Swarming Period Research Articles

Season and host-community composition inside roosts may affect host-specificity of bat flies.

Bat flies are one of the most abundant ectoparasites of bats, showing remarkable morphological adaptations to the parasitic habit, while the relationship with their hosts is characterized by a high level of specificity. By collecting bat flies from live hosts, our intention was to elucidate the seasonal differences in bat fly occurrence and to describe factors regulating the level of incipient host specificity. Our results indicate that the prevalence and the intensity of infestation is increasing from spring to autumn for most host species, with significant differences among different fly species. Males showed higher infestation levels than females in autumn, suggesting a non-random host choice by flies, targeting the most active host sex. Bat-bat fly host specificity shows seasonal changes and host choice of bat flies are affected by the seasonal differences in hosts' behavior and ecology, the intensity of infestation and the species composition of the local host community. Nycteribiid bat flies showed lower host specificity in the swarming (boreal autumn) period, with higher prevalence recorded on non-primary hosts. Choosing a non-primary bat host may be an adaptive choice for bat flies in the host's mating period, thus increasing their dispersive ability in a high activity phase of their hosts.

First record of Rhinolophus ferrumequinum in north-western Bohemia, Czech Republic (Chiroptera: Rhinolophidae)

A male greater horseshoe bat (Rhinolophus ferruequinum) was netted at the entrance to the abandoned Mauritius mine (50°23’32”N, 12°50’01”E; 1018 m a. s. l.) in the Krušné Hory Mts (Ore Mountains) on 2 September 2023. This is the first record of this species in north-western Bohemia and first record outside the hibernation period for the whole Bohemia. The site is situated beyond the northern limits of the continuous distribution range of the species. Mist netting campaigns during the swarming period have been taking place at the site regularly since 2005 (except 2006 and 2022) and Rhinolophus ferruequinum was never recorded there before.

Updip Fluid Flow in the Crust of the Northeastern Noto Peninsula, Japan, Triggered the 2023 Mw 6.2 Suzu Earthquake During Swarm Activity

AbstractAn Mw 6.2 earthquake occurred in Suzu, northeastern Noto Peninsula, Japan, on 5 May 2023, followed by many aftershocks. Before this mainshock‐aftershock sequence, an intense earthquake swarm lasted in the vicinity for 2.5 years. Here, we estimated the rupture process of the Mw 6.2 mainshock and relocated >20,000 surrounding small earthquakes. The results show that systematic upward migration occurred via a complex network of faults in the preceding swarm period and that the mainshock rupture was initiated near the shallow end of the swarm earthquakes. The mainshock rupture propagated farther updip, followed by many aftershocks in the shallow extension. Upward fluid movement likely caused systematic upward earthquake migration from a depth of 18–5 km. The present results indicate the importance of monitoring swarm events since large (M > 6) and dangerous earthquakes can occur during such swarms.

Swarms and mainshock–aftershocks sequences are both triggered by fluids in the Ubaye Region (Western Alps)

SUMMARYThe Ubaye Region (French Western Alps) is one of the most seismically active regions in France. It is regularly struck by mainshock–aftershocks sequences like in 1959 (ML 5.3), seismic swarms (2003–2004), and complex sequences (2012–2015) characterized by successive mainshocks clustered in time and space. This diversity of seismic behaviour highlights the complex processes at play in this area. To improve our understanding of these processes, in this study, we compile a regional catalogue of existing focal mechanisms, completed by 100 new calculated focal mechanisms of aftershocks following the 07/04/2014 mainshock (ML 5.1). The oriented stress-state we reconstruct for different periods and subareas are similar to each other and to previous published values focusing on swarm periods. We then calculate fluid pressure required to trigger the earthquakes. Most of the events (65 per cent) need fluid overpressure between 15 and 40 MPa (17 to 40 per cent of the hydrostatic pressure) with a median value of 24 per cent. Moreover, even the largest events, like the mainshocks in the 2012–2015 sequence, appear to be triggered by fluid pressure, similarly as events within swarm sequences. However, while fluid overpressure decreases with time in an aftershock sequence, it varies randomly at high levels during a swarm sequence. Therefore, based on a fault-valve model, we propose that: (1) the fluids trapped in the fault plane tend toward lithostatic pressure and trigger the mainshock rupture and (2) part of the aftershocks are induced by the diffusing fluid pressure. On the contrary, swarms need external, likely deep, fluid pressure feedings. Fluid pressure is likely to be a common triggering mechanism of the seismicity in the Ubaye Region, even if the involved processes should differ to explain the different types of seismic sequences.

