Genetic diversity of the mitochondrial ND1 gene in the olive fly, Bactrocera oleae (Rossi, 1790) (Diptera: Tephritidae) from Tunisia

The infestation due to the olive fruit fly, Bactrocera oleae (Rossi), the key pest in most of world olive groves, has been monitored in six years, from 2004 to 2008 and in 2014, in eight coastal Sicilian olive groves consisting of ‘Cerasuola’ and ‘Nocellara del Belice’ cultivars. Infestation was recorded following the classical sampling method based on olive collection and dissection, in order to count live olive fruit fly instars (eggs, larvae and pupae) and exit holes. Four different infestation indexes, all of them calculated using data recorded at harvest, have been used to assess their relationship with the main three quality parameters of the olive oil obtained from the same olive samples processed within 24 hours by quality oil mills: free acidity (% oleic acid), peroxides (mEq O2 /kg of oil) and total phenols (mg·kg−1 oil). Each year and in each olive grove up to five plots were differently treated with different products allowed in organic agriculture, stopping sprays at least one month before harvest, obtaining different infestation levels. In this study a total of 43 theses were tested, 10 of them involving ‘Cerasuola’ and 33 ‘Nocellara del Belice’. The two indexes based on the exit holes produced by mature larvae in olives resulted strictly and positively correlated to the lowering of oil quality. Moreover, among the two infestation indexes based on the occurrence of exit holes at harvest, percentage of olives with exit holes and No. of exit holes per 100 olives, the latter is more sensitive in presence of high infestation levels. No significant relation between infestation indexes and total phenols resulted in our analyses. Nevertheless, when olives are harvested since the end of October to mid-November, and processed by quality oil mills, olives bearing up to 45 % of exit holes produced high quality extra virgin olive oil. Furthermore, all olives bearing up to 62 % of exit holes still produced extra virgin olive oil. Our results, in spite of the widespread prejudices involving an overestimation of damages due to low olive fly infestation, are very close to recent studies on correlation between olive fly attacks and olive oil quality. Late harvesting can lead to worse results at the same olive fly exit holes levels, confirming that timing and quality procedures of harvesting and oil extraction are important almost as much as olive fly control.

The olive fruit fly, specialized to become monophagous during several life stages, remains the most important olive tree pest with high direct production losses, but also affecting the quality, composition, and inherent properties of the olives. Thought to have originated in Africa is nowadays present wherever olive groves are grown. The olive fruit fly evolved to harbor a vertically transmitted and obligate bacterial symbiont -Candidatus Erwinia dacicola- leading thus to a tight evolutionary history between olive tree, fruit fly and obligate, vertical transmitted symbiotic bacterium. Considering this linkage, the genetic diversity (at a 16S fragment) of this obligate symbiont was added in the understanding of the distribution pattern of the holobiont at nine locations throughout four countries in the Mediterranean Basin. This was complemented with mitochondrial (four mtDNA fragments) and nuclear (ten microsatellites) data of the host. We focused on the previously established Iberian cluster for the B. oleae structure and hypothesised that the Tunisian samples would fall into a differentiated cluster. From the host point of view, we were unable to confirm this hypothesis. Looking at the symbiont, however, two new 16S haplotypes were found exclusively in the populations from Tunisia. This finding is discussed in the frame of host-symbiont specificity and transmission mode. To understand olive fruit fly population diversity and dispersion, the dynamics of the symbiont also needs to be taken into consideration, as it enables the fly to, so efficiently and uniquely, exploit the olive fruit resource.

