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Diapause induction and clock mechanism in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae)
Journal of Insect Physiology 50 (2004) 373–381 www.elsevier.com/locate/jinsphys
Diapause induction and clock mechanism in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae) Xiaoping Wang a,b, Feng Ge a, Fangsen Xue c,, Lanshao You b b
a Institute of Zoology, Chinese Academy of Science, Beijing 100080, China College of Plant Protection, Hunan Agricultural University, Changsha 410128, China c Institute of Entomology, Jiangxi Agricultural University, Nanchang 330045, China
Received 30 September 2003; received in revised form 29 December 2003; accepted 4 January 2004
Abstract Photoperiodic control of diapause induction was investigated in the short-day species, Colaphellus bowringi, which enters sumv mer and winter diapause as adult in the soil. Photoperiodic responses at 25 and 28 C revealed a critical night length between 10 and 12 h; night lengths 12 h prevented diapause, whereas night lengths <12 h induced summer diapause in different degree. Experiments using non-24-h light–dark cycles showed that the duration of scotophase played an essential role in the determination of diapause. Night-interruption experiments with T¼ 24 h showed that diapause was effectively induced by a 2-h light pulse in most scotophases; whereas day-interruption experiments by a 2-h dark break had a little effect on the incidence of diapause. The experiments of alternating short-night cycles (LD 16:8) and long-night cycles (LD 12:12) during the sensitive larval period showed that the information of short nights as well as long nights could be accumulated. Nanda–Hamner experiments showed three declining peaks of diapause at 24 h circadian intervals. Bu¨nsow experiments showed two very weak peaks for diapause induction, one being 8 h after lights-off, and another 8 h before lights-on, but it did not show peaks of diapause at a 24 h interval. These results suggest that the circadian oscillatory system constitutes a part of the photoperiodic clock of this beetle but plays a limited role in its photoperiodic time measurement. # 2003 Elsevier Ltd. All rights reserved. Keywords: Colaphellus bowringi; Diapause; Photoperiodism; Nanda–Hamner experiments; Bu¨nsow experiments
1. Introduction The fact that insects and mites (as well as many other organisms) are able to discriminate long days from short days, with important developmental consequences, has led to the concept of photoperiodic time measurement. Photoperiodic time measurement of diapause induction has been investigated in a number of insects and mites, and a variety of models have been developed for photoperiodic clock in these species. According to some of these models, the photoperiodic clock is based on a mechanism separate from the circadian system, that is, a so-called ‘‘hourglass.’’ According to other models, the clock is based on one or more circadian oscillators that may be coupled to each other
Corresponding author. Fax: +0086-791-3814107. E-mail address: [email protected] (F. Xue).
0022-1910/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jinsphys.2004.01.002
and may or may not show a certain degree of damping (see Vaz Nunes and Saunders, 1999). The experimental evidence for the participation of circadian oscillation in photoperiodic time measurement comes almost exclusively from two types of experiments, the so-called Nanda–Hamner protocol and the Bu¨nsow protocol (Nanda and Hamner, 1958 Bu¨nsow, 1960). In Nanda– Hamner experiments, insects or mites are exposed to photoperiods with extended night lengths coupled with a fixed length of light. In Bu¨nsow experiments, animals are exposed to photoperiods with an extended night length, which is systematically interrupted by a 1- or 2h scanning pulse of light. If, in such protocols the incidence of diapause rises and falls with a period of about 24 h, it is generally interpreted as involvement for the presence of a circadian clock. If the photoperiodic response with either protocol does not show rhythmic fluctuations with a period of about 24 h, it suggests for
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an hourglass clock or a rapidly damping oscillator (Saunders and Lewis, 1987). The cabbage beetle, Colaphellus bowringi Baly, is a serious pest of crucifers in the mountain areas of the Jiangxi Province, primarily feeding on the developing leaves of radish, Raphanus sativus and Chinese cabbage, Brassica chinensis. The beetle aestivates and hibernates as adult in the soil. There are two distinct infestation peaks in the field, one in spring and a second in autumn (Xue et al., 2002a). The cabbage beetle is a short-day species. However, its photoperiodic response highly depends on temperature. All adults v enter diapause at 20 C regardless of photoperiod. High temperatures strongly weaken the diapauseinducing effect of long day lengths. The diapauseaverting influence of short day lengths is expressed only v at temperatures above 20 C (Xue et al., 2002b). The beetle is an ideal experimental animal for a formal analysis of the photoperiodic clock, as it is very easy to rear, and it takes no more than 18 days for a photov periodic response experiment at 25 C. In the present study, we investigated diapause induction in C. bowringi with various light–dark cycles, night-interruption experiments, and Nanda–Hamner and Bu¨nsow protocols to analyze the photoperiodic time measurement of this insect.
2. Materials and methods The laboratory strain of C. bowringi used for the experiments has already been described by Xue et al. (2002b). The experiments were performed with the offspring of non-diapause adults obtained by rearing larv vae at 25 C and LD 12:12 that avert diapause. Just after hatching the larvae were transferred to round plastic boxes with a layer of soil and fresh radish leaves. Each box contained at least 50 individuals and two replicates were tested under each treatment. All experiments were executed in illuminating incubators (LRH-250-GS) equipped with four fluorescent
30 W tubes controlled by an electric timer. Light intensity at the level of the beetles was 500–700 lx and variv ation of temperatures was 1 C. The scotophase was controlled manually by enclosing the rearing boxes in opaque hoods. The critical night length is defined as the night length that elicits 50% diapause response. As diapause inducv tion declined at the temperature of 28 C, we took the midpoint between the maximal and minimal response as the critical night length for this species. Diapausing adults of C. bowringi were very easy to identify, because all diapausing adults have a digging behaviour and burrow into the soil after 4–6 days of v feeding at 25 or 28 C.
3. Results 3.1. Photoperiodic response curves under 24-h light–dark cycles Photoperiodic response curves for diapause induction in C. bowringi were similar at constant temperav tures of 25 and 28 C, but diapause occurred at a lower v v level at 28 C than at 25 C (Fig. 1). The critical night length appeared to be between 10 and 12 h. Photoperiods with dark phases from 12 to 24 h prevented diapause effectively, whereas short nights <12 h induced diapause in different degree. Short nights of 4– 8 h resulted in the highest diapause (100% diapause at v v 25 C; over 70% diapause at 28 C), whereas diapause induction was 74.6% in LD 2:22 and 54.9% in LL at 25 v v C, and 29.8% in LD 2:22 and13.3% in LL at 28 C. 3.2. Photoperiodic responses under non-24-h light–dark cycles Photophases of 10, 12, 14 and 16 h were combined with different lengths of scotophase of 4–24 h (Fig. 2). When scotophases were 4 and 8 h, all individuals entered diapause regardless of the length of photo-
Fig. 1. Photoperiodic response curves for the induction of diapause in Colaphellus bowringi under 24 light–dark cycles at constant temperatures v of 25 and 28 C. n ¼ 51 124 for each point.
