Interommatidial sensilla of the praying mantis: their central neural projections and role in head-cleaning behavior

Somatotopic organization among parallel sensory pathways that promote a grooming sequence in Drosophila

Mechanosensory neurons located across the body surface respond to tactile stimuli and elicit diverse behavioral responses, from relatively simple stimulus location-aimed movements to complex movement sequences. How mechanosensory neurons and their postsynaptic circuits influence such diverse behaviors remains unclear. We previously discovered that Drosophila perform a body location-prioritized grooming sequence when mechanosensory neurons at different locations on the head and body are simultaneously stimulated by dust (Hampel et al., 2017; Seeds et al., 2014). Here, we identify nearly all mechanosensory neurons on the Drosophila head that individually elicit aimed grooming of specific head locations, while collectively eliciting a whole head grooming sequence. Different tracing methods were used to reconstruct the projections of these neurons from different locations on the head to their distinct arborizations in the brain. This provides the first synaptic resolution somatotopic map of a head, and defines the parallel-projecting mechanosensory pathways that elicit head grooming.

Somatotopic organization among parallel sensory pathways that promote a grooming sequence in Drosophila

Mechanosensory neurons located across the body surface respond to tactile stimuli and elicit diverse behavioral responses, from relatively simple stimulus location-aimed movements to complex movement sequences. How mechanosensory neurons and their postsynaptic circuits influence such diverse behaviors remains unclear. We previously discovered that Drosophila perform a body location-prioritized grooming sequence when mechanosensory neurons at different locations on the head and body are simultaneously stimulated by dust (Hampel et al., 2017; Seeds et al., 2014). Here, we identify nearly all mechanosensory neurons on the Drosophila head that individually elicit aimed grooming of specific head locations, while collectively eliciting a whole head grooming sequence. Different tracing methods were used to reconstruct the projections of these neurons from different locations on the head to their distinct arborizations in the brain. This provides the first synaptic resolution somatotopic map of a head, and defines the parallel-projecting mechanosensory pathways that elicit head grooming.

Morphology of interommatidial sensilla of Discocephalini (Heteroptera: Pentatomidae: Discocephalinae)

Interommatidial sensilla have been explored for their taxonomic value and other aspects in Diptera and Lepidoptera. In Heteroptera, Eurystethus is the only genus where these structures were examined in delimiting subgenera and species. This study investigates the presence, distribution, and morphology of interommatidial sensilla in Discocephalinae species and discusses the sensilla's value for cladistic and taxonomic appraisals. Twenty species of 18 genera were analyzed: 16 Discocephalini genera, one genus in Ochlerini, and one genus in Edessinae. Species' heads were observed from photographs taken with light microscopy (LM) and scanning electron microscopy (SEM). From these images, we identified eleven types of sensilla, classified into chaetica, trichoidea and coeloconica. In LM, only sensilla chaetica with a length of 40-100 μm were visible, present in six species. Under the SEM at least one type of sensillum was visible in 19 of the 20 species analyzed. No difference between the various kinds of sensilla were apparent between males and females or adults and nymphs of a given species. Both subgenera of Eurysthetus have the same type of sensillum (chaeticum type I), which suggests this is not a delimiting feature. We conclude that sensilla chaetica can be a valuable character to delimit groups of genera within Discocephalini.

A study of the role of vision in the foraging behaviour of the pyrrhocorid bug Antilochus conquebertii (Insecta; Hemiptera; Pyrrhocoridae)

Our study aims to describe (1) external morphology of the compound eye of Antilochus conquebertii, (2) postembryonic changes involving the eye's shape and size and (3) behaviour of the animal with respect to the organization of the compound eye. With each moult of the insect, the structural units of the compound eye increase in size as well as the number, resulting in an overall increase in eye size. The resolution of the adult eye is better than the young one. The adult possesses UV and polarization sensitivity in its eye. Parallel to the changes of the eye the behaviour of the adult animal changes, rendering it increasingly nocturnal and less active in under illuminated conditions. The current study describes the eye and its functional relationship with the behaviour of the animal at the nymphal and adult developmental stage.

Simultaneous activation of parallel sensory pathways promotes a grooming sequence in Drosophila

A central model that describes how behavioral sequences are produced features a neural architecture that readies different movements simultaneously, and a mechanism where prioritized suppression between the movements determines their sequential performance. We previously described a model whereby suppression drives a Drosophila grooming sequence that is induced by simultaneous activation of different sensory pathways that each elicit a distinct movement (Seeds et al., 2014). Here, we confirm this model using transgenic expression to identify and optogenetically activate sensory neurons that elicit specific grooming movements. Simultaneous activation of different sensory pathways elicits a grooming sequence that resembles the naturally induced sequence. Moreover, the sequence proceeds after the sensory excitation is terminated, indicating that a persistent trace of this excitation induces the next grooming movement once the previous one is performed. This reveals a mechanism whereby parallel sensory inputs can be integrated and stored to elicit a delayed and sequential grooming response.

Compound eyes of insects and crustaceans: Some examples that show there is still a lot of work left to be done

Similarities and differences between the 2 main kinds of compound eye (apposition and superposition) are briefly explained before several promising topics for research on compound eyes are being introduced. Research on the embryology and molecular control of the development of the insect clear-zone eye with superposition optics is one of the suggestions, because almost all of the developmental work on insect eyes in the past has focused on eyes with apposition optics. Age- and habitat-related ultrastructural studies of the retinal organization are another suggestion and the deer cad Lipoptena cervi, which has an aerial phase during which it is winged followed by a several months long parasitic phase during which it is wingless, is mentioned as a candidate species. Sexual dimorphism expressing itself in many species as a difference in eye structure and function provides another promising field for compound eye researchers and so is a focus on compound eye miniaturization in very small insects, especially those that are aquatic and belong to species, in which clear-zone eyes are diagnostic or are tiny insects that are not aquatic, but belong to taxa like the Diptera for instance, in which open rather than closed rhabdoms are the rule. Structures like interommatidial hairs and glands as well as corneal microridges are yet another field that could yield interesting results and in the past has received insufficient consideration. Finally, the dearth of information on distance vision and depth perception is mentioned and a plea is made to examine the photic environment inside the foam shelters of spittle bugs, chrysales of pupae and other structures shielding insects and crustaceans.