Bacterial Volatile Organic Compounds Shape the Chemical Ecology of Sitophilus zeamais

Microbial volatile organic compounds (VOCs) are key modulators of insect behavior. These low molecular weight compounds influence ecological interactions and hold potential as sustainable agents in pest control. Sitophilus zeamais, a major pest of stored maize worldwide, causes significant post-harvest losses. While fungal VOCs have been studied in grain storage systems, bacterial-insect interactions remain poorly understood. This study evaluated the effects of VOCs emitted by four Enterococcus strains isolated from maize grains on the behavior and mortality of S. zeamais. Maize grains were inoculated with bacterial cultures, and VOCs were identified using gas chromatography-mass spectrometry. Behavioral responses were assessed in a two-choice olfactometer using both bacterial blends and individual pure compounds at varying concentrations. Additional assays included fumigation tests for toxicity and evaluation of oviposition behavior through egg staining in treated grains. Results showed that bacterial VOCs significantly affected the behavior and survival of S. zeamais, supporting their bioactive potential and involvement in interspecific interactions. Acetoin, acetic acid, and diacetyl were identified as the predominant volatiles. Among them, acetic acid acted as a repellent while also stimulating oviposition, acetoin functioned as an attractant, and diacetyl stood out for its toxicity, with effects observed even at low concentrations. These findings highlight the ecological relevance of bacterial volatiles in modulating insect behavior in stored grain systems and contribute to a broader understanding of the chemically mediated interactions between microorganisms and insects in confined environments.