Measurement of the threshold sensitivity of honeybees to weak, extremely low-frequency magnetic fields

Non-contact exposure to dinotefuran disrupts honey bee homing by altering MagR and Cry2 gene expression

Dinotefuran is known to negatively affect honeybee (Apis mellifera) behavior, but the underlying mechanism remains unclear. The magnetoreceptor (MagR, which responds to magnetic fields) and cryptochrome (Cry2, which is sensitive to light) genes are considered to play important roles in honey bees' homing and localization behaviors. Our study found that dinotefuran, even without direct contact, can act like a magnet, significantly altering MagR expression in honeybees. This non-contact exposure reduced the bees' homing rate. In further experiments, we exposed foragers to light and magnetic fields, the MagR gene responded to magnetic fields only in the presence of light, with Cry2 playing a key switching role in the magnetic field receptor mechanism (MagR-Cry2). Yeast two-hybrid and BiFc assays confirmed an interaction of these two genes. Moreover, the bees' homing rate was significantly reduced when the expression of these genes was decreased using RNAi. These findings suggest that changes in MagR and Cry2 expression are critical to the reduction in homing ability caused by non-contact dinotefuran exposure. This study reveals the potential navigation mechanisms of honey bees during homing and foraging and shows that the impact of dinotefuran on honey bee populations is more extensive than previously understood.

An experimental study on the effect of non-ionizing electromagnetic fields on honey bees

Due to the increase in data rate in mobile communication and the widespread use of mobile internet, electromagnetic communication systems are increasing daily. This situation causes increases in the use of more mobile communication devices and environmental non-ionizing Electromagnetic Field (EMF) levels. The rise of bee deaths and colony losses in beekeeping parallel to the increase of the EMF sources cause the concept of "electromagnetic pollution" to be considered among the reasons. Therefore, studying the effects of non-ionizing Electromagnetic Radiation (EMR) on the health of living things is one of the most significant issues today. The bees determine their direction with the Earth's magnetic field. Electromagnetic signals emitted by GSM base stations, etc. may affect the direction-finding capabilities of honey bees and constitute a stress factor. In this study, the aim was to determine the effect of EMF on honey bees and honey yield. Honey bee colonies were used, obtained from the same farm in the Trabzon region, and equalized in all respects. Moreover, these colonies were divided into five groups randomly as experiments and control groups. The experiment hives were exposed to the EMF in the frequency band of the Wi-Fi signals (2.4 GHz) and the high-voltage line (50 hz). The control hives are located far away from the EMR sources. The study was repeated in the second year to confirm the results. During the investigation, some physiological and behavioural effects of bees, such as aggressiveness, brood area, etc. were determined based on EMR exposure.

Biological Effects of Magnetic Storms and ELF Magnetic Fields

Magnetic fields are a constant and essential part of our environment. The main components of ambient magnetic fields are the constant part of the geomagnetic field, its fluctuations caused by magnetic storms, and man-made magnetic fields. These fields refer to extremely-low-frequency (<1 kHz) magnetic fields (ELF-MFs). Since the 1980s, a huge amount of data has been accumulated on the biological effects of magnetic fields, in particular ELF-MFs. However, a unified picture of the patterns of action of magnetic fields has not been formed. Even though a unified mechanism has not yet been generally accepted, several theories have been proposed. In this review, we attempted to take a new approach to analyzing the quantitative data on the effects of ELF-MFs to identify new potential areas for research. This review provides general descriptions of the main effects of magnetic storms and anthropogenic fields on living organisms (molecular-cellular level and whole organism) and a brief description of the main mechanisms of magnetic field effects on living organisms. This review may be of interest to specialists in the fields of biology, physics, medicine, and other interdisciplinary areas.

Biological Effects of Electric, Magnetic, and Electromagnetic Fields from 0 to 100 MHz on Fauna and Flora: Workshop Report

ABSTRACT

This report summarizes effects of anthropogenic electric, magnetic, and electromagnetic fields in the frequency range from 0 to 100 MHz on flora and fauna, as presented at an international workshop held on 5-7 November in 2019 in Munich, Germany. Such fields may originate from overhead powerlines, earth or sea cables, and from wireless charging systems. Animals and plants react differentially to anthropogenic fields; the mechanisms underlying these responses are still researched actively. Radical pairs and magnetite are discussed mechanisms of magnetoreception in insects, birds, and mammals. Moreover, several insects as well as marine species possess specialized electroreceptors, and behavioral reactions to anthropogenic fields have been reported. Plants react to experimental modifications of their magnetic environment by growth changes. Strong adverse effects of anthropogenic fields have not been described, but knowledge gaps were identified; further studies, aiming at the identification of the interaction mechanisms and the ecological consequences, are recommended.

Low-level EMF effects on wildlife and plants: What research tells us about an ecosystem approach

There is enough evidence to indicate we may be damaging non-human species at ecosystem and biosphere levels across all taxa from rising background levels of anthropogenic non-ionizing electromagnetic fields (EMF) from 0 Hz to 300 GHz. The focus of this Perspective paper is on the unique physiology of non-human species, their extraordinary sensitivity to both natural and anthropogenic EMF, and the likelihood that artificial EMF in the static, extremely low frequency (ELF) and radiofrequency (RF) ranges of the non-ionizing electromagnetic spectrum are capable at very low intensities of adversely affecting both fauna and flora in all species studied. Any existing exposure standards are for humans only; wildlife is unprotected, including within the safety margins of existing guidelines, which are inappropriate for trans-species sensitivities and different non-human physiology. Mechanistic, genotoxic, and potential ecosystem effects are discussed.

