Orientation to polarized light in tethered flying honeybees

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.

Synergistic negative effects between a fungicide and high temperatures on homing behaviours in honeybees

Interactions between environmental stressors may contribute to ongoing pollinator declines, but have not been extensively studied. Here, we examined the interaction between the agricultural fungicide Pristine (active ingredients: 25.2% boscalid, 12.8% pyraclostrobin) and high temperatures on critical honeybee behaviours. We have previously shown that consumption of field-realistic levels of this fungicide shortens worker lifespan in the field and impairs associative learning performance in a laboratory-based assay. We hypothesized that Pristine would also impair homing and foraging behaviours in the field, and that an interaction with hot weather would exacerbate this effect. Both field-relevant Pristine exposure and higher air temperatures reduced the probability of successful return on their own. Together, the two factors synergistically reduced the probability of return and increased the time required for bees to return to the hive. Pristine did not affect the masses of pollen or volumes of nectar or water brought back to the hive by foragers, and it did not affect the ratio of forager types in a colony. However, Pristine-fed bees brought more concentrated nectar back to the hive. As both agrochemical usage and heat waves increase, additive and synergistic negative effects may pose major threats to pollinators and sustainable agriculture.

Visual learning in tethered bees modifies flight orientation and is impaired by epinastine

Visual-orientation learning of a tethered flying bee was investigated using a flight simulator and a novel protocol in which orientation preference toward trained visual targets was assessed in tests performed before and after appetitive conditioning. Either a blue or a green rectangle (conditioned stimulus, CS) was associated with 30% sucrose solution (unconditioned stimulus, US), whereas the other rectangle was not paired with US. Bees were tested in a closed-looped flight simulator 5 min after ten pairings of the US and CS. Conditioned bees were preferentially oriented to the CS after such training. This increase in preference for CS was maintained for 24 h, indicating the presence of long-term memory. Because the total orienting time was not altered by conditioning, conditioning did not enhance orientation activity itself but increased the relative time for orientation to CS. When 0.4 or 4 mM epinastine (an antagonist of octopamine receptors) was injected into the bee's head 30 min prior to the experiment, both short- and long-term memory formation were significantly impaired, suggesting that octopamine, which is crucial for appetitive olfactory learning in insects, is also involved in visual orientation learning.

Three-dimensional attitude determination strategy for fused polarized light and geomagnetism

Using polarized light sensors to obtain only two-dimensional heading information does meet actual needs in navigation. Instead, an alternative method is proposed that uses the positional information of the Sun and geomagnetic information to calculate the three-dimensional attitude of a vehicle. First, the theoretical background of the polarization mode of skylight is described, and the scheme in using the atmospheric polarization pattern to calculate the solar position is presented. Second, the traditional three-axis attitude-determination (TRIAD) algorithm that exploits the solar position vector and the geomagnetic vector to obtain the three-dimensional attitude and the optimized TRIAD algorithm are introduced. Static and turntable experiments are described that verify the accuracy of the attitude calculation. Experimental results show that when using the optimized TRIAD algorithm, the root mean square errors for the roll angle, pitch angle, and heading angle are 0.1225°, 0.668°, and 1.0234°, respectively. This means that the optimized TRIAD algorithm performs significantly better than the traditional TRIAD algorithm and demonstrates that using the solar position and the geomagnetic information to obtain the three-dimensional attitude of the vehicle is very effective.