Biological Characteristics of a Non-Photoperiodic-Diapause Strain of the Cabbage Beetle Colaphellus Bowringi (Coleoptera: Chrysomelidae)
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Entomological Science (2017) 20,50–56 doi: 10.1111/ens.12226 ORIGINAL ARTICLE Biological characteristics of a non-photoperiodic-diapause strain of the cabbage beetle Colaphellus bowringi (Coleoptera: Chrysomelidae) † † Qian-Qian TAN , Rui-Qi ZHOU , Wen LIU, Lian FENG and Xiao-Ping WANG Hubei Insect Resources Utilization and Sustainable Pest Management Key Laboratory, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, China Abstract Comparison of biological characteristics between diapausing and non-diapausing strains of insects provides some insights into the mechanisms regulating diapause. In this study, biological characteristics, especially diapause characteristics and life-history traits, of a non-photoperiodic-diapause (NPD) strain of the cabbage beetle Colaphellus bowringi were compared with those of a normal, high-diapause (HD) strain that enters diapause in response to either long day length or low temperature. The NPD strain did not enter diapause at any photoperiod at 22°C or higher, but still had a capacity to enter diapause at low temperatures. Although diapause could be induced in both strains by exposure to 20°C, the proportion of individuals having shorter diapause duration was greater in the NPD strain compared to the HD strain. The NPD strain had significantly lower hatching and larval survival rates, longer developmental duration of immature stages, smaller body size and lower longevity and female fecundity compared to the HD strain. The NPD strain of this species is a promising model for investigating diapause regulation in insects in general. Key words: diapause induction, diapause termination, life-history traits. INTRODUCTION that diapause incidence and diapause intensity are linked (Sims 1980). As well, comparison of biological Diapause is a strategy to adapt to seasonal environments. characteristics such as life-history traits between non- In many insects and mites, diapause is regulated by diapause and diapause strains could provide insights into environmental stimuli such as photoperiod and the physiological and molecular mechanisms between temperature, and their responses to environmental stimuli diapause and life-history traits (Scheiner & Istock 1991). often show intra- and inter-population variation (Henrich Strains so far named as “non-diapause” are not always & Denlinger 1982; Tauber et al. 1986; Danks 1987; truly non-diapausing, but they are often insensitive to only Saunders 2002). Non-diapause strains are examples of one of the diapause-inducing stimuli. For example, non- such variation and are excellent materials to analyze photoperiodic-diapause strains that are insensitive to diapause characteristics and mechanisms (Tauber et al. diapause-inducing action of photoperiod could enter 1986; Danks 1987; Riihimaa & Kimura 1988; Ito 2009; diapause at low temperatures (Riihimaa & Kimura Coleman et al. 2014). For example, diapause intensity of 1988; Hodkova & Socha 1995). In such cases, a low-diapause strain is weaker than that of a high- comparison of photoperiod-induced diapause and low- diapause strain in Papilio zelicaon, suggesting a possibility temperature-induced diapause could provide a cue to understanding diapause characteristics and mechanisms. Quantifying such differences between non-diapause and Correspondence: Xiao-Ping Wang, College of Plant Science and diapause strains is an essential step for improving our Technology, Huazhong Agricultural University, Wuhan 430070, understanding of the mechanisms regulating diapause. China. Email: [email protected] The cabbage beetle, Colaphellus bowringi Baly † (Coleoptera: Chrysomelidae), is a serious pest of These authors contributed equally to this work. Received 11 April 2016; accepted 21 June 2016; first published cruciferous vegetables in the mountainous areas of China 17 August 2016. (Xue et al. 2002a). The Xiushui population (29°1′N, © 2016 The Entomological Society of Japan Non-photoperiodic-diapause C. bowringi 114°4′E) of this pest has two distinct peaks of occurrence was obtained. This strain is still maintained under the with one generation appearing in spring and one to three same condition in our laboratory. generations in autumn (Xue et al. 2002a). This beetle typically enters diapause as adults in soil in response to Insect rearing conditions either long day lengths or low temperatures; diapause is induced by long day length at temperatures above 20°C, All larvae and adults used in this study were kept in – but by temperature alone below 20°C (Xue et al. 2002b; incubators (SPX 250IC; Boxun Medical Instruments, Wang et al. 2004). In April, when the daily mean Shanghai, China) and fed on fresh radish leaves temperature is below 20°C, the first-emerging adults enter (Raphanus stativus var. longipinnatus), which were summer diapause mainly in response to low temperature. provided daily (Ma et al. 2011). However, adult beetles that emerged after early May when the daily mean temperature becomes higher than 20°C