The current project will unravel the potential of using the olive fly microbiome in pest management strategies. The rationality of the proposed research follows the below statements (S) and concomitant questions (Q):
S1: There is a strong co-evolutionary relationship of the specialist B.oleae with olive fruits having developed special organs to harbor a bacterial symbiont to counteract the inhibitory effect of oleuropein.
Q1.1: Do different cultivars produce different amounts of oleuropein and does that correlates with the level of B.oleae infestations?
Q1.2: Is there E.dacicola population differentiation and does it relates with cultivars amount of oleuropein?
Q1.3: Is the marked differentiation between Iberian and Italic B.oleae populations [23], also accompanied by obligate symbiont differentiation? Can this be linked to the predominant regional cultivars?
S2: B.oleae is a holometabolic species. At metamorphosis there is a radical remodeling of the gut and other organs, with the elimination of the entire larval gut and contents [24]. Not only the developmental stage but also sex and ecological factors influence the microbiome.
Q2.1: To what extent does live stage and habits change the presence and abundance of E.dacicola?
Q2.2: Is there a shift in symbiotic bacteria populations across insect life stages?
Q2.3: What is the core microbiome associated to B.oleae?
S3: Gut bacteria of insects contribute mainly to nutrition, protection from parasites and pathogens, modulation of immune responses, and communication.
Q3.1: The microbiome of different insects has been shown to aid in several functions, some potentially relevant for the life style of B.oleae (namely, N supplementation, overcoming oxidative stress, detoxification, mating competitiveness, antibacterial/antifungal activity). Will putative functional analyses of the bacteria associated with B.oleae, in its different life stages, identify other [than E.dacicola] relevant partners?
Approach
To answer the above questions a combination of field trials, laboratory work -advanced microscopy, chemistry and molecular biology including metagenomics- and ecological and (phylo)genetic modelling will be employed.
There is a need to release the selective pressure imposed by the long term use of dimethoate in the olive orchards. To define a detox strategy to be integrated in a pest management strategy, there is the need to identify the regions where resistance has developed to high levels and mutated alleles are facing risk of fixation in the local populations. These regions are to be tagged as priority for intervention. An easy to perform test for resistance alleles will be developed, using this first screening as method validation. Such a test intends to be a valuable tool for monitoring resistance frequencies, and thus aid in decision making for the delineation of sustainable pest management approaches. Pest management programs need to make use of appropriate decision-making processes for application of pesticides, along with employment of cultural measures, cultivar resistance, and biological agents.
The current project will evaluate some of the most widely used cultivars attempting to link the assumed and observed resistance to the olive fly with oleuropein levels and to the symbiont population, particularly with Erwinia dacicola. Several chemical factors are known to influence cultivar susceptibility (e.g. composition in natural waxes, volatiles, phenolic compounds) [25]; however, it seems to be the inhibitory effect of oleuropein that is counteracted by the symbiotic bacteria E.dacicola [17] and hence the emphasis on this phenolic compound in the understanding of this trichotomy.
This putative connection between obligate-symbiont, oleuropein content and cultivar susceptibility might on itself became a good starting point for alternative biological management approaches. The degree of host-symbiont specificity can be used as tool, particularly if vulnerable olive fly stages are identified. However, the microbiome of the olive fly might be a source of alternative biological agents, not in the classical view of predators and parasitoids, but on a more sophisticated symbiosis-based approach. Therefore, the current project will identify the core microbiome associated to B.oleae and characterize potential shifts on the symbiotic community in function of life stage/habits. Furthermore, determining the functional attributes of the microbiome is essential for understanding their role on host metabolism and for postulate on microorganism potential use in a symbiosis based strategy. This functional profiling will add other potential partners, besides E.dacicola, with key functions related to life habits.
Altogether, with this research, the first steps will be taken to gather the necessary knowledge for the design and testing of symbiosis mediated olive fly control strategies.