The Insects has been the standard textbook in the field since the first edition published over forty years ago. Building on the strengths of Chapman's original text, this long-awaited 5th edition has been revised and expanded by a team of eminent insect physiologists, bringing it fully up-to-date for the molecular era. The chapters retain the successful structure of the earlier editions, focusing on particular functional systems rather than taxonomic groups and making it easy for students to delve into topics without extensive knowledge of taxonomy. The focus is on form and function, bringing together basic anatomy and physiology and examining how these relate to behaviour. This, combined with nearly 600 clear illustrations, provides a comprehensive understanding of how insects work. Now also featuring a richly illustrated prologue by George McGavin, this is an essential text for students, researchers and applied entomologists alike.

The insects: structure and function.

A hypothesis about sensorimotor integration (the λ model) is described and applied to movement control and kinesthesia. The central idea is that the nervous system organizes positional frames of reference for the sensorimotor apparatus and produces active movements by shifting the frames in terms of spatial coordinates. Kinematic and electromyographic patterns are not programmed, but emerge from the dynamic interaction among the system s components, including external forces within the designated frame of reference. Motoneuronal threshold properties and proprioceptive inputs to motoneurons may be cardinal components of the physiological mechanism that produces positional frames of reference. The hypothesis that intentional movements are produced by shifting the frame of reference is extended to multi-muscle and multi-degrees-of-freedom systems with a solution of the redundancy problem that allows the control of a joint alone or in combination with other joints to produce any desired limb configuration and movement trajectory. The model also implies that for each motor behavior, the nervous system uses a strategy that minimizes the number of changeable control variables and keeps the parameters of these changes invariant. Examples are provided of simulated kinematic and electromyographic signals from single- and multi-joint arm movements produced by suggested patterns of control variables. Empirical support is provided and additional tests of the model are suggested. The model is contrasted with others based on the ideas of programming of motoneuronal activity, muscle forces, stiffness, or movement kinematics.

The origin and use of positional frames of reference in motor control

In the absence of much passive stability, flying insects rely upon active stabilisation, necessitating the provision of rich sensory feedback across a range of modalities. Here we consider from a sensory perspective what quantities flying insects measure, in order to ask from a mechanical perspective why they should want to do so. We consider each of the sensory modalities separately and uncover three general principles. Firstly, we find that insects have evolved to measure changes in kinematic state, rather than absolute state. For example, although the antennae may be loosely thought of as airspeed sensors, we show that they are configured as a sophisticated adaptive sensing system which is much more appropriate for measuring changes in airspeed than absolute airspeed. Secondly, we find that insect sensory systems are tuned to sense self-motion components in specific directions. For example, certain visual interneurons of flies operate as matched filters that are tuned to detect the optic flow fields induced specifically by rotation about one particular axis. Thirdly, we find that insects commonly combine sensory input from across modalities to form composite, multi-modal quantities which they use as feedback to the control system. For example, certain individually identified descending interneurons combine input from the compound eyes, ocelli, antennae, and cephalic wind-sensitive hairs into one composite signal which is then used in flight control. We infer from these three general organisational principles that insects are configured to sense excitation of their natural modes of motion. This natural-mode sensing hypothesis: (1) explains why insects should want to sense changes in state rather than absolute state; (2) predicts what specific directions of motion they should sense, and (3) specifies how sensory input from different modalities should be combined.

Sensory Systems and Flight Stability: What do Insects Measure and Why?