Effects of non-ionizing electromagnetic fields on flora and fauna, Part 2 impacts: how species interact with natural and man-made EMF

Ambient levels of nonionizing electromagnetic fields (EMF) have risen sharply in the last five decades to become a ubiquitous, continuous, biologically active environmental pollutant, even in rural and remote areas. Many species of flora and fauna, because of unique physiologies and habitats, are sensitive to exogenous EMF in ways that surpass human reactivity. This can lead to complex endogenous reactions that are highly variable, largely unseen, and a possible contributing factor in species extinctions, sometimes localized. Non-human magnetoreception mechanisms are explored. Numerous studies across all frequencies and taxa indicate that current low-level anthropogenic EMF can have myriad adverse and synergistic effects, including on orientation and migration, food finding, reproduction, mating, nest and den building, territorial maintenance and defense, and on vitality, longevity and survivorship itself. Effects have been observed in mammals such as bats, cervids, cetaceans, and pinnipeds among others, and on birds, insects, amphibians, reptiles, microbes and many species of flora. Cyto- and geno-toxic effects have long been observed in laboratory research on animal models that can be extrapolated to wildlife. Unusual multi-system mechanisms can come into play with non-human species - including in aquatic environments - that rely on the Earth's natural geomagnetic fields for critical life-sustaining information. Part 2 of this 3-part series includes four online supplement tables of effects seen in animals from both ELF and RFR at vanishingly low intensities. Taken as a whole, this indicates enough information to raise concerns about ambient exposures to nonionizing radiation at ecosystem levels. Wildlife loss is often unseen and undocumented until tipping points are reached. It is time to recognize ambient EMF as a novel form of pollution and develop rules at regulatory agencies that designate air as 'habitat' so EMF can be regulated like other pollutants. Long-term chronic low-level EMF exposure standards, which do not now exist, should be set accordingly for wildlife, and environmental laws should be strictly enforced - a subject explored in Part 3.

Extremely Low-Frequency Electromagnetic Field Impairs the Development of Honeybee (Apis cerana)

Simple Summary

The ELF-EMF pollution generated by the increase in electrically powered devices and power lines, accompanied by economic development, has a widespread effect on surrounding organisms. Honeybees are one of the most important pollinators. The decline in the honeybee population caused by a variety factors, including EMFs, has attracted attention worldwide. It was already known that ELF-EMFs could impair the ability of learning and cognition, causing foraging bees to lose their ability to find their way home. The pollination ability of foraging bees is derived from the rearing quantity of larvae and continuous eclosion of new adult bees in the colony. However, the effect of ELF-EMFs on honeybee larvae is not clear. The aims and objectives of this study were therefore to investigate it. The results showed that ELF-EMF exposure decreases honeybee survival rate and body weight and extends the duration of development time. Transcriptome sequencing showed that ELF-EMF exposure decreases the biological process of nutrient and energy metabolism, impedes the degradation of larvae tissues and the rebuilding of pupae tissues in the metamorphosis process, and seriously interferes with the growth and development of honeybee larvae. This provides an experimental basis and new perspective for protecting honeybee populations from ELF-EMF pollution.

Abstract

Increasing ELF-EMF pollution in the surrounding environment could impair the cognition and learning ability of honeybees, posing a threat to the honeybee population and its pollination ability. In a social honeybee colony, the numbers of adult bees rely on the successful large-scale rearing of larvae and continuous eclosion of new adult bees. However, no studies exist on the influence of ELF-EMFs on honeybee larvae. Therefore, we investigated the survival rate, body weight, and developmental duration of first instar larvae continuously subjected to ELF-EMF exposure. Moreover, the transcriptome of fifth instar larvae were sequenced for analyzing the difference in expressed genes. The results showed that ELF-EMF exposure decreases the survival rate and body weight of both white-eye pupae and newly emerged adults, extends the duration of development time and seriously interferes with the process of metamorphosis and pupation. The transcriptome sequencing showed that ELF-EMF exposure decreases the nutrient and energy metabolism and impedes the degradation of larvae tissues and rebuilding of pupae tissues in the metamorphosis process. The results provide an experimental basis and a new perspective for the protection of honeybee populations from ELF-EMF pollution.

A Transmissive Theory of Brain Function: Implications for Health, Disease, and Consciousness

Identifying a complete, accurate model of brain function would allow neuroscientists and clinicians to make powerful neuropsychological predictions and diagnoses as well as develop more effective treatments to mitigate or reverse neuropathology. The productive model of brain function, which has been dominant in the field for centuries, cannot easily accommodate some higher-order neural processes associated with consciousness and other neuropsychological phenomena. However, in recent years, it has become increasingly evident that the brain is highly receptive to and readily emits electromagnetic (EM) fields and light. Indeed, brain tissues can generate endogenous, complex EM fields and ultraweak photon emissions (UPEs) within the visible and near-visible EM spectra. EM-based neural mechanisms, such as ephaptic coupling and non-visual optical brain signaling, expand canonical neural signaling modalities and are beginning to disrupt conventional models of brain function. Here, we present an evidence-based argument for the existence of brain processes that are caused by the transmission of extracerebral, EM signals and recommend experimental strategies with which to test the hypothesis. We argue for a synthesis of productive and transmissive models of brain function and discuss implications for the study of consciousness, brain health, and disease.

