Bimodal modulation of background activity in an identified descending interneuron

In the absence of any obvious input, sensory neurons and interneurons can display resting or spontaneous activity. This is often regarded as noise and removed through trial averaging, although it may reflect history-dependent modulation of tuning or fidelity and, thus, be of functional relevance to downstream interneurons. We investigated the history dependence of spontaneous activity in a pair of identified, bimodal descending interneurons of the stick insect, called contralateral ON-type velocity-sensitive interneurons (cONv). The bilateral pair of cONv conveys antennal mechanosensory information to the thoracic ganglia, where it arborizes in regions containing locomotor networks. Each cONv encodes the movement velocity of the contralateral antenna, but also substrate vibration as induced by discrete tapping events. Moreover, cONv display highly fluctuating spontaneous activity that can reach rates similar to those during antennal movement at moderate velocities. Hence, cONv offer a unique opportunity to study history-dependent effects on spontaneous activity and, thus, encoding fidelity in two modalities. In this work, we studied unimodal and cross-modal effects as well as unilateral and bilateral effects, using bilateral recordings of both cONv neurons, while moving one antenna and/or delivering taps to induce substrate vibration. Tapping could reduce spontaneous activity of both neurons, whereas antennal movement reduced spontaneous activity of the contralateral cONv neuron only. Combination of both modalities showed a cooperative effect for some parameter constellations, suggesting bimodal enhancement. Since both stimulus modalities could cause a reduction of spontaneous activity at stimulus intensities occurring during natural locomotion, we conclude that this should enhance neuronal response fidelity during locomotion. NEW & NOTEWORTHY The spontaneous activity in a pair of identified, descending insect interneurons is reduced depending on stimulus history. At rest, spontaneous activity levels are correlated in both interneurons, indicating a common drive from background activity. Whereas taps on the substrate affect both interneurons, antennal movement affects the contralateral interneuron only. Cross-modal interaction occurs, too. Since spontaneous activity is reduced at stimulus intensities encountered during natural locomotion, the mechanism could enhance neuronal response fidelity during locomotion.

The movement of “false antennae” in butterflies with “false head” wing patterns

In many butterfly species of the family Lycaenidae, the morphology and color pattern of the hind wings, together with certain behaviors, suggests the presence of a false head (FH) at the posterior end of the perching individual. This FH is considered an adaptation to escape from visually oriented predators. A frequent component of the FH are the tails that presumably resemble the antennae, and the typical hind wings back-and-forth movement along the sagittal plane (HWM) performed while perching apparently move the tails in a way that mimics antennal movement. By exposing 33 individuals from 18 species of Lycaenidae to a stuffed insectivorous bird, we tested two alternative hypotheses regarding HWM. The first hypothesis proposes that, when the butterfly is observed at close range, the HWM distorts the shape of the false head thus reducing its deceiving effect and, therefore, selection will favor butterflies that stop moving their wings when a predator is close by; the second hypothesis says that an increase in the frequency of HWM improves its deflective effect when the butterfly confronts a predator at close range. Our results tend to support the second hypothesis because half of the butterflies started to move their hind wings or increased the rate of HWM when exposed to the stuffed bird; however a substantial proportion of butterflies (30%) stopped moving their hind wings or decreased the rate of HWM as expected from the first hypothesis. Our observations also showed that there is great variation in the rates of HWM, and demonstrated the existence of alternative ways of producing “vivid” movement of the hind wing tails (the “false antennae”) in the absence of HWM.

