How does Neoseiulus californicus McGregor respond to sublethal doses of entomopathogenic fungus Beauveria bassiana (Hyp.: Cordycipitaceae)?

Abstract

Two-spotted spider mite, Tetranychus urticae Koch (Acari: Prostigmata), is one of the most economically important mite species, mainly controlled by chemical acaricides. Natural enemies have been assessed as reliable alternatives for management of this phytophagous mite. In the current project, demographic characteristics of Neoseiulus californicus McGregor (Acari: Phytoseiidae) to sublethal concentrations (LC₁₀ = 6.76 × 10², LC₂₀ = 8.74 × 10³ and LC₃₀ = 55.38 × 10³ conidia ml^-1) of entomopathogenic fungus, Beauveria bassiana (Bals.) Vuill. TV strain were investigated under laboratory conditions at 25 ± 2°C, 70 ± 5% RH and a photoperiod of 16:8 (L:D) h. Our results indicated that when adult predators were exposed to LC₂₀ and LC₃₀ of B. bassiana, the oviposition period was significantly reduced compared with other treatments. Neoseiulus californicus fecundity was significantly greater in the control (37 eggs) than in LC₃₀ (24 eggs). Life table analysis revealed that the net reproductive rate (R₀) declined as the sublethal concentrations of B. bassiana increased. The most striking result to emerge from the data is that not only intrinsic (r); but also, finite rate of increase (λ) was not significantly affected by different concentrations of B. bassiana. Our findings revealed some potential interactions of B. bassiana and N. californicus during their combinations for managing T. urticae that may be helpful for optimising control of this important pest.