J. Acarol. Soc. Jpn., 27(1): 1-11. May 25, 2018 © The Acarological Society of Japan http://www.acarology-japan.org/ 1 Tick predation by the pseudoscorpion Megachernes ryugadensis (Pseudoscorpiones: Chernetidae), associated with small mammals in Japan* Kimiko OKABE1†, Shun’ichi MAKINO1, Takuya SHIMADA2‡, Takuya FURUKAWA1, Hayato IIJIMA1 and Yuya WATARI1 1Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba, Ibaraki, 305-8687 Japan 2Tohoku Research Center, Forestry and Forest Products Research Institute, 92-25 Nabeyashiki, Shimokuriyagawa, Morioka, Iwate, 020-0123 Japan (Received 7 January 2018; Accepted 11 March 2018) ABSTRACT Ticks are obligate blood feeders that parasitize a variety of vertebrates and can be serious pests for these animals. Due to public concerns about the risk of chemical controls, there is a high demand for biological control agents to reduce tick populations and the spread of tick-borne diseases. In this study, we observed tick predation by the pseudoscorpion Megachernes ryugadensis in a laboratory for the first time. Adult and tritonymphal M. ryugadensis were collected in the field during phoresis on Japanese wood mice and transferred to a Petri dish. These pseudoscorpions preyed on larval Haemaphysalis ticks and nymphal and adult Haemaphysalis megaspinosa. Most pseudoscorpions fed on two to three larval ticks on the first day following tick transfer. There were no significant differences between male and female pseudoscorpions in the numbers of larval ticks consumed or the numbers of days required to consume all ticks. Although there was no significant difference between the numbers of days to consume nymphal and adult male ticks, male pseudoscorpions consumed adult female ticks significantly faster than did female pseudoscorpions. Although the sample sizes in this study were small, the tritonymphal pseudoscorpion displayed similar trends in the predation of larval and nymphal ticks. Further study is required to obtain detailed information on the life history traits of the tick and pseudoscorpion and the impacts of the tick on small rodents and their nest fauna to determine the role of M. ryugadensis as a natural enemy of ticks. Key words: biological control, natural enemy, nidicolous species, rodent, symbiosis * Supplementary videos are available on the website of the Acarological Society of Japan (http://www/acarology- japan.org/). † Corresponding author: email: [email protected] ‡ Present address: Forestry and Forest Products Research Institute, Tsukuba. DOI: 10.2300/acari.27.1 2 Kimiko OKABE et al. INTRODUCTION Ixodida or ticks are obligate blood feeders that parasitize a variety of vertebrates and can be serious pests for these animals through blood reduction, disease transmission, or injuries caused by primary and/or secondary irritation at the attachment site (Oliver, 1989). In wild animals, especially those that are small and/or slender, blood loss to parasites such as ticks is not trivial; thus, they have developed avoidance strategies including grooming and cleaning (Hart, 1992; Schmid-Hempel, 2014; Loker and Hofkin, 2015). Large numbers of ticks can cause substantial economic losses in livestock and transmit various kinds of human disease agents including Lyme disease, Japanese spotted fever, and severe fever with thrombocytopenia syndrome (SFTS) (Fukunaga et al., 1995; Ishikura et al., 2002; Jongejan and Uilenberg, 2004; Parola et al., 2005; Takahashi et al., 2013). Chemical control of ticks has been widely implemented, and potential biological control agents have been listed and tested (Samish and Rehacek, 1999; Samish et al., 2001, 2004; Willadsen, 2006). Because chemical controls are not necessarily effective in reducing tick-borne diseases, and public concerns about environmental pollution by these agents have been raised, there is a high demand for biological agents to control tick populations, in combination with chemical controls (Samish et al., 2004). Pseudoscorpions (Arachnida, Pseudoscorpiones), which include more than 3,200 species, are known to live under soil around the litter layer, under the bark of dead trees, or near vertebrates, e.g., on guano in caves or in rodent nests (Weygoldt, 1969; Harvey, 1992; Murienne et al., 2008). All pseudoscorpions are predators of small arthropods; they can ambush approaching prey, often at their nest entrance, but sometimes actively approach prey alone or in cooperation with conspecifics (Weygoldt, 1969; Del-Claro and Tizo-Pedroso, 2009). The predatory behaviors of some species are relatively well described: they use palpal chelae on the pedipalpi to sense and prey on living arthropods and suck their body fluid (Weygoldt, 1969); however, behaviors of some species remain unknown. Some pseudoscorpions, including