The behaviour of adult Sitona lepidus Gyllenhal (Coleoptera Curculionidae) in response to white clover

Individual adult Sitona lepidus were given the choice between damaged or undamaged seedlings mature plants of white clover damp soil or a blank in laboratory experiments carried out in a simple olfactometer Adult weevils displayed five different behavioural responses two of which head lifting and antennal movement appeared to be associated with host location In choice tests 7484 of adults chose a white clover plant over the blank or damp soil When given a choice 72 of adults selected white clover seedlings over mature plants Root and leaf damage did not affect response of S lepidus to white clover seedlings

A Method for Chronically Implanting Stimulating Electrodes into the Brains of Locusts, and some Results of Stimulation

1. Methods are described for implanting permanent stainless-steel electrodes into the brains of locusts, for stimulating the brain under near-normal conditions, and for localizing the electrode subsequently. 2. Threshold currents measured under these conditions are lower than those required in acute preparations, or if the animal is restrained. 3. The results of stimulation are described for four common aspects of behaviour. These are antennal movement, locomotion, feeding and sexual behaviour. 4. The effect of stimulation on antennal and locomotory movements largely confirms previous work on crickets. 5. Feeding and foraging behaviour, which is a very common result, is shown to be almost completely determined by peripheral stimuli at the time of brain stimulation. The role of the latter is permissive or disinhibitory rather than causal or excitatory. 6. Integrated sexual behaviour is occasionally inhibited, but never elicited, by stimulation. This contrasts with observations on crickets, and its implications are discussed.

ROW-TYPE OVIPOSITION IN NEODIPRION SAWFLIES AS EXEMPLIFIED BY THE EUROPEAN PINE SAWFLY, N. SERTIFER (GEOFF.)

Many Neodiprion sawflies lay their eggs in a row in small pockets cut into the edges of the mature needles of various pines. These rows of eggs are remarkable for the regularity of the spacing between successive egg pockets. The regularity of egg spacing by N. sertifer is shown to arise from a stereotyped pattern of leg movements during the shift between the sites of successive egg pockets. Spacing is effected by two sets of leg movements, in each of which the three pairs of legs move forward in order from back to front. While the effective forward movement of all legs is the same, the total forward movement of the metathoracic legs is greater than that of the other legs by an amount equal to the length of an egg pocket. The metathoracic legs retrace their steps by this length as the initial incision for each new egg pocket is cut, evidently providing the force by which this incision is made. The grip-points of the legs are on the needle edge opposite to that receiving eggs, so that the wider the needle, the greater the proportion of leg length required to reach across it, and the smaller the proportion of leg movement reflected in the spacing between eggs. In this way egg spacing varies inversely with needle width. Observations on copulation, antennal movement, and related oviposition behavior are included.

Flight Activity in the Blowfly, Calliphora Erythrocephala, in Relation to Wind Speed, With Special Reference to Adaptation

1. A study has been made of the effect of wind speed on the flight activity of a population of the blowfly Calliphora erythrocephala in a small wind tunnel. 2. Under the experimental conditions wind has an activating effect up to about 0·7 m./sec., above which it inhibits flight. 3. Below 0·5 m./sec., activity decreases rapidly with decrease of wind speed and then remains at or close to the lower value. The increase of activity arising from increase of wind speed is much slower, the state of low activity tending to persist. 4. At speeds between 0·5 and 4·5 m./sec. the changes of activity in response to both increase and decrease of wind are very rapid and are followed by a considerable degree of adaptation in each case. 5. Inhibition of activity by the change of wind speed from 0·5 to 4·5 m./sec. and to 8·0 m./sec. results from the movement of the third antennal joint relative to the head. 6. When this antennal movement is prevented, the change to 4·5 m./sec. causes activation if the initial activity is low, and the change to 8·0 m./sec. causes an increase of walking activity although flight is decreased for mechanical reasons. 7. Exposure to the higher speeds causes an additional depression of activity not dependent on movement of the third antennal joint.

Relation of the Rate of Antennal Movement in Daphnia to the Number of Eggs Carried in the Brood Pouch

The rate of antennal swimming movements of Daphnia is proportional to the number of eggs or young carried in the brood pouch. An increased rate of antennal movement is not a direct result of the better nutrition which produces more eggs. The increased swimming rate may be necessary to counteract a change in centre of gravity caused by the posterior position of the brood pouch containing eggs.