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Temperature and Photoperiodic Response of Diapause Induction and Diapause Physiology in Aphidius Gifuensis Ashmead

Author: LiYuYan
Tutor: ZhangLiSheng
School: Chinese Academy of Agricultural Sciences
Course: Agricultural Entomology and Pest Control
Keywords: Aphidius gifuensis Ashmead Diapause Temperature Photoperiod Physiology
CLC: S433
Type: Master's thesis
Year: 2011
Downloads: 46
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Abstract

Aphidius gifuensis Ashmead is a solitary endoparasitoid of aphid, which can be utilized for the biological control of aphids in agriculture. In recent years, it become one of the most important natural enemy insects of the aphids and got great attentions from the world. At present, although there were so many studies focusing on biology, ecology, and application of large-scale breeding of A. gifuensis, the much detailed study about diapause of A. gifuensis has not been reported. The research on diapause of A. gifuensis not only could promote the large-scale propagation in the practical release, but also could prolong the product shelf-life and persistency period of A. gifuensis used in biocontrol, meanwhile, which could contribute to understand the developmental characteristics and dynamics of natural enemy insects and enhance the efficiency of pest biocontrol. Furthermore, it could help us to realize the developmental mechanisms of natural enemy insects deeply and explore the adaptation mechanism and evolution paths of insects.In the paper, the overwintering situations in diapause of A. gifuensis, such as diapause rate, instar, maintenance, the conditions of diapause inducement and so on, was studied in field. The basic ecological research related to diapause was also studied. Furthermore, the effects of photoperiod, temperature and parental experience on diapause induction of A. gifuensis were deep discussed. Meanwhile, the physiology of diapausing and non-diapausing A. gifuensis were explored as well. These results provide an example for diapause research of A. gifuensis, and supply a technical support for large-scale propagation and application. The main research results as follows:In an experimental field study, up to 81.82% of A. gifuensis hibernated mostly as mature larvae and a minority as pupae under natural conditions in northern China. The second or third instar was the most sensitive larval stage for acceptance the diapause inducing signal. Diapause duration was approximately 4 or 5 months, of which the longest is 150 days. Temperature below 0°C was contributed to diapause maintenance. Low temperature and short day length were the two key factors that initiated diapause. A. gifuensis began to terminate diapause from March in the following year, fewer diapaused individuals can be found after June.Significant differences among different development durations of A. gifuensis (from egg to mummy, mummy to adult and egg to adult) were observed in all treatments. The developmental periods were shortened significantly with the increasing of temperature. Low temperature has inhibitory effects on growth and development. A. gifuensis took 11.74 days to accomplish a generation, spent 7.90 days from eggs to mummification, and 3.89 days for the parasitoids developing in mummies to emerge as adults at a constant temperature of 25°C. The developmental threshold temperature and the effective accumulated temperature were relatively high for Beijing population of A. gifuensis, and it required 218.65 degree-days for eggs developing into adult and the developmental threshold temperature was 6.68°C.Temperature played a more vital role than photoperiod in the process of inducing diapause. Diapause was induced successfully under the temperature below 12°C and a short day length (L8: D16). At 8°C, up to 54.35% of A. gifuensis entered diapause. When the day length shortened to 6h, the diapause rate was only 43.38% at 8°C. Under a long day length of L14: D10, high temperature was unable to induce A. gifuensis into diapause and the diapause rate was only 1.79% at 10°C. Diapause rate was 50.7% under conditions of low-temperature (10 oC) and a short day length (L8: D16). However, the diapause rate decreased significantly when the photoperiod was 14h and 6h. The effects of photoperiod on diapause induction were not significant at 25 oC. Long day, medium or short day lengths were unable to induce diapause of A. gifuensis. Thermoperiod also had an effect on diapause induction of A. gifuensis, and a high day temperature (cryophase) with a low night temperature (thermophase) could induce a higher proportion of individuals into diapause. But the diapause rate was not high, only 28.57% parasitoids were induced into diapause under a thermoperiod of C18: T6 (25°C: 5°C). In addition, a suboptimal thermoperiod also had a lethal effect. The larvae of 2nd~3rd instars had a higher death rate under lower cryophase temperatures or longer treatment periods at the same thermophase temperature. When the cryophase was constant, the larger the thermoperiodic amplitude change was and