Uncorr Ected Proof

http://www.paper.edu.cn Effects of thermoperiods on diapause induction in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae) XIAO-PING. WANG1,2, FANG-SEN XUE3 , FENG GE1 , CHENG- AI ZHOU2 and L A N - S H A O Y O U 2 1Institute of Zoology, Chinese Academy of Science, Beijing, 2Department of Plant Protection, Hunan Agricultural University, Changsha and 3Institute of Entomology, Jiangxi Agricultural University, Nanchang, China Abstract. The effects of thermoperiods on diapause induction in continuous darkness or under a 12 : 12 h LD photoperiod were investigated in the cabbage beetle, Colaphellus bowringi Baly, a typical short-dayPROOF species. The diapause response curves both at different constant temperatures and at the thermocycle of format CT x: (24 À x) h (16 : 28 C) under continuously dark rearing conditions showed that the incidence of diapause depended mainly on whether or not the mean temperature was 20 Cor20 C. If the mean temperature was 20 C, all 1 individuals entered diapause; if >20 C, the incidence of diapause declined gradually with increasing mean temperatures. The thermocycle (CT 12 : 12 h) with a series of different cryophases (8–22 C) and thermophases (24–32 C) under continuous darkness demonstrated a cryophase response threshold temperature of approximately 19 C and a thermophase response threshold temperature of approximately 31 C. Thermoperiodic amplitude (temperature difference between cryophase and thermophase) was shown to have a significant influence on diapause induction at the mean temperatures of 22, 23 and 24 C, but not at 25 C. Thermoperiodic responses under LD 12 : 12 h clearly showed that the incidence of diapause was influencedECTED strongly by the photophase temperature. The thermoperiod under LD 12 : 12 h induced a much lower incidence of diapause than the thermoperiod with the same temperature in continuous darkness. The ecological significance of thermoperiodic induction of diapause in this species is discussed. Key words. Colaphellus bowringi, diapause induction, photoperiod, temperature, thermoperiod. Introduction (photophase). Although much more variable than the photoperiod, daily thermocycles also form a predictable Under natural conditions, insects are exposed to a 24 h daily seasonal pattern of change. This pattern can play an import- temperature cycle (thermocycle) and to seasonal patterns of ant influence on diapause induction. However, the effects of such daily cycles. Thus, insects have evolved in an environ- temperature on diapause induction are often examined ment in which the cool phase (cryophase) of thermocycle under conditions of constant temperature in most insects tends to occur during the dark phase (scotophase) of the and mites, whereas relatively few investigations have been cycle and the warm phase (thermophase) during light performed with thermocycles (see Beck, 1980; Saunders, 1982; Beck, 1985; Tauber et al., 1986; Danks, 1987; Brown & Phillips, 1991; Lenga & Huignard, 1992; Vaz Nunes, UNCORR 1998; Fantinou & Kagkou, 2000). Thermoperiodic effects Correspondence: Fang-Sen Xue,Institute of Entomology, Jiangxi Agricultural University, Nanchang 2330045, PR China. Fax: þ86 on determination of diapause have been investigated by 791 381 4107; e-mail: [email protected] experiments in which the thermocycle is combined with 转载中国科技论文在线 http://www.paper.edu.cn 2 X.-P. Wang et al. the photocycle, or the thermocycle is run in continuous The thermocycles are described in the results below in darkness. The effects of the thermoperiod on diapause terms of phase duration temperature. For example, a thermo- induction may be summed up as follows: (i) a daily thermoperiod comprised a 12 h cryophase at 16 C and a 12 h ther- cycle is known to have diapause-inducing properties in the mophase at 28 C is abbreviated as CT 12 : 12 h (16 : 28 C). absence of a light cycle; (ii) the thermocycle may simulate or The mean temperature of a given thermoperiod was calcu- substitute for the photocycle in the determination of lated on the basis of hourly temperatures through the 24-h diapause; (ii) in a few species, the thermocycle per se can cycle. The thermoperiodic amplitude represents the number induce diapause through daily patterns of high and low of degrees of temperature difference between the cryophase temperature that are analogous to inductive light-dark and thermophase. patterns; (iv) thermoperiodic cues could be perceived in The criterion for recognizing diapause in C. bowringi is ways very similar to those for photoperiod, including a very simple, because diapausing adults burrow into the soil simple response threshold temperature to define the cryo- and become dormant after several days of feeding (Xue phase and thermophase; and (v) the thermoperiodic and et al., 2002b). photoperiodic induction curves are similar in some species. Using the SAS statistical software package (SAS Institute, The cabbage beetle, Colaphellus bowringi Baly, is a serious Cary, NC), some data were tested with one-way analysis of pest of cruciferous vegetables in the mountain areas of variance (ANOVA) with Duncan’s comparison