Biological Characteristics Of A Non-photoperiodic-diapause Strain In The Cabbage Beetle Colaphellus Bowringi (Coleoptera: Chrysomelidae)

The non-diapause strains are important tools for the exploration of diapause molecular mechanism and diapause genetics in insects. Understanding the biological characteristics of non-diapause strains is the foundation of using them to explore the diapause mechanism. The cabbage beetle Colaphellus bowringi Baly(Coleoptera: Chrysomelidae) is a serious pest of cruciferous vegetables. The beetle enters summer and winter diapause as adult in the soil. The Xiushui population is induced to diapause by long-day photoperiod at temperature above 20 °C. This natural population is a high-diapause strain. Our laboratory has obtained one line of the non-photoperiodicdiapause strain in C. bowringi. In this study, the life-history traits and diapause characteristics were compared between the non-photoperiodic-diapause and highdiapause strain in C. bowringi. The main results are as follows:1. Life-history traits of the non-photoperiodic-diapause strain in C. bowringiThe non-photoperiodic-diapause strain had significantly lower rate of egg hatching, lower survival rate of larvae, lighter fresh weight and dry weight of pupae and adults, lower rate of mating, lower mating frequency, shorter longevity, less fecundity and longer developmental duration of immature stages compared with those of the high-diapause strain in C. bowringi. No matter which strain the female of the non-photoperiodicdiapause strain mating with, the longevity, fecundity and rate of egg hatching were significantly lower than that of the high-diapause strain. Meanwhile, the mating times had a positive effect on the fecundity and rate of egg hatching in the high-diapause strain and had a positive effect on the female longevity and rate of egg hatching in the non-photoperiodic-diapause strain. The results suggested that the differences of reproductive adaptability between the two strains had relationship with females. And the mating times has an effect on reproductive adaptability of the high-diapause and non-photoperiodic-diapause strains in C. bowringi.2. Diapause characteristics of the non-photoperiodic-diapause strain in C. bowringiWhen the diapause was induced for the non-photoperiodic-diapause and high- diapause strains in C. bowringi under 20 °C and darkness, the diapause termination were observed under natural condition. The diapause duration of the non-photoperiodicdiapause strain was significantly shorter than that of the high-diapause strain. The diapause termination of the non-photoperiodic-diapause strain was significantly earlier than that of the high-diapause strain. The effects of temperature on diapause induction were measured in the two strains and the offspring of the post-diapause individuals under 18 °C, 20 °C, 22 °C, 24 °C and 26 °C with continuous darkness. The diapause incidence of the high-diapause strain decreased gradually with the increasing temperatures. Almost all individuals of the non-photoperiodic-diapause strain entered diapause at 18°C and 20°C, whereas only 5.71%- 0.58% individuals entered diapause from 22°C to 26°C. The effects of photoperiod on diapause induction were also measured under LD 8:16 h, LD 10:14 h, LD 12:12 h, LD 14:10 h and LD 16:8 h at 22 °C. The diapause incidence of the high-diapause strain increased gradually with the increasing day length in the high-diapause strain. No obvious photoperiodic response was observed in the nonphotoperiodic-diapause strain and the offspring of the post-diapause individuals, only a few individuals entered diapause. The results showed that the diapause intensity of the non-photoperiodic-diapause was lower than the high-diapause strain. The effects of temperature on diapause induction were still existed in the non-photoperiodic-diapause strain and the non-diapause trait might be hereditary.Our study verified the life-history traits and diapause characteristics of the non-photoperiodic-diapause strain in C. bowringi. This study showed that the non-photoperiodic-diapause strain in C. bowringi is an outstanding material to explore the molecular mechanism of insect diapause induced by photoperiod. What’s more, the results provided more insights of studies on diapause genetics and diapause molecular mechanism.