Characterisation of the RNA interference response against the long-wavelength receptor of the honeybee.

Targeted knock-down is the method of choice to advance the study of sensory and brain functions in the honeybee by using molecular techniques. Here we report the results of a first attempt to interfere with the function of a visual receptor, the long-wavelength-sensitive (L-) photoreceptor. RNA interference to inhibit this receptor led to a reduction of the respective mRNA and protein. The interference effect was limited in time and space, and its induction depended on the time of the day most probably because of natural daily variations in opsin levels. The inhibition did not effectively change the physiological properties of the retina. Possible constraints and implications of this method for the study of the bee's visual system are discussed. Overall this study underpins the usefulness and feasibility of RNA interference as manipulation tool in insect brain research.

Detection of patches of coloured discs by bees.

To find out how grouping of flowers into patches improves their detectability by hymenopteran pollinators, we trained honeybees and bumblebees to detect groups of three spatially separated disks and compared results with the detection limit for single disks. When the discs presented contrast to the long-wavelength-sensitive (L) receptor, grouping of disks improved the detectability. The disks were optically resolvable for the honeybee eye. The improvement of detectability was stronger for bumblebees than for honeybees. When disks did not present contrast to the L-receptor, the grouping did not improve the detectability, i.e. the detection limit was set by the size of a single disk. We conclude that in bees the neural mechanisms that improve detectability of grouped elements require input from the L-receptor. Our results indicate that grouping of flowers into sparse patches can improve their detectability by bees, even when individual flowers can be optically resolved by the eyes of bees, as long as flowers can be detected by the long-wavelength-sensitive receptor.

Involvement of alpha-bungarotoxin-sensitive nicotinic receptors in long-term memory formation in the honeybee (Apis mellifera).

In the honeybee Apis mellifera, multiple-trial olfactory conditioning of the proboscis extension response specifically leads to long-term memory (LTM) which can be retrieved more than 24 h after learning. We studied the involvement of nicotinic acetylcholine receptors in the establishment of LTM by injecting the nicotinic antagonists mecamylamine (1 mM), alpha-bungarotoxin (alpha-BGT, 0.1 mM) or methyllycaconitine (MLA, 0.1 mM) into the brain through the median ocellus 20 min before or 20 min after multiple-trial learning. The retention tests were performed 1, 3, and 24 h after learning. Pre-training injections of mecamylamine induced a lower performance during conditioning but had no effect on LTM formation. Post-training injections of mecamylamine did not affect honeybees' performances. Pre-training injections of MLA or post-training injection of alpha-BGT specifically induced LTM impairment whereas acquisition as well as memory retrieval tested 1 or 3 h after learning was normal. This indicates that brain injections of alpha-BGT and MLA did not interfere with learning or medium-term memory. Rather, these blockers affect the LTM. To explain these results, we advance the hypothesis that honeybee alpha-BGT-sensitive acetylcholine receptors are also sensitive to MLA. These receptors could be essential for triggering intracellular mechanisms involved in LTM. By contrast, medium-term memory is not dependent upon these receptors but is affected by mecamylamine.