Bronislaw Cymborowski

The role of juvenile hormone during larval-pupal transformation of Spodoptera littoralis: Switchover in the sensitivity of the prothoracic gland to juvenile hormone

Application of JHA to the final instar of Spodoptera littoralis larvae before they attain maximal body weight causes delay to or completely blocks the onset of metamorphosis, as indicated by the dorsal vessel exposure. When the same dose of JHA is administered to the larvae just after their attaining maximal body weight, at the time of the onset of gut-emptying, metamorphosis is substantially accelerated. By means of ligature experiments, it is shown that JHA has a direct effect on the prothoracic glands. It inhibits them at the beginning of the final instar and then stimulates them shortly before pupation. It seems that under normal conditions JH is necessary for pupal cuticle formation; those larvae which pupate without JH show adult characteristics.

Circadian changes in protein synthesis in the neurosecretory cells of the central nervous system of Acheta domesticus

Abstract Synthesis of proteins and accumulation of neurosecretion in the neurosecretory cells of the pars intercerebralis and of the suboesophageal ganglion of Acheta domesticus were studied in the diurnal cycle by the autoradiographic method and by staining the neurosecretion. The insects were cultured under LD 12:12 conditions. The light period started at 6.00. It was demonstrated that both processes occur in a cyclic manner. The maximum of protein synthesis in the neurosecretory cells of the pars intercerebralis takes place in the light period at 14.00. In the neurosecretory cells of the suboesophageal ganglion this peak occurs during the period of darkness at about 24.00. After a period of intensified protein synthesis, an increase was observed in the degree to which neurosecretion accumulated in the cells studied. The changes observed were associated with the changes in the locomotor activity of the insects studied.

Circadian changes in RNA synthesis in the neurosecretory cells of the brain and suboesophageal ganglion of the house cricket

Abstract By the use of autoradiography an investigation was made in vitro of the daily cycle of intensity of RNA synthesis in the neurosecretory cells of the pars intercerebralis and the ventral cells of the suboesophageal ganglion in Acheta domesticus cultured under LD 12 : 12 conditions (rhythmic) and LL conditions (non-rhythmic). It was found that RNA synthesis in these centres of the nervous system of rhythmic insects takes place in a cyclic manner. The maximum RNA synthesis in the neurosecretory cells of the pars intercerebralis was observed immediately after the light period began. In the cells of the suboesophageal ganglion, however, we found two periods of intensive RNA synthesis, the first of which was shifted by about 6 hr in relation to the phase of intensive RNA synthesis in the pars intercerebralis. At the same time it was shown that a change takes place in the cross-section area of the nuclei of the neurosecretory cells of the pars intercerebralis and suboesophageal ganglion of crickets cultured under conditions of alternating light and darkness. In insects cultured under constant light conditions, RNA synthesis in the neurosecretory cells of the pars intercerebralis and the suboesophageal ganglion was not found to be cyclic. It is suggested that rhythmic lighting changes play a role in the process of forming the cyclic character of RNA synthesis in the centres of the central nervous system examined. The changes observed in the function of the neurosecretory cells of the pars intercerebralis and the suboesophageal ganglion were connected with the locomotor activity of the crickets.

Control of the circadian rhythm of locomotor activity in the house cricket

Abstract A detailed analysis was made of the locomotor activity of Acheta domesticus under conditions of 12 hr light and 12 hr darkness (LD 12 : 12) and of continuous darkness (DD). Under LD 12 : 12 it was found that there are three types of insects: (1) those beginning the period of increased locomotor activity immediately after darkness falls, (2) considerably before this time, and (3) considerably after this time. Under DD conditions the greater amount of the insects have a free-running rhythm shorter than 24 hr, while only a small percentage have a rhythm of more than 24 hr. Destruction of the neurosecretory cells of the pars intercerebralis by means of radio waves leads to the formation of hyperactivity and loss of locomotor activity rhythm when more than half of these cells are destroyed. Injection of reserpine into the insects haemolymph with doses of 10 μg/g of body weight results in a reduction in locomotor activity and produces arrhythmicity for 2 to 3 days under LD 12 : 12 conditions. Under DD conditions, however, this same dose results in a total and irretrievable loss of free-running rhythm. Histological studies of the brain of crickets following injection of reserpine show a large degree of accumulation of neurosecretion in the cells of the pars intercerebralis as compared with control insects. A hypothesis is put forward as to the way in which the brain centres regulating locomotor rhythm act in crickets.

Juvenilizing effect of cooling on Galleria mellonella

Cooling of larvae of G. mellonella in the final instar results in a serious disturbance in their later development. Such disturbance concerns the transition to additional larval stages, loss of the ability to spin cocoons, and the formation of individuals incapable of continuing normal development. The kind of disturbances and their degree depends on the age of cooled larvae and the cooling time applied. Cooling of 1- and 2-day-old larvae results in their transition to additional larval stages, while cooling larvae aged from 3 to 7 days of the duration of instar VII causes the formation of a large number of individuals incapable of further development. The loss of the capacity to spin cocoons depends solely on the cooling time applied.