most Megachernes (Chernetidae) species are unique in that they maintain close relationships with small rodents by inhabiting their nests and exploiting them for migration (phoresy) (Hoff and Clawson, 1952; Francke and Vallegas-Guzmán, 2006; Harvey et al., 2012). Megachernes ryugadensis was first collected on bat guano in a cave in Kochi, Japan, and was later recorded in bumblebee nests or body surfaces of the brown rat, Rattus norvegicus and Japanese mole, Mogera wogura during phoresy in Japan except for the Nansei Islands (Morikawa, 1954, 1960; Sato and Sakayori, 2015). Although Morikawa (1954 and 1960) suggested that the species fed on ticks in guano, no evidence was provided. In a preliminary study, we found that M. ryugadensis was commonly phoretic on forest mice in Morioka, Japan. In this study, we focused on tick predation by this species. To assess the performance of M. ryugadensis as a natural enemy of ticks, parasitizing wild animals including small rodents, we observed predatory behavior of M. ryugadensis on ticks. Because we were not able to observe their behavior under natural conditions, we supplied common ticks (Haemaphysalis megaspinosa) at different developmental stages to M. ryugadensis pseudoscorpions in a laboratory and observed interactions between these species. Small rodents Tick predation by Megachernes ryugadensis 3 host a wide range of immature ixodids (Oliver, 1989); therefore, we estimated the potential performance of M. ryugadensis as a natural enemy of ticks based on our laboratory experiments. MATERIAL AND METHODS Collection of materials We collected the pseudoscorpion M. ryugadensis (Fig. 1) in phoresis on the large Japanese wood mouse Apodemus speciosus and the small Japanese wood mouse A. argenteus (Rodentia: Muridae), which were trapped using Sherman traps in a deciduous forest located within the Takizawa research forest of Iwate University, Morioka, Iwate, Japan (39°47’N, 141°09’E, approximately 200 m a.s.l.). Adult and tritonymphal M. ryugadensis were removed from rodents with forceps during rodent sampling in the field and maintained in the laboratory in a plastic cup (diameter at top: 5 cm, height: 3.5 cm) with wet wood pieces at the bottom (thickness: ca. 1 cm) and covered by a lid with small holes for ventilation. Once per week, approximately 30 acarid mites (mostly adults), which had probably originated from a wild lucanid beetle (Dorcus rectus) and been reared on dry yeast, were released into the cup as food. We collected ticks at all stages using the flagging method (Fujimoto et al., 1986) in forests in Nikko, Tochigi, in October 2017 and some unfed adult ticks and fed nymphal and adult ticks from dead sika deer in November 2017. Living ticks were identified in a laboratory to stages and at the species (nymphal and adult ticks) or genus level (larvae) using published identification keys (Fujita and Takada, 2007; Yamauchi and Takada, 2015). As H. megaspinosa was abundant, we used this species in pseudoscorpion predation experiments. We maintained living ticks, for 1 week at most, on moistened flannel in a plastic bag at 15 ± 2℃ or in a plastic bottle in a refrigerator at around 5℃. Predation experiment We used adult and tritonymphal pseudoscorpions collected within the previous 4 months (August–November 2017) and 6 months (June–November 2017), respectively. About 24 h prior to the experiments, we confined each M. ryugadensis in a small plastic Petri dish (diameter: 3.7 cm, height: 1.1 cm) with a small amount of wet peat moss in the middle of the dish to maintain moisture and provide a hiding place for the pseudoscorpion. In our preliminary experiments, pseudoscorpions survived for at least 5 days without food under these conditions. We released tick(s) into the Petri dish as prey using a fine paintbrush. We transferred five larval ticks, one nymphal tick, or one adult tick to a Petri dish containing a pseudoscorpion. We conducted eight and five replicates for each sex of adult pseudoscorpion to examine the predation of larval ticks and of the other stages, respectively (Table 1). Due to limited sample sizes, we conducted four and two replicates of tritonymphal pseudoscorpion introduction for larval and nymphal ticks, respectively (Table 1). For the same reason, we did not provide adult ticks as prey. We used a different pseudoscorpion in each replicate to avoid any influence of previous feeding experience. Petri dishes containing a pseudoscorpion and tick(s) were sealed with plastic paraffin film (Parafilm) and maintained in a thermostatic chamber (25 ± 2°C, 60 ± 10% relative humidity, and 12 h light:12 h dark). We checked M. ryugadensis survival and the number of ticks consumed daily by opening the 4 Kimiko OKABE et al. lid (also providing ventilation) until