X. Wang et al. / Journal of Insect Physiology 50 (2004) 373–381
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v
Fig. 2. Diapause incidence in Colaphellus bowringi under non-24-h photoperiodic cycles at 25 C. n ¼ 69 114 for each point.
phase. With scotophases ranging from 12 to 24 h, most of the individuals developed without diapause independent of the length of the photophase. The results suggest that the incidence of diapause was determined by the length of the scotophase. 3.3. Interruption experiments of photoperiodic response The night of LD 12:12 was systematically interrupted v by a 2-h light pulse at 25 C (Fig. 3). The result showed that early and late light pulses reversed the long night effect and induced diapause effectively. The
light pulse induced 20.4% diapause at 4–6 h after the onset of scotophase. To determine the effect of day interruption, photophase of LD 14:10 (a most effective diapause-inducing photoperiod) was systematically interrupted by a 2-h dark pulse (Fig. 4). The result showed that only the dark pulse 3–4 h after lights-on suppressed diapause, while others had no effect. 3.4. Accumulation of short-night and long-night cycles Xue et al. (2002b) have shown sensitive period in C. v bowringi is mainly during the larval period at 25 C.
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v
Fig. 3. Night interruption for diapause induction of Colaphellus bowringi in a LD 12:12 25 C regime. The scotophase was systematically scanned by a 2-h light pulse.
v
Fig. 4. Diapause response by day interruption in a LD 14:10 25 C regime in Colaphellus bowringi. The photophase was systematically scanned by a 2-h dark pulse.
The larval period lasts for 8 days (including one day of prepupal stage). Fig. 5 shows the diapause incidence under LD 16:8 was 94%, 16% under LD 12:12 and 42% in continuous light when only the larvae were exposed to the photoperiods for 8 days, but pupae and adults were held in LL. The LL induced intermediate rate of diapause. To investigate whether only the diapause-promoting effect of short nights is accumulated or the diapausereversing effect of long nights is accumulated or both occur, the larvae were exposed to alternating (Fig. 6A) or non-alternating (Fig. 6B) short-night (LD 16:8) and long-night cycles (LD 12:12) and pupae and adults were placed in LL. When one short-night cycle (LD
Fig. 5.
16:8) alternated with one long-night cycle (LD 12:12) during larval period or vice versa, the diapause-averting effect of long nights was strongly expressed (only 26.1% diapause in Fig. 6Aa; 34.2% diapause in Fig. 6Ab). However, when two or more short-night cycles alternated with equal number of long-light cycles (i.e. the larvae were exposed to three consecutive or four cumulative short-night cycles in the first 6 days of larval period), the diapause-inducing effect of short nights was expressed (48.6% diapause in Fig. 6Ad; 66.0% diapause in Fig. 6Ae; 66.3% diapause in Fig. 6Ah), whereas when two or more long-night cycles alternated with the same number of short-night cycles (i.e. the larvae were exposed to three consecutive or
v
Incidence of diapause in Colaphellus bowringi when exposed to A: continuous light (LL); B: LD 12:12 and C: LD 16:8 at 25 C.
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Fig. 6. Incidence of diapause in Colaphellus bowringi in response to alternating (a) or non-alternating (b) short-night cycles (LD 16:8) and longv night cycles (LD 12:12) at 25 C.
four cumulative long-night cycles in the first 6 days of larval period), the diapause-averting effect of long nights was expressed (Fig. 6Ac,f). It seems that the diapause-inducing effect of short nights is more dependent on the number of consecutive cycles than is the diapause-averting effect of long nights. Similar results were also shown in experiments that used non-alternating cycles (Fig. 6B). The diapause-inducing effect of short nights increased (from 69.5% diapause to 93.0% diapause in Fig. 6Ba–d) with an increasing number of consecutive cycles (from two short-night cycles to five short-night cycles), whereas the diapause-averting effect of long nights did not show a significant change among the different sequent cycles (25.3% diapause for two long-night cycles in Fig. 6Be; 24.4% diapause for three long-night cycles in Fig. 6Bf; 24.1% diapause for four long-night cycles in Fig. 6Bg; 18.6% diapause for five long-night cycles in Fig. 6Bh). These results indicate that the information of consecutive shortnight cycles can be accumulated effectively during the larval period. 3.5. Nanda–Hamner experiment (or resonance experiment) In Nanda–Hamner experiments, the beetles were v exposed to repeated cycles at 25 C in which the duration of the light was 12 and 16 h but the scotophase was varied from 4 to 60 h in 4 h intervals (Fig. 7).
Three peaks of diapause induction were observed in both photoperiodic responses when the scotophase was 4–8, 28–32 and 52 h. However, the second and the third peaks were much smaller than the first peak. 3.6. Bu¨nsow experiments In Bu¨nsow experiments, the beetle were exposed to a cycle of 12 h of light and an extended scotophase of 36, 48 and 60 h. The scotophases were scanned by a 2-h light pulse at 4-h intervals (Fig. 8). The photoperiodic response curves exhibited two very weak peaks of diapause induction, the first peak occurred 8 h after the onset of darkness, the second 8 h before lights-on, but the photoperiodic response curves did not show circadian peaks at a 24-h interval.
4. Discussion The photoperiodic response shown by C. bowringi is of the typical short-day type. All scotophases 12 h inhibited diapause effectively, whereas scotophases <12 h induced summer diapause in different degree. The highest rate of diapause was found in the short scotophases of 4–8 h. The diapause incidence decreased at the extremely short scotophase of LD 22:2 and LL (Fig. 1). In many long-day insects, the photoperiodic response curves for diapause induction showed that the
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v
Fig. 7. Incidence of diapause in Colaphellus bowringi in resonance experiments using a constant photophase of 12 or 16 h at 25 C. n ¼ 71 123 for each point.
