Evaluation of the compatibility of entomopathogenic fungi and two botanical insecticides tondexir and palizin for controlling Galleria mellonella L. (Lepidoptera: Pyralidae)

Interactions between insect pathogenic fungi and insecticides can be both positive and negative for pest control. In the first part of this study, the insecticidal efficacy of entomopathogenic fungi including Beauveria bassiana (Bals.) Vuill., Lecanicillium (= Verticillium) lecanii (Zimm.) Zare & Gams, and Metarhizium anisopliae (Metsch.) Sor. was tested against different larval instars of Galleria mellonella using a dipping bioassay method. In addition, the toxicity of two botanical insecticides, tondexir (TON) and palizin (PAL) was evaluated against 7th instar G. mellonella. In the second part of this study, the effect of TON and PAL on spore germination of B. bassiana and L. lecanii was determined. Subsequently, the effect of the application of a sub-lethal concentration of TON (414.24 ppm) or PAL (116.44 ppm) at 24 h prior to the application of an LC50 of B. bassiana or L. lecanii was evaluated in 7th instar G. mellonella. The lowest LC50 values were found against 7th instar G. mellonella which were 4.64 x 10(5) and 1.83 x 10(6) conidia ml(-1) for B. bassiana and L. lecanii, respectively. The LC50 values for TON and PAL against 7th instar G. mellonella were 1868 and 735.68 ppm, respectively. TON and PAL showed significantly lower effects on the germination of B. bassiana than on the germination of L. lecanii. The highest inhibition of germination was caused by TON at concentrations of 2500 and 4000 ppm (20.8 and 24.3% inhibition, respectively). Both insecticides significantly reduced the susceptibility of larval G. mellonella to B. bassiana infection. PAL reduced the effectiveness of L. lecanii against larval G. mellonella. However, the infectivity of L. lecanii was not affected by the application of a sublethal concentration of TON. The use of these botanical insecticides with fungi in integrated control programs for G. mellonella is discussed.