Herbivore-Dependent Induced Volatiles in Pear Plants Cause Differentialattractive Response by Chrysoperla Externa (Neuroptera: Chrysopidae)

Abstract

While chemical control is still the primary strategy for insect pest management in fruit production, alternative strategies such as biological control need to be incorporated. Biological control may benefit from the behavioral manipulation of natural enemies using volatile organic compounds (VOCs). Among these, herbivore-induced plant volatiles (HIPVs) provide potential tools for attracting or retaining predators and parasitoids of insect pests. In southern South America, the pear psylla Cacopsylla bidens (Hemiptera: Psyllidae) has become a major pest in pear orchards. In this study, we identified VOCs emitted by pear plants in response to attack by C. bidens and compared these with VOCs induced by a leaf-chewing insect, Argyrotaenia sphaleropa (Lepidoptera: Tortricidae). Moreover, we evaluated the behavioral response of Chrysoperla externa (Neuroptera: Chrysopidae) to HIPVs from pear plants damaged by either herbivore. Plants damaged by the pear psylla emitted VOC blends with increased amounts of aliphatic aldehydes. In contrast, leafroller damage resulted in increased amounts of benzeneacetonitrile, (E)-4,8-dimethylnona-1,3,7-triene, ꞵ-ocimene and caryophyllene. In olfactometer bioassays, larvae of C. externa were attracted to herbivore-damaged plants when contrasted with undamaged plants. When plant odors from psylla-damaged were contrasted with those of leafroller-damaged plants, C. externa larvae preferred the former, also showing shorter response lag-times and higher response rates when psylla-damaged plants were present. Our results suggest that psylla-induced aliphatic aldehydes may be used as prey-specific chemical cues by chrysopid larvae. Our findings contributes to the general notion of using semiochemicals as tools for attracting and retaining natural enemies in agroecosystems.