Olive fly management through symbiosis-based strategies: looking for Trojan horse candidates
Summary
Olive and olive oil are the essential components of the Mediterranean diet, and are consumed worldwide. Growers experience severe losses in their production of table olives and olive oil which are due to the olive fly. These have been managed mainly through the use of dimethoate, an organophosphate being banned from the EU due to health risks. Additionally, in this "arms race" between men and pest, the flies have evolved pesticide resistance. Screening for populations where the wild type (susceptible flies) is still prevalent will allow identifying hotspots for targeted mitigation measures that will limit resistance. Development of non-insecticidal pest management methods for this olive pest are thus at a "premium", as the combination of non-chemical methods that may be individually less efficient than pesticides can generate valuable synergies. Hence, the more tools we have the better. The current project aims to introduce a novel strategy into the management of olive fly: a symbiosis-based strategy. Basically, in the quest for finding the' natural enemies of the pest, we will focus on the "enemies within". Olive fly, like many other organisms, require microbial symbioses for survival and strategies implying the disruption of these symbioses or symbiont-mediated manipulation of insect traits (like a Trojan horse) are promising tools in pest management approaches. We will combine field trials, laboratory work -advanced microscopy, chemistry and molecular biology including metagenomics- and ecological and (phylo)genetic modelling to tackle a set of issues, that are "sine qua non" for such a strategy: (i) evaluate the microbial community structure; (ii) define the key microorganisms; and (iii) plan the strategy to restore the suitable community in function of the aim. Altogether, with this project, the first steps will be taken towards the design of symbiosis mediated olive fly control strategies.
Goals, activities and expected/achieved results
Goals
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 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?
Activities
Task 1: Dimethoate resistance-associated Ace alleles
Task 2: Biological material collection and assessemnt of infestation state
Task 3: Oleuropein detection and quantification
Task 4: olive flies' obligate-symbiont degree of differentiation
Task 5: symbiont co-differentiation
Task 6: link between both host and symbiont with ecological conditions
Task 7: collection of biological material for metabarcoding, based on previous tasks findings
Task 8: life stages dependence on E.dacicola
Task 9: bacterial community via metabarcoding
Task 10: overall critical data interpretation
Results
Outcome T1: frequency of dimethoate resistance
Outcome T2: infestation level and material for task 3 and task 4
Outcome T3: estimation of oleuropein per maturation state and cultivar to relate with infestation level and E.dacicola haplotype
Outcome T4: presence and abundance of E.dacicola in its relation to cultivar maturation [Task2], levels of oleuropein [Task3] and larvae generation.
Outcome T5: extent to which host population differentiation is accompanied by obligate main symbiont differentiation
Outcome T6: population differentiation of both host and symbiont in relation to different ecological determinants with emphasis on predominant cultivars
Outcome T7: biological material collected
Outcome T8: host-symbiont ontogeny and identification of vulnerability stages
Outcome T9: Bacterial community associated to B.oleae
Outcome T10: main findings and their relevance
