JHR 96: 949-954 (2023) Boe Se JOURNAL OR. She tones doi: 10.3897/jhr.96.1 13486 SHORT COMMUNICATION () I Tymenopter a 4 https://jhr.pensoft.net Thelnternaonl Society of Hymenopexriss, RESEARCH Male-biased night foraging by bumblebees (Hymenoptera, Apidae, Bombus spp.) in Taiwan Yun-Chen Hsieh!?’, Joe Chun-Chia Huang? , Wen-Chi Yeh?, Chun-Yang Tsai*, Chien-Jung Lin’, Sheng-Shan Lu? | Institute of Ecology and Evolutionary Biology, National Taiwan University, Taipei City, Taiwan 2. Forest Protection Division, Taiwan Forestry Research Institute, Taipei City Taiwan 3 Department of Life Science, National Taiwan Normal University, Taipei City, Taiwan 4 Department of Forestry and Natural Resources, National Ilan University, Yilan City Taiwan § Fushan Research Center, Taiwan Forestry Research Institute, Yuanshan Township, Taiwan Corresponding author: Sheng-Shan Lu (sslu@tfri.gov.tw) Academic editor: C. K. Starr | Received 29 September 2023 | Accepted 28 October 2023 | Published 7 November 2023 https:/lzoobank. org/ DC2BCD C6-B278-4FAD-A2EB-C9B1D1437A10 Citation: Hsieh Y-C, Huang JC-C, Yeh W-C, Tsai C-Y, Lin C-J, Lu S-S (2023) Male-biased night foraging by bumblebees (Hymenoptera, Apidae, Bombus spp.) in Taiwan. Journal of Hymenoptera Research 96: 949-954. https:// doi.org/10.3897/jhr.96.113486 Abstract Known nocturnal behaviors of bees in the superfamily Apoidea, including the genus Bombus, were almost exclusively of females. Here we report observations of active free-ranging male Bombus at night in the plant nursery of the Fushan Research Center, Taiwan, in April 2022. Nectar feeding by males at inflorescences was confirmed by tongue-licking in the absence of pollen collecting. The numbers of active female and male bum- blebees during the daytime were close to equal. In contrast, only males were found to be active in the night. Our observations suggest that such nocturnal activity is facultative. This finding not only provides a rare case of noc- turnal activity in free-ranging Bombus, but also demonstrates that such behaviors can vary between the sexes. Keywords Bombus flavescens, nocturnal behavior, sex-biased Circadian rhythm represents a key mechanism regulating temporal patterns of activity and physiological processes in animals. Given species tend to be diurnal, nocturnal or crepus- cular, depending on whether their main active times are during daylight hours, at night or in twilight. The timing of daily activity may involve distinct selection forces on account of * These authors contributed equally to this research and share first authorship. Copyright Yun-Chen Hsieh et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 950 Yun-Chen Hsieh et al. / Journal of Hymenoptera Research 96: 949-954 (2023) light conditions, weather, the distribution of important resources, and predation risk. Fur- thermore, synchronization with conspecifics of daily activity may be important in social and reproductive interactions (Sullivan 1981; Frisch and Koeniger 1994). On the other hand, asynchronization of daily activity among conspecifics could favor individuals via avoidance of severe intraspecific competition for critical resources (Alanara et al. 2001). Bumblebees (Hymenoptera; Apidae; Bombus) are a group of large social bees. ‘The ge- nus is most abundant in the northern hemisphere, where it provides critical pollination ser- vices to many crops and wild plants (Prys-Jones and Corbet 2011). While observations to date show both sexes to be active mainly or exclusively in the daytime, Chittka et al. (1999) recorded nocturnal feeding by B. impatiens workers in captive condition. Here we report observations of nocturnal activity in free-ranging male Bombus from northeastern Taiwan. The observations were mainly made at the plant nursery of Fushan Research Cent- er (24.7556°N, 121.5959°E) in Yilan County, Taiwan, from early to mid-April 2022. The climate is characterized by a strong seasonality that is mainly driven