Efficacy of native isolates of metarhizium anisopliae and beauveria bassiana against the invasive ambrosia beetle, xylosandrus germanus blandford (Coleoptera: Curculionidae: Scolytinae)

Abstract

The invasive ambrosia beetle, Xylosandrus germanus Blandford (Coleoptera: Curculionidae: Scolytinae), is one of the most significant pests in hazelnut orchards in Turkey. Chemical control of the beetle is very difficult, because it spends the majority of its life in the sapwood of host trees. In this study, entomopathogenic fungi (EPF), Metarhizium anisopliae (TR-106 isolate), and Beauveria bassiana (TR-217 isolate) were tested against the female adults of X. germanus under laboratory conditions by two different methods. In the first method, conidial concentrations (1 × 106 and 1 × 108 conidia ml−1) of the fungal isolates were directly applied to the beetles in Petri dishes (2 ml per dish), using a Potter spray tower. In the second method, the same conidial concentrations were applied on a sterile hazelnut branch placed in the Petri dishes, and then, beetles were released in dishes. The Petri dishes were incubated at 25 ± 1 °C and 75 ± 5% RH, 16:8-h light:dark photoperiod. Lethal time values (LT50 and LT90) for the isolates were calculated, using Probit analysis. As a result, LT50 and LT90 values of M. anisopliae isolate at 1 × 108 conidia ml−1 were 4.43 and 6.01 days, respectively, at the beetle application method and 3.97 and 5.68 days, respectively, at the branch application method. LT50 and LT90 values were 6.03 and 10.80 days, respectively, at 1 × 108 conidia ml−1, when B. bassiana was applied directly on the beetles and 5.96 and 11.79 days at the same concentration, when it was applied on the branch application method. M. anisopliae at 1 × 108 conidia ml−1 caused 100% mortality rate at the end of the 8th day in the two application methods. The mortality rates when applying 1 × 108 conidia ml−1 of B. bassiana recorded 64% and 80% by the end of the 8th day on branch and insect application methods, respectively. The efficiency of 1 × 106 conidia ml−1 of the isolates was lower than 1 × 108 conidia ml−1 against X. germanus in both application methods. This study showed that the isolates of TR-106 and TR-217 had a significant potential as biological control agents against X. germanus.