The effect of a green leaf volatile on host plant finding by larvae of a herbivorous insect

The role of a general green Leaf volatile (glv) in host finding by larvae o f the oligophagous chrysomelid Cassida denticollis was investigated using a new bioassay which takes into account the need for neonate larvae of this species to climb fresh host plants from the ground. A "stem arena" was desi gned in which plant stems of the host, tansy (Tanacetum vulgare), and stem dummies (tooth picks), both wrapped in perforated filter paper, were offere d to neonate larvae. The wrapping allowed olfactory responses to be tested by preventing access to contact stimuli of stems and dummies. Larvae signif icantly preferred to climb the wrapped tansy stems over dummies after a per iod of 15 min. The test glv, (Z)-3-hexen-1-ol, was not attractive when appl ied to dummies. However, when the glv was applied to the bottom of the aren a, the ability of larvae to discriminate between host stems and untreated d ummies was significantly enhanced. More larvae climbed wrapped host stems t han dummies even within 5 min. While numerous other herbivorous insects are known to be directly attracted by glv, this study shows that a singly offe red glv on its own is unattractive to an herbivore but enhances the herbivo re's ability to differentiate between host and nonhost plants.