Shear-wave splitting patterns in Perachora (Eastern Gulf of Corinth, Greece)

The Eastern Gulf of Corinth (EGoC) is one of the most seismically active areas in Greece. It is monitored by local and regional seismic stations of the Hellenic Unified Seismic Network (HUSN). In 2020, a high-yield seismic sequence, lasting over five months, occurred at the Perachora peninsula. This provided a unique opportunity to investigate the anisotropic properties of the upper crust in the area, which lacks relevant studies. The sequence exhibited characteristics of a seismic swarm, with the strongest event having a magnitude of 3.7. In the herein analysis, we use recordings from suitable HUSN stations for two periods: (a) 2008 to 2019, a period of scarce seismicity, to identify background anisotropy and (b) the 2020 seismic swarm period. We used a fully automated method to measure shear-wave splitting properties. After considering a shear-wave window of 45° and several quality criteria, we determined a complex state of anisotropy, with NE-SW directions of polarization (𝜑) prevailing pre-2020, while a dominant WNW-ESE orientation was observed during the swarm (with secondary NE-SW and N-S trends). The spatial distribution of 𝜑 did not offer any strong correlation with local faults. Additionally, 𝜑 seemed to rotate in 2015 and 2020, with variations of normalized time-delays being present during the crisis. These observations, along with indications regarding fluid diffusion during the swarm, led us to hypothesize that shear-wave splitting in the EGoC is mainly driven by high pressure gradients. A better understanding of pre‑2020 seismicity and more local stations to record future seismicity would be required to further specify the connection between fluid processes and seismic anisotropy in the area.

Prehibernation swarming in temperate bats: a critical transition between summer activity and hibernation

In this contribution to Dr. Brock Fenton's Festschrift, we briefly reflect on Dr. Fenton's seminal works examining bat swarming behaviour in Ontario and use these reflections as a launch pad to conduct a global review on autumn swarming in bats, and underlying hypotheses to explain this behaviour. Our review frames the swarming period as a time of critical transitions, during which bats must balance multiple life history trade-offs, and we consider how various intrinsic and extrinsic factors may contribute to inter- and intraspecific differences in autumn behaviour. We discuss the transition away from summer residency, including maternity colony breakup, day roosting, and migration during autumn. We review key life history elements of swarming, including mating behaviours and associated reproductive condition, genetic exchange during swarming, and variation among sexes, ages, and species. Finally, we discuss the behaviours and physiological states of bats transitioning from the swarming period to hibernation. Throughout, we identify common patterns and also exceptions. Over 50 years of research has yielded many insights into autumn swarming, but knowledge gaps remain. Future research focus on a greater diversity of species will reveal general principles underlying the transition from summer active season, through the swarming period, and into winter hibernation.

Comparison of microzooplankton community structure before and during Acromitus flagellatus swarm in the estuarine waters of northern Bay of Bengal

The scyphozoan jellyfish Acromitus flagellatus (Maas, 1903) formed massive aggregations in the River Saptamukhi channel, situated in Sundarbans, the world’s largest deltaic ecosystem. The present study in this mangrove-fringed estuary aims to find the variations in the community structure of microzooplankton (protists and metazoans of 20-200μm size class) before the onset of the swarm and during it. It also briefly documents the trophic cascade exerted by the swarming A. flagellatus on the lower trophic levels. The taxonomic groups representing the microzooplankton community from this study included ciliates, dinoflagellates (heterotrophic and mixotrophic), rotifers, foraminiferans, and metazoan larvae (copepod nauplii, bivalve larvae, gastropod larvae, polychaete larvae). Copepod nauplii dominated the abundance in all stations both before the swarm (BS) and during the swarm (DS). Regarding the species composition of protists, tintinnids dominated the ciliate community, while heterotrophic dinoflagellates dominated the dinoflagellate community, contributing 32% and 30% of protist composition in the BS survey and 37% and 23% of protist composition in the DS survey, respectively. The abundance of another protist group, the planktonic foraminiferans, was very low and was obtained only in the DS survey. In terms of diversity composition and abundance, the microzooplankton community when compared to the BS survey, showed little difference during the A. flagellatus swarming event (DS), except for a few exceptions. Notably, during the swarm period, microzooplankton abundance showed a positive relationship with A. flagellatus numbers, while the mesozooplankton abundance reduced significantly, exhibiting the top-down control by A. flagellatus in the pelagic food web.