diapause-inducing effect of long nights declined with ultra-long nights (>19 h). This is shown, for example, by Danilevskii (1965) for the cabbage butterfly, Pieris v brassicae (at 24 C); Masaki and Kikukawa (1981) for the Indian meal moth, Plodia interpunctella; Saunders (1983) for the linden bug, Pyrrhocoris apterus; Yoshida and Kimura (1995) for the fly, Chymomyza costata (at v 20 C); Kroon et al. (1997) for the spider mite, Tetrav nychus urticae (at 22 C). All the tested cases of photoperiodic response in long-day species are highly sensitive to night interruption, and the long night effect can be reversed by light pulses (Beck, 1980; Saunders, 1982a). However, the sensitive position to light pulse varied considerably among different species. Some insects exhibit two points of apparent light sensitivity (the so-called A and B peaks). Some insects show only one peak (A or B peak). Some show a wide plateau, in which all scotophases separated by a light pulse that are shorter than the critical night length averted diapause effectively (Koveos et al., 1993; Wei et al., 2001). Even the same species may have different patterns of response depending on the experimental conditions (Masaki, 1984). In the short-day species C. bowringi, a 2-h light pulse reversed the long night effect in most positions of scotophases and exhibited a bimodal response of diapause induction (Fig. 3), whereas a 2-h dark break had a little effect on the incidence of diapause (Fig. 4). This suggests that photoperiodic response in short-day species is also highly sensitive to night interruption. The photoperiodic response needs a photoperiodic ‘clock’ to measure whether the part of a light/dark
cycle is longer or shorter than the critical night length as well as a ‘counter’ to accumulate the photoperiodic information during the sensitive period. It has been shown that the accumulation of photoperiodic information can be achieved in different ways in different insects. In the aphid Megoura viciae, long-night cycles are accumulated in a straightforward fashion independent of the accompanying photophase (Hardie and Vaz Nunes, 1994), whereas the effect of short nights is dependent on the photophase length (Hardie, 1990). In the flesh fly Sarcophaga argyrostoma and the black bean aphid Aphis fabae, long-night accumulation is temperature compensated, but short-night accumulation is not (Saunders, 1992; Vaz Nunes and Hardie, 1999). In the spider mite T. urticae and the large cabbage white butterfly P. brassicae, long and short-night cycles seem to be accumulated in different ways (Veerman and Vaz Nunes, 1987; Dumortier, 1994). In the cabbage moth Mamestra brassicae, however, only long nights are accumulated, not short nights (Goryshin and Tyshchenko, 1973). In the present work, we have shown that in C. bowringi, when one short-night cycle (LD 16:8) is alternated with one long-night cycle (LD 12:12) during larval period or vice versa, the diapauseaverting effect of long nights is strongly expressed (Fig. 6A). It could be inferred that the information of a long-night cycle can be accumulated effectively one by one. However, when two or more short-night cycles alternate with equal number of long-night cycles, the diapause-inducing effect of short nights is expressed (Fig. 6Ad,e,h). It therefore seems that a consecutive exposure to short-night cycles (at least 2 days) is
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v
Fig. 8. Incidence of diapause in Colaphellus bowringi in Bu¨nsow experiments at 25 C with a constant photophase of 12 h and a scotophase of 36 h (A), 48 h (B), and 60 h (C) which was systematically scanned by a 2-h light pulse. n ¼ 56 93 for each point.
required for diapause induction. The results indicate that information about short nights as well as long nights can be accumulated during larval period in this species, but in different ways. Nanda–Hamner protocols have now been applied to a large number of insects and three mites in relation to induction (see Vaz Nunes and Saunders, 1999; Wei et al., 2001). In some species, both negative and positive Nanda–Hamner results for diapause induction have been obtained depending on temperature, e.g. in S. argyrostoma (Saunders, 1973, 1982b), Drosophila auraria (Pittendrigh, 1981), Ostrinia nubilalis (Takeda and Skopik, 1985), Aleyrotes proletella (Adams, 1986), P. brassicae (Veerman et al., 1988), Amblyseius potentillae (Van Houten and Veenendaal, 1990), Calliphora
vicina (Vaz Nunes et al., 1990), Drosophila triauraria (Yoshida and Kimura, 1993), M. brassicae (Kimura and Masaki, 1993) and Pseudopidorus fasciata (Wei et al., 2001). In C. bowringi, Nanda–Hamner experiv ments at a constant temperature of 25 C yield positive results with three declining peaks of diapause at 24 h intervals. However, in these Nanda–Hamner experiments with C. bowringi, it is impossible to prov duce circadian peaks of diapause at 20 C, as at these temperatures all individuals enter diapause regardless of photoperiods (Xue et al., 2002a, b). The above-mentioned results may suggest that a negative Nanda–Hamner response does not necessarily mean that the clock is based on a noncircadian (hourglass) mechanism. The three declining peaks of diapause
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occurring in Nanda–Hamner experiments in C. bowringi could be interpreted in terms of the damped circadian oscillator model (Lewis and Saunders, 1987; Saunders and Lewis, 1987). The model proposes that the oscillator making up the clock is not self-sustained but rather damps out within a few cycles unless maintained at higher amplitude by a train of ‘‘strong’’ light pulses. Bu¨nsow experiments for diapause induction have been conducted with nine insect species and the mite, T. urticae (see Vaz Nunes and Saunders, 1999). In three insect species, the fly D. triauraia (Yoshida and Kimura, 1993), M. brassicae (Kimura and Masaki, 1993) and P. fasciata (Wei et al., 2001), Bu¨nsow experiments were ‘‘negative’’. In C. bowringi Bu¨nsow experiments caused two weak peaks of diapause: the first peak occurred 8 h after lights-off, the second peak occurred 8 h before lights-on, but its photoperiodic response did not show peaks of diapause at a 24-h interval. In C. bowringi, the Bu¨nsow experiments did not produce circadian rhythmicity in response to 2-h light pulses, possibly because the circadian oscillator damps below threshold and 2-h light pulses are insufficient strong to boost the oscillation above that threshold. Thus, further investigations are needed. The results obtained in Nanda–Hamner experiments and Bu¨nsow experiments may suggest that a circadian oscillatory system constitutes a part of the photoperiodic clock of C. bowringi but plays a limited role in its photoperiodic time measurement. Acknowledgements We thank Dr. H.R. Spieth for his critical reading of the manuscript and helpful comments and also thank two anonymous referees for their valuable comments. The research was supported in part by grants from National Natural Science Foundation of China (39960016), Jiangxi Provincial Key Research Program (2003) and Innovation Programs of Chinese Academy of Sciences (KSCX2-1-02, KSCX2-sw-103 and KSCX3I0Z-04).
References Adams, A.J., 1986. The photoperiodic clock of the cabbage whitefly, Aleyrodes proletella: resonance experiments at three temperatures. Journal of Insect Physiology 32, 567–572. Beck, S.D., 1980. Insect Photoperiodism, second ed. Academic Press, New York. Bu¨nsow, R.C., 1960. The circadian rhythm of photoperiodic responsiveness in Kalanchoe. Cold Spring Harbor Symposium on Quantitative Biology 25, 257–260. Danilevskii, A.S., 1965. Photoperiodism and Seasonal Development of Insect. Oliver and Boyd, London, pp. 238, (English translation).
