Received: 5 October 2020 | Revised: 28 October 2020 | Accepted: 8 November 2020 DOI: 10.1111/jen.12843 ORIGINAL CONTRIBUTION Laboratory evaluation of Orthocentrus brachycerus (Hymenoptera: Ichneumonidae), as a potential biological control agent in mushroom cultivation Hiromi Mukai | Hiroshi Kitajima Department of Forest Entomology, Forestry and Forest Products Research Institute, Abstract Tsukuba, Japan Fungus gnats in the genus Neoempheria Osten Sacken (Diptera: Mycetophilidae) are Correspondence serious pests of the shiitake mushroom, Lentinula edodes (Berk.) Sing. (Agaricales: Hiromi Mukai, Department of Forest Omphalotaceae), a prize edible. Recently, we found that the parasitoid wasp Entomology, Forestry and Forest Products Research Institute, 1 Matsuno-sato, Orthocentrus brachycerus Humala & Lee, 2020 (Hymenoptera: Ichneumonidae) at- Tsukuba, Ibaraki 305-8687, Japan. tacks larvae of Neoempheria. We have shown in previous research that O. brachycerus Email: [email protected] suppresses population growth of Neoempheria in simulated cultivation conditions, Funding information and thus shows potential for use as a biological control agent. However, the behav- Japan Society for the Promotion of Science, Grant/Award Number: 20K15562; Forestry ioural and ecological aspects of this wasp have not been studied. Here, under con- and Forest Products Research Institute, trolled laboratory conditions, we investigated the fecundity, longevity and host stage Grant/Award Number: 201707 specificity of O. brachycerus against Neoempheria larvae. We found that O. brachy- cerus are prolific throughout their life cycle. On average, female O. brachycerus made over 140 attempts to parasitize pest larvae, and over 90% of Neoempheria larvae were parasitized or died before emergence. Parasitoid females kept at 20°C survived for an average of 15.4 ± 3.58 days, and some females survived >30 days. Females continued to oviposit eggs throughout their life cycle and parasitized all stages of host larvae, but not eggs. These observations indicate that O. brachycerus may be effective for control of Neoempheria larvae in shiitake cultivation facilities. These re- sults provide a basis for establishing a protocol for using O. brachycerus in mushroom cultivation. KEYWORDS endoparasitoid, fecundity, fungus gnat, natural enemy, Orthocentrinae, shiitake 1 | INTRODUCTION Sueyoshi et al., 2015). Three species of Neoempheria are pests in shiitake-growing greenhouses: Neoempheria carinata Sueyoshi, Fungus gnats in the genus Neoempheria Osten Sacken (Diptera: 2014, N. bifurcata Sueyoshi, 2014 and N. dilatata Sueyoshi, Mycetophilidae) are important pests of the shiitake mush- 2014 (Sueyoshi, 2014). Most shiitake mushrooms are grown in room, Lentinula edodes (Berk.) Sing. (Agaricales: Omphalotaceae) vinyl greenhouses under controlled environmental conditions (Kitajima & Kawashima, 2012; Kitajima et al., 2012; Sueyoshi, 2014; using mycelial blocks made from oak chip and sawdust because This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. © 2020 The Authors. Journal of Applied Entomology published by Wiley-VCH GmbH J Appl Entomol. 2020;00:1–10. wileyonlinelibrary.com/journal/jen | 1 2 | MUKAI AND KITAJIMA mycelial blocks are lighter and easier to handle than bed logs (Chen Biological control using parasitoid wasps in shiitake cultiva- et al., 2000). However, once pests enter the sealed greenhouses, tion facilities would be a novel and useful method for control of they increase at an astonishing rate (Kitajima & Kawashima, 2012; Neoempheria. The Ichneumonidae (Hymenoptera; Ichneumonidae) Kitajima et al., 2012). Larval feeding within the mycelia and fruiting attack the immature stages of insects and spiders, eventually killing bodies of shiitake causes direct damage and provides a pathway their hosts, with very few exceptions. Therefore, they could play an for secondary feeding by other insects as well as colonization by important role as regulators of insect populations, both in natural fungi and bacteria that may contribute to further decay (Kitajima & and in artificial environment systems, making them promising agents Kawashima, 2012; Kitajima et al., 2012). for biological control (Klopfstein et al., 2019). Thus, pest control strategies with low environmental impact, that When managing insect pests in agricultural fields by releasing are food safe, and that are not vulnerable to development of insecti- parasitoids, it is important to know the number of parasitoids re- cide resistance are needed. In Europe and North America, the pests quired to maintain insect pest populations below economic injury of the common mushroom, Agaricus bisporus (Lange) Sing., such as levels (Apple & Smith, 1976; Onstad, 1987). Previous studies have sciarids (Diptera: Sciaridae) and phorids (Diptera: Phoridae), are con- developed models to determine the number of parasitoids required trolled by applying nematodes, microorganisms and predatory mites for pest control and have reported that it is important to know how such as entomopathogenic nematodes of the genus Steinernema many hosts will be parasitized by an individual wasp over her life (Nematoda: Steinernematidae), S. feltiae (Filipjev) and S. carpocapsae span (Urano et al., 2011). However, there is no information about (Weiser) (Erler et al., 2009; Jess & Bingham, 2004; Katumanyane adult fecundity and longevity of Orthocentrinae, because these par- et al., 2018; Navarro & Gea, 2014; Scheepmaker et al., 1998; asitoid wasps are difficult to observe in the field. To utilize parasitoid Shamshad et al., 2008); the bacterium Bacillus thuringiensis (Berliner) wasps in shiitake cultivation, it is necessary to clarify their ecology var. israelensis (Shamshad, 2010); and predatory mites in the genus and bionomics. Hypoaspis (Acari: Hypoaspidae) (Jess & Bingham, 2004; Jess & The aim of this study was to clarify the fecundity, longevity and Kilpatrick, 2000; Navarro et al., 2020). In these countries, integrated host stage specificity of the parasitoid wasp O. brachycerus under pest management (IPM) focusing on the use of natural enemies has laboratory conditions. We established the laboratory colonies of been actively promoted, but this strategy has not been used much Neoempheria spp. and O. brachycerus and investigated the interac- in Asian countries, including Japan. As in agriculture, there is an in- tions between these wasps and their host flies. These data will con- creasing need for alternative methods of pest control, including bio- tribute to assessing its suitability as a new biological control agent logical control, in mushroom cultivation (Jess & Bingham, 2004; Jess against fungus gnats and establishing a protocol for use of parasitoid & Kilpatrick, 2000; Jess & Schweizer, 2009; Navarro & Gea, 2014). wasps in mushroom cultivation. Several approaches to reduce populations of Neoempheria have been studied. Adult Neoempheria can be captured in traps, such as ultraviolet light-emitting diode traps and water-pan traps (Sonoda 2 | MATERIALS AND METHODS et al., 2014). Physical removal, such as by washing mycelial blocks, is effective against larvae of Neoempheria (Forestry & Forest Products 2.1 | Origin of study insects Research Institute, 2020). In addition to these methods, it has recently been demonstrated that insect–parasitic microorganisms are effective It was not possible to identify the presence or absence of para- for control of fungus gnats (Kitajima et al., 2018). The entomopatho- sitism by wasps in host larvae. Therefore, we initially collected genic nematode S. carpocapsae and the bacterium B. thuringiensis have Neoempheria carinata larvae as the source of study insects and then recently been registered as biopesticides and are attracting attention obtained the Orthocentrus brachycerus adults that emerged from as a new method for pest control in shiitake cultivation in Japan. the parasitized larvae and N. carinata adults that emerged from Recently, we found that parasitoid wasps in the Orthocentrinae the non-parasitized larvae. The Neoempheria carinata larvae were (Hymenoptera: Ichneumonidae) attack Neoempheria larvae (Mukai & originally collected from a farmer's facility in Tomioka City, Gunma Kitajima, 2019). We reported that after releasing N. carinata larvae Prefecture, Japan, from 2016 to 2019. The insects were maintained in a simulated shiitake cultivation greenhouse, the next generation in a laboratory at the Department of Forest Entomology, Forestry of the Neoempheria population was significantly smaller in plots con- and Forest Products Research Institute, Japan. Larvae were reared taining parasitoids than in control plots without parasitoids (Mukai & individually in the laboratory in small plastic cups (40 mm diameter, Kitajima, 2019). Watanabe et al. (2020) identified this parasitoid as 25 mm high, CP Chemical Co., Ltd.). Each larva was with a piece Orthocentrus brachycerus Humala et al., 2020. This parasitoid species of fresh mycelial block (approximately 20 × 20 × 10 mm, Hokken is distributed in areas of Japan where shiitake cultivation facilities Co., Ltd.) as food and checked for eclosion daily to obtain newly are present, including the islands Honshu, Hokkaido, Kyushu and emerged N. carinata and O. brachycerus. All insects were reared and Okinawa, and this species may be an important