Daily, Seasonal and Inter-Annual Variation in Activity Within a Common Pipistrelle Swarming Site and Hibernaculum

Seasonal swarming by bats in underground sites in late summer and early autumn is increasingly understood to play a vital role in their life-cycle, relating both to nuptial activity and to the use of swarming sites as hibernacula. The common pipistrelle (Pipistrellus pipistrellus) is a largely commensal species in which seasonal swarming often occurs in built structures, which have been hypothesised to serve as mass hibernacula during the coldest part of the winter. A number of detailed studies of P. pipistrellus swarming sites have recorded year-round patterns of activity, as well as the demographic make-up of the visiting bats, but there has been relatively little study of overnight patterns of activity, or how swarming interacts with weather conditions at a variety of scales. This study uses auditory monitoring data, recorded continuously over a 27 month period in a P. pipistrellus swarming site within a built structure in northern England, to derive a detailed phenology of bat activity within the site, and uses generalised additive modelling to explain daily variation in activity in terms of seasonal trends modified by fluctuating weather conditions. Results suggest that cool conditions delay the onset of swarming in spring and late summer, and can suppress swarming behaviour even at the height of the swarming period, leading to a pronounced pulse of activity when temperatures rise, and the extension of activity into mid-Autumn. Roosting also occurred at the study site during the swarming period, and was associated with significant flying during the day in warm temperatures, which may reflect a search for cooler roosting locations. Overnight activity occurred throughout the hibernation period, but little evidence emerged for an influx of bats to a mass hibernaculum at the start of the winter.

The effect of a lack of uncapped brood on social interactions between honey bee workers and the queen

Vibro-acoustic communication is used by honey bees in many different social contexts. Our previous research showed that workers interact with their queen outside of the swarming period by means of wing-beating behaviour. Therefore, the aim of this study was to verify the hypothesis that the wing-beating behaviour of workers attending the queen stimulates her to lay eggs. The behaviour of workers and the queen was recorded using a high-speed camera, at first in the presence of uncapped brood in the nest and then without one. None of the queens performed wing-beating behaviour. On the other hand, the workers attending the queen demonstrated this behaviour two times per minute, on average, even in the presence of uncapped brood in the nest. After removing the combs with the uncapped brood, the incidence of wing-beating behaviour increased significantly to an average of four times per minute. Wing-beating behaviour did not differ significantly in its characteristics when uncapped brood was present or absent in the nest. During 3 days after removing the combs with the uncapped brood, there was no significant increase in the rate of egg lying by the queen. Therefore, the results presented here do not convincingly confirm that the wing-beating behaviour of workers affects the rate of queen's egg-lying. This negative result can be related to colony disturbance and longer time required by the queen to increase egg production.

Attempt to Identify Sex Hormones in the Bodies of Selected Norway Spruce Bark Beetles

A gas chromatography technique was applied to the adults of Ips typograhus (L.) and Pityogenes chalcographus (L.) collected from pheromone traps placed in Norway spruce stands in southern Poland in distinguished population swarming periods for the qualitative and quantitative determination of steroid compound differences between insect sexes. Ten not yet identified for bark beetle compounds from the group of sterols, including cholestenone, 4,6-cholestadiene-3-one, choles-4-en-3,6-dione and 17β-Hydroxyandrosta-1,4-dien-3-one benzoate, which can potentially act as gender hormones were detected. The presence of ecdysone and 20-hydroxyecdysone in the bodies of the studied bark beetles was confirmed. However, slight differences in the content of ecdysteroids in the bodies of males and females may be only the remains of the insect’s metamorphosis. Due to the small differences in the extracted compounds between the females and males, their variability in concentrations during the swarming period seems to be useless as a basis for sex determination.