Effects of non-ionizing electromagnetic fields on flora and fauna, part 1. Rising ambient EMF levels in the environment

Ambient levels of electromagnetic fields (EMF) have risen sharply in the last 80 years, creating a novel energetic exposure that previously did not exist. Most recent decades have seen exponential increases in nearly all environments, including rural/remote areas and lower atmospheric regions. Because of unique physiologies, some species of flora and fauna are sensitive to exogenous EMF in ways that may surpass human reactivity. There is limited, but comprehensive, baseline data in the U.S. from the 1980s against which to compare significant new surveys from different countries. This now provides broader and more precise data on potential transient and chronic exposures to wildlife and habitats. Biological effects have been seen broadly across all taxa and frequencies at vanishingly low intensities comparable to today's ambient exposures. Broad wildlife effects have been seen on orientation and migration, food finding, reproduction, mating, nest and den building, territorial maintenance and defense, and longevity and survivorship. Cyto- and geno-toxic effects have been observed. The above issues are explored in three consecutive parts: Part 1 questions today's ambient EMF capabilities to adversely affect wildlife, with more urgency regarding 5G technologies. Part 2 explores natural and man-made fields, animal magnetoreception mechanisms, and pertinent studies to all wildlife kingdoms. Part 3 examines current exposure standards, applicable laws, and future directions. It is time to recognize ambient EMF as a novel form of pollution and develop rules at regulatory agencies that designate air as 'habitat' so EMF can be regulated like other pollutants. Wildlife loss is often unseen and undocumented until tipping points are reached. Long-term chronic low-level EMF exposure standards, which do not now exist, should be set accordingly for wildlife, and environmental laws should be strictly enforced.

Long-term inhibition of ferritin2 synthesis in trophocytes and oenocytes by ferritin2 double-stranded RNA ingestion to investigate the mechanisms of magnetoreception in honey bees (Apis mellifera)

Behavioral studies indicate that honey bees (Apis mellifera) have a capacity for magnetoreception and superparamagnetic magnetite is suggested to be a magnetoreceptor. The long-term inhibition of magnetite formation can be employed to explore the bee's magnetoreception. A recent study shows that magnetite formation, ferritin2 messenger RNA (mRNA) expression, and the protein synthesis of ferritin2 in trophocytes and oenocytes were all inhibited by a single injection of ferritin2 double-stranded RNA (dsRNA) into the hemolymph of honey bees but how to maintain this knockdown of ferritin2 for the long-term is unknown. In this study, we injected ferritin2 dsRNA into the hemolymph of worker bees three times every six days to maintain long-term inhibition; however, multi-microinjections accelerated the death of the bees. To overcome this problem, we further reared newly emerged worker bees daily with ferritin2 dsRNA throughout their lives, demonstrating no impact on their lifespans. Follow-up assays showed that the mRNA expression and protein synthesis of ferritin2 were persistently inhibited. These findings verified that daily ferritin2 dsRNA ingestion not only displays the long-term inhibition of mRNA expression and protein synthesis of ferritin2, but also did not damage the bees. This method of long-term inhibition can be used in behavioral studies of magnetoreception in honey bees.

Numerical tests of magnetoreception models assisted with behavioral experiments on American cockroaches

Many animals display sensitivity to external magnetic field, but it is only in the simplest organisms that the sensing mechanism is understood. Here we report on behavioural experiments where American cockroaches (Periplaneta americana) were subjected to periodically rotated external magnetic fields with a period of 10 min. The insects show increased activity when placed in a periodically rotated Earth-strength field, whereas this effect is diminished in a twelve times stronger periodically rotated field. We analyse established models of magnetoreception, the magnetite model and the radical pair model, in light of this adaptation result. A broad class of magnetite models, based on single-domain particles found in insects and assumption that better alignment of magnetic grains towards the external field yields better sensing and higher insect activity, is shown to be excluded by the measured data. The radical-pair model explains the data if we assume that contrast in the chemical yield on the order of one in a thousand is perceivable by the animal, and that there also exists a threshold value for detection, attained in an Earth-strength field but not in the stronger field.

Extremely Low-Frequency Electromagnetic Fields Entrain Locust Wingbeats

Extremely low-frequency electromagnetic fields (ELF EMFs) have been shown to impact the behavior and physiology of insects. Recent studies have highlighted the need for more research to determine more specifically how they affect flying insects. Here, we ask how locust flight is affected by acute exposure to 50 Hz EMFs. We analyzed the flights of individual locusts tethered between a pair of copper wire coils generating EMFs of various frequency using high-speed video recording. The mean wingbeat frequency of tethered locusts was 18.92 ± 0.27 Hz. We found that acute exposure to 50 Hz EMFs significantly increased absolute change in wingbeat frequency in a field strength-dependent manner, with greater field strengths causing greater changes in wingbeat frequency. The effect of EMFs on wingbeat frequency depended on the initial wingbeat frequency of a locust, with locusts flying at a frequency lower than 20 Hz increasing their wingbeat frequency, while locusts flying with a wingbeat frequency higher than 20 Hz decreasing their wingbeat frequency. During the application of 50 Hz EMF, the wingbeat frequency was entrained to a 2:5 ratio (two wingbeat cycles to five EMF cycles) of the applied EMF. We then applied a range of ELF EMFs that were close to normal wingbeat frequency and found that locusts entrained to the exact frequency of the applied EMF. These results show that exposure to ELF EMFs lead to small but significant changes in wingbeat frequency in locusts. We discuss the biological implications of the coordination of insect flight in response to electromagnetic stimuli. © 2021 Bioelectromagnetics Society.

Possible Mechanism for Synchronized Detection of Weak Magnetic Fields by Nerve Cells

We propose that biological systems may detect static and slowly varying magnetic fields by the modification of the timing of firing of adjacent nerve cells through the local influence of the magnetic field generated by current from one cell's firing on its nearest neighbors. The time delay of an adjacent nerve cell pulse with respect to the initial clock nerve cell pulse could serve as a signal for sensing the magnitude and direction of the magnetic field in a direction perpendicular to the current flows in the cells. It has been shown that changes in static magnetic fields modify concentrations of reactive oxygen species, calcium, pH, the growth rates of fibrosarcoma cells, and membrane potentials. These are linked to changes in membrane potentials that can either inhibit or accelerate the firing rate of pacemaker or clock cells. This mechanism may have applications to animals' use of magnetic fields for navigation or other purposes, possibly in conjunction with other mechanisms. Bioelectromagnetics. © 2020 Bioelectromagnetics Society.

