Chaoliang Lei

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.

Studies on feeding and trophallaxis in the subterranean termite Odontotermes formosanus using rubidium chloride

Differences in feeding and trophallaxis among castes of the fungus‐cultivating higher subterranean termite Odontotermes formosanus Shiraki (Isoptera: Termitidae) were determined using rubidium (Rb) as a tracer. In the feeding study, workers and third instars fed directly on Rb‐treated filter paper and acquired the highest levels of Rb content. Although fifth and sixth instars obtained the Rb content over the marked level, the feeding ability of the caste was very poor. However, soldiers did not feed on Rb‐treated filter paper. In the trophallaxis study, worker, soldier, and fifth‐ and sixth‐instar recipients paired with Rb‐fed worker donors had a significantly higher Rb content than those paired with control donors. Results indicate that soldiers are completely dependent on workers for nutrition. Workers and fifth and sixth instars may obtain nutritional material from foraging workers. When third‐instar recipients were paired with Rb‐fed worker donors, they did not have a significantly higher Rb content than when they were paired with control donors, suggesting that the frequency of worker/third instar trophallaxis was very low. Transfer efficiency from the four trophallactic combinations ranged from 1.2 (worker donors to third‐instar recipients) to 12.9% (worker donors to soldier recipients). Accordingly, nutritional material from foraging workers could be transferred to non‐foraging workers, soldiers, and fifth and sixth instars by trophallaxis; however, third instars rarely obtain nutritional material from foraging workers, because they are capable of feeding within the nest.

Variation in sexual size dimorphism among populations: testing the differential-plasticity hypothesis.

Sexual size dimorphism (SSD) is a common phenomenon in animals and varies widely among species and among populations within species. Much of this variation is likely due to variance in selection on females vs. males. However, environmental variables could have different effects on females vs. males, causing variation in dimorphism. In this study, we test the differential‐plasticity hypothesis, stating that sex‐differential plasticity to environmental variables generates among‐population variation in the degree of sexual dimorphism. We examined the effect of temperature (22, 25, 28, and 31 °C) on sexual dimorphism in four populations of the cockroach Eupolyphaga sinensis Walker (Blattaria: Polyphagidae), collected at various latitudes. We found that females were larger than males at all temperatures and the degree of this dimorphism was largest at the highest temperature (31 °C) and smallest at the lowest temperature (22 °C). There is variation in the degree of SSD among populations (sex*population interaction), but differences between the sexes in their plastic responses (sex*temperature interaction) were not observed for body size. Our results indicated that sex‐differential plasticity to temperature was not the cause of differences among populations in the degree of sexual dimorphism in body size.

Sexual size dimorphism decreases with temperature in a blowfly, Chrysomya megacephala (Fabricius) (Diptera: Calliphoridae)

1. There is wide intra‐specific variation in sexual size dimorphism (SSD). Much of this variation is probably as a result of sexual differences in the selective pressure on body size. However, environmental variables could affect males and females differently, causing variation in SSD.

Dynamics of sex ratio, fresh weight and nutrient contents at five developmental stages of alates in the subterranean termite Reticulitermes chinensis

Sex ratio, fresh weight and nutrient contents were examined at five developmental stages of alates in the subterranean termite Reticulitermes chinensis Snyder, including sixth-instar nymphs, callow alates, dark alates, flying alates and dealates. The results showed that the sex ratio of callow alates and dark alates was highly female biased, but there were no significant differences in the percentage of females and males at sixth-instar nymphs, flying alates, and dealates. The fresh weights of alates declined with the developmental stages, suggesting a dynamic process in which the termites continue to shrink and harden. Meanwhile, the weights of female alates were significantly higher than weights of male alates in all five stages. There were no significant differences in the protein titers of the five developmental stages of alates. Flying alates were observed to have the highest triglyceride level, but a low glucose titer. This suggested that the main energy for flight of alates is provided by the breakdown of triglyceride reserves. Alates regardless of developmental stages, workers and soldiers had no significant differences in the cholesterol titers for the two extraction methods. Interestingly, there was a significantly negative linear correlation between the titer of glucose and the titer of triglyceride in both female alates and male alates during the five developmental stages, suggesting that the indirect mutual transformation between glucose and triglyceride might occur in the energy metabolism of all alates in R. chinensis.

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):

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.

The Morphology and Temperature-dependent Development of Mylabris phalerata Pallas (Coleoptera: Meloidae)

Abstract The morphology and life history of Mylabris phalerata Pallas (Coleoptera: Meloidae) were observed. The effect of temperature on the duration of immature stages of M. phalerata reared at 18, 22, 25, 28, 31, and 34°C was determined. The adaptable temperature for artificial mass rearing was ≥28°C. Lower developmental thresholds were estimated to be 6.38, 6.29, 7.72, 7.08, 5.25, 17.62, and 5.58°C for egg, larval instars L1, L2, L3, L4, L5 and pupa, respectively, and the thermal constant was 1,715.59 degree-days for total immature stages, using the linear model. Based on the developmental cycle of M. phalerata, its known geographic distribution, and temperature data, diapause is attributed to the overwintering fifth-instar larva.

Biological characteristics and environmental adaptation of four phenotypes of Propylea japonica (Thunberg) (Coleoptera: Coccinellidae).

ABSTRACT Four main phenotypes of Propylea japonica (Thunberg) occur in Wuhan, China: ancora, dionea,feliciae, and tessellata. The occurrence of these phenotypes in broad bean, wheat, and com was investigated. Body size, prey capacity, and starvation resistance were assessed for their relatedness to the different phenotypes. Individuals of ancora were dominant in the three crops and abundance of feliciae and tessellata was low. In various crops, the body length of feticiae adults was found to be larger than that of tessellata, and body width of ancora females was larger than that of tessellata females. Males of ancora consumed more Aphis craccivora Koch (about 45 per day) than males of feliciae. There were, however, no significant differences in starvation resistance among the four phenotypes. Our results demonstrated that the most abundant phenotype, ancora, had some advantages in terms of body width and voracity, while the less dominant phenotypes (feliciae and tessellata) were, respectively, less voracious and of smaller size. This indicates that body size and prey capacity may relate to the variable phenotype abundance occurring in crop environments.

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.