Animals must routinely deal with barriers as they move through their natural environment. These challenges require directed changes in leg movements and posture performed in the context of ever changing internal and external conditions. In particular, cockroaches use a combination of tactile and visual information to evaluate objects in their path in order to effectively guide their movements in complex terrain. When encountering a large block, the insect uses its antennae to evaluate the object’s height then rears upward accordingly before climbing. A shelf presents a choice between climbing and tunneling that depends on how the antennae strike the shelf; tapping from above yields climbing, while tapping from below causes tunneling. However, ambient light conditions detected by the ocelli can bias that decision. Similarly, in a T-maze turning is determined by antennal contact but influenced by visual cues. These multi-sensory behaviors led us to look at the central complex as a center for sensori-motor integration within the insect brain. Visual and antennal tactile cues are processed within the central complex and, in tethered preparations, several central complex units changed firing rates in tandem with or prior to altered step frequency or turning, while stimulation through the implanted electrodes evoked these same behavioral changes. To further test for a central complex role in these decisions, we examined behavioral effects of brain lesions. Electrolytic lesions in restricted regions of the central complex generated site specific behavioral deficits. Similar changes were also found in reversible effects of procaine injections in the brain. Finally, we are examining these kinds of decisions made in a large arena that more closely matches the conditions under which cockroaches forage. Overall, our studies suggest that CC circuits may indeed influence the descending commands associated with navigational decisions, thereby making them more context dependent.

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Deciding Which Way to Go: How Do Insects Alter Movements to Negotiate Barriers?

SUMMARY Here we provide the first formal quantitative analysis of dynamic stability
in a flying animal By measuring the longitudinal static stability derivatives
and mass distribution of desert locusts Schistocerca gregaria , we
find that their static stability and static control responses are insufficient
to provide asymptotic longitudinal dynamic stability unless they are sensitive
to pitch attitude (measured with respect to an inertial or earth-fixed frame)
as well as aerodynamic incidence (measured relative to the direction of
flight) We find no evidence for a `constant-lift reaction9, previously
supposed to keep lift production constant over a range of body angles, and
show that such a reaction would be inconsequential because locusts can
potentially correct for pitch disturbances within a single wingbeat The
static stability derivatives identify three natural longitudinal modes of
motion: one stable subsidence mode, one unstable divergence mode, and one
stable oscillatory mode (which is present with or without pitch attitude
control) The latter is identified with the short period mode of aircraft, and
shown to consist of rapid pitch oscillations with negligible changes in
forward speed The frequency of the short period mode (approx 10 Hz) is only
half the wingbeat frequency (approx 22 Hz), so the mode would become coupled
with the flapping cycle without adequate damping Pitch rate damping is shown
to be highly effective for this purpose — especially at the small scales
associated with insect flight — and may be essential in stabilising
locust flight Although having a short period mode frequency close to the
wingbeat frequency risks coupling, it is essential for control inputs made at
the level of a single wingbeat to be effective This is identified as a
general constraint on flight control in flying animals

Dynamic flight stability in the desert locust Schistocerca gregaria.

The integration of exteroceptive information in the flight control system of the locust was studied by determining the cellular basis of ocellar- (simple eye) mediated control of flight. Neural interactions that transform phase-independent sensory input into phase-specific motor output were characterized. Ocellar information about course deviations during flight was conveyed to the segmental thoracic ganglia by three pairs of large fast multimodal descending neurons. These made connections with thoracic motoneurons directly, via short-latency mono-or disynaptic pathways, and indirectly, via a population of intercalated thoracic interneurons. The synaptic potentials caused in the motoneurons by the direct pathway occurred at short latency and were adequate for summation with other types of sensory input. However, the strength of the synaptic effects of this pathway was weak compared with the central flight oscillator drive to the same motoneurons. In contrast, synaptic potentials evoked by the descending neurons in the thoracic interneurons were often large and brought these cells close to threshold. In turn, these interneurons always had stronger synaptic effects on postsynaptic flight motoneurons than did the descending neurons alone. We conclude that the indirect interneuronal pathway is more powerful in its effects on motoneurons than the direct pathway. Premotor thoracic interneurons, which received ocellar input appropriate for a role in correctional steering, were also rhythmically modulated during flight motor activity in phase with either depressor or elevator motoneurons. This phasic modulatory drive occurred in deafferented preparations, indicating that its source is the central oscillator for flight. Presentation of ocellar stimulation during flight motor activity showed that the central oscillatory modulation of the thoracic interneurons gated the transmission of sensory information through these interneurons. Ocellar-mediated postsynaptic potentials influenced the firing of thoracic interneurons only if they arrived during the proper phase of rhythmic drive. Thus the transmission of ocellar information from interneuron to motor neuron is possible only during appropriate phases of the flight cycle.