Ferritin RNA interference inhibits the formation of iron granules in the trophocytes of worker honey bees (Apis mellifera)

Iron granules containing superparamagnetic magnetite act as magnetoreceptor for magnetoreception in honey bees. Biomineralization of iron granules occurs in the iron deposition vesicles of trophocytes and requires the participation of actin, myosin, ferritin2, and ATP synthase. The mechanism of magnetoreception in honey bees can be explored by suppressing the formation of iron granules. Toward this goal, we injected double-stranded RNA of ferritin2 and ferritin1 into newly emerged worker honey bees to knock down these genes via RNA interference. We confirmed that mRNA and protein production of the ferritins was inhibited, leading to immature iron granules. Downregulating ferritin2 and ferritin1, moreover, leads to different deposition morphology of 7.5-nm diameter iron particles, indicating that the two genes play different roles in the formation of iron granules in worker honey bees.

Reanalysis of an oft-cited paper on honeybee magnetoreception reveals random behavior

While mounting evidence indicates that a phylogenetically diverse group of animals detect Earth-strength magnetic fields, a magnetoreceptor has not been identified in any animal. One possible reason that identifying a magnetoreceptor has proven challenging is that, like many research fields, magnetoreception research lacks extensive independent replication. Independent replication is important because a subset of studies undoubtedly contain false positive results and without replication it is difficult to determine whether the outcome of an experiment is a false positive. However, we report here a reanalysis of a well-cited paper on honeybee magnetoreception demonstrating that the original paper represented a false positive finding caused by incorrect estimates of probability. We also point out how good experimental design practices could have revealed the error prior to publication. Hopefully, this reanalysis will serve as a reminder of the importance of good experimental design in order to reduce the likelihood of publishing false positive results.

Extremely Low Frequency Electromagnetic Fields impair the Cognitive and Motor Abilities of Honey Bees

Extremely low frequency electromagnetic field (ELF EMF) pollution from overhead powerlines is known to cause biological effects across many phyla, but these effects are poorly understood. Honey bees are important pollinators across the globe and due to their foraging flights are exposed to relatively high levels of ELF EMF in proximity to powerlines. Here we ask how acute exposure to 50 Hz ELF EMFs at levels ranging from 20–100 µT, found at ground level below powerline conductors, to 1000–7000 µT, found within 1 m of the conductors, affects honey bee olfactory learning, flight, foraging activity and feeding. ELF EMF exposure was found to reduce learning, alter flight dynamics, reduce the success of foraging flights towards food sources, and feeding. The results suggest that 50 Hz ELF EMFs emitted from powerlines may represent a prominent environmental stressor for honey bees, with the potential to impact on their cognitive and motor abilities, which could in turn reduce their ability to pollinate crops.

In-vivo biomagnetic characterisation of the American cockroach

We present a quantitative method, utilising a highly sensitive quantum sensor, that extends applicability of magnetorelaxometry to biological samples at physiological temperature. The observed magnetic fields allow for non-invasive determination of physical properties of magnetic materials and their surrounding environment inside the specimen. The method is applied to American cockroaches and reveals magnetic deposits with strikingly different behaviour in alive and dead insects. We discuss consequences of this finding to cockroach magneto-reception. To our knowledge, this work represents the first characterisation of the magnetisation dynamics in live insects and helps to connect results from behavioural experiments on insects in magnetic fields with characterisation of magnetic materials in their corpses.

Linking magnetite in the abdomen of honey bees to a magnetoreceptive function

Previous studies of magnetoreception in honey bees, Apis mellifera, focused on the identification of magnetic material, its formation, the location of the receptor and potential underlying sensory mechanisms, but never directly linked magnetic material to a magnetoreceptive function. In our study, we demonstrate that ferromagnetic material consistent with magnetite plays an integral role in the bees' magnetoreceptor. Subjecting lyophilized and pelletized bee tagmata to analyses by a superconducting quantum interference device generated a distinct hysteresis loop for the abdomen but not for the thorax or the head of bees, indicating the presence of ferromagnetic material in the bee abdomen. Magnetic remanence of abdomen pellets produced from bees that were, or were not, exposed to the 2.2-kOe field of a magnet while alive differed, indicating that magnet exposure altered the magnetization of this magnetite in live bees. In behavioural two-choice field experiments, bees briefly exposed to the same magnet, but not sham-treated control bees, failed to sense a custom-generated magnetic anomaly, indicating that magnet exposure had rendered the bees' magnetoreceptor dysfunctional. Our data support the conclusion that honey bees possess a magnetite-based magnetoreceptor located in the abdomen.

Magnetic Sensing through the Abdomen of the Honey bee

Honey bees have the ability to detect the Earth’s magnetic field, and the suspected magnetoreceptors are the iron granules in the abdomens of the bees. To identify the sensing route of honey bee magnetoreception, we conducted a classical conditioning experiment in which the responses of the proboscis extension reflex (PER) were monitored. Honey bees were successfully trained to associate the magnetic stimulus with a sucrose reward after two days of training. When the neural connection of the ventral nerve cord (VNC) between the abdomen and the thorax was cut, the honey bees no longer associated the magnetic stimulus with the sucrose reward but still responded to an olfactory PER task. The neural responses elicited in response to the change of magnetic field were also recorded at the VNC. Our results suggest that the honey bee is a new model animal for the investigation of magnetite-based magnetoreception.

