Effects of Water Activity and Temperature on Entomopathogenic Fungal Culture, Implications on Conidia Integrity and Virulence

Abstract

Effects of available water for microbial growth, water activity (a w) and incubation temperature on qualities of conidia produced by three entomopathogenic fungi, Beauveria bassiana, Isaria farinosa and Metarhizium anisopliae were evaluated in vitro. Sabouraud Dextrose Agar (SDA) (Sigma-Aldrich, 0.995 a w) and SDA containing calculated amounts of glycerol were prepared to create different osmotically-stressed media (a w = 0.98 or 0.96) and poured into 9 cm Petridishes. Agar plugs of seven days old cultures were transferred into the plates, sealed with parafilm and incubated at three different temperatures, 25, 30 and 35°C for 14 days. Harvested conidia from cultures grown at the three levels of interacting a w and temperatures were described in relation to the growth conditions; A1-, A2-and A3-conidia, interacting growth conditions being 0.995 a w x 25°C, 0.995 a w x 30°C and 0.995 a w x 35°C respectively. Similarly, B1-, B2-and B3-conidia (0.98 a w x 25-35°C) and C1-, C2-and C3-conidia (0.96 a w x 25-35°C). The conidia were tested for germination on different osmotically stressed media and virulence was evaluated using Galleria-model mortality bioassay. Germination rates of conidia was based on a 24-hour incubation period at 25°C while virulence was measured by the median lethal time (LT 50) against Galleria mellonella larvae. There were significant variabilities in germination rates and virulence in relation to incubation temperature, osmotic status

Microbiological Control of Carpocoris Fuscispinus (Hemiptera: Pentatomidae), a Pest of Onion and Leek Seed Crops

“…Since nymphs inoculated with I. fumosorosea seemed to die after day four, sporulation would have occurred in drier conditions than it occurred for B. bassiana which sporulated during the first four days of experiment. Several sources claim that sporulation of entomophagous fungi depends strongly on water availability (Arthurs & Thomas, 2001;Borisade, 2018).…”