Encontro Ciência 2017- 3 a 5 Julho, Lisboa
Olive fly management today:
the search for pesticide-less alternatives

Nobre, F. T. Rei

Olive is an ancient ubiquitous crop of considerable socioeconomic importance, being a major agro-ecosystem in the Mediterranean basin. Through time, the olive fly (Bactrocera oleae) has evolved to exploit this exquisite resource and is now able to use unripe olives completing several generations before ripe fruit become available. Production losses are high: it has been held responsible for losses of up to 80% of oil value and 100% of some table cultivars. Over the last decades, the management of olive fly has been based on the use of dimethoate. However, resistance to dimethoate had evolved, involving mutations of the Ace-gene, and it is spreading fast (with resistance frequencies up to 0.90 in some locations).

We are developing a rapid method to detect the three well known mutations (2 SNPs and 1 indel) related to the Ace-gene conferring resistance to dimethoate and screening for populations where the wild type is still prevalent. A reduction on selection pressures, by excluding the use of this organophosphate, is crucial to limit occurrence and generalization of resistance and allow the ‘wild type’ flies to increase in the population.  Non-insecticidal pest management methods for this olive pest are thus at a premium. We are convinced that the future of pest management lies on integration: the combination of methods that may be individually less efficient than pesticides can generate valuable synergies.

An extensive characterization of sympatric putative predators and parasitoids of the olive fly is ongoing. The natural enemies’ populations have the advantage of coexisting in time and space, classically have a high reproductive response to slight increases in host density, and some show seasonal reproductivity responding to the pest population. In a selection of promising species in maintaining pest populations at non-economic densities, a confirmation of their role will be obtained through molecular probes: looking for olive fly mtDNA in the predators, and for parasitoid mtDNA in the olive fly larvae. In the quest for finding natural enemies, our work does not forget the ‘enemies within’. Olive fly, like many other organisms, require microbial symbioses for survival.

Because many microorganisms cannot be classified exclusively as beneficial, harmless or deleterious, strategies implying the disruption of microbial symbioses or symbiont-mediated manipulation of insect traits are promising tools in pest management approaches. Overall, the target is a more sustainable production of olives while preventing risks, protecting the environment and promoting resources efficiency.