Yasuhiko Watari

Adult eclosion timing of the onion fly, Delia antiqua, in response to daily cycles of temperature at different soil depths

For insects pupating in the soil, the day/night temperature cycle may provide a primary time cue (Zeitgeber) for adult eclosion to occur at an appropriate time of the day. In the soil, however, the phase of temperature cycle is delayed with depth because of the low heat conductivity of the soil. Therefore pupae located deeper in the soil may compensate for the depth-dependent phase delay of Zeitgeber to avoid mistimed emergence. We examined the adult eclosion timing of the onion fly, Delia antiqua, pupating at different depths in soil and under various thermoperiods in the laboratory to determine if such compensation indeed occurs. We found that D. antiqua is able to compensate for the depth-dependent phase delay of the Zeitgeber by advancing the eclosion timing in response to the amplitude of the temperature cycle decreasing with depth.

Comparison of the circadian eclosion rhythm between non-diapause and diapause pupae in the onion fly, Delia antiqua.

The influence of pupal diapause on adult eclosion rhythm of Delia antiqua was investigated. When non-diapause and diapause pupae were exposed to various photoperiods at 15, 20 and 25 degrees C, both of them emerged as adults close to the light-on time, but the phase of eclosion varied with photoperiod and temperature. Moreover, there was a significant difference in the eclosion time between non-diapause and diapause pupae; the eclosion peak of diapause pupae was earlier than that of non-diapause pupae. When non-diapause and diapause pupae were transferred to constant darkness (DD) after having experienced LD 12:12 at 15, 20 and 25 degrees C, both showed circadian rhythmicity in eclosion. Although the free-running period (tau) decreased slightly as temperature increased in both non-diapause and diapause pupae, the latter tended to show shorter tau than the former. This observation suggests that the observed difference in eclosion time in LD cycles between non-diapause and diapause pupae is due to differences in tau.

Interacting effect of thermoperiod and photoperiod on the eclosion rhythm in the onion fly, Delia antiqua supports the two-oscillator model.

Daily light and temperature cycles entrain adult eclosion rhythms in many insect species, but little is known about their interaction. We studied this problem in the onion fly, Delia antiqua. Pupae were subjected to various combinations of a photoperiod of 12L:12D and thermoperiods. The thermoperiods consisted of 12h warm phase (W) and 12h cool phase (C), giving a mean temperature of 25 degrees C with different temperature steps of 8, 4 and 1 degrees C. As the phase relation of the two Zeitgebers was varied, the phase of eclosion rhythm was shifted, depending on the phase angle with the light cycle and the amplitude of the temperature cycle. When the temperature step in the thermoperiod was 8 degrees C (WC 29:21 degrees C), the eclosion rhythm was entrained mainly to thermoperiod rather than photoperiod. In the regime with a 4 degrees C temperature step (WC 27:23 degrees C), both thermoperiod and photoperiod affected eclosion rhythm, and a phase jump of the eclosion rhythm occurred when the warm phase of thermoperiod was delayed 15-18h from light-on. In regimes with a 1 degrees C temperature step (WC 25.5:24.5 degrees C), the eclosion rhythm was completely entrained to photoperiod. The observed interacting effect of light and temperature cycle on the eclosion rhythm in D. antiqua can be explained by the two-oscillator model proposed by Pittendrigh and Bruce (1959).

Comparison of the circadian eclosion rhythm between non-diapause and diapause pupae in the onion fly, Delia antiqua: the effect of thermoperiod.

When non-diapause and diapause pupae of Delia antiqua were exposed to various thermoperiods where thermophase (T) was 25 degrees C and the cryophase (C) was 15 or 20 degrees C (TC(15) or TC(20)) in constant darkness (DD), the majority of both types of flies emerged before the rise in temperature. Eclosion time was delayed at the lower cryophase temperature. Moreover, there was a significant difference in the time of adult eclosion between non-diapause and diapause pupae; diapause pupae eclosed earlier than non-diapause pupae. When the two types of pupae were transferred to a constant low temperature (15 or 20 degrees C) after having experienced TC(15) or TC(20) 12:12 h, they showed circadian rhythmicity in eclosion. The free-running period (tau) of the eclosion rhythm changed after transfer to constant low temperatures in both non-diapause and diapause pupae, suggesting that this change represents a transient cycle until the temperature-sensitive oscillator is coupled again to the temperature-insensitive pacemaker. However, diapause pupae tended to show a shorter tau than non-diapause pupae. This observation suggests that the difference in adult eclosion time under thermoperiodic conditions between non-diapause and diapause pupae is related to their different tau s.

Melatonin in drinking water influences a circadian rhythm of locomotor activity in the house cricket, Acheta domesticus

Abstract The locomotor activity of Acheta domesticus in light–dark (LD) cycles became more synchronous, i.e. it had a smaller variance around the mean, as the concentration of melatonin in drinking water increased. The ratio of night activity to total activity was increased and the acrophase was delayed by melatonin drinking. Bouts of activity also decreased in LD cycles as the concentration of melatonin increased. The number of activity bouts in the free-running rhythm in DD, however, was not influenced by the melatonin concentration. The most apparent effect of melatonin on the activity in LD cycles seems to be the elimination of day-time activity. Not only did melatonin eliminate day-time activity to give a better synchronization in LD cycles but it also affected the free-running rhythm, which tended to be more synchronized, i.e. the activity became more concentrated, as the concentration of melatonin increased. The amplitude of free-running rhythms also increased as the melatonin concentration increased, even at 100 μg melatonin/ml, though the amplitude in DD was lower than that in LD cycles.

