Leaf-beetle larvae produce glandular secretions that contain salicylaldehyde, a metabolic by-product that is derived from the catabolism of salicin and saligenin. Previous studies revealed that salicylaldehyde was a potent antifungal and antibacterial agent in vitro, but little was known about when it was released or which microorganisms it could kill. Larvae of Phratora vitellinae were placed in glass vials and their headspace was analysed by gas chromatography, which confirmed that the main volatile component of the secretions was salicylaldehyde. Glands can be everted to dispense secretions during predator attack, but close inspection of the cuticle above the glandular reservoir using scanning electron microscopy revealed furrow-shaped openings through which the larvae could continuously secrete volatile compounds. The larvae are therefore permanently surrounded by a cloud of salicylaldehyde.
Draining of glandular contents prior to exposure to fungal spores significantly reduced the survival of larvae, and the authors propose that fumigation of fungal spores by the perfume cloud might prevent spore germination and reduce the chances of infection. Moreover, treating cultured Bacillus thuringiensis serovar tenebrionis and B. thuringiensis serovar kurstaki with concentrations of salicylaldehyde either directly or as a volatile inhibited bacterial growth, and therefore the deadly perfume could kill bacterial and fungal pathogens.
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