Symbiosis disruption in the olive fruit fly, Bactrocera oleae (Rossi), as a potential tool for sustainable control

Gut microbiota metagenomics and mediation of phenol degradation in Bactrocera minax (Diptera, Tephritidae)

BACKGROUND

Gut microbiota mediating insect-plant interactions have many manifestations, either by provisioning missing nutrients, or by overcoming plant defensive reactions. However, the mechanism by which gut microbiota empower insects to survive by overcoming a variety of plant secondary metabolites remains largely unknown. Bactrocera minax larvae develop in immature citrus fruits, which present numerous phenolic compounds that challenge the larvae. To explore the role of gut microbes in host use and adaptability, we uncovered the mechanisms of phenol degradation by gut microbes using metagenomic and metatranscriptomic analyses, and verified the degradation ability of isolated and cultured bacteria. Research on this subject can help develop potential strain for the environmental friendly pest management operations.

RESULTS

We demonstrated the ability of gut microbes in B. minax larvae to degrade phenols in unripe citrus. After antibiotic treatment, coniferyl alcohol and coumaric aldehyde significantly reduced the survival rate, body length and body weight of the larvae. The metagenomic and metatranscriptomic analyses in B. minax provided evidence for the presence of genes in bacteria and the related pathway involved in phenol degradation. Among them, Enterococcus faecalis and Serratia marcescens, isolated from the gut of B. minax larvae, played critical roles in phenol degradation. Furthermore, supplementation of E. faecalis and S. marcescens in artificial diets containing coniferyl alcohol and coumaric aldehyde increased the survival rate of larvae.

CONCLUSION

In summary, our results provided the first comprehensive analysis of gut bacterial communities by high-throughput sequencing and elucidated the role of bacteria in phenol degradation in B. minax, which shed light on the mechanism underlying specialist insect adaption to host secondary metabolites via gut bacteria. © 2024 Society of Chemical Industry.

Copper nanoparticles interfere with insecticide sensitivity, fecundity and endosymbiont abundance in olive fruit fly Bactrocera oleae (Diptera: Tephritidae)

BACKGROUND

The potential of copper nanoparticles (Cu-NPs) to be used as an alternative control strategy against olive fruit flies (Bactrocera oleae) with reduced sensitivity to the pyrethroid deltamethrin and the impact of both nanosized and bulk copper hydroxide (Cu(OH)2) on the insect's reproductive and endosymbiotic parameters were investigated.

RESULTS

The application of nanosized and bulk copper applied by feeding resulted in significant levels of adult mortality, comparable to or surpassing those achieved with deltamethrin at recommended doses. Combinations of Cu-NPs or copper oxide nanoparticles (CuO-NPs) with deltamethrin significantly enhanced the insecticide's efficacy against B. oleae adults. When combined with deltamethrin, Cu-NPs significantly reduced the mean total number of offspring compared with the control, and the number of stings, pupae, female and total number of offspring compared with the insecticide alone. Both bulk and nanosized copper negatively affected the abundance of the endosymbiotic bacterium Candidatus Erwinia dacicola which is crucial for the survival of B. oleae larvae.

CONCLUSION

The Cu-NPs can aid the control of B. oleae both by reducing larval survival and by enhancing deltamethrin performance in terms of toxicity and reduced fecundity, providing an effective anti-resistance tool and minimizing the environmental footprint of synthetic pesticides by reducing the required doses for the control of the pest. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Inhibitory activity of some short-chain aliphatic aldehydes on pheromone and ammonium carbonate-mediated attraction in olive fruit fly, Bactrocera oleae

BACKGROUND

The olive fruit fly (OFF), Bactrocera oleae (Rossi), is the main insect pest of olive trees worldwide. Legislation limits to the use of some synthetic larvicidal insecticides is leading to the development of new control options for preventive control of adult flies. In the present study, the biological activity of four short-chain aliphatic aldehydes, namely hexanal, (E)-2-hexenal, heptanal and (E)-2-heptenal, previously reported as repellents to the OFF adults was investigated.

