In vitro effect of pesticides on the germination, vegetative growth, and conidial production of two strains of Metarhizium anisopliae

Entomopathogenic fungi are widely used as biological control agents against a broad range of insect and arachnid pests. However, the control efficacy of entomopathogenic fungi is variable because of unfavourable and fluctuating environmental conditions and intrinsic factors. One strategy to enhance entomopathogenic fungi efficacy is a combined use of entomopathogenic fungi and low dosages of pesticides. These sub-lethal dosages of chemicals can increase the control efficiency of entomopathogenic fungi but only if they do not affect the fungi. Adverse effects could include the inhibition of germination and/or vegetative growth as well as conidiogenesis. The present study investigated the in vitro effects of different concentrations of fipronil, permethrin, imidacloprid, NeemAzal, and amitraz as potential candidates for combined applications on two strains of the entomopathogenic fungus Metarhizium anisopliae (MA). MA was inoculated on a medium amended with five different concentrations (0.32-200 ppm) of the abovementioned pesticides. The germination, vegetative growth, and sporulation were evaluated. The results showed, according to a physiology parameter compatibility classification, that all pesticides were compatible with both tested MA strains. Only fipronil in the higher dose rates of 40 and 200 ppm was close to moderately toxic to MA-7. Furthermore, only higher concentrations of the pesticides caused a slight inhibition (about 15%) of conidial germination and a reduction in colony size. Sporulation was reduced at most by approximately 50% by 40 or 200 ppm of fipronil or amitraz, respectively. Therefore, it is possible to use the tested pesticides in combination with either strain of MA for an integrated pest management approach. Studies on the effect of these combinations on target organisms are in progress.