Notes on the hosts of Trissolcus Ashmead (Hymenoptera: Scelionidae) from China

Abstract Background Trissolcus Ashmead (Hymenoptera: Scelionidae) is a cosmopolitan genus of egg-parasitoid wasps associated with stink bugs (Pentatomidae, Scutelleridae, Urostylididae), many of which are important insect pests. Documentation of host associations for these wasps, which we here provide via museum specimens, can support their use as biological control agents of invasive stink bugs. New information The hosts of seven Trissolcus species are reported from China: Trissolcus cultratus (Mayr) (hosts: Hippotiscus dorsalis Stål, Pentatomidae; Urochela luteovaria Distant, Urostylididae), Trissolcus elasmuchae (Watanabe) (host: Niphe elongata (Dallas), Pentatomidae), Trissolcus japonicus (Ashmead) (hosts: Erthesina fullo (Thunberg), Pentatomidae; Rhaphigaster nebulosa (Poda), Pentatomidae), Trissolcus latisulcus (Crawford) (host: Poecilocoris latus Dallas, Scutelleridae), Trissolcus mitsukurii (Ashmead) (host: Pentatomidae), Trissolcus semistriatus (Nees von Esenbeck) (host: Eurydema sp., Scutelleridae), Trissolcus yamagishii Ryu (host: Niphe elongata (Dallas), Pentatomidae).


Introduction
Species of Trissolcus are egg parasitoids of stink bugs, many of which are important agricultural pests. During the past decade, the Asian fauna of Trissolcus has received increased attention, driven largely by the search for biological control agents to manage two invasive stink bugs of global significance: Halyomorpha halys (Stål) and Bagrada hilaris (Burmeister) (Pentatomidae). The research required to develop effective biological control programs against these pests is multifaceted and includes taxonomy, behavior, ecology, molecular diagnostics and assessments of host specificity for candidate biocontrol agents (Qiu et al. 2007, Yang et al. 2009, Matsuo et al. 2014, Gariepy et al. 2018, Tortorici et al. 2019, Konopka et al. 2016, Santacruz et al. 2017, Zhang et al. 2017, Boyle et al. 2019. Host range testing can be accelerated if information about parasitoid-host interactions in the native range of a pest is already available. For example, if a stink bug is known to be attacked by very few parasitoid species, this provides a shortlist for additional testing. Similarly, if a parasitoid is known to attack many species in its native range, it is unlikely to be considered sufficiently specific to be introduced in the invaded range of the pest as a biocontrol agent. Zhejiang Univerity in Hangzhou is a leading institution in building insect collections in China, with emphasis on parasitic Hymenoptera (Chen et al. 2014). Importantly, many parasitoid wasps in this collection were reared from a variety of hosts, dating back to the 1930s and thus it contains a wealth of historical and biological information on parasitoidhost associations. However, many of these specimens, especially in the family Scelionidae, have not been identified to the species level. The current study focuses on the genus Trissolcus reared from field-collected eggs and is the first effort to fully investigate the parasitoid-host data of these invaluable specimens.

Materials and methods
This work is based on specimens deposited in the Institute of Insect Sciences, Zhejiang University, Hangzhou, China (ZJU). The label data of all specimens have been georeferenced and recorded in the Hymenoptera Online database. Specimens were identified to species using the keys of  and Tortorici et al. (2019). Images and measurements were made using a Nikon SMZ25 microscope with a Nikon DS-Ri 2 digital camera system. Images were post-processed with Adobe Photoshop CS6 Extended. samplingProtocol: none specified;eventDate: 1980-12  ).

Biology
Host associations. This species was reared from the eggs of Niphe elongata (Dallas) (Pentatomidae) in China.

Biology
Host associations. This species has previously been recorded emerging from the eggs of Halyomorpha halys (Stål) in China (Yang et al. 2009). In this study, we found that this species has also been reared from the eggs of Erthesina fullo (Thunberg)

Biology
Host associations. This species was reared from the eggs of some unidentified species of Pentatomidae in China.

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Materials Notes
This species is newly recorded from China.

Summary of host associations
A total of 123 specimens were examined and seven species are recognized. The hosts recorded on specimen label data are summarized below:

Discussion
Specimens housed in museum and university collections are an immense and often irreplaceable source of biological information. This study produced immediately-applicable data that was gleaned from a historic collection simply by identifying specimens and recording label data. It is difficult and, sometimes, impossible to identify host eggs to species, based on morphology alone and several Trissolcus species in our study were reared from eggs identified only as Pentatomidae. New methods in molecular diagnostics that can identify trophic interactions from parasitized eggs have been used to overcome this challenge and identify associations between scelionid parasitoids and stink bugs (Gariepy et al. 2018, Lomeli-Flores et al. 2019. Implementation of this approach on specimens in insect collections can further expand the data that can be harvested from these institutional resources.