the stronger the lethal effect did on parasitoids. Temperature and photoperiod significantly affected the developmental periods, adult emergence and diapause rate of A. gifuensis, respectively. Temperature played a greater role than photoperiod on diapause induction, and the interaction between them was very significant (P<0.01). The effect of low temperature on diapause induction could be inhibited by long day length, and the diapause incidence was decreased obviously due to affecting by long photoperiod. Low temperature and short day length could be the two key factors in diapause induction of A. gifuensis. More parasitoids would enter into diapause if the two factors interacted.The effect of parental experienced low temperature and short day or long lay length on dipause rate of progeny was not significantly. The diapause rate was 0.59% and 1.88%, respectively, and there was no significant difference between them. There was no obvious difference between the diapause rates of progeny and parental either parental experienced short or long photoperiod at a low temperature. However, the effect of low temperature accumulated between generations was significant. Low temperature had a lethal effect on eggs and young larvae. Under the condition (10°C and L14: D10), the development of offspring was prolonged significantly, and the emergence rate decreased obviously. But the cumulative effect of low temperature weakened at a high temperature (14°C, L8: D16), there was no significant effect of parental experience on developmental periods and adult emergence.The total sugar content of diapausing A. gifuensis was significantly higher than non-diapausing individuals, the former was 1.3~1.4 times than the latter at the same stages. The consumption of total sugar was not more during diapause. When diapause was terminated, the total sugar content fell by 1/4 than diapausing larvae. A significant difference was observed between the glycogen content of diapausing and non-diapausing A. gifuensis. The glycogen content of the early diapause period was 1.44 times higher than non-diapausing individuals. Meanwhile, both the contents of diapausing larvae and pupae that terminated diapause were lower than non-diapausing A. gifuensis significantly. Their glycogen content was only 53.58% and 52.41% of non-diapausing individuals, respectively. The glycogen content of diapausing A. gifuensis changed obviously at different diapause stages. It was at a high level of 5.58μg/mg in the early diapause period, but declined straightly during diapause duration, which decreased by 53.05% than the early diapause period. Until diapause termination, it was only 13.62% of the early diapause period. Diapausing A. gifuensis main accumulated trehalose, which belonged to trehalose accumulation-type. Trehalose could be used as a key physiological indicator for judging the state of diapause. The trehalose contents of the early diapause period and diapausing larvae were all higher than non-diapausing individuals significantly, which were 1.87 and 1.53 times of non-diapausing A. gifuensis, respectively. The differences of trehalose contents at different diapausing stages were significant. The content was up to the highest value of 12.23μg/mg in the period of diapause, which was 1.49 times than the early diapause period and 1.57 times than diapause termination. Furthermore, a significant transforming relationship existed between glycogen and trehalose during diapause, while the glycogen transformed into trehalose gradually. Glycerol and sorbitol content were at a high level in diapausing A. gifuensis, but the differences were not significant compared to the non-diapausing individuals. Glycerol and sorbitol content during diapause were all higher than in the early diapause period and diapause termination significantly. The protein content of diapausing A. gifuensis was lower than non-diapausing markedly, but there was no significant difference in the early diapause period. With the development of diapause, the protein content decreased significantly firstly, and then increased slightly. It was 64.72μg/mg in the early diapause period, and dropped by 7.8μg/mg when A. gifuensis entered into diapause. Until diapause terminated, the protein content increased by 0.23μg/mg than diapausing larvae, and the increase was not significant. The trehalase activities of diapausing A. gifuensis was significantly lower than non-diapausing individuals, only was 67.16% and 63.75% of non-diapausing A. gifuensis at the same stage, respectively. But there was no significant difference between diapause termination stages and non-diapausing stages. Trehalase activities decreased gradually during diapause, which was 5.42OD/g.min in the early diapasue period, and fell by 27.31% when A. gifuensis entered into diapause. At diapause termination, the trehalase activity was only 2.72OD/g.min. And a significant difference was observed among different diapause stages. These changes of trehalase activities could allow diapausing larvae to keep a high level of trehalose.

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