Biocontrol of <i>Acanthoscelides obtectus</i> by volatile organic compounds from <i>Streptomyces</i> species

The insecticidal activity of microbial volatile organic compounds (mVOCs) remains underexplored, especially that of mVOCs produced by members of the Streptomyces genus (actinobacteria). mVOCs emitted by actinobacteria could represent a promising alternative for the biocontrol of insect pests, including the common bean weevil Acanthoscelides obtectus. mVOCs from five Streptomyces species, cultured axenically on wheat grains, were tested in vitro for their toxic effects on A. obtectus at the adult stage. The bioinsecticidal efficacy of mVOCs from Streptomyces species was further validated using pure VOCs at different concentrations. All Streptomyces species produced mVOCs with insecticidal activity, which was observed within 24 h to 96 h. The mVOCs from three strains (CIAD-IA69, CIAD-CA07, and CIAD-CA27) caused 100% mortality within 24 h of exposure. These mVOCs also impaired female reproductive performance, reducing both oviposition and egg viability. 3-penten-2-one, eucalyptol, and 2-pentanone caused 100% mortality within 4 h at concentrations of 25, 35, and 43 ppmv, respectively. The LD50 obtained with pure VOCs declined with exposure time, confirming their time-dependent toxicity. The LT50 values decreased as the concentration increased. The selected Streptomyces species produced mVOC that efficiently controlled A. obtectus.