Lack of Evidence for Transmission of Verticillium dahliae by the Olive Bark Beetle Phloeotribus scarabaeoides in Olive Trees

Verticillium wilt of olive, caused by Verticillium dahliae Kleb., is one of the most important diseases affecting olive crops in the Mediterranean area. With the aim to evaluate the role of Phloeotribus scarabaeoides (Bernard) (olive bark beetle) as a dispersal vector of V. dahliae, several experiments were conducted in semi-controlled conditions from May 2009 to April 2012. Groups of olive trees (2.5-year-old) certified free from V. dahliae were covered by a mosquito net and exposed to adults of P. scarabaeoides by three different ways: (1) branches or trunks collected in several olive orchards from trees severely affected by Verticillium wilt and showing apparent entry holes (mating galleries) of P. scarabaeoides; (2) adults of olive bark beetle extracted from damaged branches collected in the field; (3) adults from damaged branches that were superficially inoculated with V. dahliae. The fungus V. dahliae was not detected either by microbiological and molecular techniques from shoots of olive trees with galleries of the insect or from any of the tissues of the collected beetle adults from the galleries. Additionally, Verticillium wilt disease symptoms were not observed in olive trees exposed to the olive bark beetles. Moreover, the pathogen was never detected from any beetle adults that were recovered from the mating galleries of branches or trunks collected in several olive orchards from trees severely affected by Verticillium wilt. We conclude that P. scarabaeoides is not a vector of V. dahliae under the investigated experimental conditions.

Diversity and distribution of nematodes associated with bark beetles in Israel

Summary Bark beetles (Curculionidae: Scolytinae) have a significant economic impact on forest stands and agricultural settings in Israel. We focus on nematodes associated with bark beetles collected from different host plants attacked by Scolytinae. The sampling was conducted in forest plantations and fruit tree orchards in several areas in Israel. A total of 430 beetle specimens of eight species were examined for the presence of nematodes. Fifteen nematode species were detected and identified based on molecular and morphological characteristics. Among the examined scolytids, the pine bark beetle, Orthotomicus erosus, the most widely distributed and frequently occurring species in Israel, was accompanied by the highest nematode diversity, with 11 species recovered. Nematode associations with the almond bark beetle (Scolytus amygdali), the olive bark beetle (Phloeotribus scarabaeoides) and the fig bark beetle (Hypoborus ficus) were recorded for the first time. Our study thus supplies novel information on scolytid-associated nematodes in Israel.

Monitoring of Population of Scolytinae in Olive Culture

Monitoring of insects is important to analyze the species present in culture of economic interest, to verify the period of highest incidence and quantify the damages caused by the pest insects. Here, we aim to assess the diversity of bark beetles in an olive orchard. The experiment was assessed in fortnightly series throughout a year and conducted with a completely randomized experimental design, consisting of three treatments: T1: homogeneous olive culture; T2: heterogeneous olive culture; T3: border area. An ethanol trap was used for the sampling of bark beetles. The species Hypothenemus eruditus, Xyleborus linearicolis and Hypothenemus seriatus showed greater abundance among the treatments. The decrease of abundance, diversity and dominance of bark beetles occurred in the heterogeneous culture (T2). Homogeneous cultures (T1) are more susceptible to the attack of pest-insects due to the lower ecological balance among associate, predator or parasitoid insects. Border areas (T3) showed an increased diversity of arboreal species, favoring the higher incidence of insects. In spring, there is a greater incidence of bark beetles, what reinforces the need for monitoring during this period. So far, there are no evidences of bark beetles infesting olive trees in the area, or the presence of Phloeotribus scarabaeoides, which is the pest bark beetle of olive cultures.