Thermal Tolerance and Media Preferences of Entomopathogenic Fungal Isolates Virulent to Pachnoda interrupta

Abstract

Chafer (Pachnoda interrupta) (Olivier) (Coleoptera: Scarabaeidae) is a serious pest of sorghum with a wide host range attacking over 37 crops in Africa in general and in Ethiopia in particular; and its control is solely dependent on synthetic insecticides. The cultural characteristics of five isolates of entomopathogenic fungi pathogenic to P. interrupta selected for their biological control were compared using the measurable parameters of germination, radial growth and sporulation on four (MEA, PDA, SDA and SDY) artificial media at five (15, 20, 25, 30, 35) different temperature levels. All the isolates, except PPRC2, achieved between 60-100% germination on all of the media used and at temperature levels of 20, 25 and 30 °C. PPRC2 germinated generally below 40% on PDA, SDA and SDAY. All of the abovementioned temperature levels supported better vegetative growth of the isolates in all of the media. The highest (31.17 mm) radial growth was recorded from MP3POST on SDA at 20 °C. Moreover, high spore production was recorded at these temperature levels with all the isolates producing above 2.23 x 10H) spores/mL. The highest number (8.77 x 10IU spores/mL) of spores was produced by IC-279 at 25 °C on SDA medium. All of the selected isolates exhibited good germination, radial growth and sporulation at temperature levels of 20, 25 and 30 °C on all of the tested media. However, relatively better radial growth and spore yield were obtained on SDA and SDAY media than on MEA and PDA at 30 °C. The two Metarhzium anisopliae isolates (PPRC51 and PPRC2) that had shown good performance with reference to in vitro characteristics are recommended as potential candidates for development of mycoinsectides against P. interrupta.