Circadian activity rhythm of the house fly continues after optic tract severance and lobectomy

Under constant conditions, locomotor activity in about 50% of 63 adult Musca domestica continued to be rhythmic after bilateral severance of optic tracts or bilateral lobectomy. Apparently, the optic lobes of Musca do not contain the oscillator for rhythmic control of locomotor activity as has been proposed for other insects. In 20% of the individuals, several circadian components of activity rhythms were found after operation indicating a role of the optic lobes in the coupling of oscillators. The remaining 30% of the flies with severed optic tracts appeared to be arrhythmic. Most of these flies had vacuolized tissue in the central brain. However, disruption of rhythmicity did not correlate with a common pattern of degeneration. Therefore no conclusions can be drawn as to the localization of the circadian control of locomotor activity in the brain. Flies showing an arrhythmic activity pattern could still be synchronized by LD cycles. Activity did not occur solely during the light period as is the case in controls; but was phase delayed by about 6 hr towards the dark period. Since all flies with severed optic tracts could be synchronized by LD cycles, Musca domestica must possess extraocular photoreceptors.

Effect of azadirachtin on development, juvenile hormone and ecdysteroid titres in chilled Galleria mellonella larvae

Azadirachtin inhibited in a dose-dependent manner cold-induced supernumerary moults of last-instar Galleria mellonella larvae. Inhibition of supernumerary moults was greatest immediately after injection of azadirachtin into cold-treated, 1-day-old, last instars. Azadirachtin also induced disturbances in larval and pupal ecdysis and in metamorphic processes resulting in the formation of various intermediates and finally death. Azadirachtin decreased cold-induced elevation of juvenile hormone titres in the larval body but it had no effect on the allatotropic activity of the brain. However, it might have an effect on the prothoracicotropic function of the brain since, in chilled and azadirachtin-treated larvae, the ecdysteroid peak was higher and was delayed by 24h as compared with the first ecdysteroid peak in controls.

Transplantation of circadian pacemaker in the house cricket, Acheta domesticus L.

Abstract Destruction of neurosecretory cells in the pars intercerebralis of the brain causes the loss of locomotor activity rhythms and creates hyperactivity. When the brain is taken from a rhythmic cricket having both short‐period activity rhythm (S‐PAR) or long‐period activity rhythm (L‐PAR) and is implanted into the abdomen of such an arrhythmic recipient, it produces a characteristic locomotor activity rhythm of the host cricket. The implanted brain has an inhibitory effect on the locomotor activity of a hyperactive and arrhythmic recipient.

Circadian locomotor activity rhythms and their entrainment to light-dark cycles continue in flies (Calliphora vicina) surgically deprived of their optic lobes

Abstract In adult blow flies (Calliphora vicina), unilateral or bilateral cuts between the optic lobes and the brain, or complete bilateral lobectomy, failed to interrupt the circadian rhythm of locomotor activity or its entrainment to a daily light: dark cycle. It is concluded that the relevant circadian pacemakers are not within the optic lobes and that the compound eyes are not the photoreceptors for entrainment. As in other holometabolous insects, the pacemakers (the “clock”) and the photoreceptors may lie in the brain.

Circadian rhythms in behaviour and in the visual system of the blow fly, Calliphora vicina

Abstract Flies exhibit circadian rhythms in their locomotor activity and in the sensitivity of the visual system to light. In their visual system, circadian rhythms have been detected not only in the retina but also in the first optic neuropile, the lamina. In the lamina two classes of interneuron, L1 and L2, which receive photoreceptor input, exhibit daily size changes in their lamina axons. In principle, these two circadian rhythms, in the flys behaviour and in structural changes in the lamina, could both be controlled by the same oscillator or by different oscillators. To examine these two alternatives we have studied both rhythms in the blow fly Calliphora vicina. The locomotor activity rhythm of C. vicina was monitored in light/dark (LD 12:12) and in constant darkness (DD). After this, each fly was fixed and the cross-sectional areas of L1 and L2s lamina axons were examined during the day and night in LD, and in the flys active and rest periods in DD. In LD, L1 and L2s axons were larger during the day than during the night and the larger sizes correlated with the activity of the flies. Moreover, arrhythmic flies showing a high activity level had larger cells than less active flies. In DD, however, both circadian rhythms became out of phase. The results indicate a correlation between both circadian rhythms, which run in-phase in LD, larger cell sizes corresponding to higher activity in the flies. In DD, however, they run independently, so that these rhythms are probably generated by different circadian clocks.