23 © The Author(s) 2019. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. Research Drought Stress Impairs Communication Between Solanum tuberosum (Solanales: Solanaceae) and Subterranean Biological Control Agents Mahnaz Hassani-Kakhki, 1 Javad Karimi, 1,4, Fahim El Borai, 2,3 Nabil Killiny, 2 Mojtaba Hosseini, 1 Lukasz L. Stelinski, 2 and Larry Duncan 2 1 Biocontrol and Insect Pathology Laboratory, Department of Plant Protection, School of Agriculture, Ferdowsi University of Mashhad, Azadi Square, Vakilabad Highway, Mashhad 9177948974, Iran, 2 Citrus Research and Education Center, University of Florida, IFAS, 700 Experiment Station Road, Lake Alfred, FL 33850, 3 Plant Protection Department, Faculty of Agriculture Zagazig University, Zagazig 44519, Egypt, and  4 Corresponding author, e-mail: jkb@um.ac.ir , javadkarimi10@gmail.com Subject Editor: Chris Weldon Received 24 May 2019; Editorial decision 30 August 2019 Abstract The attraction of entomopathogenic nematodes (EPNs) to herbivore-injured plant roots has been documented recently to be a common tritrophic interaction. Belowground tritrophic interactions are especially subject to modulation by many abiotic factors including drought. In this study, complementary greenhouse experi- ments were conducted to understand how drought stress might affect a potato plant’s impact on EPN be- havior. In separate trials, the responses of the EPN Steinernema diaprepesi (Nguyen and Duncan) (Rhabditida: Steinernematidae) to root herbivory by larvae of the weevil Diaprepes abbreviatus (Linnaeus) (Coleoptera: Curculionidae), in well-watered and drought stressed potato plants, were measured using soil-matrix olfact- ometers with two arms. The drought treatments were initiated in 30-d old plants. Drought-stressed potato plants received water when potentiometers read approximately 20 kPa, while for well-watered plants, the number was 8 kPa. Four weeks after initiating the treatments, 400 ml water was added to all pots, immedi- ately before starting the experiments. The experiments revealed that S. diaprepesi infective juveniles (IJs) did not migrate preferentially toward drought-stressed or well-watered plants when neither were subjected to herbivory [t (21)  = 1.13, P = 0.269]. However, plants with roots damaged by herbivory attracted more S. diaprepesi IJs if they were well watered than if they were drought stressed [t (24)  = 3.19, P = 0.004]. If both plants in the ol- factometers were drought stressed, EPNs moved preferentially toward those with root herbivory than those with undamaged roots [t (23)  = 3.19, P = 0.004]. No difference was detected in gas chromatography profles between droughted and well-watered plant roots subjected to herbivory [F (24, 336)  = 0.68, P = 0.87]. GC ana- lysis showed that three compounds, including 3-nonanone [t (6)  = 4.83, P = 0.003], artemisyl ketone [t (7)  = 6.21, P = 0.000], and benzoic acid, 4-ethoxy-, ethyl ester [t (7)  = −4.22, P = 0.004] were signifcantly higher in drought stressed than control plant roots. These results indicate that potatoes, like other plants, can recruit EPNs in re- sponse to root herbivory, and that drought stress dampens this tritrophic interaction where choice is involved. Additional research that resolves the mechanisms of these interactions may provide insights to exploit EPNs for crop protection. Key words: entomopathogenic nematode, tritrophic interaction, herbivory, potato, drought Entomopathogenic nematodes (EPNs) in two families, Steinernematidae and Heterorhabditidae, are insect-specifc para- sites that live in soil (Hazir et al. 2016). EPNs have been used in classical and augmentation biological control programs to suppress population density of pest insects in cryptic habitats in a variety of agroecosystems (El-Borai et al. 2007, Denno et al. 2008). The in- fective juvenile (IJ) stage of EPNs, the only free-living stage, relies on endosymbiotic bacteria (Xenorhabdus spp. in steinernematid nema- todes and Photorhabdus spp. in heterorhabditids) to kill their prey after penetrating the insect’s body through natural openings or the cuticle. The IJs release the bacteria into the insect’s hemocoel, re- sulting in septicemia, with death of the insect usually in 24–48 h. The nematodes utilize the cadaver to complete one to three generations. Development stops at the IJ stage when host nutrients are depleted Annals of the Entomological Society of America, 113(1), 2020, 23–29 doi: 10.1093/aesa/saz050 Advance Access Publication Date: 1 November 2019 Research Downloaded from https://academic.oup.com/aesa/article-abstract/113/1/23/5610791 by University of Florida user on 18 February 2020