The utility of Trichoderma spp. isolates to control of Xylosandrus germanus Blandford (Coleoptera: Curculionidae: Scolytinae)

The invasive ambrosia beetle, Xylosandrus germanus Blandford (Coleoptera: Curculionidae: Scolytinae), is a serious pest of hazelnut in Turkey, which is the biggest hazelnut producer in the world. In this study, the utility of four isolates representing different Trichoderma species (T. harzianum, T. hamatum, T. asperellum, and T. atroviride) was evaluated on survival, gallery behavior and brood production of X. germanus by effecting the symbiotic fungal development at laboratory conditions. Hazelnut branches were exposed to fungal suspensions (1 × 106 and 1 × 108 conidia mL−1 doses) for about 30 s. and transferred to individual plastic boxes. Ten healthy females of X. germanus were released into each box to determine the effect of the treatment of mycoparasite isolates. The antagonistic effect of Trichoderma species on symbiotic fungus was evaluated in dual-culture experiments in Petri dishes. The survival and gallery production of the pest were not directly affected by treatment of two different doses of all four Trichoderma species. The growth of the symbiotic fungus, however, was suppressed significantly by Trichoderma isolates in beetle galleries as well as on Petri dishes. Moreover, symbiotic fungal growth and eggs, larvae, and pupae of the beetle were not observed in the galleries carved out by females within the branches treated with two concentrations of T. harzianum, T. asperellum, and T. atroviride. Some of the galleries in the branches treated with T. hamatum had very sparse mycelial growth and fewer broods compared to the control. Our findings showed that the Trichoderma species may be potential biological control agents against X. germanus.