The Effect of Extremely Low Frequency Alternating Magnetic Field on the Behavior of Animals in the Presence of the Geomagnetic Field

It is known that the geomagnetic field can influence animal migration and homing. The magnetic field detection by animals is known as magnetoreception and it is possible due to two different transduction mechanisms: the first one through magnetic nanoparticles able to respond to the geomagnetic field and the second one through chemical reactions influenced by magnetic fields. Another behavior is the magnetic alignment where animals align their bodies to the geomagnetic field. It has been observed that magnetic alignment of cattle can be disrupted near electric power lines around the world. Experimentally, it is known that alternating magnetic fields can influence living beings, but the exact mechanism is unknown. The parametric resonance model proposes a mechanism to explain that effect on living beings and establishes that, in the presence of a constant magnetic field, molecules associated with biochemical reactions inside cells can absorb resonantly alternating magnetic fields with specific frequencies. In the present paper, a review is made about animal magnetoreception and the effects of alternating magnetic fields in living beings. It is suggested how alternating magnetic fields can interfere in the magnetic alignment of animals and a general conclusion is obtained: alternating magnetic field pollution can affect the magnetic sensibility of animals.

Does the Earth's magnetic field serve as a reference for alignment of the honeybee Waggle dance?

The honeybee (Apis mellifera) waggle dance, which is performed inside the hive by forager bees, informs hive mates about a potent food source, and recruits them to its location. It consists of a repeated figure-8 pattern: two oppositely directed turns interspersed by a short straight segment, the "waggle run". The waggle run consists of a single stride emphasized by lateral waggling motions of the abdomen. Directional information pointing to a food source relative to the sun's azimuth is encoded in the angle between the waggle run line and a reference line, which is generally thought to be established by gravity. Yet, there is tantalizing evidence that the local (ambient) geomagnetic field (LGMF) could play a role. We tested the effect of the LGMF on the recruitment success of forager bees by placing observation hives inside large Helmholtz coils, and then either reducing the LGMF to 2% or shifting its apparent declination. Neither of these treatments reduced the number of nest mates that waggle dancing forager bees recruited to a feeding station located 200 m north of the hive. These results indicate that the LGMF does not act as the reference for the alignment of waggle-dancing bees.

Detection of magnetic field intensity gradient by homing pigeons (Columba livia) in a novel "virtual magnetic map" conditioning paradigm

It has long been thought that birds may use the Earth's magnetic field not only as a compass for direction finding, but that it could also provide spatial information for position determination analogous to a map during navigation. Since magnetic field intensity varies systematically with latitude and theoretically could also provide longitudinal information during position determination, birds using a magnetic map should be able to discriminate magnetic field intensity cues in the laboratory. Here we demonstrate a novel behavioural paradigm requiring homing pigeons to identify the direction of a magnetic field intensity gradient in a “virtual magnetic map” during a spatial conditioning task. Not only were the pigeons able to detect the direction of the intensity gradient, but they were even able to discriminate upward versus downward movement on the gradient by differentiating between increasing and decreasing intensity values. Furthermore, the pigeons typically spent more than half of the 15 second sampling period in front of the feeder associated with the rewarded gradient direction indicating that they required only several seconds to make the correct choice. Our results therefore demonstrate for the first time that pigeons not only can detect the presence and absence of magnetic anomalies, as previous studies had shown, but are even able to detect and respond to changes in magnetic field intensity alone, including the directionality of such changes, in the context of spatial orientation within an experimental arena. This opens up the possibility for systematic and detailed studies of how pigeons could use magnetic intensity cues during position determination as well as how intensity is perceived and where it is processed in the brain.

Magnetoreception in laboratory mice: sensitivity to extremely low-frequency fields exceeds 33 nT at 30 Hz

Magnetoreception in the animal kingdom has focused primarily on behavioural responses to the static geomagnetic field and the slow changes in its magnitude and direction as animals navigate/migrate. There has been relatively little attention given to the possibility that weak extremely low-frequency magnetic fields (wELFMF) may affect animal behaviour. Previously, we showed that changes in nociception under an ambient magnetic field-shielded environment may be a good alternative biological endpoint to orientation measurements for investigations into magnetoreception. Here we show that nociception in mice is altered by a 30 Hz field with a peak amplitude more than 1000 times weaker than the static component of the geomagnetic field. When mice are exposed to an ambient magnetic field-shielded environment 1 h a day for five consecutive days, a strong analgesic (i.e. antinociception) response is induced by day 5. Introduction of a static field with an average magnitude of 44 µT (spatial variability of ±3 µT) marginally affects this response, whereas introduction of a 30 Hz time-varying field as weak as 33 nT has a strong effect, reducing the analgesic effect by 60 per cent. Such sensitivity is surprisingly high. Any purported detection mechanisms being considered will need to explain effects at such wELFMF.

How do honeybees use their magnetic compass? Can they see the North?

While seeking food sources and routes back to their hive, bees make use of their advanced nervous and sensory capacities, which underlie a diverse behavioral repertoire. One of several honeybee senses that is both exceptional and intriguing is magnetoreception - the ability to perceive the omnipresent magnetic field (MF) of the Earth. The mechanism by which animals sense MFs has remained fascinating as well as elusive because of the intricacies involved, which makes it one of the grand challenges for neural and sensory biology. However, investigations in recent years have brought substantial progress to our understanding of how such magneto-receptor(s) may work. Some terrestrial animals (birds) are reported to be equipped even with a dual perception system: one based on diminutive magnetic particles - in line with the original model which has also always been hypothesized for bees - and the other one, as the more recent model describes, based on a sensitivity of some photochemical reactions to MF (radical-pair or chemical mechanism). The latter model postulates a close link to vision and supposes that the animals can see the position of the geomagnetic North as a visible pattern superimposed on the picture of the environment. In recent years, a growing body of evidence has shown that radical-pair magnetoreception might also be used by insects. It is realistic to expect that such evidence will inspire a re-examination and extension or confirmation of established views on the honeybee magnetic-compass mechanism. However, the problem of bee magnetoreception will not be solved at the moment that a receptor is discovered. On the contrary, the meaning of magnetoreception in insect life and its involvement in the orchestration of other senses is yet to be fully understood. The crucial question to be addressed in the near future is whether the compass abilities of the honeybee could suffer from radio frequency (RF) smog accompanying modern civilization and whether the fitness of this dominant pollinator might be affected by RF fields. The goal of this review is to provide an overview of the path that the behavioral research on honeybee magnetoreception has taken and to discuss it in the context of contemporary data obtained on other insects.

