An assessment of biological control of Polygraphus major Stebbing, 1903 (Coleoptera: Curculionidae) by entomopathogenic fungi

Recently the use of fungal entomopathogens against bark beetles has gained increasing attention throughout the world and researchers continue to seek highly pathogenic fungal isolates for controlling beetle pests. In the present study, the efficacy of three entomopathogenic fungi, namely Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae sensu lato (Metchnikoff) Sorokin and Lecanicillium lecanii (Zimmerman) Zare & Gams, was tested against Polygraphus major Stebbing, 1903 under laboratory conditions. Each fungal suspension contained 1.0 × 109 spores of fungi in 1 ml. An insecticide - Cyclone was also used as positive control in the experiment. The mortality caused by these fungi was recorded in treated branches and petri plate assay. In treated branches, B. bassiana and M. anisopliae s. l. caused higher mortality, i.e. 57.77 and 46%, respectively, after 10 days of treatment and 98 and 92.77%, respectively, after 20 days of treatment. The results of the petri plate assay revealed that P. major adults were highly susceptible to both applied fungal species and insecticide. However, B. bassiana and M. anisopliae s. l. caused higher percentage mortalities after six days of treatment, i.e. 100 and 91.66%, respectively. The percentage mortality caused by application of the insecticide was 69%. L. lecanii was observed to be significantly less virulent (mortality 46.66%) in all fugal treatments. After observing the promising nature of the three entomopathogenic fungi by testing them, we arrive at the conclusion that the tested fungi have a potential for the control of P. major, and further field experiments are warranted to investigate their efficacy under more practical conditions.