Biocontrol of the western conifer seed bug, Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae) using indigenous entomopathogenic fungi

Abstract

Background: The western conifer seed bug, Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae), is one of the major pest in seed orchards of various conifers, significantly affects pine seed production and causes economic damage. Biological control by natural enemies has been well studied, but its entomopathogens have been poorly studied. In this study, the efficacy of twelve indigenous entomopathogenic fungi belonging to the genera Beauveria, Metarhizium, and Isaria on L. occidentalis adults was investigated. Results: All isolates were found to be pathogenic at a concentration of 10(7) conidia/ml where the virulence ranged from 16 to 90%. Moreover, the virulence of two Metarhizium flavoviride isolates (As2 and As18) reached 90% at 10(7) conidia/ml concentration. In addition, L. occidentalis treated with M. flavoviride As18 (LT50 = 2.53 days) died more rapidly than with M. flavoviride As2 (LT50 = 5.83 days) at the same treated concentration. For concentration-dependent virulence for isolate As18, five conidia concentrations: 10(3), 10(4), 10(5), 10(6), and 10(7) conidia/ml were used. Also, the median lethal (LC50) value of As18 isolate was estimated to be 7.61 x 10(3) conidia/ml after 10 days of treatment. Since L. occidentalis is known to accumulate during overwintering, conidial transmission among adults was investigated. Unfortunately, horizontal transmission between adults did not occur. Conclusion: The isolate M. flavoviride As18, which had low LC50 and LT50 values, appeared to be a promising biological control agent against L. occidentalis. This isolate should be formulated as a myco-insecticide and tested under field conditions in further studies.