RESULTS

Electroantennography (EAG) recordings showed that antennae of OFF males and females are able to perceive the test compounds in a wide range of doses. In field trapping experiments, reservoir-type polypropylene (PP) membrane dispensers loaded with individual compounds did not elicit a significant attraction of OFF males and females. On the contrary, a significant reduction of male catches was noticed when sex pheromone dispensers and PP membrane dispensers, loaded with one of the test compounds, were applied on the same white sticky traps ≈20 cm apart. Likewise, male and female catches in yellow sticky traps baited with ammonium carbonate (AC) dispensers as food attractant were significantly reduced by the presence of PP membrane dispensers of individual aliphatic aldehydes on the same traps. In small plots control trials, solid formulations of the four aldehydes into a bentonite clay support induced a significant reduction of the OFF active infestation mainly when C6 and C7 aldehyde-activated bentonites were used.

CONCLUSION

Short-chain aliphatic aldehydes showed inhibitory effects on sex pheromone and food attractant-mediated attraction of OFF. Results of field trials suggest potential of short-chain aliphatic aldehydes to develop new semiochemical-based OFF control options. © 2024 Society of Chemical Industry.

Aldehyde-containing clays: a sustainable approach against the olive tree pest, Bactrocera oleae

A set of organic/inorganic layered materials was obtained by functionalizing a montmorillonite-containing bentonite natural clay with linear aliphatic C6 or C7 aldehydes through a cost-effective and technologically simple incipient-wetness deposition method. The solids were investigated by means of a multi-technique approach (X-ray powder diffraction, XRPD, scanning electron microscopy, SEM, Fourier-transform infrared spectroscopy, FT-IR, thermogravimetric analysis, TGA, elemental analysis and solid-state nuclear magnetic resonance, ssNMR) to clarify the nature of the deposited organic species and the mode of interaction between the aldehyde and the clay. Since both natural clays and short-chain linear aldehydes find application as alternative strategies in the control of the olive fruit fly, Bactrocera oleae, the hybrid layered materials were tested under real-life conditions and their insect-inhibiting capability was evaluated in open-field trials on olive tree orchards in Tuscany, Central Italy. Specific tests were conducted to evaluate the resistance of the solids to weathering and their capability to provide a constant and long-lasting release of the bioactive ingredient. Aldehyde-containing bentonite clays have shown promising performance in controlling B. oleae infestation (with up to 86-95% reduction of affected olive fruits) in open-field trials across two years in two locations with different pedological and meteo-climatic characteristics.

Oviposition-Deterrent Effect of a High-Quality Natural Zeolite on the Olive Fruit Fly Bactrocera oleae, under Different Conditions of Temperature and Relative Humidity

In recent years, the number of available chemical pesticides has been dramatically reduced, urging the need for the discovery of alternatives to chemical pesticide products such as, among others, natural zeolites (zeolitic rocks). We determined the mineralogical and chemical composition of a specific and continuous layer of zeolitic rock sample (ZeotP) from Petrota, Evros, Greece, and evaluated its oviposition-deterrent effect on the olive fruit fly Bactrocera oleae Gmelin (Diptera: Terphritidae). The tested natural zeolite contained 70 wt. % clinoptilolite, 18 wt. % amorphous material, 7 wt. % feldspars, 4 wt. % cristobalite, and 1 wt. % quartz. We tested the oviposition-deterrent effect of ZeotP mixed or not with an emulsifier adjuvant, NU-FILM-P®, in water and applied it to the surface of olive fruits. The ZeotP oviposition-deterrent effect on the olive fly was very high under a series of tested temperatures (17 °C, 20 °C, 25 °C, and 30 °C) and RHs (23%, 33%, 55%, 75%, and 94%). In addition, the ZeotP residual deterrent effect after equable water spraying was high, like the respective effect of the pyrethroid insecticide Decis® (deltamethrin). Our results may contribute to the effective control of the olive fruit fly using an alternative to chemical pesticides: natural zeolite (zeolitic rocks) products.

Influence of Chabazite Zeolite Foliar Applications Used for Olive Fruit Fly Control on Volatile Organic Compound Emission, Photosynthesis, and Quality of Extra Virgin Olive Oil

