Sublethal concentrations of spinosad synergize the pathogenicity of fungi to larvae of Ephestia kuehniella (Lepidoptera: Pyralidae)

Abstract

We evaluated the effi cacy of four entomopathogenic fungi (EPF) and their compatibility with the bioinsecticide spinosad for control of Ephestia kuehniella (Zeller) under laboratory conditions. Three EPF, including Beauveria bassiana (Balsamo-Criveili) Vuillemin isolates Z1 and Iran 1395C, Lecanicillium (= Verticillium) lecanii (Zimmerman) Zare & Gams, isolate Iran 229, and Purpureocillium (Paecilomyces) lilacinum (Thom) Luangs-ard, Hywel-Jones & Samson, isolate Iran 1026 were tested against third and fi fth larval instars of Ephestia kuehniella using a fi lter paper bioassay. Mortality caused by the EPF ranged from 63.3-72.5% for third instars and 50-65.5% for fi fth instars, with LT 50 ranging from 8.4-10.5 d and 10.1-12.9 d, respectively. The effect of spinosad at LC 10 (= 26.2 ppm) on EPF spore germination was evaluated and found to be negligible, ranging from 0% for B. bassiana Z1 to 5.7% for P. lilacinum. The LC 50 values for spinosad against third and fi fth instar E. kuehniella larvae were 452.5 and 1446 ppm, respectively. Subsequently, spinosad at LC 10 was applied to third instar E. kuehniella larvae 24 h before application of the EPFs at LC 50 . The addition of spinosad to applications of L. lecanii and B. bassiana Z1 and Iran1395C isolates synergized their pathogenicity to E. kuehniella larvae, whereas the effect was merely additive for P. lilacinum. Our results suggest that these EPF isolates can be used effectively in combination with spinosad for management of E. kuehniella in stored products.