Bacteria isolated from biodiverse Mediterranean island habitats yield a large array of biopesticidal metabolites against mosquito larvae

ABSTRACT Microbes are prolific in synthesizing diverse compounds in response to varying environmental conditions, many of which have applications in insect pest control. Fewer than 20,000 of the estimated millions of bacteria have been named, and only a small subset of known bacteria has led to the development of some of today’s most critical pesticides, so the potential for discovering new insecticidal compounds from bacteria remains vast. We collected 1,663 bacterial isolates from environmental samples across diverse habitats in Crete. Screening 788 of these for larvicidal activity against Culex pipiens molestus identified 108 unique larvicidal isolates, with 37 causing 100% mortality in less than 3 days; these top hits represent 20 genera, many of which are novel in the arena of candidate biopesticides. Our 37 top isolates mediated their larvicidal activity after inactivation, indicating that metabolites or proteins rather than infections mediated mortality. Three new isolates of Chryseobacterium and Pseudomonas produce insecticidal factors that achieved 100% mortality within 48 h. While non-polar extractions were primarily responsible for larvicidal activity, promising polar extractions also showed potential as novel biopesticidal agents.IMPORTANCEThe development of environmentally friendly, biological solutions to combat insecticide resistance and contribute to effective vector management strategies has become increasingly important in recent decades. The study presented herein describes the discovery of a number of novel insecticidal-metabolite-producing bacteria demonstrating high efficiency and rapid action. Furthermore, some basic chemistry of the active metabolites is investigated, facilitating accelerated development of the newly discovered bacterial isolates and metabolites. In particular, three isolates: a Chryseobacterium and two Pseudomonas species, each of which are highly potent larvicidal agents, and whose active metabolites are of differentiated base chemistry. The impact of this work is to heighten awareness of the vast potential of bacteria as a source of novel tools for insect control strategies, and it is hoped that the work will lay the foundation for the development of several new tools that demonstrate high efficacy as applied biopesticides.