Volatiles from cotton plants infested by Agrotis segetum (Lep.: Noctuidae) attract the larval parasitoid Microplitis mediator (Hym.: Braconidae)

Authors: LI, MENGYU - Institute Of Plant Protection - China; XIA, SHIKE - Institute Of Plant Protection - China; ZHANG, TAO - Institute Of Plant Protection - China; Williams, Livy; XIAO, HAIJUN - Institute Of Plant Protection - China; LU, YANHUI - Institute Of Plant Protection - China

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2022
Publication Date: 3/24/2022
Citation: Li, M., Xia, S., Zhang, T., Williams III, L.H., Xiao, H., Lu, Y. 2022. Volatiles from cotton plants infested by Agrotis segetum (Lep.: Noctuidae) attract the larval parasitoid Microplitis mediator (Hym.: Braconidae). Plants. 11(7):863. https://doi.org/10.3390/plants11070863.
DOI: https://doi.org/10.3390/plants11070863

Interpretive Summary: Caterpillars are serious pests of many crops throughout the world. Beneficial insects are useful in controlling these pests, and may use odors from damaged plants as ‘distress signals’ to find their hosts. Thus, understanding the interactions between feeding by caterpillars, plant distress signals, and attraction of beneficial insects has important implications for pest control. We conducted experiments to characterize the chemical profiles of cotton plants damaged by a previously unstudied caterpillar species in comparison to undamaged plants, and to evaluate the degree of attraction a beneficial insect exhibits to the plant odor signals. Our results indicate that infestation caused a 15-fold increase in the production of plant odors in comparison to undamaged plants. Further, the beneficial insect was more strongly attracted to these damaged plants than to undamaged plants. Our findings indicate that plant distress signals play an important role in mediating the interactions between this caterpillar and the beneficial insect. Plant odors, many of which are already commercially-produced, have potential to be used to increase attack rates on caterpillars, thereby improving pest management.

Technical Abstract: Herbivore induced plant volatiles (HIPVs), chemicals produced by plants infested by herbivorous insects, can act as kairomones that recruit natural enemies of the pest herbivore. Agrotis segetum (Denis et Schiffermüller) is an important pest of cotton seedlings, and the braconid, Microplitis mediator (Haliday), is an important mortality factor of this pest’s larvae. In olfactometer tests, M. mediator, when offered treatments that included healthy foliage, infested foliage, or infested roots, preferred A. segetum-infested cotton plants to healthy cotton plants. In GC-MS analyses of plant-emitted volatiles, we found that compounds emitted increased 14.9- and 13.3- fold after leaf infestation and root infestation, respectively compared to the healthy control plants. Volatiles identified were mainly p-xylene, nonanal, tetradecane, decanal, benzaldehyde, ß-caryophyllene, and humulene, while linalool was only present in the leaf-infestation treatment. In addition, principal component analysis indicated that all 18 compounds were associated with the infested plants, especially ß-caryophyllene, p-xylene, and decanal. These compounds play a crucial role in modulating the interactions between A. segetum and M. mediator, and regulating parasitoid behavior. Our results indicate that it may be possible to enhance the biological control of A. segetum by M. mediator through the application of HIPVs.