Targeting the click beetle Agriotes obscurus with entomopathogens as a concept for wireworm biocontrol

Applications of Metarhizium brunneum Petch (Ascomycota: Hypocreales: Clavicipitaceae) isolate LRC112 conidia caused high mortality to Agriotes obscurus L. (Coleoptera: Elateridae) click beetles in field trials. Banded conidiated rice (4.4 × 10¹⁴ conidia ha⁻¹) and conidia dust (5.0 × 10¹³ conidia ha⁻¹) resulted in 93.3 % ± 7.3 and 91.3 % ± 3.0 mortality after 18 days, while aqueous conidia suspension spray (5.0 × 10¹³ conidia ha⁻¹) with and without 80 g ha⁻¹ spinosad resulted in 68.2 % ± 17.7 and 52.6 % ± 17.4 mortality. Differences in results between 2012 and 2013 were attributed to rainfall, with pronounced effects in 2012 (rain beginning 35 h post treatment) and minimal effects in 2013 (rain beginning at 4 h). In another field experiment, beetles dosed with 1.49 × 10⁷ ± 5.08 × 10⁶ conidia per beetle retained 4.6 % of conidia after seven days while conidia viability on beetle bodies remained unchanged. The results inferred opportunities for controlling click beetles using fungal entomopathogens, and for horizontal transmission of the inoculum.