Dumortier, B., 1994. The ‘‘circadian paradigm’’: a test of involvement of the circadian system in the photoperiodic clock. Journal of Theoretical Biology 166, 101–112. Goryshin, N.I., Tyshchenko, G.F., 1973. Accumulation of photoperiodic information during diapause induction in the cabbage moth, Barathra brassicae L. (Lepidoptera, Noctuidae). Entomological Review 52, 173–176. Hardie, J., 1990. The photoperiodic counter, quantitative day-length effects and scotophase timing in the vetch aphid Megoura viciae. Journal of Insect Physiology 36, 939–949. Hardie, J., Vaz Nunes, M., 1994. The aphid photoperiodic counter. In: Leather, S.R., Watt, A.D., Mills, N.J., Walters, K.F.A. (Eds.), Individuals Populations and Patterns in Ecology. Intercept, UK, pp. 13–23. Kimura, Y., Masaki, S., 1993. Hourglass and oscillator expression of photoperiodic diapause response in the cabbage moth Mamestra brassicae. Physiological Entomology 18, 240–246. Koveos, D.S., Kroon, A., Veerman, A., 1993. The same photoperiodic clock may control induction and maintenance of diapause in the spider mite Tetranychus urticae. Journal of Biological Rhythms 8, 265–282. Kroon, A., Veenendaal, R.L., Veerman, A., 1997. Photoperiodic induction of diapause in the spider mite Tetranychus urticae: qualitative or quantitative time measurement? Physiological Entomology 22, 357–364. Lewis, R.D., Saunders, D.S., 1987. A damped circadian oscillator model of an insect photoperiodic clock. I. Description of the model on a feedback control system. Journal of Theoretical Biology 128, 47–59. Masaki, S., 1984. Unity and diversity in insect photoperiodism. In: Porter, R., Collins, G.M. (Eds.), Photoperiodic Regulation of Insect and Molluscan Hormones. Ciba Foudation Symposium No.104. Pitman, London, pp. 7–24. Masaki, S., Kikukawa, S., 1981. The diapause clock in a moth: response to temperature signals. In: Follett, B.K., Follett, D.E. (Eds.), Biological Clocks in Seasonal Reproductive Cycles. Scientechnica, Bristol, UK, pp. 102–112. Nanda, K.K., Hamner, K.C., 1958. Studies on the nature of the endogenous rhythm affecting photoperiodic response of Biloxi soybean. Botanical Gazette 120, 14–25. Pittendrigh, C.S., 1981. Circadian organization and the photoperiodic phenomena. In: Follett, B.K., Follett, D.E. (Eds.), Biological Clocks in Seasonal Reproductive Cycles. Scientechnica, Bristol, UK, pp. 1–35. Saunders, D.S., 1973. The photoperiodic clock in the flesh-fly, Sarcophaga argyrostoma. Journal of Insect Physiology 19, 1941–1954. Saunders, D.S., 1982a. Insect Clocks. 2. Pergamon Press, Oxford, pp. 409. Saunders, D.S., 1982b. Photoperiodic induction of pupal diapause in Sarcophaga argyrostoma: temperature effects on circadian resonance. Journal of Insect Physiology 28, 305–310. Saunders, D.S., 1983. A diapause induction–termination asymmetry in the photoperiodic responses of the linden bug, Pyrrhocoris apterus, and an effect of near-critical photoperiods on development. Journal of Insect Physiology 29, 399–405. Saunders, D.S., 1992. The photoperiodic clock and ‘counter’ in Sarcophaga argyrostoma: experimental evidence consistent with ‘external coincidence’ in insect photoperiodism. Journal of Comparative Physiology A 170, 121–127. Saunders, D.S., Lewis, R.D., 1987. A damped circadian oscillator model of an insect photoperiodic clock. III. Circadian and ‘‘hourglass’’ response. Journal of Theoretical Biology 128, 73–85. Takeda, M., Skopik, S.D., 1985. Geographic variation in the circadian system controlling photoperiodism in Ostrinia nubilalis. Journal of Comparative Physiology A 156, 653–658. Van Houten, Y.M., Veenendaal, R.L., 1990. Effects of photoperiod, temperature, food and relative humidity on the inductions of dia-
X. Wang et al. / Journal of Insect Physiology 50 (2004) 373–381 pause in the predatory mite Amblyseius potentillae. Experimental and Applied Acarology 10, 111–128. Vaz Nunes, M., Hardie, J., 1999. The effect of temperature on the photoperiodic ‘counter’ for female morph and sex determination in two clones of the black bean aphid, Aphis fabae. Physiological Entomology 24, 339–345. Vaz Nunes, M., Saunders, D.S., 1999. Photoperiodic time measurement in insects: a review of clock models. Journal of Biological Rhythms 14, 84–104. Vaz Nunes, M., Kenny, N.A.P., Saunders, D.S., 1990. The photoperiodic clock in the blowfly Calliphora vicina. Journal of Insect Physiology 36, 61–67. Veerman, A., Vaz Nunes, M., 1987. Analysis of the operation of the photoperiodic counter provides evidence for hourglass time measurement in the spider mite Tetranychus urticae. Journal of Comparative Physiology A 160, 421–430. Veerman, A., Beekman, M., Veenendall, R.L., 1988. Photoperiodic induction of diapause in the large white butterfly, Pieris brassicae:
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evidence for hourglass time measurement. Journal of Insect Physiology 34, 1063–1069. Xue, F.S., Li, A.Q., Zhu, X.F., Gui, A.L., Jiang, P.L., Liu, X.F., 2002a. Diversity in life history of the beetle, Colaphellus bowringi. Acta Entomologica sinica 45, 494–498, (in Chinese). Xue, F.S., Spieth, H.R., Li, A.Q., Hua, A., 2002b. The role of photoperiod and temperature in determination of summer and winter diapause in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae). Journal of Insect Physiology 48, 279–286. Wei, X.T., Xue, F.S., Li, A.Q., 2001. Photoperiodic clock of diapause induction in Pseudopidorus fasciata (Lepidoptera: Zygaenidae). Journal of Insect Physiology 47, 1367–1375. Yoshida, M.T., Kimura, M.T., 1993. The photoperiodic clock of Drosophila triauraria: involvement of two processes in the nightlength measurement system. Journal of Insect Physiology 9, 101– 106. Yoshida, M.T., Kimura, M.T., 1995. The photoperiodic clock in Chymomyza costata. Journal of Insect Physiology 41, 217–222.
