Effect of Organic Farming and Agricultural Abandonment on Beneficial Arthropod Communities Associated with Olive Groves in Western Spain: Implications for Bactrocera oleae Management

Agricultural abandonment and intensification are among the main land-use changes in Europe. Along with these processes, different proposals have been developed to counteract the negative effects derived from agricultural intensification, including organic management. In this context, we aimed to determine how organic management and farmland abandonment affect Bactrocera oleae and its main groups of natural enemies: hymenopteran parasitoids, spiders, ants, carabids, and staphylinids. Between May and October 2018, four samplings were carried out in nine olive groves (three under organic management, three under traditional management, and three abandoned) in a rural area on the border between Spain and Portugal (Salamanca, Western Spain). Our results suggested differences between the natural enemy community composition of abandoned and organic groves, with slightly higher levels of richness and abundance in abandoned groves. We found no differences between organic and traditional groves. The managed olive groves sustained a different natural enemy community but were similarly rich and diverse compared with the more complex abandoned groves, with the latter not acting as a reservoir of B. oleae in our study area. Both systems may provide complementary habitats; however, further abandonment could cause a reduction in heterogeneity at the landscape scale and, consequently, a biodiversity loss.

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.

Landscape Simplification Increases Bactrocera Oleae Abundance In Olive Groves: Populations Dynamics In Different Land Uses.

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 of B.oleae abundance within the olives 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.

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.

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.