Xingmiao Zhou

Effects of photoperiod and temperature on diapause induction and termination in the swallowtail, Sericinus montelus

Abstract Sericinus montelus overwinters as diapausing pupae. In the present study, the effects of photoperiod and temperature on diapause induction and termination of diapause are investigated. The results obtained demonstrate that high temperature can reverse the effect of short day‐lengths on diapause induction. Under an LD 12 : 12 h photoperiod, all pupae enter diapause at 15, 20 and 25 °C, whereas all pupae develop without diapause at 35 °C. No pupae enter diapause under an LD 14 : 10 h photoperiod when the temperature is above 20 °C. Photoperiodic response curves obtained at 25 and 30 °C indicate that S. montelus is a long‐day species and the critical day‐length is approximately 13 h at 25 °C. At 25 °C, the duration of diapause is shortest when the diapausing pupae are maintained under an LD 16 : 8 h photoperiod and increases under LD 14 : 10 h and LD 12 : 12 h photoperiods. Under an LD 16 : 8 h photoperiod, the duration of diapause is shortest when the diapausing pupae are maintained at 25 °C, followed by 20 and 30 °C, and then at 15 °C. These results suggest that a moderate temperature favours diapause development under a diapause‐averting photoperiod in this species. The duration of diapause induced by an LD 12 : 12 h photoperiod is significantly longer at 25 °C than those at 15, 20 and 30 °C, and is shortest at 15 °C. At 25 °C, the duration of diapause induced by LD 6 : 18, LD 12 : 12 and LD 13 : 11 h photoperiods is similar and longer than 90 days. Thus, the diapause‐inducing conditions may affect diapause intensity and a photoperiod close to the critical day‐length has significant influence on diapause intensity in S. montelus.

Geographic variation in photoperiodic diapause induction and diapause intensity in Sericinus montelus (Lepidoptera: Papilionidae)

Abstract  Due to the risk of extinction and ornamental value of the swallowtail butterfly, Sericinus montelus Gray (Lepidoptera: Papilionidae) in China, knowledge about local adaptations is important for the conservation and economical utilization of the species. In the present study, photoperiodic diapause induction and diapause intensity of S. montelus populations from Jiamusi (46°37′N), Beijing (40°15′N), Zibo (36°48′N), Fangxian (32°36′N), Wuhan (30°33′N) and Huaihua (27°33′N) were characterized at 25°C. Logistic regression analysis revealed a significant population × hours of light interaction, confirming that photoperiodic responses varied among populations. The critical photoperiod was positively correlated with latitude and increased toward the north at a rate of about 1 h for each 6.67 degrees of latitude. Survival analyses indicated that survival time of diapausing pupae before adult eclosion differed significantly among populations at 25°C and 16 : 8 L : D h. The mean duration of pupal diapause was also positively correlated with latitude. Our study reveals geographic variation in the critical photoperiod for diapause induction and in diapause intensity of S. montelus. These results provide useful information for our general understanding about seasonal adaptation in insects and may also be used to predict how geographic populations respond to climate warming.

Development, survival and reproduction of the Brassica leaf beetle, Phaedon brassicae Baly (Coleoptera: Chrysomelidae) under different thermal conditions

Phaedon brassicae is a serious pest of brassicaceous vegetables in Japan and China, but the effects of thermal changes on development, survival and reproduction is not well demonstrated. In this study, effects of constant temperatures and thermoperiods simulated alternating high summer temperatures on the development, survival and reproduction were examined in this beetle at 12L:12D. At constant temperatures, egg hatch and survival of larvae and pupae were highest at 28, 24, and 24°C respectively. Within the range of 12–30°C, the developmental periods of immature stages decreased significantly with increasing temperature, but a delay in development was observed at 30°C. The developmental zeros were estimated at 7.1, 6.9 and 7.1°C and thermal constants of 87.7, 178.6 and 68.0 degree-days were estimated for the development of the eggs, larvae and pupae, respectively. Adult longevity decreased with increasing temperature, but there were no significant differences among temperatures (16–28°C). Fecundity at 24°C (768.68 ± 385.44 eggs per female) was significantly greater than at other temperatures. The optimal temperature is approximately 24°C. Moreover, high alternating temperatures had little effect on egg hatch, but higher thermophase (6 h) temperatures retarded the survival of larvae and pupae. No individual survived to eclosion at thermoperiods with thermophase temperature of 38°C. High temperatures (above 34°C) lasting several hours had detrimental effects on survival, development and reproduction in P. brassicae.