Comparison of diapause between strains enter summer diapause mainly in response to long day The effect of photoperiod was studied in each strain by length. Adults of late-autumn generations enter winter examining diapause incidence under LD 8:16, LD 10:14, diapause in response to low temperatures (Xue et al. LD 12:12, LD 14:10 and LD 16:8 at 22°C, and the effect 2002b). of temperature was studied by examining diapause This paper describes key biological characteristics of a incidence at 18, 20, 22, 24 and 26°C under constant previously reported non-photoperiodic-diapause (NPD) darkness. All the individuals were reared under either of strain (Ma et al. 2011) of C. bowringi,particularly the above experimental conditions from the egg stage until differences in responses to photoperiod and temperature, their diapause attributes were determined at the adult diapause intensity and life-history traits between the stage. The determination of diapause attributes were made NPD and high-diapause (HD) strains of this species. The after adult feeding for 14 days at 18°C, 12 days at 20°C, results suggest that the NPD strain of C. bowringi could 9days at 22°C, and 5–6 days at 24 and 26°C in the be a suitable model species for further investigation of transparent plastic containers filled with soil (Ma et al. diapause regulation in insects. 2011). These experiments were replicated three times with asamplesizeof60–140 per replicate. MATERIALS AND METHODS Diapausing adults of the HD and NPD strains were obtained by rearing them at a low temperature, 20°C, High-diapause strain under constant darkness (Ma et al. 2011). These beetles were placed in large glass bottles with soil to allow them More than 1000 C. bowringi individuals were collected in to burrow into soil, and then they were kept under natural Xiushui County (29°1′N, 114°4′E), Jiangxi Province, conditions from 21 January 2011 (Xue et al.2002b). China, in late November 2008. Post-diapause adults that Diapause termination in each strain was then measured had emerged from the soil were moved to transparent plastic by counting the number of post-diapause adults of each containers (height × length × width = 7.5 cm × 7.5 cm × 6 cm) strain that had emerged from the soil each day; newly formassrearing(Xueet al. 2002a). The offspring of these emerged adults were removed daily from 2011 to 2013. beetles reared under diapause-averting conditions (25°C Emergence was monitored until 10 November 2013. under conditions of 12 h light : 12 h dark (LD 12:12) was regarded as a high-diapause (HD) strain and reliably entered diapause in response to long photoperiods at Comparison of life-history traits temperatures above 20°C. The following life-history traits of the HD and NPD strains were investigated under diapause-averting Non-photoperiodic-diapause strain conditions (25°C and LD 12:12; Xue et al. 2002b). Another 500–600 C. bowringi individuals had previously been collected at Xiushui in late November Hatching rate and larval and pupal survivorship 2006. Post-diapause adults were reared under weak Newly laid eggs of each strain were randomly sampled, diapause-inducing conditions (22°C and LD 13:11) and incubated on wet filter paper in a plastic Petri dish non-diapause individuals were obtained. This non- (diameter 7.0 cm) and the number of larvae hatched was diapause founder population was then kept under recorded daily. Newly hatched larvae of each strain were diapause-inducing conditions (22°C and LD 16:8). By reared on fresh radish leaves in a transparent plastic continuing to rear non-diapausing individuals for 22 container until pupation, and the numbers of individuals generations, a non-photoperiodic-diapause (NPD) strain that pupated and emerged as adult were recorded. This Entomological Science (2017) 20,50–56 51 © 2016 The Entomological Society of Japan Q.-Q. Tan et al. experiment was replicated three times, with each replicate comprising 100–150 individuals. Developmental duration of immature stages The number of larvae hatched was recorded for each strain at a 12 h interval. Newly hatched larvae of each strain were reared in transparent plastic containers containing fresh radish leaves until pupation, and pupae were then placed in individual tubes until adult emergence. The numbers of individuals that pupated and emerged as adults were recorded at a 12 h interval. The overall sample size was approximately 150–200. Body weight of pupae and adults Experimental individuals were sexed at the pupal stage (Wang et al. 2006). Approximately 80 3-day-old pupae and 40 4-day-old adults were weighed for each strain. Thereafter, they were dried at 80°C for 24 h and then measured for dry weight. Adult longevity and fecundity Thirty-six adult females were individually paired with a male and reared in plastic Petri dishes. The total number of eggs laid by female adults and survival of both sexes were recorded daily until all adults died. Statistical analysis Data analyses were conducted using SPSS 11.5 (SPSS Inc., Chicago, IL, USA). Percentage data were normalized by Figure 1 Photoperiodic (A) and thermal (B) responses of the arcsine square-root transformation prior to analysis.