Laboratory-based toxicity of scale insect pathogen Moelleriella raciborskii (Zimm.) (Hypocreales: Clavicipitaceae) crude extracts and isolated compounds against Tetranychus truncatus Ehara (Acari: Tetranychidae)

Abstract

Tetranychus truncatus is a phytophagous spider mite that is one of the economic pests of agricultural and economic crops. Its control has been and still is based mainly on the use of chemical controls. Since pesticides compatibility with natural enemies is a main concern for IPM programs, the aim of this study was carried out to explore the toxicity, repellency, oviposition deterrent and eggs hatching inhibition of crude ethyl acetate extract of Moelleriella raciborskii and their secondary metabolites against adults and eggs of T. truncatus. The results indicated that M. raciborskii crude extract at 5% (w/v) had high contact toxicity (89% mortality) on adult females of T. truncatus. The LC50 value was 1.476%, 1.026 and 0.732% after 24, 48 and 72 h posttreatment. Among the two steroidal and two hopane triterpenes separated from the ethyl acetate extract, 3β-acetoxy-15α,22-dihydroxyhopane was identified as the most active compound with LC50 values of 0.232% (w/v), followed by ergosterol, ergosterol 5, 8-endoperoxide with LC50 values of 0.235% and 0.318% at 72 h posttreatment, respectively. In addition, 3β-acetoxy-15α,22-dihydroxyhopane showed strong repellency (70.19%) and ergosterol and ergosterol 5, 8-endoperoxide decreased egg production of T. truncatus by 70.35 and 67.98%, respectively. Strong oviposition deterrent (ODI=100) was noted when 0.5% (w/v) crude extract was applied on half of the leaf disc. The crude ethyl acetate extract of M. raciborskii could have potential for the development of novel acaricides to control T. truncatus for use in an integrated pest management program.