Stingless bees (Meliponini): senses and behavior.

Stingless bees (Hymenoptera, Apidae, Meliponini) are by far the largest group of eusocial bees on Earth. Due to the diversity of evolutionary responses to specific ecological challenges, the Meliponini are well suited for comparative studies of the various adaptations to the environment found in highly eusocial bees. Of particular interest are the physiological mechanisms underlying the sophisticated cooperative and collective actions of entire colonies, which form the basis of the ecological success of the different bee species under the particular conditions prevailing in their respective environment. The present Special Issue of the Journal of Comparative Physiology A provides a sample of the exciting diversity of sensorial and behavioral adaptations in stingless bees, particularly concerning (1) the sensory bases for foraging, (2) chemical communication, and (3) the behavioral ecology of foraging.

Effects of diphenyliodonium salt addition on the adhesive and mechanical properties of an experimental adhesive.

OBJECTIVES: The aim of this study was to assess the microtensile bond strength (µTBS), nanoleakage (NL), nano-hardness (NH) and Young's modulus (YM) of resin-dentine bonding components formed by an experimental adhesive system with or without inclusion of diphenyliodonium salt (DPIH) in the camphorquinone-amine (CQ) system. METHODS: On 12 human molars, a flat superficial dentine surface was exposed by wet abrasion. A model simplified adhesive system was formulated (40 wt.% UDMA/MDP, 30 wt.% HEMA and 30 wt.% ethanol). Two initiator systems were investigated: 0.5 mol% CQ+1.0 mol% EDMAB and 0.5 mol% CQ+1.0 mol% EDMAB+0.2 mol% DPIH. Each adhesive was applied and light-cured (10s; 600 mW/cm(2)). Composite build-ups were constructed incrementally and resin-dentine specimens (0.8mm(2)) were prepared. For NL, 3 bonded sticks from each tooth were coated with nail varnish, placed in the silver nitrate, polished down with SiC papers and analysed by EDX-SEM. NH and YM were performed on the hybrid layer in 2 bonded sticks from each teeth. The remaining bonded sticks were tested on µTBS (0.5mm/min). The data from each test were submitted to a Student t-test (α=0.05). RESULTS: No significant difference was found for µTBS between groups (p>0.05). Significant lower NL and higher NH and YM were found in the hybrid layer and adhesive layer produced with the iodinium salt-containing adhesive (p<0.05). CONCLUSIONS: The inclusion of the DPIH to the traditional CQ is a good strategy to improve the adhesive and mechanical properties of a simplified etch-and-rinse adhesive system.

In search of differences between the two types of sensory cells innervating spider slit sensilla (Cupiennius salei Keys.).

The metatarsal lyriform organ of the spider Cupiennius salei is a vibration detector consisting of 21 cuticular slits supplied by two sensory cells each, one ending in the outer and the other at the inner slit membrane. In search of functional differences between the two cell types due to differences in stimulus transmission, we analyzed (1) the adaptation of responses to electrical stimulation, (2) the thresholds for mechanical stimulation and (3) the representation of male courtship vibrations using intracellular recording and staining techniques. Single- and multi-spiking receptor neurons were found among both cell types, which showed high-pass filter characteristics. Below 100-Hz threshold, tarsal deflections were between 1 degrees and 10 degrees. At higher frequencies, they decreased down to values as small as 0.05 degrees, corresponding to 4.5-nm tarsal deflection in the most sensitive cases. Different slits in the organ and receptor cells with slow or fast adaptation did not differ in this regard. When stimulated with male courtship vibrations, both types of receptor cells again did not differ significantly regarding number of action potentials, latency and synchronization coefficients. Surprisingly, the differences in dendrite coupling were not reflected by the physiological responses of the two cell types innervating the slits.

Thoracic vibrations in stingless bees (Melipona seminigra): resonances of the thorax influence vibrations associated with flight but not those associated with sound production.