The olive fruit fly, specialized to become monophagous during several life stages, remains the most important olive tree pest with high direct production losses, but also affecting the quality, composition, and inherent properties of the olives. Thought to have originated in Africa is nowadays present wherever olive groves are grown. The olive fruit fly evolved to harbor a vertically transmitted and obligate bacterial symbiont -Candidatus Erwinia dacicola- leading thus to a tight evolutionary history between olive tree, fruit fly and obligate, vertical transmitted symbiotic bacterium. Considering this linkage, the genetic diversity (at a 16S fragment) of this obligate symbiont was added in the understanding of the distribution pattern of the holobiont at nine locations throughout four countries in the Mediterranean Basin. This was complemented with mitochondrial (four mtDNA fragments) and nuclear (ten microsatellites) data of the host. We focused on the previously established Iberian cluster for the B. oleae structure and hypothesised that the Tunisian samples would fall into a differentiated cluster. From the host point of view, we were unable to confirm this hypothesis. Looking at the symbiont, however, two new 16S haplotypes were found exclusively in the populations from Tunisia. This finding is discussed in the frame of host-symbiont specificity and transmission mode. To understand olive fruit fly population diversity and dispersion, the dynamics of the symbiont also needs to be taken into consideration, as it enables the fly to, so efficiently and uniquely, exploit the olive fruit resource.

BackgroundThe olive fruit fly, Bactrocera oleae, is the major arthropod pest of commercial olive production, causing extensive damage to olive crops worldwide. Current control techniques rely on spraying of chemical insecticides. The sterile insect technique (SIT) presents an alternative, environmentally friendly and species-specific method of population control. Although SIT has been very successful against other tephritid pests, previous SIT trials on olive fly have produced disappointing results. Key problems included altered diurnal mating rhythms of the laboratory-reared insects, resulting in asynchronous mating activity between the wild and released sterile populations, and low competitiveness of the radiation-sterilised mass-reared flies. Consequently, the production of competitive, male-only release cohorts is considered an essential prerequisite for successful olive fly SIT.ResultsWe developed a set of conditional female-lethal strains of olive fly (named Release of Insects carrying a Dominant Lethal; RIDL®), providing highly penetrant female-specific lethality, dominant fluorescent marking, and genetic sterility. We found that males of the lead strain, OX3097D-Bol, 1) are strongly sexually competitive with wild olive flies, 2) display synchronous mating activity with wild females, and 3) induce appropriate refractoriness to wild female re-mating. Furthermore, we showed, through a large proof-of-principle experiment, that weekly releases of OX3097D-Bol males into stable populations of caged wild-type olive fly could cause rapid population collapse and eventual eradication.ConclusionsThe observed mating characteristics strongly suggest that an approach based on the release of OX3097D-Bol males will overcome the key difficulties encountered in previous olive fly SIT attempts. Although field confirmation is required, the proof-of-principle suppression and elimination of caged wild-type olive fly populations through OX3097D-Bol male releases provides evidence for the female-specific RIDL approach as a viable method of olive fly control. We conclude that the promising characteristics of OX3097D-Bol may finally enable effective SIT-based control of the olive fly.

BackgroundContrary to other Tephritidae, female but also male olive flies, Bactrocera oleae release pheromones during their sexual communication. Alpha-pinene, a common plant volatile found in high amounts in unripe olive fruit and leaves has been detected as one of the major components of the female pheromone. However, possible effects of α-pinene and that of other host volatiles on the mating behavior of the olive fly have not been investigated. MethodologyUsing wild olive flies, reared on olive fruit for 3 generations in the laboratory, we explored whether exposure of male and female olive flies to α-pinene affects their sexual performance. ResultsExposure of sexually mature adult olive flies to the aroma of α-pinene significantly increases the mating performance over non-exposed individuals. Interestingly, exposure to α-pinene boosts the mating success of both males and female olive flies. ConclusionsThis is the first report of such an effect on the olive fly, and the first time that a single plant volatile has been reported to induce such a phenomenon on both sexes of a single species. We discuss the possible associated mechanism and provide some practical implications.

Climate change is expected to alter the geographic distribution and abundance of many species. Here we examine the potential effects of climate warming on olive (Olea europaea) and olive fly (Bactrocera oleae) across the ecological zones of Arizona–California (AZ–CA) and Italy. A weather-driven physiologically-based demographic model was developed from the extensive literature and used to simulate the phenology, growth and population dynamics of both species. Observed weather for several years from 151 sites in AZ–CA and 84 sites in Italy were used in the study. Three climate-warming scenarios were developed by increasing observed average daily temperature 1°, 2° and 3°C. Predictions of bloom dates, yield, total fly pupae and percent infestation were mapped using GRASS GIS. Linear multiple-regression was used to estimate the effects of weather on yield and fly abundance. Olive has a much wider temperature range of favorability than olive fly. The model predicted the present distributions of both species and gave important insights on the potential effects of climate warming on them. In AZ–CA, climate warming is expected to contract the range of olive in southern desert areas, and expand it northward and along coastal areas. Olive fly is currently limited by high temperature in the southern part of its range and by cold weather in northern areas. Climate warming is expected to increase the range of olive fly northward and in coastal areas, but decrease it in southern areas. In Italy, the range of olive is expected to increase into currently unfavorable cold areas in higher elevations in the Apennine Mountains in central Italy, and in the Po Valley in the north. Climate warming is expected to increase the range of olive fly northward throughout most of Italy.