by the north- east monsoon in the winter and occasional typhoons in the late summer and early fall. The weather is generally mild and humid with a mean annual temperature of 18.2 °C and precipitation of 3,888 mm (Tu et al. 2023). The surrounding vegetation is pri- marily submontane evergreen broadleaf forest (Su et al. 2010). The plant nursery was established by Taiwan Forestry Research Institute (T-ER.I.) to conserve endemic and threatened native plants. Since the observation area in the plant nursery had no insect exclusion nets, bumblebees can access the plants freely. An additional 1.6-km transect line was set along a trail of the nearby Fushan Botanical Garden in the later phase of the study, when many dicot plants were in bloom. Bees’ nocturnal behavior was initially noted by direct visual observation with lights from torch and headlamp. Later we utilized a night-vision video cam recorder (Canon XA40, Japan) with an 850 nm infrared torch (Nightfox NB5, U.K.) in order to record nocturnal activity without presenting a visual light stimulus. Bees found to be walking, flying, wing fluttering, or showing leg movements or nectar feeding were considered active. Nectar feeding is evidenced by extension of the tongues and licking movements at flowers, along with the absence of pollen-collecting movements. Three bumblebee species have been reported from the Fushan area: B. bicoloratus, B. eximius, and B. flavescens (S.S.L., Y.C.H., and W.C.Y. unpublished data). We identi- fied bees to species according to a key of the three species (Suppl. material 1) based on Starr (1992). However, the diagnostic traits to distinguish B. eximius and B. flavescens cannot be applied with confidence to active individuals, so that the two species are combined in our data as B. eximius/B. flavescens. Six male bumblebees were spotted in active status on Ligustrum pricei during a night walk in the plant nursery between 20:50 and 21:00 on April 5", 2022. All active bumblebees walked slowly among the branches and inflorescences and inspected both opened and unopened flowers during most of the observation time. One individual flew with wings slowly fluttering, from L. pricei to a neighboring plant. While the bees were in contact with stigma and pistil, they often extended their tongues in the typical nectar licking behavior (Fig. 1). No pollen collection actions were performed by the bees, consistent with feeding on nectar. Male-biased night foraging behavior of Bombus bees in Taiwan 951 Additional observations of B. eximius/B. flavescens were made at the plant nursery and botanical garden (Table 1). While active bumblebees of both sexes had been seen at both sites in the daytime, nocturnal foraging behavior was again recorded solely from male bumblebees at the plant nursery (Suppl. material 2). No active females were observed in the three additional survey nights, but one inactive worker was recorded with two males on Ajuga dictyocarpa. In the only daytime observation, we recorded a similar number of male and worker B. eximius!B. flavescens, feeding at L. pricei and A. dictyocarpa. Diurnality is considered the predominant habit in bees. Nocturnal and crepuscular activities have been reported from several genera of Apidae and Halictidae, includ- ing Apis, Bombus, Lasioglossum, Megalopta and Xylocopa, but exclusively from females (Chittka et al. 1999; Burgett and Sukumalanand 2000; Wcislo et al. 2004; Kelber et al. 2006; Tierney et al. 2008; Young et al. 2021). Our observation of facultative nocturnal foraging by B. eximius/B. flavescens provides a case of male bees showing considerable plasticity in daily activity pattern. Night light has been suggested as a critical environmental factor driving nocturnal activities in bees (Kelber et al. 2006; Warrant 2008). In our case, the B. eximius/B. fla- vescens in Fushan were attracted by and licked unopened flowers of L. pricei (Suppl. ~ a Figure |. A male bumblebee at Ligustrum pricei flowers at night. 