Diversity and virulence of soil-dwelling fungi Isaria spp. and Paecilomyces spp. against Solenopsis invicta (Hymenoptera: Formicidae)

To comprehend the diversity and potential control of soil-dwelling fungi, Isaria and Paecilomyces, against the red imported fire ant Solenopsis invicta (Hymenoptera, Formicidae), an investigation was carried out between 2004 and 2008. From 258 soil samples collected from 16 central and southern provinces and cities in China, a total of 171 isolates of the genra Isaria and Paecilomyce were isolated, and the species I. javanicus, P. marquandii and I. fumosoroseus were found more abundant than I. cateniobliquus, P. carneus, P. inflatus and P. lilacinus. Geographic differences of isolating rates were observed as well. Samples from the southern areas had higher fungal isolating rates than those from the central areas. Subsequently, 47 isolates were further tested for pathogencity against the red imported fire ant. All isolates except P115 showed certain pathogenic potential (the mean is 52.3% at 4000 conidiospores/mL) to the ant. I. javanicus was the most effective species with a mean pathogenicity of 80.6%, while pathogenicities of P. marquandii, P. gunni and I. fumosoroseus were 44, 21 and 49%, respectively. Furthermore, the more effective isolates P028 of I. javanicus and P003 of I. fumosoroseus were tested in a virulence experiment. The LD₅₀ values of P028 and P003 against major and miner workers were determined as 412,280 and 854,451 conidiospores/cm², respectively. Meanwhile, the LT₅₀ values at 1000 conidiospores/cm² were 7.1 and 6.6 d in isolate P003 and 6.8 and 6.6 d in isolate P028.