BackgroundThe olive fly, Bactrocera oleae, is the most important insect pest in olive production, causing economic damage to olive crops worldwide. In addition to extensive research on B. oleae control methods, scientists have devoted much effort in the last century to understanding olive fly endosymbiosis with a bacterium eventually identified as Candidatus Erwinia dacicola. This bacterium plays a relevant role in olive fly fitness. It is vertically transmitted, and it benefits both larvae and adults in wild populations; however, the endosymbiont is not present in lab colonies, probably due to the antibiotics and preservatives required for the preparation of artificial diets. Endosymbiont transfer from wild B. oleae populations to laboratory-reared ones allows olive fly mass-rearing, thus producing more competitive flies for future Sterile Insect Technique (SIT) applications.ResultsWe tested the hypothesis that Ca. E. dacicola might be transmitted from wild, naturally symbiotic adults to laboratory-reared flies. Several trials have been performed with different contamination sources of Ca. E. dacicola, such as ripe olives and gelled water contaminated by wild flies, wax domes containing eggs laid by wild females, cages dirtied by faeces dropped by wild flies and matings between lab and wild adults. PCR-DGGE, performed with the primer set 63F-GC/518R, demonstrated that the transfer of the endosymbiont from wild flies to lab-reared ones occurred only in the case of cohabitation.ConclusionsCohabitation of symbiotic wild flies and non-symbiotic lab flies allows the transfer of Ca. E. dacicola through adults. Moreover, PCR-DGGE performed with the primer set 63F-GC/518R was shown to be a consistent method for screening Ca. E. dacicola, also showing the potential to distinguish between the two haplotypes (htA and htB). This study represents the first successful attempt at horizontal transfer of Ca. E. dacicola and the first step in acquiring a better understanding of the endosymbiont physiology and its relationship with the olive fly. Our research also represents a starting point for the development of a laboratory symbiotic olive fly colony, improving perspectives for future applications of the Sterile Insect Technique.

Escudete, which is caused by Botryosphaeria dothidea, is a disease that is widely distributed in the Mediterranean basin, but is of little general importance. Nevertheless, serious attacks have been observed on occasion, which have caused a considerable reduction in the quality of table olives. The incidence of the pathogen has been associated with damage caused by the olive fly (Bactrocera oleae) and the presence of a possible vector agent, i.e., the midge Prolasioptera berlesiana, whose larvae can feed on fly eggs (although the role the midge may play in the spread of this disease is not well known). Therefore, it is necessary to clarify these interactions to adopt appropriate disease control measures. Studies were conducted in olive orchards planted with the Gordal Sevillana, Picudo, and Hojiblanca olive cultivars. Field surveys were carried out in order to sample their fruits for laboratory analysis, and several bioassays were also performed. Moreover, the population of B. oleae adults was monitored using traps that were baited with food attractants. The results indicated that the three agents developed and evolved in parallel under field conditions. Thus, the midges were attracted by the oviposition punctures caused in fruits by olive fruit flies, regardless of whether the punctures contained eggs. All the investigated olive fruits in which midges were present inside punctures created by olive fruit flies exhibited typical symptoms of escudete, which is necessary for the development of this disease. Forty-eight hours after fly punctures were artificially simulated in the olive fruits, 48.0% of them contained a midge, whereas no midges appeared in the artificially created shapeless wounds in the fruits. This indicates that an olive fly egg is not required for the development of midges; however, they do prefer punctures made by B. oleae. Moreover, when the olive fruits were incubated in a humid chamber, the B. dothidea fungus only appeared in those fruits that contained midges, thus indicating a close relationship between these two agents. Additionally, the midges were able to complete their entire development from egg to adult under controlled conditions, and they fed on the pure cultures of the B. dothidea fungus. Furthermore, although no pathogens were present in the immature midges, some of the pathogens could have been isolated from the inner tissues of the adult female midges. The fact that mycangia is present in the abdomen of P. berlesiana supports the hypothesis that their relationship with B. dothidea may be mutualistic and that they may act as a vector for the fungus.

