Olive fruit fly and its obligate symbiont Candidatus Erwinia dacicola: Two new symbiont haplotypes in the Mediterranean basin

Utilizing Olive Fly Ecology Towards Sustainable Pest Management

The olive fly (Bactrocera oleae, OLF) is a major pest of global significance that occurs in places where olive cultivation thrives. This paper highlights the economic and environmental damage caused by OLF infestations, including reduced olive oil yield and quality, disrupted supply chains, and ecosystem imbalances due to heavy insecticide use. Understanding olive fly ecology is crucial for developing effective control strategies. The review explores the fly's life cycle, its relationship with olive trees, and how environmental factors like temperature and humidity influence population dynamics. Additionally, studying the role of natural enemies and agricultural practices can pave the way for sustainable control methods that minimize environmental harm. Climate change, intensive cultivation, and the development of resistance to insecticides necessitate a shift towards sustainable practices. This includes exploring alternative control methods like biological control with natural enemies and attract-and-kill strategies. Furthermore, a deeper understanding of OLF ecology, including its response to temperature and its ability to find refuge in diverse landscapes, is critical for predicting outbreaks and implementing effective protection strategies. By employing a holistic approach that integrates ecological knowledge with sustainable control methods, we can ensure the continued viability of olive cultivation, protect the environment, and produce high-quality olive oil.

The biogeographic patterns of the olive fly and its primary symbiont Candidatus Erwinia dacicola across the distribution area of the olive tree

The olive fly, Bactrocera oleae (Rossi, 1790), is the major insect pest of olives attacking both cultivated and wild olive. Bactrocera oleae carries a primary and vertically transmitted symbiont, the bacterium Candidatus Erwinia dacicola. As any primary symbiont, it plays an important role in the reproduction and lifespan of the fly. The genetic 16S rRNA diversity of the primary symbiont and the mitochondrial haplotype variation of the insect host were simultaneously examined in 54 olive fly populations. The aim was to unravel the biogeographic patterns of this economically relevant host-bacteria interaction across a wide distribution area. Three symbiont haplotypes were identified. The primary symbiont showed a lower haplotype diversity than that of its host, a characteristic indicative of a long-term interaction. A significant genetic and geographic association between host and primary symbiont was observed, with an East-West genetic differentiation pattern in the Mediterranean basin, coinciding with the historical genetic distribution of the olive tree. The study shows promise, informing and aiding the development of future tools for the control of the olive fly.

Anna Karenina as a promoter of microbial diversity in the cosmopolitan agricultural pest Zeugodacus cucurbitae (Diptera, Tephritidae)

Gut microbial communities are critical in determining the evolutive success of fruit fly phytophagous pests (Diptera, Tephritidae), facilitating their adaptation to suboptimal environmental conditions and to plant allelochemical defences. An important source of variation for the microbial diversity of fruit flies is represented by the crop on which larvae are feeding. However, a "crop effect" is not always the main driver of microbial patterns, and it is often observed in combination with other and less obvious processes. In this work, we aim at verifying if environmental stress and, by extension, changing environmental conditions, can promote microbial diversity in Zeugodacus cucurbitae (Coquillett), a cosmopolitan pest of cucurbit crops. With this objective, 16S rRNA metabarcoding was used to test differences in the microbial profiles of wild fly populations in a large experimental setup in Eastern Central Tanzania. The analysis of 2,973 unique ASV, which were assigned to 22 bacterial phyla, 221 families and 590 putative genera, show that microbial α diversity (as estimated by Abundance Coverage Estimator, Faith's Phylogenetic Diversity, Shannon-Weiner and the Inverse Simpson indexes) as well as β microbial diversity (as estimated by Compositional Data analysis of ASVs and of aggregated genera) significantly change as the species gets closer to its altitudinal limits, in farms where pesticides and agrochemicals are used. Most importantly, the multivariate dispersion of microbial patterns is significantly higher in these stressful environmental conditions thus indicating that Anna Karenina effects contribute to the microbial diversity of Z. cucurbitae. The crop effect was comparably weaker and detected as non-consistent changes across the experimental sites. We speculate that the impressive adaptive potential of polyphagous fruit flies is, at least in part, related to the Anna Karenina principle, which promotes stochastic changes in the microbial diversity of fly populations exposed to suboptimal environmental conditions.

Olive Fruit Fly Symbiont Population: Impact of Metamorphosis

The current symbiotic view of the organisms also calls for new approaches in the way we perceive and manage our pest species. The olive fruit fly, the most important olive tree pest, is dependent on an obligate bacterial symbiont to its larvae development in the immature fruit. This symbiont, Candidatus (Ca.) Erwinia dacicola, is prevalent throughout the host life stages, and we have shown significant changes in its numbers due to olive fruit fly metamorphosis. The olive fruit fly microbiota was analyzed through 16S metabarcoding, at three development stages: last instar larvae, pupae, and adult. Besides Ca. E. dacicola, the olive fruit flies harbor a diverse bacterial flora of which 13 operational taxonomic units (grouped in 9 genera/species) were now determined to persist excluding at metamorphosis (Corynebacterium sp., Delftia sp., Enhydrobacter sp., Kocuria sp., Micrococcus sp., Propionibacterium sp., Pseudomonas sp., Raoultella sp., and Staphylococcus sp.). These findings open a new window of opportunities in symbiosis-based pest management.