Bactrocera oleae (Rossi) (Diptera: Tephritidae) Response to Different Blends of Olive Fruit Fly-Associated Yeast Volatile Compounds as Attractants

The olive fruit fly, Bactrocera oleae (Rossi) is economically the most important olive pest, causing yield losses in all olive growing areas where is detected. Considering that EU requires the reduction of pesticide use by up to 100% by 2050, more effective non-pesticide lures for B. oleae monitoring and/or controlling are needed. This research was aimed at investigating the attractiveness of different blends of olive fruit fly-associated yeast volatiles toward B. oleae. Three blends of olive fruit fly-associated yeast volatiles: isoamyl alcohol and 2-phenethyl alcohol; isoamyl alcohol, 2-phenethyl alcohol and 2-phenethyl acetate; and isoamyl alcohol, 2-phenethyl acetate and isobutyl acetate were selected and tested on yellow sticky traps for attraction of B. oleae in olive orchard. Results showed that traps containing all tested blends of olive fruit fly-associated yeast volatile compounds, in total, were significantly more attractive to B. oleae and were not significantly attractive to green lacewings, compared to the control. Among them, the most promising was the one containing the blend of isoamyl alcohol, 2-phenethyl acetate and isobutyl acetate because its attractiveness was constantly significant during investigation compared to the others. This blend in the future could lead us to the discovery of a new attractant for the monitoring and/or controlling of B. oleae.

Olive Landscape Affects Bactrocera oleae Abundance, Movement and Infestation

The economic importance of Bactrocera oleae (Rossi) and the problems associated with insecticides make necessary new management approaches, including deeper biological knowledge and its relationship with landscape structure. Landscape complexity reduces B. oleae abundance in late summer–autumn in areas of high dominance of olive groves, but the effect of landscape structure in spring and in areas less dominated by olive groves has not been studied. It is also unknown whether the insect disperses from olive groves, using other land uses as a refugee in summer. This work evaluates the effect of landscape structure on olive fruit fly abundance and movement in spring and autumn, and infestation in autumn, in central Spain, an area where the olive crop does not dominate the landscape. A cost–distance analysis is used to evaluate the movement of the fly, especially trying to know whether the insects move away from olive groves in summer. The results indicate that B. oleae abundance is consistently lower in complex landscapes with high scrubland area (CAS), patch richness (PR) and Simpson landscape diversity index (SIEI), and low olive grove area (CAO). The cost–distance analysis shows that the fly moves mainly in spring, and amongst olive groves, but there is no evidence that land uses other than olive groves serve as a summer refuge. Olive fly infestation decreased with decreasing CAO and increasing CAS and SIEI, accordingly with the effect of landscape on abundance. Thus, mixing olive groves with other land uses, which are not a source of flies, can help improve control of this important pest.

Bioactivity of Carlina acaulis Essential Oil and Its Main Component towards the Olive Fruit Fly, Bactrocera oleae: Ingestion Toxicity, Electrophysiological and Behavioral Insights

Among botanical insecticides based on essential oils (EOs) or their main components, Carlina acaulis EO and the aromatic polyacetylene carlina oxide, constituting more than 90% of its EO, were recently proven to be effective against the larvae and adults of some insect vectors and pests. In this study, the toxicity of C. acaulis EO and carlina oxide were tested on Bactrocera oleae adults using a protein bait formulation. The LC50 values of the C. acaulis EO and carlina oxide were 706 ppm and 1052 ppm, respectively. Electroantennographic (EAG) tests on B. oleae adults showed that both carlina EO and oxide elicited EAG dose-dependent responses in male and female antennae. The responses to the EO were significantly higher than those to carlina oxide, indicating that other compounds, despite their lower concentrations, can play a relevant role. Moreover, Y-tube assays carried out to assess the potential attractiveness or repellency of carlina oxide LC90 to B. oleae adults showed that it was unattractive to both males and females of B. oleae, and the time spent by both sexes in either the control or the treatment arm did not differ significantly. Overall, this study points out the potential use of C. acaulis EO and carlina oxide for the development of green and effective “lure-and-kill” tools.

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

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.

