Abstract

The acaricidal activity of secondary metabolites from an entomopathogenic fungus,Hypocrella raciborskii Zimm. in controlling two-spotted spider mite, Tetranychus urticaeKoch (Acari: Tetranychidae) is explored in this study as a new agent for pest control. The crude extract was prepared in ethyl acetate. Secondary metabolites were elucidated using Nuclear Magnetic Resonance and High-Resolution Mass Spectrometry analysis. The major secondary metabolites of the crude extract were ergosterol, dustanin (15α, 22-dihydroxyhopane) and 3β-acetoxy-15α,22-dihydroxyhopane. The crude extract and pure compounds were used to determine their toxicity, repellency and oviposition deterrence against T. urticae, under the laboratory conditions. Crude extract of 3% w/v showed a strong contact toxicity (97% mortality, one day after treatment) and residual toxicity (80%, three days after treatment). Ergosterol induced 75% mite mortality in a residual toxicity bioassay. Females topically sprayed with 3% crude extract had their egg production reduced by 97%. Direct spraying of 3β-acetoxy-15α, 22-dihydroxyhopane and dustanin reduced egg production of T. urticae by 71 and 70%, respectively. Both crude extract and pure compounds had relatively slight repellency effect on T. urticae.

Key words: Fungal metabolites, bioassay, two-spotted spider mite