Bactrocera oleae is the main pest in olive groves, and its management requires a sustainable perspective to reduce the use of chemical products. Landscape context is being considered as an important driver of pest reduction, but results on B. oleae show inconsistency to date. Most of landscape-pest control studies focus on the dynamics of the pests within the focal crop, ignoring these dynamics in other land uses. Here we present a study in which we analyze the seasonal population dynamics of the olive pest B. oleae in the most important land uses of a typical olive landscape in Portugal. We found that B. oleae is present in all the land uses and the dynamics are very similar to those in the olive groves. However, the presence of these land uses in the landscape did not display any increase in B. oleae abundance within the olive groves. In contrast, a landscape mainly composed by olive groves increased the abundance of this pest. Importantly, more diverse landscapes surrounding olive groves reduce the abundance of the olive fly. Based on these findings, we can conclude that B. oleae is present in all the land uses of the studied landscape but that this presence does not imply an increase of B. oleae in olive groves. Indeed, other land uses can promote landscape diversification which is a driver of the reduction of B. oleae populations in olive groves. We thus encourage olive stakeholders to increase landscape diversification around their farms by promoting/restoring other crops/habitats.

Comparison of two laboratory cultures of Psyttalia concolor (Hymenoptera: Braconidae), as a parasitoid of the olive fruit fly

In the Mediterranean basin, organophosphate (OP) insecticides have been used intensively to control olive fly populations. Acetylcholinesterase (Ace) is the molecular target of OP insecticides, and three resistance-associated mutations that confer different levels of OP insensitivity have been identified. In this study, genotypes of olive fly Ace were determined in field-collected populations from broad geographical areas in Turkey. In addition, the levels of asymmetry of wing and leg characters were compared in these populations. Our study revealed the existence of a genetically smooth stratification pattern in OP resistance allele distribution in the olive fly populations of Turkey. In contrast to earlier findings, the frequency of Δ3Q was found to be lower in the Aegean region, where the populations have been subjected to high selection pressure. Results based on the morphological differences among the samples revealed a similar pattern for both sides and did not demonstrate a clear separation. The frequencies and geographic range of resistance alleles indicate that they were selected in the Aegean coast of Turkey and then spread westward towards Europe. One possible explanation for the absence of morphological asymmetry in olive fly samples might be the presence of modifier allele(s) that compensate for the increase in asymmetry.

Research was conducted in 2013 on the presence of one of the most important olive pests, olive fruit fly (Bactrocera oleae Gmel.), following different plant protection treatments in Kastelir near Porec (Croatia). In this research on an olive grove planted with the cultivar 'Leccino', the experiment was set up with five treatments: conventional plant protection, organic plant protection, pyrethrin, consociation of olive and planted pyrethrum (Tanacetum cinerariifolium (Trevir.) Sch. Bip.), and control. Olive fruit fly presence was monitored weekly using separate pheromone traps on each treatment, and comparison between the treatments was performed. The climatic conditions in Istria were also monitored during 2013. The average number of captured adult olive fruit flies varied between treatments, with the largest average number detected on the control (12.7), while the greatest presence of olive fly life stages was detected on organic treatments (3.8). The smallest average number of captured adult olive flies was detected on pyrethrin treatment (5.7), while the smallest presence of olive fly life stages was detected on conventional treatments (0.9); however, the differences in both these cases were not statistically significant. In addition, olive flies were monitored by yellow sticky trap. The highest yield was determined on conventional treatment (9.3 kg tree‑1), while the lowest yield was on consociation and organic treatment (8.8 kg tree‑1); however, the difference between the two was not statistically significant.