Diapause induction and clock mechanism in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae) Xiaoping Wang a,b, Feng Ge a, Fangsen Xue c,, Lanshao You b b
a Institute of Zoology, Chinese Academy of Science, Beijing 100080, China College of Plant Protection, Hunan Agricultural University, Changsha 410128, China c Institute of Entomology, Jiangxi Agricultural University, Nanchang 330045, China
Received 30 September 2003; received in revised form 29 December 2003; accepted 4 January 2004
Abstract Photoperiodic control of diapause induction was investigated in the short-day species, Colaphellus bowringi, which enters sumv mer and winter diapause as adult in the soil. Photoperiodic responses at 25 and 28 C revealed a critical night length between 10 and 12 h; night lengths 12 h prevented diapause, whereas night lengths <12 h induced summer diapause in different degree. Experiments using non-24-h light–dark cycles showed that the duration of scotophase played an essential role in the determination of diapause. Night-interruption experiments with T¼ 24 h showed that diapause was effectively induced by a 2-h light pulse in most scotophases; whereas day-interruption experiments by a 2-h dark break had a little effect on the incidence of diapause. The experiments of alternating short-night cycles (LD 16:8) and long-night cycles (LD 12:12) during the sensitive larval period showed that the information of short nights as well as long nights could be accumulated. Nanda–Hamner experiments showed three declining peaks of diapause at 24 h circadian intervals. Bu¨nsow experiments showed two very weak peaks for diapause induction, one being 8 h after lights-off, and another 8 h before lights-on, but it did not show peaks of diapause at a 24 h interval. These results suggest that the circadian oscillatory system constitutes a part of the photoperiodic clock of this beetle but plays a limited role in its photoperiodic time measurement. # 2003 Elsevier Ltd. All rights reserved. Keywords: Colaphellus bowringi; Diapause; Photoperiodism; Nanda–Hamner experiments; Bu¨nsow experiments
1. Introduction The fact that insects and mites (as well as many other organisms) are able to discriminate long days from short days, with important developmental consequences, has led to the concept of photoperiodic time measurement. Photoperiodic time measurement of diapause induction has been investigated in a number of insects and mites, and a variety of models have been developed for photoperiodic clock in these species. According to some of these models, the photoperiodic clock is based on a mechanism separate from the circadian system, that is, a so-called ‘‘hourglass.’’ According to other models, the clock is based on one or more circadian oscillators that may be coupled to each other
Corresponding author. Fax: +0086-791-3814107. E-mail address: [email protected] (F. Xue).
0022-1910/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jinsphys.2004.01.002
and may or may not show a certain degree of damping (see Vaz Nunes and Saunders, 1999). The experimental evidence for the participation of circadian oscillation in photoperiodic time measurement comes almost exclusively from two types of experiments, the so-called Nanda–Hamner protocol and the Bu¨nsow protocol (Nanda and Hamner, 1958 Bu¨nsow, 1960). In Nanda– Hamner experiments, insects or mites are exposed to photoperiods with extended night lengths coupled with a fixed length of light. In Bu¨nsow experiments, animals are exposed to photoperiods with an extended night length, which is systematically interrupted by a 1- or 2h scanning pulse of light. If, in such protocols the incidence of diapause rises and falls with a period of about 24 h, it is generally interpreted as involvement for the presence of a circadian clock. If the photoperiodic response with either protocol does not show rhythmic fluctuations with a period of about 24 h, it suggests for
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an hourglass clock or a rapidly damping oscillator (Saunders and Lewis, 1987). The cabbage beetle, Colaphellus bowringi Baly, is a serious pest of crucifers in the mountain areas of the Jiangxi Province, primarily feeding on the developing leaves of radish, Raphanus sativus and Chinese cabbage, Brassica chinensis. The beetle aestivates and hibernates as adult in the soil. There are two distinct infestation peaks in the field, one in spring and a second in autumn (Xue et al., 2002a). The cabbage beetle is a short-day species. However, its photoperiodic response highly depends on temperature. All adults v enter diapause at 20 C regardless of photoperiod. High temperatures strongly weaken the diapauseinducing effect of long day lengths. The diapauseaverting influence of short day lengths is expressed only v at temperatures above 20 C (Xue et al., 2002b). The beetle is an ideal experimental animal for a formal analysis of the photoperiodic clock, as it is very easy to rear, and it takes no more than 18 days for a photov periodic response experiment at 25 C. In the present study, we investigated diapause induction in C. bowringi with various light–dark cycles, night-interruption experiments, and Nanda–Hamner and Bu¨nsow protocols to analyze the photoperiodic time measurement of this insect.
2. Materials and methods The laboratory strain of C. bowringi used for the experiments has already been described by Xue et al. (2002b). The experiments were performed with the offspring of non-diapause adults obtained by rearing larv vae at 25 C and LD 12:12 that avert diapause. Just after hatching the larvae were transferred to round plastic boxes with a layer of soil and fresh radish leaves. Each box contained at least 50 individuals and two replicates were tested under each treatment. All experiments were executed in illuminating incubators (LRH-250-GS) equipped with four fluorescent
30 W tubes controlled by an electric timer. Light intensity at the level of the beetles was 500–700 lx and variv ation of temperatures was 1 C. The scotophase was controlled manually by enclosing the rearing boxes in opaque hoods. The critical night length is defined as the night length that elicits 50% diapause response. As diapause inducv tion declined at the temperature of 28 C, we took the midpoint between the maximal and minimal response as the critical night length for this species. Diapausing adults of C. bowringi were very easy to identify, because all diapausing adults have a digging behaviour and burrow into the soil after 4–6 days of v feeding at 25 or 28 C.
3. Results 3.1. Photoperiodic response curves under 24-h light–dark cycles Photoperiodic response curves for diapause induction in C. bowringi were similar at constant temperav tures of 25 and 28 C, but diapause occurred at a lower v v level at 28 C than at 25 C (Fig. 1). The critical night length appeared to be between 10 and 12 h. Photoperiods with dark phases from 12 to 24 h prevented diapause effectively, whereas short nights <12 h induced diapause in different degree. Short nights of 4– 8 h resulted in the highest diapause (100% diapause at v v 25 C; over 70% diapause at 28 C), whereas diapause induction was 74.6% in LD 2:22 and 54.9% in LL at 25 v v C, and 29.8% in LD 2:22 and13.3% in LL at 28 C. 3.2. Photoperiodic responses under non-24-h light–dark cycles Photophases of 10, 12, 14 and 16 h were combined with different lengths of scotophase of 4–24 h (Fig. 2). When scotophases were 4 and 8 h, all individuals entered diapause regardless of the length of photo-
Fig. 1. Photoperiodic response curves for the induction of diapause in Colaphellus bowringi under 24 light–dark cycles at constant temperatures v of 25 and 28 C. n ¼ 51 124 for each point.
