Assessing the theoretical nectar accessibility on flowering weeds from the olive grove for the olive moth and three natural enemies

Abstract

Several studies have shown that manipulating flowering weeds within an agro-ecosystem can have an important role in pest control by natural enemies, by providing them nectars, which are significant sources of nutrition for adults. However, flowering weeds have also been found to have a negative impact when insect pests benefit from the same food sources. Thus, before proceeding with a manipulation program, candidate plants must be screened in order to identify those which provide resources to natural enemies and not to pests. The aim of this study was to assess if, theoretically, the olive moth, Prays oleae and three of its main natural enemies (the parasitoids, Chelonus eleaphilus and Elasmus flabellatus, and the predator Chrysoperla carnea) can access the nectar from 21 flowering weeds from the olive grove, by analyzing the architecture of the flowers as well as the mouthpart structure of the pest and its enemies. The architecture of the flowers was studied by measuring corolla opening and corolla depth. For the mouthpart structure of P. oleae, the proboscis length of recently dead individuals was measured, while for natural enemies, as elongated ¬mouthparts are missing, the head width was measured, as this is the limiting factor in exploiting nectar from deep, narrow flower corollas. All measurements were done with an ocular micrometer fitted to a stereoscopic microscope, by using the computer software Digital Imaging Solutions. The combinations of measurements on floral architecture and mouthpart structure have allowed conclusions on the theoretical nectar accessibility for the four insect species.