The olive fruit fly (Bactrocera oleae Rossi) is the most dangerous pest of olive fruits and negatively influences the chemical and sensory quality of the oil produced. Organic farms have few tools against this pest and are constantly looking for effective and sustainable products such as geomaterials, i.e., zeolite. Since a particle film covers the canopy, a study was carried out on the olive tree's responses to zeolite foliar coating. The tested treatments were natural zeolite (NZ), zeolite enriched with ammonium (EZ), and Spintor-Fly® (SF). EZ was associated with higher photosynthetic activity with respect to the other treatments, while no differences were found between SF and NZ. Foliar treatments affect the amount of BVOC produced in both leaves and olives, where 26 and 23 different BVOCs (biogenic volatile organic compounds) were identified but not the type of compounds emitted. Foliar treatment with EZ significantly affected fruit size, and the olive fruit fly more frequently attacked the olives, while treatment with NZ had olives with similar size and attack as those treated with Spintor-Fly®; no difference in oil quantity was detected. Oil produced from olives treated with NZ presented higher values of phenolic content and intensities of bitterness and spiciness than oils from those treated with EZ and SF. According to the results of this study, using zeolite films on an olive tree canopy does not negatively influence plant physiology; it has an impact on BVOC emission and the chemical and sensory characteristics of the oil.

COI Haplotyping and Comparative Microbiomics of the Peach Fruit Fly, an Emerging Pest of Egyptian Olive Orchards

The peach fruit fly, Bactrocera zonata (Tephritidae), is economically relevant as a highly polyphagous pest infesting over 50 host plants including commercial fruit and horticultural crops. As an invasive species, B. zonata was firmly established in Egypt and holds potential to spread further across the Mediterranean basin. The present study demonstrated that the peach fruit fly was found multiplying in olive orchards at two distant locations in Egypt. This is the first report of B. zonata developing in olives. COI barcoding has revealed evidence for high diversity across these peach fruit fly populations. These data are consistent with multiple rather than a single event leading to both peach fruit fly invasion to Egypt and its adaptation to olive. Comparative microbiomics data for B. zonata developing on different host plants were indicative for microbiome dynamics being involved in the adaptation to olive as a new niche with a potential adaptive role for Erwinia or Providencia bacteria. The possibility of symbiont transfer from the olive fruit fly to the peach fruit fly is discussed. Potentially host switch relevant bacterial symbionts might be preferred targets of symbiosis disruption strategies for integrated pest management or biological control of B. zonata.

Glutamicibacter halophytocola-mediated host fitness of potato tuber moth on Solanaceae crops

BACKGROUND

The potato tuber moth (PTM), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a destructive pest of Solanaceae crops worldwide. α-solanine and α-chaconine are toxic steroidal glycoalkaloids (SGAs) in Solanaceae crops and are most abundant in potatoes (Solanum tuberosum L.), accounting for more than 95% of the total SGAs. PTM grows on potatoes with a higher concentration of SGAs. Gut bacteria play an important role in the physiology and behavior of insects. To understand the role of gut bacteria of PTM in host adaptability, we isolated and identified major SGA (α-chaconine and α-solanine)-degrading gut bacteria in the gut of PTM by a selective medium and analyzed their degradability and degradation mechanism.

RESULTS

The gut Glutamicibacter halophytocola S2 of PTM with high degradation capacity to α-solanine and α-chaconine were detected by liquid chromatography mass spectrometry (LC-MS) and identified by morphological and 16S rRNA gene sequence analysis. A gene cluster involving α-rhamnosidases, β-glucosidases, and β-galactosidases was identified by whole-genome sequencing of G. halophytocola S2. These genes had higher expression on the α-solanine medium. PTM inoculated with the isolated G. halophytocola S2 obtained higher fitness than antibiotic-treated PTM.

CONCLUSION

The G. halophytocola S2 in the gut of PTM could degrade the major toxic α-solanine and α-chaconine in potatoes. This enhances the fitness of PTM feeding on potatoes with high SGA contents. The results provide a theoretical foundation for the integrated pest management of PTM and provide an effective strain for the treatment of α-solanine and α-chaconine in potato food. © 2022 Society of Chemical Industry.

Dynamic interactions between the symbiont Candidatus Erwinia dacicola and its olive fruit fly host Bactrocera oleae

The olive fruit fly, Bactrocera oleae, the most serious pest of olives, requires the endosymbiotic bacterium Candidatus Erwinia dacicola in order to complete its development in unripe green olives. Hence, a better understanding of the symbiosis of Ca. E. dacicola and its insect host may lead to new strategies for B. oleae control. The relative abundance of bacteria during the fly life cycle comparing black and green olives was estimated by real time quantitative PCR revealing significant fluctuations during development in black olives with a peak of the bacteria in the second instar larvae. By microscopy analysis of larvae, we show that the bacteria reside extracellularly in the gastric caeca. During the transition to late third instar larvae, the bacteria were discharged into the midgut concomitant with a change in caeca size and morphology due to the contraction of the muscles surrounding the caeca. A similar alteration was also observed in a laboratory strain devoid of bacteria. To further investigate the symbiotic interaction and the change in caeca morphology a comparative transcriptomics analysis was undertaken. Samples of dissected caeca from second and third instar larvae collected from the field as well as second instar larvae from a laboratory strain devoid of symbionts showed significant changes in transcript expression. This highlighted genes associated with the developmental changes revealed by the microscopic analysis as well as responses to microorganisms.

