Abstract
Beetles share with other eukaryotes an innate immune system that
mediates endogenous defense against pathogens. In addition, larvae of
some taxa produce fluid exocrine secretions that contain antimicrobial
compounds. In this paper, we provide evidence that larvae of the brassy
willow leaf beetle Phratora vitellinae constitutively release volatile
glandular secretions that combat pathogens in their microenvironment.
We identified salicylaldehyde as the major component of their
enveloping perfume cloud, which is emitted by furrow-shaped openings of
larval glandular reservoirs and which inhibits in vitro the growth of
the bacterial entomopathogen Bacillus thuringiensis. The suggested role
of salicylaldehyde as a fumigant in exogenous antimicrobial defense was
confirmed in vivo by its removal from glandular reservoirs. This
resulted in an enhanced susceptibility of the larvae to infection with
the fungal entomopathogens Beauveria bassiana and Metarhizium
anisopliae. Consequently, we established the hypothesis that
antimicrobial defense in beetles can be expanded beyond innate immunity
to include external disinfection of their microenvironment, and we
report for the first time the contribution of fumigants to
antimicrobial defense in animals.
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