. In this PhD thesis, we investigated the effects of individual bacteria from nectar on parasitoid longevity and the potential of wild Mediterranean flowering plants in attracting parasitoids. Specifically, we aimed to (i) examine whether nectar fermentations by bacteria can affect the longevity of diverse parasitoids indirectly (i.e. through changes in the chemical profile of the nectar due to bacterial metabolism); (ii) assess whether bacterial cells themselves can directly affect parasitoid longevity when added in the nectar; and (iii) evaluate whether Mediterranean flowering plants can attract parasitoids. To address the first research goal, 14 bacteria that had been isolated from the nectar of buckwheat flowers (Fagopyrum esculentum) were used in bioassays with 10 insect parasitoid species belonging to seven different families. For the second research goal, five among the above 14 bacteria were tested in bioassays with Trissolcus basalis, the most widely used solitary egg parasitoid of Nezara viridula. The latter, commonly known as the southern green stink bug, is a cosmopolitan and polyphagous pest that feeds mainly on various crops, such as soybean and tomatoes. Additionally, for the third objective, six wild flowering plants that are commonly found in Sicilian agroecosystems were tested with T. basalis. We aimed to find potential alternatives to buckwheat, an annual dicotyledonous broadleaved plant known for the beneficial effects on parasitoid performance but not well-adapted to the Mediterranean dry conditions. Altogether, our results underline the role of flowering plants for the enhancement of biological pest control and shed light on nectar microbes as “hidden players” mediating plant-parasitoid interactions. Further research should focus on the verification of our findings in more realistic setups to assist farmers in their endeavor to implement resilient agricultural practices.