Olfactory cues from plants infected by powdery mildew guide foraging by a mycophagous ladybird beetle

• Published in: PloS one 2011-08, Vol.6 (8), p.e23799-e23799
• Main Authors: Tabata, Jun, De Moraes, Consuelo M, Mescher, Mark C
• Format: Article
• Language: English
• Subjects: Agricultural management; Agriculture; Agronomy; Airborne microorganisms; Alcohols; Allelochemicals; Animal behavior; Animals; Ascomycota - physiology; Beetles; Benzyl alcohol; Biological Assay; Biological control; Biological pest control; Biology; Chemistry; Coccinellidae; Coleoptera; Coleoptera - physiology; Cucurbita - microbiology; Cucurbita moschata; Cues; Disease control; Ecology; Erysiphales; Feeding Behavior - physiology; Flowers & plants; Foraging behavior; Fungi; Fungicides; Gas chromatography; Herbivores; Impact resistance; Infections; Insects; Ladybugs; Leaves; Linalool; Octanol; Odorants; Odors; Olfactory Pathways - physiology; Olfactory stimuli; Plant Diseases - microbiology; Podosphaera; Powdery mildew; Psyllobora vigintimaculata; Strategic planning (Business); Volatile compounds; Volatile Organic Compounds - analysis; Volatiles
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0023799

Powdery mildews (Erysiphales) are economically important plant pathogens that attack many agricultural crops. Conventional management strategies involving fungicide application face challenges, including the evolution of resistance and concerns over impacts on non-target organisms, that call for investigation of more sustainable alternatives. Mycophagous ladybird beetles (Coleoptera: Coccinellidae) feed on powdery mildew and have considerable potential as biological control agents; however, the foraging ecology and behavior of these beetles is not well understood. Here we document the olfactory cues presented by squash plants (Cucurbita moschata) infected by powdery mildew (Podosphaera sp.) and the behavioral responses of twenty-spotted ladybird beetles (Psyllobora vigintimaculata) to these cues. Volatile analyses through gas chromatography revealed a number of volatile compounds characteristic of infected plants, including 3-octanol and its analogues 1-octen-3-ol and 3-octanone. These compounds are typical "moldy" odorants previously reported in volatiles collected from other fungi. In addition, infected plants exhibited elevated emissions of several compounds also observed in collections from healthy leaves, including linalool and benzyl alcohol, which are reported to have anti-fungal properties. In Y-tube choice assays, P. vigintimaculata beetles displayed a significant preference for the odors of infected plants compared to those of healthy plants. Moreover, beetles exhibited strong attraction to one individual compound, 1-octen-3-ol, which was the most abundant of the characteristic fungal compounds identified. These results enhance our understanding of the olfactory cues that guide foraging by mycophagous insects and may facilitate the development of integrated disease-management strategies informed by an understanding of underlying ecological mechanisms.