Magnetic characterization of isolated candidate vertebrate magnetoreceptor cells

Over the past 50 y, behavioral experiments have produced a large body of evidence for the existence of a magnetic sense in a wide range of animals. However, the underlying sensory physiology remains poorly understood due to the elusiveness of the magnetosensory structures. Here we present an effective method for isolating and characterizing potential magnetite-based magnetoreceptor cells. In essence, a rotating magnetic field is employed to visually identify, within a dissociated tissue preparation, cells that contain magnetic material by their rotational behavior. As a tissue of choice, we selected trout olfactory epithelium that has been previously suggested to host candidate magnetoreceptor cells. We were able to reproducibly detect magnetic cells and to determine their magnetic dipole moment. The obtained values (4 to 100 fAm(2)) greatly exceed previous estimates (0.5 fAm(2)). The magnetism of the cells is due to a μm-sized intracellular structure of iron-rich crystals, most likely single-domain magnetite. In confocal reflectance imaging, these produce bright reflective spots close to the cell membrane. The magnetic inclusions are found to be firmly coupled to the cell membrane, enabling a direct transduction of mechanical stress produced by magnetic torque acting on the cellular dipole in situ. Our results show that the magnetically identified cells clearly meet the physical requirements for a magnetoreceptor capable of rapidly detecting small changes in the external magnetic field. This would also explain interference of ac powerline magnetic fields with magnetoreception, as reported in cattle.

Assessment of toxicity of nanoparticles using insects as biological models

Nanomaterials have become increasingly important in medicine, manufacturing, and consumer products. The fundamental understanding in effects of nanoparticles (NPs) on and their interactions with biomolecules and organismal systems have yet to be achieved. In this chapter, we firstly provide a brief review of the interactions between nanoparticles and biological systems. We will then provide an example by describing a novel method to assess the effects of NPs on biological systems, using insects as a model. Nanoparticles were injected into the central nervous system of the discoid cockroach (Blaberus discoidalis). It was found that insects became hyperactive compared to negative control (water injections). Our method could provide a generic method of assessing nanoparticles toxicity.

The effects of acute exposure to magnetic fields on morphometric characteristics of bombyxin-producing neurosecretory neurons in gypsy moth caterpillars

PURPOSE

To examine the effects of acute exposure to strong static magnetic fields and extremely low frequency magnetic fields, on neurosecretory neurons which synthesise insulin-like neurohormone.

MATERIALS AND METHODS

Immunocytochemical detection of bombyxin-like material in the protocerebral neurosecretory neurons of Lymantria dispar caterpillars was performed using a monoclonal antibody directed against a synthetic dekapeptide corresponding to the N-terminus of the bombyxin A-chain. Caterpillars were exposed to strong static magnetic fileds (235 mT) and extremely low frequency magnetic fields (2 mT) for three days after moulting into the 4th instar.

RESULTS

We report the presence of immunoreactive molecules in A2 type of medial neurosecretory neurons (nsn) in caterpillars' brain of L. dispar. The three-day exposure of caterpillars to stresogenic external magnetic fields changed the size of A2 type nsn, their nuclei and the intensity of protein band in the region of bombyxin molecular mass (4-6 kD) after exposure to extremely low frequency magnetic fields in comparison to control group and group treated by strong static magnetic fields.

CONCLUSION

These are the first data on the influence of external magnetic fields on the polyphagous phytophagous forest pest L. dispar L. (Lepidoptera: Lymantridae) indicating an intensive synthesis of insulin-like neurosecretory material.

Lizards respond to an extremely low-frequency electromagnetic field

Animals from a wide range of taxa have been shown to possess magnetic sense and use magnetic compasses to orient; however, there is no information in the literature on whether lizards have either of these abilities. In this study, we investigated the behavioral responses of a diurnal agamid lizard (Pogona vitticeps) to a sinusoidal extremely low-frequency electromagnetic field (ELF-EMF; 6 and 8 Hz, peak magnetic field 2.6 μT, peak electric field 10 V m−1). Fourteen adult lizards were divided randomly into two groups (the EMF and control groups; each group had three males and four females). The EMF group received whole-body exposure to ELF-EMF and the control group did not. Lizards in the EMF group were exposed to ELF-EMF for 12 h per day (during the light period). The number of tail lifts was monitored beginning 3 days before exposure and ending after 5 days of exposure. For each individual, the average number of tail lifts per day was calculated. The average number of tail lifts per individual per day was greater in the EMF group than in the control group (20.7±6.3 and 9.1±4.5 tail lifts, respectively, N=7 each, P=0.02). We confirmed the reproducibility of this response by a cross-over trial. These results suggest that at least some lizards are able to perceive ELF-EMFs. Furthermore, when the parietal eye of the lizards was covered with a small round aluminum ‘cap’ which could block light, the tail-lifting response to ELF-EMF disappeared. Our experiments suggest that (1) lizards perceive EMFs and (2) the parietal eye may be involved in light-dependent magnetoreceptive responses.