Oviposition Deterrent Activity of Fungicides and Low-Risk Substances for the Integrated Management of the Olive Fruit Fly Bactrocera oleae (Diptera, Tephritidae)

Simple Summary

The olive fruit fly Bactrocera oleae is a very common pest infesting olive orchards wherever they are cultivated, representing the greatest threat to olive production and oil quality. Although broad-spectrum insecticides are often used to protect olive crops against B. oleae, there is increasing concern about their effects on the environment and human health. An important tool in integrated olive fly management could be the use of products with a repellency and oviposition deterrence effect. This research yielded experimental evidence of significant oviposition deterrent activity on the olive fly as side effects of substances used in olive growing such as fungicides or plant biostimulants, highlighting the potential use of these products in B. oleae management.

Abstract

The control of Bactrocera oleae is fundamental to decreasing the significant production loss in olive cultivation. However, traditional containment based on the use of synthetic insecticides has been encountering serious limitations due to their negative effect on human health and the environment. Within the scope of integrated olive fly management, the use of products with repellency and oviposition deterrent activity might represent a more eco-friendly solution. In this study, we tested the oviposition deterrent activity of some commercial formulations already used in olive tree crops as fungicides (copper oxychloride, dodine, mancozeb, pyraclostrobin and difeconazole) and plant bio-stimulants (tannins, clay, flavonoids and a zinc-copper-citric acid biocomplex). The trials were conducted testing the oviposition behavior of mated olive fly females in both choice and no-choice assays. Our results showed that most of the substances have affected the ovipositional activity of the olive fly, except for difeconazole. Moreover, some products (copper oxychloride, flavonoids and tannins) have proven to differently influence the flies’ oviposition comparing the two tests. The repellent effect of these commercial products should be further studied to prove whether the repellency was due either to the active ingredient or to the co-formulants, and to assess their effect in the open field.

Field and Laboratory Efficacy of Low-Impact Commercial Products in Preventing Olive Fruit Fly, Bactrocera oleae, Infestation

Simple Summary

The adoption of sustainable methods for herbivore pest control has become mandatory in Europe, with the EU directive 128/09. Since then, stringent evaluation protocols have been applied to insecticides and several molecules (that are suspected to be unsafe for the environment or human health) have been banned. Hence, the evaluation of sustainable methods, e.g., preventive tools based on the manipulation of pest behaviour, must be considered. Using field and laboratory assays, we tested the efficacy of different products in preventing infestation of a key pest of olive orchards, the olive fruit fly Bactrocera oleae. Our findings may be useful for the development of control strategies in integrated pest management (IPM) and organic agriculture.

Abstract

The olive fruit fly, Bactrocera oleae, is the key pest of olive trees in several areas of the world. Given the need for the development of sustainable control methods, preventive tools, based on the manipulation of pest behaviour, must be considered. Here, under field and laboratory conditions, we tested the efficacy of different products in preventing B. oleae infestation. A field trial was conducted, from July to November 2020, in an olive orchard located in Central Italy. A table olive variety was selected and sprayed with rock powder, propolis, the mixture of both, copper oxychloride, or water (control). All treatments, except propolis, caused a reduction of B. oleae oviposition in olives, compared to the control. The mixture allowed the strongest reduction of fly infestation throughout the season, suggesting a synergistic effect. Behavioural no-choice assays were conducted to better understand the effects of treatments on B. oleae females. Compared to the control, females showed a lower preference for the central area of an arena containing an olive twig bearing two olive fruits, fully developed, but still green, treated with rock powder, plus propolis mixture. For all treatments, B. oleae showed lower oviposition events, suggesting deterrence to oviposition. Our results indicate that the tested products may have value against B. oleae, within integrated pest management (IPM) and organic agriculture.