The pars intercerebralis as a modulator of locomotor rhythms and feeding in the American cockroach, Periplaneta americana

It has been shown that in orthopteran insects each of the optic lobes (OLs) contains a circadian pacemaker controlling locomotor activity and that the pars intercerebralis (PI) modifies the activity level. However, the present study showed Period protein-like immunoreactivity (PER-ir) in the PI and dorsolateral protocerebrum (DL) as well as in the OLs in the American cockroach, Periplaneta americana, which raised the possibility that the PI or DL could be a clock element. Therefore, we removed the PI or DL surgically and observed the effects on locomotor rhythms and feeding behavior. In constant darkness (DD), cockroaches with an ablated PI (PIX-DD) showed arrhythmicity in locomotion and a massive increase in food consumption that led to increased body length and weight, while PIX cockroaches reared under LD 12:12 (PIX-LD) and the sham-treated cockroaches in DD (CNT-DD) showed rhythmicity and no increase in food consumption. Statistical analysis showed that arrhythmicity was not accompanied by hyperactivity, suggesting that the PI is involved in the regulation of locomotor activity and feeding in DD. The activities of alpha-amylase and proteases were found to be markedly elevated in the midgut of PIX-DD cockroaches but not in PIX-LD cockroaches. Taken together, these results indicate that the PI modulates locomotor rhythms and feeding behavior of cockroaches in a light-dependent manner. The PI and the OL may regulate circadian rhythms and feeding via distinct pathways.

Effects of photoperiod and aging on locomotor activity rhythms in the onion fly, Delia antiqua.

At photoperiods longer than 8h per 24h, adults of the day-active onion fly Delia antiqua showed a major peak of locomotor activity in the late photophase and also bursts of activity induced by lights-on or lights-off. At shorter photoperiods the activity peaks fused. After transfer from long photoperiods to constant darkness (DD), the rhythm free-ran, but only the major peak persisted. This suggests that only the major peak is controlled by the circadian pacemaker. At long photoperiods, the daily phase of the major peak occurred progressively later with age. As a result, the activity at short photoperiods often shifted from photophase to scotophase in old flies. The free-running period (tau) also changed with age; tau was shorter than 24h until 14-20 days after eclosion and thereafter became longer, but a few individuals repeated changes in tau. The phase delay of locomotor activity with age in D. antiqua would be attributable to the increase in tau.

Thermoperiodic regulation of the circadian eclosion rhythm in the flesh fly, Sarcophaga crassipalpis.

We recorded the eclosion time of the flesh fly, Sarcophaga crassipalpis, at different depths in the outdoor soil and under temperature cycles with various amplitudes in the laboratory, to examine the timing adjustment of eclosion in response to temperature cycles and their amplitudes in the pupal stage. In the soil, most eclosions occurred in the late morning, which was consistent with the eclosion time under pseudo-sinusoidal temperature cycles in the laboratory. The circadian clock controlling eclosion was reset by temperature cycles and free-ran with a period close to 24h. This clock likely helps pupae eclose at an optimal time even when the soil temperature does not show clear daily fluctuations. The eclosion phase of the circadian clock progressively advanced as the amplitude of the pseudo-sinusoidal temperature cycle decreased. This response allows pupae located at any depth in the soil to eclose at the appropriate time despite the depth-dependent phase delay of the temperature change. In contrast, the abrupt temperature increase in square-wave temperature cycles reset the phase of the circadian clock to the increasing time, regardless of the temperature amplitude. The rapid temperature increase may act as the late-morning signal for the eclosion clock.

The onion fly modulates the adult eclosion time in response to amplitude of temperature cycle

To confirm whether the amplitude of diel temperature cycles causes a phase shift of adult eclosion rhythm of the onion fly, Delia antiqua, the peak time (ØE) of adult eclosion was determined under various thermoperiods with a fixed temperature either in the warm or cool phase and temperature differences ranging from 1°C to 4°C between the two phases. Irrespective of the temperature level during the warm or cool phase, ØE occurred earlier with decreasing amplitude of the temperature cycle. The results strongly support the previous conclusion of Tanaka and Watari (Naturwissenschaften 90:76–79, 2003) that D. antiqua responds to the amplitude of temperature cycle as a cue for the circadian adult eclosion timing. The phase advance was larger in thermoperiods with a fixed warm-phase temperature than in those with a fixed cool-phase temperature. This might be ascribed to the interaction between the amplitude and level of temperature in the thermoperiodic regimes.

Is early morning adult eclosion in insects an adaptation to the increased moisture at dawn

Many dipteran insects emerge as adults in early morning. One of the possible explanations for the adaptive role of early morning adult eclosion in insects is that the relatively humid and cool air would favor expansion of the wing in newly emerged adults. The dry and hot air around the noon would exert a harmful effect on the expanding wing by losing water at a faster rate. To confirm this hypothesis, the effect of desiccation and high temperature on wing-expansion of newly emerged adults of the onion fly, Delia antiqua was investigated. Desiccation had no or little effect on wing expansion, but high temperatures disturbed it significantly. It is likely that the increase in temperature in the middle of the day would interfere with the wing expansion of newly emerged adults, thereby selecting for the temporal gate of the adult eclosion in the early morning.