Magnetoreception in eusocial insects: an update

Behavioural experiments for magnetoreception in eusocial insects in the last decade are reviewed. Ants and bees use the geomagnetic field to orient and navigate in areas around their nests and along migratory paths. Bees show sensitivity to small changes in magnetic fields in conditioning experiments and when exiting the hive. For the first time, the magnetic properties of the nanoparticles found in eusocial insects, obtained by magnetic techniques and electron microscopy, are reviewed. Different magnetic oxide nanoparticles, ranging from superparamagnetic to multi-domain particles, were observed in all body parts, but greater relative concentrations in the abdomens and antennae of honeybees and ants have focused attention on these segments. Theoretical models for how these specific magnetosensory apparatuses function have been proposed. Neuron-rich ant antennae may be the most amenable to discovering a magnetosensor that will greatly assist research into higher order processing of magnetic information. The ferromagnetic hypothesis is believed to apply to eusocial insects, but interest in a light-sensitive mechanism is growing. The diversity of compass mechanisms in animals suggests that multiple compasses may function in insect orientation and navigation. The search for magnetic compasses will continue even after a magnetosensor is discovered in eusocial insects.

Biophysics of magnetic orientation: strengthening the interface between theory and experimental design

The first demonstrations of magnetic effects on the behaviour of migratory birds and homing pigeons in laboratory and field experiments, respectively, provided evidence for the longstanding hypothesis that animals such as birds that migrate and home over long distances would benefit from possession of a magnetic sense. Subsequent identification of at least two plausible biophysical mechanisms for magnetoreception in animals, one based on biogenic magnetite and another on radical-pair biochemical reactions, led to major efforts over recent decades to test predictions of the two models, as well as efforts to understand the ultrastructure and function of the possible magnetoreceptor cells. Unfortunately, progress in understanding the magnetic sense has been challenged by: (i) the availability of a relatively small number of techniques for analysing behavioural responses to magnetic fields by animals; (ii) difficulty in achieving reproducible results using the techniques; and (iii) difficulty in development and implementation of new techniques that might bring greater experimental power. As a consequence, laboratory and field techniques used to study the magnetic sense today remain substantially unchanged, despite the huge developments in technology and instrumentation since the techniques were developed in the 1950s. New methods developed for behavioural study of the magnetic sense over the last 30 years include the use of laboratory conditioning techniques and tracking devices based on transmission of radio signals to and from satellites. Here we consider methodological developments in the study of the magnetic sense and present suggestions for increasing the reproducibility and ease of interpretation of experimental studies. We recommend that future experiments invest more effort in automating control of experiments and data capture, control of stimulation and full blinding of experiments in the rare cases where automation is impossible. We also propose new experiments to confirm whether or not animals can detect magnetic fields using the radical-pair effect together with an alternate hypothesis that may explain the dependence on light of responses by animals to magnetic field stimuli.

A model for encoding of magnetic field intensity by magnetite-based magnetoreceptor cells

A conceptual model is proposed for the encoding of magnetic field intensity from the motion of a chain of single-domain magnetite crystals which is located within a receptor cell, connected at one end to the cell membrane, and linked by cytoskeletal filaments to an array of mechanically gated ion channels centred on the end of the chain. In this arrangement, the physical links between the chain and ion channels will restrict the motion of the magnetite chain in response to the external magnetic field to a narrow cone with its axis through the point where the chain is attached to the membrane. The motion of the chain in the presence of an external magnetic field and thermal agitation will open a varying number of channels, causing the membrane potential to oscillate about some mean value that depends on the component of magnetic intensity oriented perpendicular to the cell membrane. The model permits estimation of magnetic intensity by integration of the motion of the magnetite chain over an area of the cell membrane, explains a number of results from physiological recordings in birds and fish, and makes testable predictions for future experimental studies. The model also provides a mechanism at the cellular level for a constant value of the Weber fraction (the ratio of the threshold sensitivity to a stimulus and the magnitude of that stimulus) for the magnetic sense but requires a separate gain control mechanism for modulation of sensitivity over a range of background fields. If magnetic field detection and encoding works as proposed in the model, the magnetoreceptor system may also be able to reconstruct the magnetic field vector using information about the vertical and horizontal axes from the eyes, gravity detectors, or both.

Magnetoreception system in honeybees (Apis mellifera)

Honeybees (Apis mellifera) undergo iron biomineralization, providing the basis for magnetoreception. We showed earlier the presence of superparamagnetic magnetite in iron granules formed in honeybees, and subscribed to the notion that external magnetic fields may cause expansion or contraction of the superparamagnetic particles in an orientation-specific manner, relaying the signal via cytoskeleton (Hsu and Li 1994). In this study, we established a size-density purification procedure, with which quantitative amount of iron granules was obtained from honey bee trophocytes and characterized; the density of iron granules was determined to be 1.25 g/cm³. While we confirmed the presence of superparamagnetic magnetite in the iron granules, we observed changes in the size of the magnetic granules in the trophycytes upon applying additional magnetic field to the cells. A concomitant release of calcium ion was observed by confocal microscope. This size fluctuation triggered the increase of intracellular Ca⁺² , which was inhibited by colchicines and latrunculin B, known to be blockers for microtubule and microfilament syntheses, respectively. The associated cytoskeleton may thus relay the magnetosignal, initiating a neural response. A model for the mechanism of magnetoreception in honeybees is proposed, which may be applicable to most, if not all, magnetotactic organisms.

Laboratory behavioural assay of insect magnetoreception: magnetosensitivity of Periplaneta americana

A relatively simple all-laboratory behavioural assay of insect magnetoreception has been developed. We found non-conditioned reactions of American cockroach to the periodical shifts of the geomagnetic field. The movement activity of animals individually placed into Petri dishes was scored as a number of body turns. Test groups were exposed to a 90-min interval with the horizontal component of the geomagnetic field periodically rotated by 60 degrees back and forth with 5 min periodicity. The number of body turns was compared with the preceding and following intervals and with the corresponding interval of the control group kept in the natural field. We obtained a significant increase in activity when changes in field were applied. Interestingly, the period of increased activity did not coincide precisely with the 90 min stimulation interval. The onset of animal restlessness was delayed by tens of minutes and persisted correspondingly after the stimulation stopped. A respective evaluation criterion was suggested and verified. Owing to its simplicity and minimal manipulation of the insects, together with low demands on the memory and motivation state of animals, the approach potentially may be used as a laboratory diagnostic tool indicating magnetoreception in insect neurophysiology research.