Seasonal Variation in Sex Ratio for Gray Bats (Myotis grisescens) at a Hibernaculum

The federally endangered Myotis grisescens (Gray Bat) is a cave-obligate species that exhibits swarming behavior outside hibernacula in the fall and then emerges in spring after hibernation. Sex ratios of other Myotis are documented to shift at hibernacula from male- to female-dominant in the fall swarming period, and from female- to male-dominant in the spring emergence. We captured Gray Bats during the winter of 2013, fall of 2013 and 2014, and the spring of 2014. Using chi-squared analysis to compare differences among seasons, we document changes in sex ratio for a Gray Bat population at a single large hibernaculum. The sex ratio shifted from male- to female-dominated in the fall of 2013 and 2014 and again in the spring of 2014. During the winter, while Gray Bats are hibernating, we documented a 1:1 ratio. Based on our results, it appears that Gray Bats may exhibit different behavior compared to other Myotis in the spring, possibly linked to being cave obligates.

Sex and Age Variation in the Phenology of a Common Pipistrelle Bat (Pipistrellus pipistrellus) Population in Front of a Hibernaculum

The annual life cycle of temperate bats is typically accompanied by seasonal movements. In autumn, individuals of several species display very active flying behaviour around preferred locations, often hibernacula, a behaviour called swarming. This behaviour is usually characterized by a strong male-biased sex ratio and is often considered to be related to mating. Alternatively, these groupings may be a social behaviour related to the location and quality assessment of hibernacula and may enable this information to be transferred to juveniles, the maternal guidance hypothesis. Our study reports the results of a weekly survey of a bat community in an abandoned mine in Switzerland from April to October 2009, a period longer than the swarming period. The site is characterized by numerous visiting species as well as a high number of common pipistrelle bats displaying autumnal swarming like behaviour at the entrance of the mines. Thirteen species were present at the site with a total of 1,589 individuals of which 1,404 (88%) were common pipistrelle bats allowing us to focus on intersexual and age variations in their arrival phenology. Although the recapture rate was too low to obtain a reliable population size estimator, our data suggest that the site attracts individuals from a large area, possibly from several different nursing colonies and therefore requires a national conservation status. Adult males were present at the site throughout the study period with a peak from mid-July to the end of August. Females arrived later and both sexes displayed a swarming like behaviour in July and August. During this period, the sex ratio was slightly female biased, an unexpected pattern when compared with other swarming species. The absence of a male-biased sex ratio suggests that swarming behaviour in pipistrelle bats may have functions other than mating. Juveniles of both sexes joined the site about two weeks later suggesting that the maternal guidance hypothesis also did not explain this phenology pattern. The number of days between recaptures was greater for males than females indicating that males stay longer or return more often to the sites than females. Further studies may bring insights to the understanding of the function of swarming in pipistrelle bats.

Local Depletion of Click Beetle Populations by Pheromone Traps Is Weather and Species Dependent.

Several Agriotes click beetle species are important pests of vegetables and field crops. Monitoring for beetles is generally done with pheromone-baited traps maintained in permanent locations. Since dispersal is mostly by walking, such traps may deplete populations around them, leading to underestimations of populations relative to nontrapped areas, and of concomitant risk of wireworm damage to nearby crops. We placed sets of five pitfall traps in field headland areas in 2015-2017, of which two were baited with Agriotes obscurus (L) or Agriotes lineatus (L) (Coleoptera: Elateridae) pheromone. Of these, one was maintained in a permanent location, while the other moved among the remaining positions. Traps were checked weekly over the emergence period. For A. obscurus, fixed and moving traps initially collected similar numbers, but the latter collected significantly more later in the season, indicating depletion around fixed traps. Depletion was most pronounced after a period of cold weather, and around the peak swarming period. Depletion observed for A. lineatus was not statistically significant. This indicates pheromone-baited traps used for walking insects can underestimate populations, but depletion rates vary with species and temperature and should be accounted for when traps are used to develop action thresholds or time control strategies.

