Investigating the potential of an autodissemination system for managing populations of vine weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae) with entomopathogenic fungi

Vine weevil, also known as black vine weevil, (Otiorhynchus sulcatus) is an economically important pest affecting soft fruit and nursery stock in temperate regions. We used laboratory and polytunnel experiments to investigate a novel control system based on autodissemination of spores of an entomopathogenic fungus to populations of adult vine weevils. The fungus was applied as a conidial powder, used on its own or formulated with talc, to a simple plastic refuge for vine weevils. The potential for adult weevils to disseminate the fungus was investigated first in polytunnel experiments using fluorescent powders applied to the refuge in lieu of fungal conidia. In this system, 88% of adult weevils came in contact with the powder within 48 h. When the powder was applied to five adult weevils that were then placed within a population of 35 potential recipients, it was transmitted on average to 75% of the recipient population within 7 days. Three isolates of entomopathogenic fungi (Beauveria bassiana isolate codes 433.99 and 1749.11 and Metarhizium brunneum isolate code 275.86), selected from a laboratory virulence screen. These three isolates were then investigated for efficacy when applied as conidial powders in artificial refuges placed among populations of adult weevils held in experimental boxes in the laboratory at 20 °C. Under this regime, the fungal isolates caused 70–90% mortality of adult weevils over 28 days. A final polytunnel experiment tested the efficacy of conidial powders of M. brunneum 275.86 placed in artificial refuges to increase vine weevil mortality. Overall weevil mortality was relatively low (26–41%) but was significantly higher in cages in which the conidial powders were placed in refuge traps than in cages with control traps. The lower weevil mortality recorded in the polytunnel experiment compared to the laboratory test was most likely a consequence of the greater amounts of inoculum required to kill adult weevils when conditions fluctuate between favourable and unfavourable temperatures e.g. below 15 °C. The potential of an autodissemination system for entomopathogenic fungi as a means of controlling vine weevil as part of an integrated pest management programme is discussed.