Do geomagnetic storms change the behaviour of the stingless bee guiruçu (Schwarziana quadripunctata)?

Six behavioural experiments were carried out to investigate the magnetic field effects on the nest-exiting flight directions of the honeybee Schwarziana quadripunctata (Meliponini). No significant differences resulted during six experiment days under varying geomagnetic field and the applied static inhomogeneous field (about ten times the geomagnetic field) conditions. A surprising statistically significant response was obtained on a unique magnetic storm day. The magnetic nanoparticles in these bees, revealed by ferromagnetic resonance, could be involved in the observed effect of the geomagnetic storm.

Magnetic orientation in the mealworm beetle Tenebrio and the effect of light

There is evidence for both light-dependent and light-independent mechanisms of magnetoreception of terrestrial animals. One example of a light-independent mechanism frequently cited is the magnetic compass of the mealworm beetle (Tenebrio molitor). We found that magnetoreception of the mealworm beetle per se is a replicable phenomenon but that, in contrast to earlier findings, Tenebrio only exhibited consistent magnetic compass orientation when light was present. The problem of whether the loss of orientation is due to a light-dependent magnetoreception mechanism or is instead an effect of motivation change is discussed.

The magnetic sense and its use in long-distance navigation by animals

True navigation by animals is likely to depend on events occurring in the individual cells that detect magnetic fields. Minimum thresholds of detection, perception and 'interpretation' of magnetic field stimuli must be met if animals are to use a magnetic sense to navigate. Recent technological advances in animal tracking devices now make it possible to test predictions from models of navigation based on the use of variations in magnetic intensity.

Magnetite-based magnetoreception in birds: the effect of a biasing field and a pulse on migratory behavior

To test the hypothesis that single domain magnetite is involved in magnetoreception, we treated Australian silvereyes Zosterops l. lateralis with a strong, brief pulse designed to alter the magnetization of single domain particles. This pulse was administered in the presence of a 1 mT biasing field, either parallel to the direction of the biasing field (PAR group) or antiparallel (ANTI group). In the case of magnetoreceptors based on freely moving single domain particles, the PAR treatment should have little effect, whereas the ANTI treatment should cause remagnetization of the magnetite particles involved in a receptor and could produce a maximum change in that receptor's output for some receptor configurations. Migratory orientation was used as a criterion to assess the effect on the receptor. Before treatment, both groups preferred their normal northerly migratory direction. Exposure to the biasing field alone did not affect their behavior. Treatment with the pulse in the presence of the biasing field caused both the PAR and the ANTI birds to show an axial preference for the east—west axis, with no difference between the two groups. Although these results are in accordance with magnetite-based magnetoreceptors playing a role in migratory orientation, they do not support the hypothesis that single domains in polarity-sensitive receptors are free to move through all solid angles. Possible interpretations, including other arrangements of single domains and superparamagnetic crystals, are discussed.

Ferritin in iron containing granules from the fat body of the honeybees Apis mellifera and Scaptotrigona postica

It is already known that the behaviour of the honeybee Apis mellifera is influenced by the Earth's magnetic field. Recently it has been proposed that iron-rich granules found inside the fat body cells of this honeybee had small magnetite crystals that were responsible for this behaviour. In the present work, we studied the iron containing granules from queens of two species of honeybees (A. mellifera and Scaptotrigona postica) by electron microscopy methods in order to clarify this point. The granules were found inside rough endoplasmic reticulum cisternae. Energy dispersive X-ray analysis of granules from A. mellifera showed the presence of iron, phosphorus and calcium. The same analysis performed on the granules of S. postica also indicated the presence of these elements along with the additional element magnesium. The granules of A. mellifera were composed of apoferritin-like particles in the periphery while in the core, clusters of organised particles resembling holoferritin were seen. The larger and more mineralised granules of S. postica presented structures resembling ferritin cores in the periphery, and smaller electron dense particles inside the bulk. Electron spectroscopic images of the granules from A. mellifera showed that iron, oxygen and phosphorus were co-localised in the ferritin-like deposits. These results indicate that the iron-rich granules of these honeybees are formed by accumulation of ferritin and its degraded forms together with elements present inside the rough endoplasmic reticulum, such as phosphorus, calcium and magnesium. It is suggested that the high level of phosphate in the milieu would prevent the crystallisation of iron oxides in these structures, making very unlikely their participation in magnetoreception mechanisms. They are most probably involved in iron homeostasis.

Ferromagnetic material in the eastern red-spotted newt notophthalmus viridescens

Behavioral results obtained from the eastern red-spotted newt (Notophthalmus viridescens) led to the suggestion of a hybrid homing system involving inputs from both a light-dependent and a non-light-dependent mechanism. To evaluate the possible role of a receptor based on biogenic magnetite in this animal, we performed magnetometry experiments on a set of newts previously used in behavioral assays. The natural remanent magnetization (NRM) carried by these newts was strong enough to be measured easily using a direct-current-biased superconducting quantum interference device functioning as a moment magnetometer. Isothermal remanent magnetizations were two orders of magnitude higher than the NRM, suggesting that ferromagnetic material consistent with magnetite is present in the body of the newt. The NRM has no preferential orientation among the animals when analyzed relative to their body axis, and the demagnetization data show that, overall, the magnetic material grains are not aligned parallel to each other within each newt. Although the precise localization of the particles was not possible, the data indicate that magnetite is not clustered in a limited area. A quantity of single-domain magnetic material is present which would be adequate for use in either a magnetic intensity or direction receptor. Our data, when combined with the functional properties of homing, suggest a link between this behavioral response and the presence of ferromagnetic material, raising the possibility that magnetite is involved at least in the map component of homing of the eastern red-spotted newt.