Can’t you smell that smell: asparagus beetle (Crioceris asparagi) feeding induces volatile organic compound production in asparagus

Asparagus beetle (AB) (Crioceris asparagi L.) (Chrysomelidae: Coleoptera) is a monophagous feeder on asparagus (Asparagus officinalis L.) that occurs throughout North America’s asparagus producing regions, except California, and impacts both the harvested and unharvested portions of the plant leading to unmarketable spears and fern defoliation. Our research sought to determine: 1) are herbivore induced plant volatiles being produced by asparagus ferns following feeding by AB larvae, 2) is asparagus volatile production systemic or local, and 3) is Hippodamia convergens Guérin-Méneville (Coccinellidae: Coleoptera) attracted to asparagus volatiles. In year one of the study, volatiles were collected in the field from asparagus ferns grown in insect exclusion cages that had been exposed to one of four treatments: blank control, healthy asparagus (undamaged), mechanical damage, and AB feeding damage. We found that AB damaged asparagus had significantly higher concentrations of (e)-β-ocimene, (e e)-α-farnesene, and (n)-hexadecanol than healthy or mechanically damaged asparagus ferns. In year two, local and systemic volatile release was evaluated in the field by collecting volatiles from 2 year old asparagus plants grown in insect exclusion cages with 2 fully expanded ferns arising from a single crown. AB were allowed to feed on one fern while excluded from the second and headspace was collected from the undamaged fern. We found evidence that asparagus produces volatiles systemically. In y-tube choice tests we evaluated whether H. convergens was attracted to asparagus volatiles and have identified predator attraction to individual asparagus volatile compounds. The results of this study indicate that feeding by AB larvae induces systemic volatile organic compound production in asparagus during post-harvest fern stages that may be contributing to the recruitment of AB predators through volatile cues.