Contents lists available at ScienceDirect Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/jip Mode of entry of secondary metabolites of the bacteria Xenorhabdus szentirmaii and X. nematophila into Tetranychus urticae, and their toxicity to the predatory mites Phytoseiulus persimilis and Neoseiulus californicus Duygu Cevizci a , Derya Ulug b , Harun Cimen b , Mustapha Touray b , Selcuk Hazir b , Ibrahim Cakmak a, ⁎ a Department of Plant Protection, Faculty of Agriculture, Aydin Adnan Menderes University, Aydin, Turkey b Department of Biology, Faculty of Arts and Science, Aydin Adnan Menderes University, Aydin, Turkey ARTICLEINFO Keywords: Phytoseiulus persimilis Neoseiulus californicus Secondary metabolites Tetranychus urticae Xenorhabdus Entomopathogenic nematodes ABSTRACT The bacterial metabolites in supernatants of Xenorhabdus specieshaveacaricidalactivity,butthismodeofentry intomiteshasnotyetbeenelucidated.Herein,wereportonthepossiblemodeofentryof Xenorhabdus szentirmaii and Xenorhabdus nematophila supernatantsinto Tetranychus urticae (Acari:Tetranychidae)adultfemales.Wealso assessed the toxicity of the supernatants against the developmental stages of the predatory mites, Phytoseiulus persimilis and Neoseiulus californicus (Acari:Phytoseiidae).Experimentswereconductedat25 ± 1°C,70 ± 5% relative humidity, and 16:8h light:dark conditions. Our data showed that the bioactive acaricidal compound is most efective (86.5 to 89% mortality) when the entire integument of T. urticae comes in contact with it com- pared to contact of the ventral side only (26.5–34%). Against P. persimilis and N. californicus at 6 days post- application (dpa), the eggs were not afected by the X. szentirmaii or X. nematophila supernatant, whereas mortality of the mobile stages (larva, protonymph, deutonymph, adult) was 18.5% to 39.2%. Overall, the predatory mites were less afected by the bacterial metabolites than T. urticae. We hypothesize that the difer- encesinmorphologysuchaslongerlegsandthickercuticle,aswellasthedietofthepredatorymites,reducethe contactofthebodypartstothesupernatant-treatedsurfaces.Weneedtoisolate,identify,andcharacterizethe X. szentirmaii and X. nematophila metabolite(s) and demonstrate efcacy to pestiferous mites and safety to plants, non-target organisms and the environment before it can be used as an acaricide. 1. Introduction The two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae),isoneofthemostimportantpestspeciesthatiswidely distributed globally. It attacks more than 1000 plant species, including crops such as strawberry, cotton, deciduous fruits, vegetables and or- namental plants (Migeon and Dorkeld, 2018). This pest causes ex- tensivedamagethroughitssuckingmouthpartswhilefeedingonleaves, stems and fruits. Plant chlorophyll synthesis is inhibited as a result of feeding on the leaves causing yellowing and necrotic brown spots (Cakmak et al., 2005). Furthermore, the mite feeding activity causes paleness in plant color due to their webs on the infested leaves, and continued infestation causes fruit deformation and stunts plant growth (Jeppson et al., 1975). Infestation leads to huge losses in crop quality and yields. The rapid reproduction, high fecundity, and short life cycle of T. urticae can result in resistance to many chemical pesticides in a very short period of time when they are used for mite suppression. The pesticidesusedagainstthispestalsocauseenvironmentalpollutionand adverse efects on nontarget animals including humans. Therefore, biological control agents as an alternative to chemical control of this pest are used in many countries and, as a result, predatory mites (Phytoseiidae) are most commonly used in suppression of T. urticae populations (Cakmak et al., 2006, 2009). Microorganisms such as viruses, bacteria, fungi, rickettsia, and protozoans and invertebrates such as nematodes have been reported to infect arthropods including insects and mites (Poinar and Poinar, 1998). In addition, bacterial secondary metabolites are also efective against insects and mites (Seo et al., 2012; Dhanasekaran and Thangaraj, 2014; Eroglu et al., 2019). Some of these microbes and nematodes as well as the secondary me- tabolites ofer other potential alternatives to the use of chemical pes- ticides. https://doi.org/10.1016/j.jip.2020.107418 Received 30 March 2020; Received in revised form 30 May 2020; Accepted 3 June 2020 ⁎ Corresponding author. E-mail address: icakmak@adu.edu.tr (I. Cakmak). Journal of Invertebrate Pathology 174 (2020) 107418 Available online 07 June 2020 0022-2011/ © 2020 Elsevier Inc. All rights reserved. T