The terminal abdominal ganglion of the wood cricket Nemobius sylvestris

Functional anatomy of the worker honeybee stinger (Apis mellifera)

The honeybee stinger is a powerful defense mechanism that combines painful venom, a subcutaneous delivery system, and the ability to autotomize. It is a complex organ and to function autonomously it must carry with it all the anatomical components required to operate. In this study, we combined high-speed filming, SEM imagery, and micro-CT for volumetric rendering of the stinger with a synthesis of existing literature. We present a comprehensive description of all components, including cuticular elements, musculature, nervous and glandular tissue using updated imagery. We draw from the Hymenoptera literature to make interspecific comparisons where relevant. The use of 3D reconstruction allows us to separate stinger components and present the first 3D renders of the bee stinger including the terminal abdominal ganglion and its projections. It also clarifies the in-situ geometry of the valves within the bulb and the spatial relationships among the accessory plates and accompanying musculature.

Bio-Inspired Architectures Substantially Reduce the Memory Requirements of Neural Network Models

We propose a neural network model for the jumping escape response behavior observed in the cricket cercal sensory system. This sensory system processes low-intensity air currents in the animal's immediate environment generated by predators, competitors, and mates. Our model is inspired by decades of physiological and anatomical studies. We compare the performance of our model with a model derived through a universal approximation, or a generic deep learning, approach, and demonstrate that, to achieve the same performance, these models required between one and two orders of magnitude more parameters. Furthermore, since the architecture of the bio-inspired model is defined by a set of logical relations between neurons, we find that the model is open to interpretation and can be understood. This work demonstrates the potential of incorporating bio-inspired architectural motifs, which have evolved in animal nervous systems, into memory efficient neural network models.

Deep-tissue confocal imaging of the central projections of ovipositor sensory afferents in the Egyptian cotton leafworm, Spodoptera littoralis

The pre-ovipositon behavior of moths is largely dependent upon the cues that a gravid female perceives while assessing potential oviposition sites. Assessment of such sites is accomplished, at least in part, by mechanosensory and gustatory sensilla located on the ovipositor whose sensory neurons project into the terminal abdominal ganglion (TAG). Using anterograde backfill staining, confocal laser scanning microscopy, and three dimensional reconstruction, we traced and analyzed the central projections of the sensory neurons housed in the sensilla located on the ovipositor papillae and explored the neuropilar composition of the TAG in the Egyptian cotton leafworm, Spodoptera littoralis. The TAG consists of three fused neuromeres (6-8th Ner) associated with the 6-8th abdominal segments. Within the TAG, and specifically in the 8th neuromere, four unstructured neuropilar compartments are present; the dorso-ipsilateral motor neuropil (MN), the medio-ipsilateral mechanosensory neuropil (MchN), the medio-ipsilateral small gustatory neuropil (GN), and the medio-contralateral posterior ovipositor glomerulus (Og). The Og appears quite compact, with a hollow core free of terminal arborizations. The MchN is further subdivided into 4 unstructured glomeruli in the 8th neuromere, whose afferents are subsequently extended into 3 glomeruli in the 7th and 6th neuromeres. Few neurites of the Og are populated with large dense varicosities reminiscent of neurosecretory vesicles. Given that all ovipositor nerves converge into a common ganglionic center, the TAG, we assume that this ganglion may be a center for coordination of oviposition behaviors, including movements of the ovipositor during assessment of oviposition substrates and egg laying in S. littoralis.

Responses of cricket cercal interneurons to realistic naturalistic stimuli in the field

The ability of the insect cercal system to detect approaching predators has been studied extensively in the laboratory and in the field. Some previous studies have assessed the extent to which sensory noise affects the operational characteristics of the cercal system, but these studies have only been carried out in laboratory settings using white noise stimuli of unrealistic nature. Using a piston mimicking the natural airflow of an approaching predator, we recorded the neural activity through the abdominal connectives from the terminal abdominal ganglion of freely moving wood crickets (Nemobius sylvestris) in a semi-field situation. A cluster analysis of spike amplitudes revealed six clusters, or 'units', corresponding to six different subsets of cercal interneurons. No spontaneous activity was recorded for the units of larger amplitude, reinforcing the idea they correspond to the largest giant interneurons. Many of the cercal units are already activated by background noise, sometimes only weakly, and the approach of a predator is signaled by an increase in their activity, in particular for the larger-amplitude units. A scaling law predicts that the cumulative number of spikes is a function of the velocity of the flow perceived at the rear of the cricket, including a multiplicative factor that increases linearly with piston velocity. We discuss the implications of this finding in terms of how the cricket might infer the imminence and nature of a predatory attack.

Danger detection and escape behaviour in wood crickets

The wind-sensitive cercal system of Orthopteroid insects that mediates the detection of the approach of a predator is a very sensitive sensory system. It has been intensively analysed from a behavioural and neurobiological point of view, and constitutes a classical model system in neuroethology. The escape behaviour is triggered in orthopteroids by the detection of air-currents produced by approaching objects, allowing these insects to keep away from potential dangers. Nevertheless, escape behaviour has not been studied in terms of success. Moreover, an attacking predator is more than "air movement", it is also a visible moving entity. The sensory basis of predator detection is thus probably more complex than the perception of air movement by the cerci. We have used a piston mimicking an attacking running predator for a quantitative evaluation of the escape behaviour of wood crickets Nemobius sylvestris. The movement of the piston not only generates air movement, but it can be seen by the insect and can touch it as a natural predator. This procedure allowed us to study the escape behaviour in terms of detection and also in terms of success. Our results showed that 5-52% of crickets that detected the piston thrust were indeed touched. Crickets escaped to stimulation from behind better than to a stimulation from the front, even though they detected the approaching object similarly in both cases. After cerci ablation, 48% crickets were still able to detect a piston approaching from behind (compared with 79% of detection in intact insects) and 24% crickets escaped successfully (compared with 62% in the case of intact insects). So, cerci play a major role in the detection of an approaching object but other mechanoreceptors or sensory modalities are implicated in this detection. It is not possible to assure that other sensory modalities participate (in the case of intact animals) in the behaviour; rather, than in the absence of cerci other sensory modalities can partially mediate the behaviour. Nevertheless, neither antennae nor eyes seem to be used for detecting approaching objects, as their inactivation did not reduce their detection and escape abilities in the presence of cerci.

The morphology and fine structure of the giant interneurons of the wood cricket Nemobius sylvestris

The structural and ultrastructural characteristics of giant interneurons in the terminal abdominal ganglion of the cricket Nemobius sylvestris were investigated by means of cobalt and fluorescent dye backfilling and transmission electron microscopy. The projections of the 8 eight pairs of the biggest ascending interneurons (giant interneurons) are described in detail. The somata of all interneurons analyzed are located contralateral to their axons, which project to the posterior region of the terminal ganglion and arborise in the cercal glomerulus. Neuron 7-1a is an exception, because its arborisation is restricted to the anterior region of the ganglion. The fine structure of giant interneurons shows typical features of highly active cells. We observed striking indentations in the perineural layer, enabling the somata of the giant interneurons to be very close to the haemolymph. The cercal glomerulus exhibits a high diversity of synaptic contacts (i.e. axo-dendritic, axo-axonic, dendro-axonic, and dendro-dendritic), as well as areas of tight junctions. Electrical synapses seem to be present, as well as mixed synapses. The anatomical organization of the giant interneurons is finally discussed in terms of functional implications and on a comparative basis.