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v
Fig. 2. Diapause incidence in Colaphellus bowringi under non-24-h photoperiodic cycles at 25 C. n ¼ 69 114 for each point.
phase. With scotophases ranging from 12 to 24 h, most of the individuals developed without diapause independent of the length of the photophase. The results suggest that the incidence of diapause was determined by the length of the scotophase. 3.3. Interruption experiments of photoperiodic response The night of LD 12:12 was systematically interrupted v by a 2-h light pulse at 25 C (Fig. 3). The result showed that early and late light pulses reversed the long night effect and induced diapause effectively. The
light pulse induced 20.4% diapause at 4–6 h after the onset of scotophase. To determine the effect of day interruption, photophase of LD 14:10 (a most effective diapause-inducing photoperiod) was systematically interrupted by a 2-h dark pulse (Fig. 4). The result showed that only the dark pulse 3–4 h after lights-on suppressed diapause, while others had no effect. 3.4. Accumulation of short-night and long-night cycles Xue et al. (2002b) have shown sensitive period in C. v bowringi is mainly during the larval period at 25 C.
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v
Fig. 3. Night interruption for diapause induction of Colaphellus bowringi in a LD 12:12 25 C regime. The scotophase was systematically scanned by a 2-h light pulse.
v
Fig. 4. Diapause response by day interruption in a LD 14:10 25 C regime in Colaphellus bowringi. The photophase was systematically scanned by a 2-h dark pulse.
The larval period lasts for 8 days (including one day of prepupal stage). Fig. 5 shows the diapause incidence under LD 16:8 was 94%, 16% under LD 12:12 and 42% in continuous light when only the larvae were exposed to the photoperiods for 8 days, but pupae and adults were held in LL. The LL induced intermediate rate of diapause. To investigate whether only the diapause-promoting effect of short nights is accumulated or the diapausereversing effect of long nights is accumulated or both occur, the larvae were exposed to alternating (Fig. 6A) or non-alternating (Fig. 6B) short-night (LD 16:8) and long-night cycles (LD 12:12) and pupae and adults were placed in LL. When one short-night cycle (LD
Fig. 5.
16:8) alternated with one long-night cycle (LD 12:12) during larval period or vice versa, the diapause-averting effect of long nights was strongly expressed (only 26.1% diapause in Fig. 6Aa; 34.2% diapause in Fig. 6Ab). However, when two or more short-night cycles alternated with equal number of long-light cycles (i.e. the larvae were exposed to three consecutive or four cumulative short-night cycles in the first 6 days of larval period), the diapause-inducing effect of short nights was expressed (48.6% diapause in Fig. 6Ad; 66.0% diapause in Fig. 6Ae; 66.3% diapause in Fig. 6Ah), whereas when two or more long-night cycles alternated with the same number of short-night cycles (i.e. the larvae were exposed to three consecutive or
v
Incidence of diapause in Colaphellus bowringi when exposed to A: continuous light (LL); B: LD 12:12 and C: LD 16:8 at 25 C.
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Fig. 6. Incidence of diapause in Colaphellus bowringi in response to alternating (a) or non-alternating (b) short-night cycles (LD 16:8) and longv night cycles (LD 12:12) at 25 C.
four cumulative long-night cycles in the first 6 days of larval period), the diapause-averting effect of long nights was expressed (Fig. 6Ac,f). It seems that the diapause-inducing effect of short nights is more dependent on the number of consecutive cycles than is the diapause-averting effect of long nights. Similar results were also shown in experiments that used non-alternating cycles (Fig. 6B). The diapause-inducing effect of short nights increased (from 69.5% diapause to 93.0% diapause in Fig. 6Ba–d) with an increasing number of consecutive cycles (from two short-night cycles to five short-night cycles), whereas the diapause-averting effect of long nights did not show a significant change among the different sequent cycles (25.3% diapause for two long-night cycles in Fig. 6Be; 24.4% diapause for three long-night cycles in Fig. 6Bf; 24.1% diapause for four long-night cycles in Fig. 6Bg; 18.6% diapause for five long-night cycles in Fig. 6Bh). These results indicate that the information of consecutive shortnight cycles can be accumulated effectively during the larval period. 3.5. Nanda–Hamner experiment (or resonance experiment) In Nanda–Hamner experiments, the beetles were v exposed to repeated cycles at 25 C in which the duration of the light was 12 and 16 h but the scotophase was varied from 4 to 60 h in 4 h intervals (Fig. 7).
Three peaks of diapause induction were observed in both photoperiodic responses when the scotophase was 4–8, 28–32 and 52 h. However, the second and the third peaks were much smaller than the first peak. 3.6. Bu¨nsow experiments In Bu¨nsow experiments, the beetle were exposed to a cycle of 12 h of light and an extended scotophase of 36, 48 and 60 h. The scotophases were scanned by a 2-h light pulse at 4-h intervals (Fig. 8). The photoperiodic response curves exhibited two very weak peaks of diapause induction, the first peak occurred 8 h after the onset of darkness, the second 8 h before lights-on, but the photoperiodic response curves did not show circadian peaks at a 24-h interval.
4. Discussion The photoperiodic response shown by C. bowringi is of the typical short-day type. All scotophases 12 h inhibited diapause effectively, whereas scotophases <12 h induced summer diapause in different degree. The highest rate of diapause was found in the short scotophases of 4–8 h. The diapause incidence decreased at the extremely short scotophase of LD 22:2 and LL (Fig. 1). In many long-day insects, the photoperiodic response curves for diapause induction showed that the
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v
Fig. 7. Incidence of diapause in Colaphellus bowringi in resonance experiments using a constant photophase of 12 or 16 h at 25 C. n ¼ 71 123 for each point.