Cuticular modified air sacs underlie white coloration in the olive fruit fly, Bactrocera oleae

Here, the ultrastructure and development of the white patches on thorax and head of Bactrocera oleae are analysed using scanning electron microscopy, transmission electron microscopy, and fluorescence microscopy. Based on these analyses and measurements of patch reflectance spectra, we infer that white patches are due to modified air sacs under transparent cuticle. These air sacs show internal arborisations with beads in an empty space, constituting a three-dimensional photonic solid responsible for light scattering. The white patches also show UV-induced blue autofluorescence due to the air sac resilin content. To the best of our knowledge, this research describes a specialized function for air sacs and the first observation of structural color produced by tracheal structures located under transparent cuticles in insects. Sexual dimorphism in the spectral emission also lays a structural basis for further investigations on the biological role of white patches in B. oleae.

Olive Landscape Affects Bactrocera Oleae Abundance, Movement and Damage

The olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), is a key pest of olive groves. Because of its economic importance and problems associated with chemical control, new approaches to reduce the damage caused by this pest and a deeper knowledge of the biology of the insect and the relationship of landscape structure to different biological parameters are needed. B. oleae can fly long distances and its ability to move within the landscape can determine the damage caused to olive groves. This work evaluates the effect of landscape structure on olive fruit fly abundance, movements and damage at three times of year—spring, early autumn and late autumn—in central Spain. This area is less dominated by olive groves than southern Spain, where the relationship between olive grove area and B. oleae abundance is already known. A cost-distance analysis is used to evaluate the landscape effect on the movement of the fly along the crop cycle. The olive grove area is the landscape composition factor with the greatest effect on the parameters studied, with a decrease in B. oleae abundance in a more complex landscape during spring and early autumn. The cost-distance analysis shows that the olive fruit fly moves mainly in spring, and amongst olive groves. There is no evidence that land uses other than olive groves serve as a summer refuge for B.oleae in the studied landscape context. Olive grove area and land use diversity index had significant effects on olive damage in more than one year.

Distinct Particle Films Impacts on Olive Leaf Optical Properties and Plant Physiology

The olive fruit fly is worldwide considered a major harmful pest of the olive agroecosystem. In Italy, the fruit fly infestation is traditionally countered by spraying chemical insecticides (e.g., dimethoate), but due to the recent ban of dimethoate by the Reg EU2019/1090 and the increasing awareness of consumers of food sustainability, the interest in developing chemical-free alternatives to pesticides, such as the use of particle-films, is rising. A field experiment was conducted to assess the effect of different particle films (kaolin-base and zeolitite-base) on leaf gas exchanges and leaf optical properties. Results showed that with the dust accumulation on the leaves’ surface, photosynthesis, stomatal conductance, transpiration and water use efficiency were significantly lower in kaolin-treated olive trees compared to those treated with zeolitite and to the control, while olive trees treated with zeolitite showed physiological parameters similar to the untreated plants. Microstructural differences of different particle film on the leaf and olive surfaces emerged by ESEM observations also influenced leaf optical properties. Oils produced by zeolitite-treated plants show higher intensities of gustatory and olfactory secondary flavors compared to kaolin and test oils.

Activity Monitoring of Olive Fruit Fly, Bactrocera oleae (Rossi) Males, and Effect of Temperature and Relative Humidity, at Al Quneitra Governorate, Southern Syria

This study was carried out in Al Quneitra governorate, Syria during 2017 and 2018 seasons with the aim of monitoring the activity of olive fruit fly Bactrocera oleae (Rossi) (Diptera: Tephritidae) males, in three locations of similar altitude (945-989 m above sea level), in addition to evaluating the effect of temperature and relative humidity on males activity using pheromone traps. The results obtained showed that olive fruit fly male adults activity began in the last week of May 2017 season and in the 3rd week of May 2018 season. Male adult's population reached a peak in the 4 th week of September, with an average of 126.43±33.70 males/trap in 2017 season, whereas their peak in 2018 season wasreached in mid-September with an average of 205.2±15.51 males/trap. Number of activity periods for males differed according to the season of study, and number of activity periods was 3 in 2017 and 4 in 2018. The duration of the activity period ranged from 4 to 11 weeks. The results obtained also showed a weak correlation effect of temperature and relative humidity on males activity during the two seasons, and its value was +0.16, +0.048, respectively. The monthly abundance of males differed during one season. Statistical analysis showed that the highest monthly abundance in 2017 season was in October, with an average of 192.07±14.94 males/trap with a significant difference in relation to the rest of the months, whereas in 2018 season it reached the highest monthly abundance in September, with an average of 420.33±15.18 males/trap, which significantly outperformed the rest of the months. Seasonal abundance of 2018 was significantly higher than in 2017. Keywords: Olive fruit fly, Bactrocera oleae, males’ activity, pheromone traps, temperature, relative humidity, Al Quneitra