of mean. The Jiangxi Province, P. R. China. The beetle aestivates and data were arcsine square root-transformed before analysis. hibernates as an adult in the soil. In the field, there are two distinct infestation peaks per year, one in the spring and a PROOF second in the autumn. There are four generations per year, Results one generation in the spring and three generations in the autumn (Xue et al., 2002a). Thus, the beetle tends to cause Diapause response curve at different constant temperatures more severe damage in autumn than in spring. This beetle is a under continuous darkness short-day species (Xue et al., 2002b). However, its photoperiodic response in this species is highly dependent upon tem- The effect of different constant temperatures on diapause perature. All adults enter diapause at 20 C regardless of induction was examined under continuously dark rearing the photoperiod. The diapause-averting influences of short conditions (Fig. 1). The response curve showed that tem- day lengths are expressed only at temperatures above 20 C. peratures per se couldinducediapauseintheabsenceof Therefore, in this study, this species provided an ideal experi- photoperiodic signals. All individuals entered diapause at mental animal for the study of the influence of thermo- 20 C; the incidence of diapause decreased gradually periodic and photoperiodic regimes on diapause induction. (from 68.9 to 3.3%) with the increasing temperatures (from 22 to 32 C). The result shows that the induction of diapause in C. bowringi is highly dependent upon temperature. Materials and methods ECTED The experiments were performed with the offspring of non- Thermoperiodic response curve under continuous darkness diapause adults that were obtained from larvae reared at 25 C under a 12 : 12 h LD photoperiod (an effective dia- Using a 16 C cryophase and 28 C thermophase, the pause-averting regime). The nondiapausing adults were pro- effect of phase duration on the induction of diapause was duced by an overwintering population collected in the determined under continuously dark rearing conditions in field (2910N, 11440E) in early November 2002. Just after C. bowringi. The thermoperiodic response curve thus hatching, the larvae were transferred to round plastic boxes with a layer of soil and fresh radish leaves (Raphanus stativus) and then were placed in different thermoperiodic regimes. 100 Each experimental regime was tested by rearing two or three replications, with at least 50 newly hatched larvae for 75 each replication. All experiments were conducted in illuminated incubators 50 3 (LRH-250-GS) equipped with four fluorescent 30w tubes % Diapause controlled by an automatic time switch. Light intensity at 25 the level of beetles was 500–700 lux and variation of tem- 0 peratures was Æ1 C. The transitions from one temperature 14 16 18 20 22 24 26 28 30 32 to another were controlled manually. The scotophase was ° also controlled manually by enclosing the rearing boxes in Temperature C opaque hoods. The replenishments of rations under con- Fig. 1. Thermal response curve for the induction of diapause at tinuouslyUNCORR dark rearing conditions were made during night different constant temperatures under conditions of continuous with red light and were completed within approximately darkness in the cabbage beetle, Colaphellus bowringi (n ¼ 109–157 3 min for each box. for each point). # 2004 The Royal Entomological Society, Physiological Entomology, 29, 1–7 中国科技论文在线 http://www.paper.edu.cn Effects of thermoperiods on diapause induction in C. bowringi 3 obtained (Fig. 2) clearly showed that the incidence of dia- 24 °C 26 °C pause increased gradually with the increasing duration of 100 28 °C cryophase. The critical cryophase duration was approxi- 30 °C ° mately 10.5 h; almost all of the individuals entered diapause 75 32 C when the cryophase exceeded 12 h. However, the effect of thermoperiod on diapause induction was due to the change 50 of the mean temperature of thermoperiod caused by the phase duration. As shown in Fig. 2, a mean temperature % Diapause 25 of thermoperiod < 22 C resulted in 100% diapause; 0 whereas the incidence of diapause gradually declined with 0 10121416182022 increasing mean temperatures (from 22 to 28 C). The result Cryophase °C indicates that the induction of diapause was determined principally by the mean temperature of the thermoperiod. Fig. 3. Thermoperiodic induction of diapause in the cabbage beetle, Colaphellus bowringi using a CT 12 : 12 h format with five different thermophases and cryophases from 8 to 22 C under continuous darkness. Note the cryophase threshold temperature of Thermoperiodic response threshold approximately 19 C. Two or three replications were performed for each treatment (n ¼ 69–114 for each point). A CT 12 : 12 h format, in which a series of different cryophase temperatures (8–22 C) combined with a series of much lower incidencesPROOF of diapause than the other cryophase different thermophase temperatures (24–32 C), was adopted when combined with the thermophase of 28 C, 30 Cor to determine the thermoperiodic induction of diapause 32 C.

Load more