| Cotesia vestalis (Haliday) is one of the most important solitary larval endoparasitoid of Plutella xylostella (Linnaeus). Photoperiod influences diapause beyond the maternal generation in C. vestalis. It is of momentous current significance to study profoundly maternal effects on diapause induction in C. vestalis for the improvement of the technique of diapause induction, better utilization of the diapause characteristics, and solution of the long-term storage problem faced in the practical application process. Hence, material metabolism was studied at various stages in Go reared at25±1℃under photoperiods (light:dark) of8L:16D,12L:12D, and16L:8D, and in G1reared at13℃under L8:16D. The major results are summarized as follows:1Photoperiodic effect on morphogenesis, size, and development in C. vestalisThe life history in C. vestalis is divided into four developmental stages, which are egg, larval, pupal and adult stages, and at the end of larval stage, there exists a developmental stage (prepupa), which obviously differs from early larvae in morphology. No significant influence of photoperiod on the developmental duration at each developmental stage was detected. The duration for embryonic development (egg stage), for the first, second and third instar larvae, prepupal and pupal stages in C. vestalis was36h,36h,84h,12h,24h, and108h, respectively, at25±1℃under three photoperiods. However, photoperiod had significant effect on body size. Embryo volume in Go increased gradually with the developmental time. The embryo volume at16-32h showed irregular difference among three photoperiods, but at hatching, it came to the same level. At almost all developmental time, body and caudal needle sizes of the first instar larvae under8h light were larger than those under16h light, but did not show statistically differences. The size of the second instar larvae under8h light was larger than that under16h light, especially the size of caudal vesicula at96h,108h,120h and144h. Body size and the size of caudal vesicula in the third instar larvae under8h of short photoperiod were no significant differences compared to those under16h light. The volumes in Gi diapausing prepupae and cocoons were significantly higher than those in Go nondiapausing prepupae and cocoons. At180h, the volumes in Go prepupae and cocoons under8h light were significantly higher than those under16h light, whereas the size of caudal vesicula under16h light was the largest. At192h, there was no significant difference in volume of prepupae between under8h and under16h light. The size of pupa at last day was larger under8h light compared to that under16h light. After emergence, size, and abdominal volume in adult females decreased as the light period was prolonged. The volumes in Gi eggs both before and after oviposition under8h light were the largest.2Photoperiodic effect on weight, and water content in C. vestalisFresh and dry weights were significantly heavier in G1diapausing prepupae than those in Go nondiapausing prepupae. Fresh and dry weights decreased at both the Go nondiapausing prepupal and adult stages as the light period was extended.No significant difference was detected in water content between Go nondiapausing prepupae and G1diapausing prepupae. Water content at both the Go nondiapausing prepupal and adult stages increased as the light period was prolonged. G1diapausing prepupae had significantly higher bound water content than Go nondiapausing prepupae.G0nondiapausing prepupae reared under8h and12h light had significantly higher bound water content than that reared under16h of long-light. Moreover, bound water content in the Go adult females decreased with increased photoperiod.3Maternal effect on hydrogen peroxide metabolism during diapause induction in C. vestalisThe hydrogen peroxide contents in Go prepupae and adults increased as the light period was prolonged, and there was no significant difference between Go nondiapausing prepupae and G1diapausing prepupae, however, the hydrogen peroxide content in G1eggs both before and after oviposition under8h short light was the highest. Activities of superoxide dismutase and peroxidase in Go prepupae, adults, and G1eggs both before and after oviposition increased, whereas catalase activity decreased significantly as the light period was prolonged. Compared to G1diapausing prepupae, Go prepupae under8h short light had significantly higher superoxide dismutase, lower catalase, and similar peroxidase activities. Under the three photoperiods, the variation trends of protective enzyme activities in G1eggs (before and after oviposition) were similar to the trends in Go prepupae and adults. Peroxidase and catalase activities in eggs were significantly higher after oviposition than before oviposition.4Maternal effect on lipid metabolism during diapause induction in C. vestalisTotal lipid titer between G1diapausing prepupae and Go nondiapausing prepupae under any photoperiod had no significant difference. Total lipid titer in the Go prepupae showed no significant