952 Yun-Chen Hsieh et al. / Journal of Hymenoptera Research 96: 949-954 (2023) Table |. Numbers of active and inactive B. eximius/B. flavescens individuals of each sex in each survey. Two males (FACT-00215031, FACT-00215032) identified as B. flavescens were deposited at the Forest Arthropod Collection of Taiwan (FA.C.T.) in T-ER.I. This survey session included both at the botanical garden and the plant nursery. Date Active bees Inactive bees 2022 April 5" — night 65'S - 2022 April 6" — night = - 2022 April 14" — day 1288, 1099 i 16,12 2022 April 14% — night 233 2022 April 16" — night 7 (unknown sex) material 3) and the white flower tags that we labeled on the tree several times. The misrecognition suggests that the bees used visual cues when targeting food resources. However, the two nights when active bees were observed were cloudy and dark, sug- gesting that B. eximius/B. flavescens may also use chemical cues for foraging in addition to vision (Chittka et al. 1999; Kulahci et al. 2008; Lawson et al. 2018). Studies have shown that consumption of nutrient supplements could increase low temperature tolerance and survivorship from acute cold (Owen et al. 2013; Abou- Shaara 2017). In the low elevation mountainous areas (<1000 ma.s.l.) of Taiwan, male bumblebees, especially B. flavescens, emerge in spring (Sung et al. 2011). Unlike the females feeding on nectar and collecting pollen, male bumblebees were found feeding exclusively on nectar. They feed in the day and usually stay on inflorescences in the night (Prys-Jones and Corbet 2011). Both Ligustrum pricei and Ajuga dictyocarpa blos- som in the day, and their flowers last for around 24 hours. Nectar-feeding behaviors in bumblebees suggest that the nectar is available throughout the day. On the other hand, only half of the surveyed nights showed male bumblebees on plants. During the study period, bumblebees reduced their nocturnal activity when the wind became stronger and temperature dropped, becoming active again when the wind speed lowered. It might be too energetically costly for the bees to remain active during bad weather conditions. We thank E-Ping Rau, Ping-Hsin Wang, Sz-yi Tsai, and Yider Hsu for assistance in the field, Ellen McArthur and Christopher K. Starr for the language review, Ace Kevin S. Amarga for the format review, Christopher K. Starr and an anonymous reviewer for their useful comments on a previous version. This study was supported financially by T.ER.L. (grant number 110AS-7.1.3-FI-G3) References Abou-Shaara HF (2017) Effects of various sugar feeding choices on survival and tolerance of honey bee workers to low temperatures. Journal of Entomological and Acarological Re- search 49: e6200. https://doi.org/10.4081/jear.2017.6200 Alanara A, Burns MD, Metcalfe NB (2001) Intraspecific resource partitioning in brown trout: the temporal distribution of foraging is determined by social rank. Journal of Animal Ecology 70(6): 980-986. https://doi.org/10.1046/j.0021-8790.2001.00550.x Male-biased night foraging behavior of Bombus bees in Taiwan 953 Burgett DM, Sukumalanand P (2000) Flight activity of Xylocopa (Nyctomelitta) tranquebarica: a night flying carpenter bee (Hymenoptera: Apidae). Journal of Apicultural Research 39: 75-83. https://doi.org/10.1080/00218839.2000.11101024 Chittka L, Williams NM, Rasmussen H, Thomson JD (1999) Navigation without vision: bum- blebee orientation in complete darkness. Proceedings of the Royal Society (B) 266: 45-50. https://doi.org/10.1098/rspb.1999.0602 Frisch B, Koeniger N (1994) Social synchronization of the activity rhythms of honeybees with- in a colony. Behavioral Ecology and Sociobiology 35: 91-98. https://doi.org/10.1007/ BF00171498 Kelber A, Warrant EJ, Pfaff M, Wallén R, Theobald JC, Wcislo WT, Raguso RA (2006) Light intensity limits foraging activity in nocturnal and crepuscular bees. Behavioral Ecology 17: 63-72. https://doi.org/10.1093/beheco/arj001 Kulahci IG, Dornhaus