Metagenomic Survey of the Highly Polyphagous Anastrepha ludens Developing in Ancestral and Exotic Hosts Reveals the Lack of a Stable Microbiota in Larvae and the Strong Influence of Metamorphosis on Adult Gut Microbiota

We studied the microbiota of a highly polyphagous insect, Anastrepha ludens (Diptera: Tephritidae), developing in six of its hosts, including two ancestral (Casimiroa edulis and C. greggii), three exotic (Mangifera indica cv. Ataulfo, Prunus persica cv. Criollo, and Citrus x aurantium) and one occasional host (Capsicum pubescens cv. Manzano), that is only used when extreme drought conditions limit fruiting by the common hosts. One of the exotic hosts (“criollo” peach) is rife with polyphenols and the occasional host with capsaicinoids exerting high fitness costs on the larvae. We pursued the following questions: (1) How is the microbial composition of the larval food related to the composition of the larval and adult microbiota, and what does this tell us about transience and stability of this species’ gut microbiota? (2) How does metamorphosis affect the adult microbiota? We surveyed the microbiota of the pulp of each host fruit, as well as the gut microbiota of larvae and adult flies and found that the gut of A. ludens larvae lacks a stable microbiota, since it was invariably associated with the composition of the pulp microbiota of the host plant species studied and was also different from the microbiota of adult flies indicating that metamorphosis filters out much of the microbiota present in larvae. The microbiota of adult males and females was similar between them, independent of host plant and was dominated by bacteria within the Enterobacteriaceae. We found that in the case of the “toxic” occasional host C. pubescens the microbiota is enriched in potentially deleterious genera that were much less abundant in the other hosts. In contrast, the pulp of the ancestral host C. edulis is enriched in several bacterial groups that can be beneficial for larval development. We also report for the first time the presence of bacteria within the Arcobacteraceae family in the gut microbiota of A. ludens stemming from C. edulis. Based on our findings, we conclude that changes in the food-associated microbiota dictate major changes in the larval microbiota, suggesting that most larval gut microbiota is originated from the food.

Bacterial symbiosis in Bactrocera oleae, an Achilles' heel for its pest control

Investigations on microbial symbioses in Tephritidae have increased over the past 30 years owing to the potential use of these relationships in developing new control strategies for economically important fruit flies. Bactrocera oleae (Rossi)-the olive fruit fly-is a monophagous species strictly associated with the olive tree, and among all the tephritids, its symbionts are the most investigated. The bacterium Candidatus Erwinia dacicola is the major persistent resident endosymbiont in wild B. oleae populations. Its relationship with B. oleae has been investigated since being identified in 2005. This endosymbiont is vertically transmitted through generations from the female to the egg. It exists at every developmental stage, although it is more abundant in larvae and ovipositing females, and is necessary for both larvae and adults. Studying B. oleae-Ca. E. dacicola, or other B. oleae-microbe interactions, will allow us to develop modern biological control systems for area-wide olive protection and set an example for similar programs in other important food crops. This review summarizes the information available on tephritid-microbe interactions and investigates relationships among fruit flies, bacteria and host plants; however, its focus is on B. oleae and its strict association with Ca. E. dacicola to promote environmentally friendly control strategies for area-wide pest management.

Stably inherited transfer of the bacterial symbiont Candidatus Erwinia dacicola from wild olive fruit flies Bactrocera oleae to a laboratory strain

The olive fruit fly, Bactrocera oleae, the most serious pest of olives, requires the endosymbiotic bacteria Candidatus Erwinia dacicola in order to complete its development in unripe green olives. Hence a better understanding of the symbiosis of Ca. E. dacicola and its insect host may lead to new strategies for reduction of B. oleae and thus minimize its economic impact on olive production. Studies of this symbiosis are hampered as the bacterium cannot be grown in vitro and the established B. oleae laboratory populations, raised on artificial diets, are devoid of this bacterium. Here, we sought to develop a method to transfer the bacteria from wild samples to laboratory populations. We tested several strategies. Cohabitation of flies from the field with the laboratory line did not result in a stable transfer of bacteria. We provided the bacteria directly to the egg and also in the food of the larvae but neither approach was successful. However, a robust method for transfer of Ca. E. dacicola from wild larvae or adults to uninfected flies by transplantation to females was established. Single female lines were set up and the bacteria were successfully transmitted for at least three generations. These results open up the possibilities to study the interaction between the symbiont and the host under controlled conditions, in view of both understanding the molecular underpinnings of an exciting, unique in nature symbiotic relationship, as well as developing novel, innovative control approaches.