differences among three photoperiods, either. Total lipid titer in Go adult females under8h light was significantly higher than that under16h light. Total lipid titer in G1eggs before oviposition was decreased with increased photoperiod. After oviposition, the total lipid titer in G1egg under8h light was similar to that under16h light, but both were significantly higher than that under12h light.Triglyceride content in G1diapausing prepupae was significantly higher than that in Go nondiapausing prepupae both under8h and16h light, but lower than that under12h light. Triglyceride contents in Go prepupae, adult females and G1egg before oviposition under8h light were significantly higher than those under16h light. After oviposition, however, there was no significant difference among G1eggs under three photoperiods.Free fatty acid content in G1diapausing prepupae was significantly lower than that in Go nondiapausing prepupae under three photoperiods. Free fatty acid contents in Go prepupae, and G1eggs (both before and after oviposition) under8h light were significantly lower than those under16h light. However, free fatty acid contents in the Go adult females among three photoperiods showed no significant differences.5Maternal effect on carbohydrate metabolism during diapause induction in C. vestalisTotal sugar contents in Go larvae, prepupae and pupae were significantly higher under8h light than under16h light. Total sugar content in Go adults among photoperiods showed no significant difference. In G1, the total sugar contents of eggs, larvae and prepupae decreased with increased photoperiods. Furthermore, the disparity of total sugar content across the three photoperiods in G1larvae and prepupae was much bigger than that in Go larvae and prepupae.There were no significant differences in trehalose content at all developmental stages but G1larvae, in which the content was significantly higher under12h light than that under16h light.In Go, the glycogen contents of larvae, prepupae, pupae and adult females decreased as the light period was extended, but those of adult males did not show significant difference among the three photoperiods. In G1, the glycogen contents of eggs, larvae and prepupae also decreased with increased photoperiod. Compared to that in Go, the difference of glycogen accumulation in the prepupae of G1was expanded among three photoperiods.6Maternal effect on glycogen synthase and phosphorylase during diapause induction in C. vestalisGlycogen synthase activities at all tested developmental stages of both in Go and G1were significantly higher under8h light than under16h light, with the exception of those in the pupae and adult males of Go, which both under8h light and under16h light had similar glycogen synthase activities. There were no significant differences in glycogen phosphorylase activity in Go and in the larvae of G1between under8h light and under16h light. However, the eggs in G1produced by the females which were reared under8h light had significantly higher, and the prepupae in G1produced by the females which were reared under8h light had significantly lower glycogen phosphorylase activities than those produced by the females which were reared under16h light. The activities of both two enzymes showed identical to mRNA expressions of the two enzymes at all stages both in Go and G1. Glycogen synthase mRNA expressions at all stages which or whose Go were reared under8h light were obviously higher than under16h light, whereas glycogen phosphorylase mRNA expressions were similar to16h light.7Maternal effect on hormones during diapause induction in C. vestalis20-hydroxyecdysone (20E) and juvenile hormone Ⅲ (JH Ⅲ) could be detected at all the tested stages.20E content in diapausing prepupae was significantly lower than that in nondiapausing prepupae, whereas JH Ⅲ content did not significantly differ from that in nondiapausing prepupae under the same photoperiod. The20E content in Go prepupae and adult females increased with increased photoperiods. In G1eggs (before and after oviposition),20E contents were the lowest under8h short light. JH Ⅲ contents in both Go adult females and G1eggs (after oviposition) under three photoperiods showed no significant differences.In brief, photoperiods experienced by Go significantly affect metabolism. The content of20E declined with decreased photoperiods, and glycogen was accumulated in C. vestalis in consequence of up-regulated gene expression and enhanced activity of glycogen synthase under the control of20E. H2O2as a factor transmitting information of experienced photoperiod, and glycogen are transferred to offspring through the cytoplasm. Moreover, information from the maternal generation is incorporated by offspring according to environmental conditions experienced by themselves. Ultimately, this information influences glycogen synthase and phosphorylase gene expressions and activities by continuous regulation of20E, thereby determining the proportion of progeny that enter diapause. |
PDF Full Text Request