diapause-inducing effect of long nights declined with ultra-long nights (>19 h). This is shown, for example, by Danilevskii (1965) for the cabbage butterfly, Pieris v brassicae (at 24 C); Masaki and Kikukawa (1981) for the Indian meal moth, Plodia interpunctella; Saunders (1983) for the linden bug, Pyrrhocoris apterus; Yoshida and Kimura (1995) for the fly, Chymomyza costata (at v 20 C); Kroon et al. (1997) for the spider mite, Tetrav nychus urticae (at 22 C). All the tested cases of photoperiodic response in long-day species are highly sensitive to night interruption, and the long night effect can be reversed by light pulses (Beck, 1980; Saunders, 1982a). However, the sensitive position to light pulse varied considerably among different species. Some insects exhibit two points of apparent light sensitivity (the so-called A and B peaks). Some insects show only one peak (A or B peak). Some show a wide plateau, in which all scotophases separated by a light pulse that are shorter than the critical night length averted diapause effectively (Koveos et al., 1993; Wei et al., 2001). Even the same species may have different patterns of response depending on the experimental conditions (Masaki, 1984). In the short-day species C. bowringi, a 2-h light pulse reversed the long night effect in most positions of scotophases and exhibited a bimodal response of diapause induction (Fig. 3), whereas a 2-h dark break had a little effect on the incidence of diapause (Fig. 4). This suggests that photoperiodic response in short-day species is also highly sensitive to night interruption. The photoperiodic response needs a photoperiodic ‘clock’ to measure whether the part of a light/dark
cycle is longer or shorter than the critical night length as well as a ‘counter’ to accumulate the photoperiodic information during the sensitive period. It has been shown that the accumulation of photoperiodic information can be achieved in different ways in different insects. In the aphid Megoura viciae, long-night cycles are accumulated in a straightforward fashion independent of the accompanying photophase (Hardie and Vaz Nunes, 1994), whereas the effect of short nights is dependent on the photophase length (Hardie, 1990). In the flesh fly Sarcophaga argyrostoma and the black bean aphid Aphis fabae, long-night accumulation is temperature compensated, but short-night accumulation is not (Saunders, 1992; Vaz Nunes and Hardie, 1999). In the spider mite T. urticae and the large cabbage white butterfly P. brassicae, long and short-night cycles seem to be accumulated in different ways (Veerman and Vaz Nunes, 1987; Dumortier, 1994). In the cabbage moth Mamestra brassicae, however, only long nights are accumulated, not short nights (Goryshin and Tyshchenko, 1973). In the present work, we have shown that in C. bowringi, when one short-night cycle (LD 16:8) is alternated with one long-night cycle (LD 12:12) during larval period or vice versa, the diapauseaverting effect of long nights is strongly expressed (Fig. 6A). It could be inferred that the information of a long-night cycle can be accumulated effectively one by one. However, when two or more short-night cycles alternate with equal number of long-night cycles, the diapause-inducing effect of short nights is expressed (Fig. 6Ad,e,h). It therefore seems that a consecutive exposure to short-night cycles (at least 2 days) is
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v
Fig. 8. Incidence of diapause in Colaphellus bowringi in Bu¨nsow experiments at 25 C with a constant photophase of 12 h and a scotophase of 36 h (A), 48 h (B), and 60 h (C) which was systematically scanned by a 2-h light pulse. n ¼ 56 93 for each point.
required for diapause induction. The results indicate that information about short nights as well as long nights can be accumulated during larval period in this species, but in different ways. Nanda–Hamner protocols have now been applied to a large number of insects and three mites in relation to induction (see Vaz Nunes and Saunders, 1999; Wei et al., 2001). In some species, both negative and positive Nanda–Hamner results for diapause induction have been obtained depending on temperature, e.g. in S. argyrostoma (Saunders, 1973, 1982b), Drosophila auraria (Pittendrigh, 1981), Ostrinia nubilalis (Takeda and Skopik, 1985), Aleyrotes proletella (Adams, 1986), P. brassicae (Veerman et al., 1988), Amblyseius potentillae (Van Houten and Veenendaal, 1990), Calliphora
vicina (Vaz Nunes et al., 1990), Drosophila triauraria (Yoshida and Kimura, 1993), M. brassicae (Kimura and Masaki, 1993) and Pseudopidorus fasciata (Wei et al., 2001). In C. bowringi, Nanda–Hamner experiv ments at a constant temperature of 25 C yield positive results with three declining peaks of diapause at 24 h intervals. However, in these Nanda–Hamner experiments with C. bowringi, it is impossible to prov duce circadian peaks of diapause at 20 C, as at these temperatures all individuals enter diapause regardless of photoperiods (Xue et al., 2002a, b). The above-mentioned results may suggest that a negative Nanda–Hamner response does not necessarily mean that the clock is based on a noncircadian (hourglass) mechanism. The three declining peaks of diapause
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occurring in Nanda–Hamner experiments in C. bowringi could be interpreted in terms of the damped circadian oscillator model (Lewis and Saunders, 1987; Saunders and Lewis, 1987). The model proposes that the oscillator making up the clock is not self-sustained but rather damps out within a few cycles unless maintained at higher amplitude by a train of ‘‘strong’’ light pulses. Bu¨nsow experiments for diapause induction have been conducted with nine insect species and the mite, T. urticae (see Vaz Nunes and Saunders, 1999). In three insect species, the fly D. triauraia (Yoshida and Kimura, 1993), M. brassicae (Kimura and Masaki, 1993) and P. fasciata (Wei et al., 2001), Bu¨nsow experiments were ‘‘negative’’. In C. bowringi Bu¨nsow experiments caused two weak peaks of diapause: the first peak occurred 8 h after lights-off, the second peak occurred 8 h before lights-on, but its photoperiodic response did not show peaks of diapause at a 24-h interval. In C. bowringi, the Bu¨nsow experiments did not produce circadian rhythmicity in response to 2-h light pulses, possibly because the circadian oscillator damps below threshold and 2-h light pulses are insufficient strong to boost the oscillation above that threshold. Thus, further investigations are needed. The results obtained in Nanda–Hamner experiments and Bu¨nsow experiments may suggest that a circadian oscillatory system constitutes a part of the photoperiodic clock of C. bowringi but plays a limited role in its photoperiodic time measurement. Acknowledgements We thank Dr. H.R. Spieth for his critical reading of the manuscript and helpful comments and also thank two anonymous referees for their valuable comments. The research was supported in part by grants from National Natural Science Foundation of China (39960016), Jiangxi Provincial Key Research Program (2003) and Innovation Programs of Chinese Academy of Sciences (KSCX2-1-02, KSCX2-sw-103 and KSCX3I0Z-04).
References Adams, A.J., 1986. The photoperiodic clock of the cabbage whitefly, Aleyrodes proletella: resonance experiments at three temperatures. Journal of Insect Physiology 32, 567–572. Beck, S.D., 1980. Insect Photoperiodism, second ed. Academic Press, New York. Bu¨nsow, R.C., 1960. The circadian rhythm of photoperiodic responsiveness in Kalanchoe. Cold Spring Harbor Symposium on Quantitative Biology 25, 257–260. Danilevskii, A.S., 1965. Photoperiodism and Seasonal Development of Insect. Oliver and Boyd, London, pp. 238, (English translation).