Integration of nonphaselocked exteroceptive information in the control of rhythmic flight in the locust.

The DNI, DNM and DNC descending interneurons all have very similar properties and are each at the convergence of visual, ocellar, wind-hair and other mechanoreceptor inputs. The 3 neurons respond almost exclusively to movement of the animal in space about its three axes of rotation. All are spatially and directionally selective. Movements in the preferred sense produce increasingly strong responses with amplitude and absolute position, while movements in the antipreferred sense usually elicit no response at all. Movements in the preferred sense, but towards, rather than away from, the normal flying position start to produce responses only as the animal approaches the normal flight position. The neurons function as feature detectors, responding only to specific sorts of deviation from course. DNI, DNM and DNC differ from one another principally in their directionality. DNI responds optimally to a diving banked turn to the ipsilateral side, DNM to downwards pitch, and the DNC to a diving banked turn to the contralateral side. The DN neurons contribute to the production of steering manoeuvres. They appear to be representatives of a larger class of descending interneurons bringing exteroceptive sensory input to the thoracic locomotory neuropil. The occurrence of this class of units in locusts and other insects is discussed.

Three descending interneurons reporting deviation from course in the locust. II. Physiology.

https://www.cell.com/trends/neurosciences/pdf/0166-2236(86)90079-2.pdf

Neuronal circuits controlling flight in the locust: how sensory information is processed for motor control

1. 1. This paper deals with the physiology, anatomy and function of the following classes of neurones in the locust Schistocerca : (a) neurones carrying ocellar information to the pterothorax (Descending Ocellar Neurones, DONs), (b) mesothoracic Flight Motor Neurones (FMNs), (c) a heterogenous class of inter- and intraganglionic thoracic interneurones which receive input from the DONs, here called Thoracic Ocellar Interneurones (TONs) without prejudice to their other possible inputs and functions.

2. 2. The thoracic arborizations of five different DONs are characterized. All project unilaterally to the pterothorax, four out of five to the ipsilateral mesothoracic or meso- and metathoracic ganglia. All are phasic OFF units, responding to stimulation either of one lateral ocellus or of the medial ocellus or of both, but none responded to the cephalic wind-hairs. Four of the five DONs showed no response decrement at stimulus frequencies up to 80 Hz. One showed habituation, recovery during a rest interval, and dishabituation in response to mechanical stimulation of a leg. There are more than six DONs, probably more than ten, in each connective.

3. 3. All types of recorded mesothoracic FMNs receive monosynaptic EPSPs from the DONs and/or delayed IPSPs (presumably via TONs) in at least some animals. The pattern of connection is compatible with the hypothesis that a roll or downward pitch deviation induces compensating movements of the wings to correct the deviation. Many of these DON/FMN connections were, however, only occasionally recorded. None of the ocellar EPSPs recorded in the FMNs elicited spikes.

4. 4. Most TONs receive monosynaptic EPSPs from one or more DONs, sometimes causing them to spike. Two receive delayed IPSPs, presumably via other TONs. At least one third of the recorded TONs spike in phase with either elevator or depressor FMNs during stimulated flight. Intraganglionic TONs in the mesothorax are all unilateral. Their anatomy suggests that they distribute input from DONs to various combinations of ipsilateral FMNs. Interganglionic TONs can be either unilateral or bilateral in the mesothoracic ganglion, and project unilaterally to the metathoracic (or rarely the prothoracic) ganglion, where at least one makes inhibitory synapses with a FMN.

5. 5. Phasic ocellar information reaches the FMNs by two routes. One produces fast subthreshold PSPs in the FMNs directly. The other produces spikes and PSPs in thoracic interneurones, at least some of which are phasically active during flight and are presynaptic to FMNs. The roles of the two pathways are discussed.

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C. H. F. Rowell

Papers

Integration of nonphaselocked exteroceptive information in the control of rhythmic flight in the locust.

Three descending interneurons reporting deviation from course in the locust. II. Physiology.

Neuronal circuits controlling flight in the locust: how sensory information is processed for motor control

Ocellar Input to the Flight Motor System of the Locust: Structure and Function

The taxonomy of invertebrate neurons: a plea for a new field