Abstract
In the last decades, concerns about the effects of the intensification of agriculture and the use of agrochemicals on the environment and human welfare have been rapidly increasing. Understanding food webs between different organisms in the agroecosystems hold the potential in finding new pests control tools that have less negative impact on the environment. In this light, the aim of this doctoral dissertation was to investigate chemoecological interactions between apple Malus domestica (Borkh) and two of its main aphid species, Dysaphis plantaginea (Passerini) and Aphis pomi (de Geer). Also, this dissertation aimed to study myrmecophily of aphids to enhance its sustainable management strategies. Experiments were conducted to characterize the volatiles by using by CLSA-GC-MS complemented by PTR-ToF-MS. Some volatile compounds (VOCs) were found to be released upon the infestation of both aphid species such as acetic acid (AA) and 2- phenylethanol (PET), nonanal, decanal, methyl salicylate, geranyl acetone and (E)-βcaryophyllene. Whereas, benzaldehyde and (E)-β-farnesene were exclusively identified upon the infestation of A. pomi, and linalool, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) upon the infestation with D. plantaginea. The volatiles were tested in a wind-tunnel to assess the attraction of the the aphid predator, Chrysoperla carnea (Stephens). The predator showed good attraction to a blend of AA and PET and did not respond to several aphid-induced VOCs when they were tested alone. A three-year field study conducted showed that traps baited with the same lure combinations were highly attractive to a leafroller, Archips xylosteana (L.) but not natural enemies. These results taken together proved that HIPVs released by apple trees after aphid infestations can have a role not only in tritrophic interactions but in multitrophic interactions. On another front, the myrmecophily of both aphid species D. plantaginea and A. pomi was studied to enhance biocontrol. Artificial honeydew was used to divert ants from aphid colonies to open a gap for natural enemies. D. plantaginea and A. pomi colonies were mapped from emergence to the end of the season, in addition, the numbers of the ant Lasius niger and three taxa of natural enemies, Coccinellidae, Syrphidae and Chrysoperla spp. were mapped. The results showed how myrmecophily blocks biological control. With ii ants diverted by artificial honeydew, the dynamics within the aphid colonies shifted and responses of natural enemies could be observed. Taken together, findings from these various studies in the context of multitrophic interactions, represents an important contribution towards finding new sustainable pest management strategies.