Description:
<jats:p>
Food resources contaminated with spoilage or pathogenic microorganisms pose severe problems to all higher organisms. Here, we describe a food-hygienic strategy of the emerald cockroach wasp
<jats:italic>Ampulex compressa</jats:italic>
. The wasp larvae develop on and inside the American cockroach
<jats:italic>Periplaneta americana</jats:italic>
, a host that can harbor various putrefactive microbes, as well as human and insect pathogens. From
<jats:italic>P. americana</jats:italic>
, we isolated the Gram-negative bacterium
<jats:italic>Serratia marcescens</jats:italic>
, which is a potent entomopathogen that can rapidly kill insect larvae. It is also known as a food contaminant and as an opportunistic human pathogen. Using behavioral observations and chemical analyses, we demonstrated that
<jats:italic>A. compressa</jats:italic>
larvae impregnate their cockroach hosts from inside with large amounts of an oral secretion containing a blend of γ-lactones and isocoumarins with (
<jats:italic>R</jats:italic>
)-(-)-mellein [(
<jats:italic>R</jats:italic>
)-(-)-3,4-diydro-8-hydroxy-3-methylisocoumarin] and micromolide [(4
<jats:italic>R</jats:italic>
,9
<jats:italic>Z</jats:italic>
)-octadec-9-en-4-olide] as dominant components. We fractionated hexane extracts of the secretion and investigated the antimicrobial properties of the fraction containing the lactones and isocoumarins, as well as of synthetic (
<jats:italic>R</jats:italic>
)-(-)-mellein and micromolide, against
<jats:italic>S. marcescens</jats:italic>
and a Gram-positive bacterium,
<jats:italic>Staphylococcus hyicus</jats:italic>
, in broth microdilution assays. The test fraction inhibited growth of both tested bacteria. The activity of the fraction against
<jats:italic>S. marcescens</jats:italic>
was explained by (
<jats:italic>R</jats:italic>
)-(-)-mellein alone, and the activity against
<jats:italic>S. hyicus</jats:italic>
was explained by the combined action of (
<jats:italic>R</jats:italic>
)-(-)-mellein and micromolide. Our data suggest that the specific combination of antimicrobials in the larval secretion provides an effective frontline defense against the unpredictable spectrum of microbes that
<jats:italic>A. compressa</jats:italic>
larvae may encounter during their development inside their cockroach hosts.
</jats:p>