Identification of Sex of Pupae in the Cabbage Beetle Colaphellus Bowringi Baly (Coleoptera: Chrysomelidae: Chrysomelinae)

Morphological characters have been reported for sexing pupae in many insects, especially Lepidoptera (Anton and Garrido 1996; Leskey and Bergh 2003; Genc 2005), Coleoptera (Bhattacharya et al. 1970; Sugiyama et al. 1996) and Diptera (Kuitert 1975; Mochizuki et al. 1983). In most of those insects, sexual differences are obvious in their ventral eighth-tenth abdominal segments including genital openings and appendices. However, the characters reported, although similar, are not exactly the same in all the species examined, even in the same group. The cabbage beetle, Colaphellus bowringi Baly, is a serious pest of crucifers in the mountain areas of China. The beetle enters summer and winter diapause as adult, and shows a great difference between individuals in diapause duration (from several months to more than three years). It takes no more than 18 days from egg to adult at 25uC (Xue et al. 2002; Wang et al. 2006). The beetle is an ideal experimental animal for a formal analysis of the mating behavior and the mating cost, as it is very easy to rear. However, sex discrimination of living adults is difficult, and no method for sexing pupae has been reported, although description on morphology of pupae has been made in this beetle (Ge et al. 2004). Here, we report the morphological details of pupae that are sex specific and allow sexing of living pupae. For the cabbage beetle, determination of sex can be easily made by presence or absence genital opening and protuberance on the ventral side for both two-day old male and female pupae. The differences are as follows (Fig. 1, 2):

Overwintering strategy of endoparasitoids in Chilo suppressalis: a perspective from the cold hardiness of a host

Although parasitoids ultimately kill their host, koinobiont parasitoids must protect not only themselves but also their hosts against extreme environments. In this study, the parasitism rate of Chilo suppressalis Walker (Lepidoptera: Pyralidae) was investigated, and the average body weights, supercooling points, and concentrations of glycerol (acting as a cryoprotectant) in the hemolymph were compared between parasitized and non‐parasitized larvae. Five species of koinobiont endoparasitoids parasitized the overwintering C. suppressalis larvae and the total parasitism rate was 47.6% (n = 1 537). Average body weight of parasitized larvae was significantly lower than that of non‐parasitized larvae, and the parasitism rate of the lighter group (20–30 mg) was highest. The supercooling point of parasitized C. suppressalis larvae (−15.7 ± 0.3 °C) was significantly lower than that of the non‐parasitized larvae (−14.3 ± 0.2 °C). In addition, supercooling points were not correlated with body weights between parasitized and non‐parasitized larvae, indicating that cold hardiness of parasitized larvae was enhanced by endoparasitoids. Furthermore, the concentration of glycerol in the hemolymph was significantly higher in parasitized larvae (205.0 ± 7.1 μmol ml−1) than in non‐parasitized larvae (169.8 ± 14.4 μmol ml−1), which suggests that the mechanism that decreases the supercooling point of parasitized larvae was associated with glycerol. All these results indicated that the cold hardiness of parasitized C. suppressalis larvae was enhanced by their endoparasitoids, which benefitted overwintering endoparasitoids.

Thermoperiodic response and effect of photoperiod on thermoperiodic induction of diapause in Colaphellus bowringi

The effects of thermoperiods on diapause induction under continuous darkness (DD), continuous light (LL), and an L12:D12 photoperiod were investigated in the cabbage beetle, Colaphellus bowringi Baly (Coleoptera: Chrysomelidae), a short‐day species. Diapause could be induced by thermoperiod under both LL and DD; however, in the range of 24–30 °C, lower incidences of diapause were observed under LL than under DD. The critical cryophase was found to be dependent on the mean temperature of the thermoperiod applied. Although the thermoperiodic response pattern was similar under LL and DD, the incidence of diapause was higher under LL when the duration of the cryophase did not exceed 12 h. In contrast, when the duration of the cryophase was longer than 12 h, the incidence of diapause under LL was lower or equal to that under DD. When a thermoperiod of 24 °C (cryophase) and 28 °C (thermophase) was applied, the incidence of diapause was higher under LL than under DD, regardless of the duration of the cryophase. Thermoperiodic responses under a photoperiod of L12:D12 and under DD further revealed that induction of diapause was strongly influenced by the photophase temperature. Moreover, the incidence of diapause was lower when the thermophase coincided with the photophase than when the cryophase coincided with the photophase.

Internal Reproductive System and Diapausing Morphology of the Brassica Leaf Beetle Phaedon brassicae Baly (Coleoptera: Chrysomelidae: Chrysomelinae)

Abstract The brassica leaf beetle Phaedon brassicae Baly, one of the pests of cruciferous vegetables in China and Japan, is a multivoltine species that over-winters and over-summers mainly as diapausing adults. In this paper, the internal reproductive system is described and illustrated for this species. Its morphology associated with diapause is also described. The accessory glands, lateral ejaculatory duct, common ejaculatory duct and ejaculatory sac are poorly developed in diapausing male, in contrast, these are obvious and swollen in the reproductive male. In the diapausing female, no obvious previtellogenic oocytes can be found in the ovariole. The ovarioles contain numerous previtellogenic oocytes, and the basal oocytes have visible yolk uptake in the reproductive female. In addition, the fat bodies are numerous and dark yellow in color for diapausing adults, but few and light yellow in color for reproductive adults.