A, Papaj DR (2008) Multimodal signals enhance decision making in foraging bumble-bees. Proceedings of the Royal Society B: Biological Sciences 275(1636): 797-802. https://doi.org/10.1098/rspb.2007.1176 Lawson DA, Chittka L, Whitney HM, Rands SA (2018) Bumblebees distinguish floral scent pat- terns, and can transfer these to corresponding visual patterns. Proceedings of the Royal Soci- ety B: Biological Sciences 285(1880): e20180661. https://doi.org/10.1098/rspb.2018.0661 Owen EL, Bale JS, Hayward SAL (2013) Can winter-active bumblebees survive the cold? Assessing the cold tolerance of Bombus terrestris audax and the effects of pollen feeding. PLoS ONE 8(11): e80061. https://doi.org/10.1371/journal.pone.0080061 Prys-Jones OE, Corbet SA (2011) Bumblebees (3 edn.). Pelagic Publishing, Exeter, 130 pp. Starr CK (1992) The bumble bees (Hymenoptera: Apidae) of Taiwan. Bulletin of the National Museum of Natural Science 3: 139-157. Su SH, Hsieh CF, Chang-Yang CH, Lu CL, Guan BT (2010) Micro-topographic differentia- tion of the tree species composition in a subtropical submontane rainforest in northeast- ern Taiwan. Taiwan Journal of Forestry Science 25: 63-80. https://www.tfri.gov.tw/en/ News_Content2.aspx?n=7589 &s=14070 Sullivan RT (1981) Insect swarming and mating. Florida Entomologist 64: 44-65. https://doi. org/10.2307/3494600 Sung IH, Lu SS, Chan ML, Lin MY, Chiang CH, Li CC, Yang PS (2011) A study on the size and morphological difference, seasonal occurrence and distribution features of four bumblebees from Taiwan (Hymenoptera, Apidae). Formosan Entomology 31: 309-323. https://doi.org/10.6661/TESFE.2011020 Tierney SM, Gonzales-Ojeda T, Wcislo WT (2008) Biology of a nocturnal bee, Megalopta atra (Hymenoptera: Halictidae; Augochlorini), from the Panamanian highlands. Journal of Natural History 42: 1841-1847. https://doi.org/10.1080/00222930802109124 Tu FJ, Lin CL, Huang HH (2023) Weather data from Fushan Research Center of Taiwan Forestry Research Institute — Nursery Weather Station. Taiwan Forestry Research Institute. [accessed 16 August 2023] https://metacat.tfri.gov.tw/tfri/view/ TFRIWMT.11.19 Warrant EJ (2008) Seeing in the dark: vision and visual behaviour in nocturnal bees and wasps. Journal of Experimental Biology 211(11): 1737-1746. https://doi.org/10.1242/jeb.015396 Wceislo WT, Arneson L, Roesch K, Gonzalez V, Smith A, Fernandez H (2004) The evolution of nocturnal behaviour in sweat bees, Megalopta genalis and M. ecuadoria (Hymenoptera: 954 Yun-Chen Hsieh et al. / Journal of Hymenoptera Research 96: 949-954 (2023) Halictidae): an escape from competitors and enemies? Biological Journal of the Linnean Society 83: 377-387. https://doi.org/10.1111/j.1095-8312.2004.00399.x Young AM, Kodabalagi S, Brockmann A, Dyer FC (2021) A hard day’s night: Patterns in the diurnal and nocturnal foraging behavior of Apis dorsata across lunar cycles and seasons. PLoS ONE 16(10): e0258604. https://doi.org/10.1371/journal.pone.0258604 Supplementary material | Identification keys to bumblebee species of the Fushan area Authors: Yun-Chen Hsieh, Joe Chun-Chia Huang Data type: docx Copyright notice: This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODDbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited. Link: https://doi.org/10.3897/jhr.96.113486.suppl1 Supplementary material 2 Behavior of a male bumblebee on the inflorescences of Ligustrum pricei at night Authors: Joe Chun-Chia Huang Data type: mov Copyright notice: This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODDbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited. Link: https://doi.org/10.3897/jhr.96.113486.suppl2 Supplementary material 3 A bumblebee worker licking unopened flowers of Ligustrum pricei Authors: Joe Chun-Chia Huang Data type: mov Copyright notice: This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODDbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited. Link: https://doi.org/10.3897/jhr.96.113486.suppl3