Phytoplasma infection status survey in plum psyllid (Cacopsylla pruni) population

European Stone Fruit Yellows (ESFY) phytoplasma disease causes an increasing amount of damage. This is especially true to the Gönci growing region. The insect vector of the disease, which has been shown to have a vector role during transmission experiments, is the plum psyllid (Cacopsylla pruni). In 2018, during the swarming period of plum psyllid, in 3 different settlements (Boldogkőváralja, Nagyvárad and Bekecs) 265 psyllidswere collected, from which 165 were plum psyllid. Molecular biology studies showed 106 individuals infected with phytoplasma, of which 20 were males and 86 were females.

Effects of heat on the dispersal performance of Ips typographus

AbstractUnder present climate conditions, Ips typographus (L.) is Europe's most critical disturbance agent for mature Norway spruce (Picea abies). With ongoing climate change, the bark beetle will most probably become more prominent as a pest. The aim of this study was to analyse the dispersal performance of I. typographus under various weather conditions, especially hot days with a maximum air temperature above 30°C. In a field study, marked bark beetles were released from breeding logs and could be retraced in traps distributed across the survey area. With daily collections of the trapped beetles, it was possible to analyse the flight activity and the average flight distance of the bark beetles during hot, moderate and cool days. The numbers of daily catches and the average flight distance during the hottest days (air temperature maximum ≥30°C) did not significantly differ from the moderate days (air temperature maximum ≥22°C and <30°C). The numbers of daily catches and the average flight distance during the cool days (air temperature maximum <22°C) were significantly lower than during hot and moderate days. The results give an insight on the dispersal capacity of I. typographus under climate change driven future conditions. Increased air temperatures do not seem to impair the flight performance of I. typographus. A small proportion of cool days during the swarming period even seems to favour dispersal of I. typographus.

Geomagnetic secular variation changes in Southern Africa during the SWARM period 2013 - 2018

Geomagnetic field observations from 4 magnetic observatories located in Southern Africa located at Hermanus (HER), Hartebeesthoek (HBK), Keetmanshoop (KMH) and Tsumeb (TSU) have been analysed with the main purpose to identify abrupt secular variation changes on time scales of less than 1 year. Removal of an annual variation resulting from large-scale magnetospheric and ionospheric currents by means of 12-month differences of the respective observatory monthly mean of northward component X, eastward component Y and vertical component Z, revealed clear evidence of several geomagnetic secular variation changes that took place in this region during the period between 2013 and 2018. The geomagnetic field model CHAOS6-x7, based exclusively on SWARM satellite and magnetic observatory data during this period, has been used to determine secular acceleration patterns across Southern Africa. The results obtained revealed that the observed secular variation changes took place over a range of strengths in the respective X, Y and Z components at every magnetic observatory. In addition, the respective observatories in the region also exhibited strong individual characteristics. The findings in this investigation show once again that the southern African region is characterised by unpredictable abrupt geomagnetic secular variation changes that have the potential to render linear prediction models less accurate.

Phyllophaga nitididorsis (Coleoptera: Melolonthidae), the first biennial melolonthid recorded in the Brazilian Cerrado

AbstractPhyllophaga nitididorsis Frey, a species native to Brazil, has recently been recorded as a soil pest in soybean Glycine max (L.) Merr. fields in the north‐west region of Minas Gerais (MG), Brazil. Our study aimed to evaluate the phenology of P. nitididorsis in the Cerrado of Central Brazil. The study was conducted in a field (≈300 ha) in Buritis/MG where soybean is sown in October (spring) annually. Monthly (December 2012–November 2014) samples were collected by opening trenches (50 cm × 50 cm and 30 cm in depth), recording the developmental phases of all P. nitididorsis found. Specimens collected from the field were maintained in the laboratory at 25 (±2 °C), and their development was recorded at weekly intervals. Light traps were installed in the states of Minas Gerais, Goiás (GO), and the Federal District (DF) to verify species distribution. P. nitididorsis exhibited a biennial life cycle that lasted approximately 22 months, from egg to inactive adult, and 24 months from egg until the emergence of active adults. Eggs were found in the soil in November. The larval stage lasted about 20 months (≈607 days). Second‐instar and third‐instar larvae constructed chambers in the soil to overwinter during the dry season (March to September) during the first and second years of development, respectively. Pre‐pupae were observed between July and August and pupae between July and September. Inactive adults occurred in August and September, and the swarming period was between October and November. Adult P. nitididorsis were caught in all of the States where light traps were operated. The active phases of the insect (larvae and adults) were synchronised with soybean cultivation and the rainy season (October and March) in the Cerrado. To the best of our knowledge, our study is the first to report P. nitididorsis in the states of Goiás and the Federal District. Further, this species is the first biennial melolonthid observed in the Brazilian Cerrado.