Bees generate thoracic vibrations with their indirect flight muscles in various behavioural contexts. The main frequency component of non-flight vibrations, during which the wings are usually folded over the abdomen, is higher than that of thoracic vibrations that drive the wing movements for flight. So far, this has been concluded from an increase in natural frequency of the oscillating system in association with the wing adduction. In the present study, we measured the thoracic oscillations in stingless bees during stationary flight and during two types of non-flight behaviour, annoyance buzzing and forager communication, using laser vibrometry. As expected, the flight vibrations met all tested assumptions for resonant oscillations: slow build-up and decay of amplitude; increased frequency following reduction of the inertial load; and decreased frequency following an increase of the mass of the oscillating system. Resonances, however, do not play a significant role in the generation of non-flight vibrations. The strong decrease in main frequency at the end of the pulses indicates that these were driven at a frequency higher than the natural frequency of the system. Despite significant differences regarding the main frequency components and their oscillation amplitudes, the mechanism of generation is apparently similar in annoyance buzzing and forager vibrations. Both types of non-flight vibration induced oscillations of the wings and the legs in a similar way. Since these body parts transform thoracic oscillations into airborne sounds and substrate vibrations, annoyance buzzing can also be used to study mechanisms of signal generation and transmission potentially relevant in forager communication under controlled conditions.

The sound field generated by tethered stingless bees (Melipona scutellaris): inferences on its potential as a recruitment mechanism inside the hive.

In stingless bees, recruitment of hive bees to food sources involves thoracic vibrations by foragers during trophallaxis. The temporal pattern of these vibrations correlates with the sugar concentration of the collected food. One possible pathway for transferring such information to nestmates is through airborne sound. In the present study, we investigated the transformation of thoracic vibrations into air particle velocity, sound pressure, and jet airflows in the stingless bee Melipona scutellaris. Whereas particle velocity and sound pressure were found all around and above vibrating individuals, there was no evidence for a jet airflow as with honey bees. The largest particle velocities were measured 5 mm above the wings (16.0+/-4.8 mm s(-1)). Around a vibrating individual, we found maximum particle velocities of 8.6+/-3.0 mm s(-1) (horizontal particle velocity) in front of the bee's head and of 6.0+/-2.1 mm s(-1) (vertical particle velocity) behind its wings. Wing oscillations, which are mainly responsible for air particle movements in honey bees, significantly contributed to vertically oriented particle oscillations only close to the abdomen in M. scutellaris (distances < or =5 mm). Almost 80% of the hive bees attending trophallactic food transfers stayed within a range of 5 mm from the vibrating foragers. It remains to be shown, however, whether air particle velocity alone is strong enough to be detected by Johnston's organ of the bee antenna. Taking the physiological properties of the honey bee's Johnston's organ as the reference, M. scutellaris hive bees are able to detect the forager vibrations through particle movements at distances of up to 2 cm.

A stingless bee (Melipona seminigra) marks food sources with a pheromone from its claw retractor tendons.

By depositing scent marks on flowers, bees reduce both the search time and the time spent with the handling of nonrewarding flowers. They thereby improve the efficiency of foraging. Whereas in honey bees the source of these scent marks is unknown, it is assumed to be the tarsal glands in bumble bees. According to histological studies, however, the tarsal glands lack any openings to the outside. Foragers of the stingless bee Melipona seminigra have previously been shown to deposit an attractant pheromone at sugar solution feeders, which is secreted at the tips of their tarsi. Here we show that the claw retractor tendons have specialized glandular epithelia within the femur and tibia of all legs that produce this pheromone. The secretion accumulates within the hollow tendon, which also serves as the duct to the outside, and is released from an opening at the base of the unguitractor plate. In choice experiments, M. seminigra was attracted by feeders baited with pentane extracts of the claw retractor tendons in the same way as it was attracted by feeders previously scent marked by foragers. Our results resolve the seeming contradiction between the importance of foot print secretions and the lack of openings of the tarsal glands.