The olive fruit fly, Bactrocera oleae (Rossi), is a key pest of the olive crop, whose control relies mostly on the use of insecticides. Plant peptides may represent a more environmentally-friendly tool to manage olive fly, due to their recognized role to activate and/or prime plant defence responses against pests. In this work, behavioural experiments (no-choice and two-choice) and analysis of volatile compounds were carried out to evaluate the impact of the exogenous application of the peptide systemin to olive tree on olive fly infestation, and to elucidate its mode of action to prime plant defence. The treatment of olive branches with 10 nM systemin showed to confer protection against olive fly, by reducing significantly the ovipositions (up to 3.0-fold) and the number of infested fruits (up to 2.9-fold) when compared to non-treated branches. This protective effect was even detected in neighbouring non-treated branches, suggesting the ability of systemin to trigger plant-to-plant communication. The deterrent activity of the primed olives was associated with the emission of the volatiles 2-ethyl-1-hexanol, 4-tert-butylcyclohexyl acetate and 1, 2, 3-trimethyl-benzene, which were negatively correlated with oviposition and fly infestation. Systemin has also showed to trigger the biosynthesis of specific volatiles (esters) in olives in response to fly attacks. Overall, the observed protection conferred by systemin against olive fly is likely due to the emission of specific volatiles that can act as a defence and/or as signalling molecules to upregulate the plant defence response. Thus, systemin represents a novel and useful tool to manage olive fruit fly.

Olive fruit fly, Bactrocera oleae (Gmelin), was monitored with adult captures by season and trap type, and was related to fruit volume and nonharvested fruit to elucidate the occurrence of the newly introduced pest in California. The highest numbers of adults captured in ChamP traps in olive trees, Olea europaea, were in October in an inland valley location, and in September in a coastal location. Comparisons of trap types showed that the number of olive fruit fly adults captured in Pherocon AM traps in a commercial orchard was significantly greater than in ChamP traps. A significantly greater number of females were captured in Pherocon AM traps with bait packets and pheromone lures than traps with pheromone lures alone, while a significantly greater number of adults and males were captured in traps with pheromone lures alone. Significantly more adults were captured in ChamP traps with bait packets and pheromone lures versus traps with bait packets alone. Fruit volume increased by four times from mid-June to mid-November. Olive fruit fly was found to oviposit on small olive fruit <1 cm3 shortly after fruit set, the maximum number of ovipositional sites per fruit occurred in October, and the greatest number of pupae and adults were reared from fruit collected in September and October. The highest numbers of pupae were collected from nonharvested fruit in March when high numbers of adults were captured in the same orchard.

Olive fly population was monitored weekly on two olive cultivars (Buža and Istarska bjelica), from June until mid October, in Rovinj and Livade (Istria, Croatia). The number of eggs, larvae, and pupae was established and the total and active infestation was calculated. The fruit infestations for early and for late harvesting were obtained based on the calculated regression equation. For the prediction of the changes in the oil quality parameters linear regression slopes, obtained by Koprivnjak et al., were used. We established a strong positive correlation between DD accumulation and cumulative capture of flies, as well as with the total and active fruit infestations. According to obtained results it can be stated that I. bjelica is less sensitive to decrease in total phenols amount, to increase in free fatty acids mass ratio and to increase in peroxide values comparing to Buža. Moreover, the differences in investigated parameters between earlier and late harvesting dates in I. bjelica are lower due to lower infestation predicted for both harvesting dates and due to lower sensitivity to the changes in quality parameters. Therefore, early harvesting date as a model for preventing fruit damage and as a model for preventing negative change in oil quality parameters is a valid tool. However, the effectiveness of this model could also depend on the characteristics of olive cultivar.Practical applications: Understanding the factors that affect the olive fly attack is the basis of scientific and practical interest in the production of olives and olive oil. Research of monitoring methods allows reliable forecasting and determining protection measures. Knowledge about this topic could contribute to the reduction of insecticides use and to the improvement of quality and food safety concept in olive oil production.Damaged olive fruits are proved to directly affect the quantitative and qualitative properties of olive oils. The most important fruit damage is caused by the olive fly (Bactrocera oleae Gmelin).