Dumortier, B., 1994. The ‘‘circadian paradigm’’: a test of involvement of the circadian system in the photoperiodic clock. Journal of Theoretical Biology 166, 101–112. Goryshin, N.I., Tyshchenko, G.F., 1973. Accumulation of photoperiodic information during diapause induction in the cabbage moth, Barathra brassicae L. (Lepidoptera, Noctuidae). Entomological Review 52, 173–176. Hardie, J., 1990. The photoperiodic counter, quantitative day-length effects and scotophase timing in the vetch aphid Megoura viciae. Journal of Insect Physiology 36, 939–949. Hardie, J., Vaz Nunes, M., 1994. The aphid photoperiodic counter. In: Leather, S.R., Watt, A.D., Mills, N.J., Walters, K.F.A. (Eds.), Individuals Populations and Patterns in Ecology. Intercept, UK, pp. 13–23. Kimura, Y., Masaki, S., 1993. Hourglass and oscillator expression of photoperiodic diapause response in the cabbage moth Mamestra brassicae. Physiological Entomology 18, 240–246. Koveos, D.S., Kroon, A., Veerman, A., 1993. The same photoperiodic clock may control induction and maintenance of diapause in the spider mite Tetranychus urticae. Journal of Biological Rhythms 8, 265–282. Kroon, A., Veenendaal, R.L., Veerman, A., 1997. Photoperiodic induction of diapause in the spider mite Tetranychus urticae: qualitative or quantitative time measurement? Physiological Entomology 22, 357–364. Lewis, R.D., Saunders, D.S., 1987. A damped circadian oscillator model of an insect photoperiodic clock. I. Description of the model on a feedback control system. Journal of Theoretical Biology 128, 47–59. Masaki, S., 1984. Unity and diversity in insect photoperiodism. In: Porter, R., Collins, G.M. (Eds.), Photoperiodic Regulation of Insect and Molluscan Hormones. Ciba Foudation Symposium No.104. Pitman, London, pp. 7–24. Masaki, S., Kikukawa, S., 1981. The diapause clock in a moth: response to temperature signals. In: Follett, B.K., Follett, D.E. (Eds.), Biological Clocks in Seasonal Reproductive Cycles. Scientechnica, Bristol, UK, pp. 102–112. Nanda, K.K., Hamner, K.C., 1958. Studies on the nature of the endogenous rhythm affecting photoperiodic response of Biloxi soybean. Botanical Gazette 120, 14–25. Pittendrigh, C.S., 1981. Circadian organization and the photoperiodic phenomena. In: Follett, B.K., Follett, D.E. (Eds.), Biological Clocks in Seasonal Reproductive Cycles. Scientechnica, Bristol, UK, pp. 1–35. Saunders, D.S., 1973. The photoperiodic clock in the flesh-fly, Sarcophaga argyrostoma. Journal of Insect Physiology 19, 1941–1954. Saunders, D.S., 1982a. Insect Clocks. 2. Pergamon Press, Oxford, pp. 409. Saunders, D.S., 1982b. Photoperiodic induction of pupal diapause in Sarcophaga argyrostoma: temperature effects on circadian resonance. Journal of Insect Physiology 28, 305–310. Saunders, D.S., 1983. A diapause induction–termination asymmetry in the photoperiodic responses of the linden bug, Pyrrhocoris apterus, and an effect of near-critical photoperiods on development. Journal of Insect Physiology 29, 399–405. Saunders, D.S., 1992. The photoperiodic clock and ‘counter’ in Sarcophaga argyrostoma: experimental evidence consistent with ‘external coincidence’ in insect photoperiodism. Journal of Comparative Physiology A 170, 121–127. Saunders, D.S., Lewis, R.D., 1987. A damped circadian oscillator model of an insect photoperiodic clock. III. Circadian and ‘‘hourglass’’ response. Journal of Theoretical Biology 128, 73–85. Takeda, M., Skopik, S.D., 1985. Geographic variation in the circadian system controlling photoperiodism in Ostrinia nubilalis. Journal of Comparative Physiology A 156, 653–658. Van Houten, Y.M., Veenendaal, R.L., 1990. Effects of photoperiod, temperature, food and relative humidity on the inductions of dia-
X. Wang et al. / Journal of Insect Physiology 50 (2004) 373–381 pause in the predatory mite Amblyseius potentillae. Experimental and Applied Acarology 10, 111–128. Vaz Nunes, M., Hardie, J., 1999. The effect of temperature on the photoperiodic ‘counter’ for female morph and sex determination in two clones of the black bean aphid, Aphis fabae. Physiological Entomology 24, 339–345. Vaz Nunes, M., Saunders, D.S., 1999. Photoperiodic time measurement in insects: a review of clock models. Journal of Biological Rhythms 14, 84–104. Vaz Nunes, M., Kenny, N.A.P., Saunders, D.S., 1990. The photoperiodic clock in the blowfly Calliphora vicina. Journal of Insect Physiology 36, 61–67. Veerman, A., Vaz Nunes, M., 1987. Analysis of the operation of the photoperiodic counter provides evidence for hourglass time measurement in the spider mite Tetranychus urticae. Journal of Comparative Physiology A 160, 421–430. Veerman, A., Beekman, M., Veenendall, R.L., 1988. Photoperiodic induction of diapause in the large white butterfly, Pieris brassicae:
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evidence for hourglass time measurement. Journal of Insect Physiology 34, 1063–1069. Xue, F.S., Li, A.Q., Zhu, X.F., Gui, A.L., Jiang, P.L., Liu, X.F., 2002a. Diversity in life history of the beetle, Colaphellus bowringi. Acta Entomologica sinica 45, 494–498, (in Chinese). Xue, F.S., Spieth, H.R., Li, A.Q., Hua, A., 2002b. The role of photoperiod and temperature in determination of summer and winter diapause in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae). Journal of Insect Physiology 48, 279–286. Wei, X.T., Xue, F.S., Li, A.Q., 2001. Photoperiodic clock of diapause induction in Pseudopidorus fasciata (Lepidoptera: Zygaenidae). Journal of Insect Physiology 47, 1367–1375. Yoshida, M.T., Kimura, M.T., 1993. The photoperiodic clock of Drosophila triauraria: involvement of two processes in the nightlength measurement system. Journal of Insect Physiology 9, 101– 106. Yoshida, M.T., Kimura, M.T., 1995. The photoperiodic clock in Chymomyza costata. Journal of Insect Physiology 41, 217–222.