Bats of the medieval Jeroným mine (western Bohemia, Czech Republic): results of a long-term monitoring in the hibernation and swarming periods (Chiroptera)

The medieval mine of Jeroným (Jerome) is one of the most important bat localities known in western Bohemia. Ten bat species have been detected there, including Myotis emarginatus which is very rare in the western part of the Czech Republic. Numbers of wintering bats have been monitored since 1995 and show an upward trend there, even after the opening of a part of the mine to the public during summer (since 2014). The highest numbers of wintering bats correspond to unusually cold winters in 2017 (347 inds.) and 2013 (156 inds.). Mistnetting during the swarming period has been carried out annually since 2009. Numbers of netted bats have been decreasing, probably due to the existence of a new visitor centre built near the entrance to the underground. Species compositions recorded during the hibernation and swarming periods are very similar, but proportions of particular species are different. Myotis daubentonii, M. myotis and M. nattereri were the most abundant bat species during hibernation, while Myotis nattereri, M. daubentonii and Plecotus auritus during the swarming period. Swarming numbers of Myotis mystacinus and M. brandtii have been growing in the last several years. Myotis bechsteinii was detected repeatedly, while Eptesicus nilssonii and Myotis emarginatus (wintering) and Nyctalus noctula (swarming) only once each. The swarming activity of bats was highest 2.5–5.5 hours after sunset. In total, 436 bats were ringed, about 6% of them were recaptured at the site. Some of the ringed bats were recorded at other localities, Myotis myotis at distances up to 39 km, and M. nattereri up to 21 km.

How climate influences the biology and behaviour of Phyllophaga capillata (Coleoptera: Melolonthidae) in the Brazilian Cerrado

AbstractPhyllophaga capillata (Blanchard) is the most important soil pest in soybean crops in Central Brazil (Federal District and Goiás state). The objective of this work was to study the bio‐ecology of P. capillata in the field in the Cerrado of Central Brazil, relating its biology and behaviour to the climatic characteristics of this biome. The study was conducted over three years in a soybean [Glycine max (L.) Merr.] production area (≈6000 ha) in the Federal District. Field samplings were taken to observe the biological stages of P. capillata, preferred oviposition sites and the adult swarming period. Phyllophaga capillata presented an univoltine cycle that lasted about 10 months of egg to inactive adults, and 12 months until the appearance of active adults. Eggs were found in the field in October and November. The larval stage occurred between November and June. Pre‐pupae were observed in June and the pupae between July and August. Inactive adults were observed in August and September, and the swarming period was between September and December. Females preferred to oviposit in sites with taller plants. This species synchronises its active phases (larvae and active adults) with soybean cultivation and the rainy season (October/March) in the Brazilian Cerrado. Alternatives for pest management based on their bio‐ecological characteristics are presented.

Swarm of Tintinnopsis uruguayensis in the estuarine waters of Kochi, Southwest coast of India

Microzooplankton play an important connecting role in the aquatic food webs. During our bimonthly time series observation on microzooplankton ecology and dynamics in the estuarine waters of Kochi, Southwest coast of India, dense swarming of Tintinnopsis uruguayensis was noticed. The contribution of T. uruguayensis during the swarm period was 98.4% of the total microzooplankton density. The swarming of T. uruguayensis during the postmonsoon (November 2015) could be related to the higher concentrations of food supply. The results demonstrate a statistically significant positive relationship between the swarm of T. uruguayensis and the small centric diatom Thalassiosira decipiens. Our observation suggest that the increase of Thalassiosira decipiens contributed to the proliferation of T. uruguayensis.