Hemolymph Ecdysteroid Levels Research Articles

Reproductive division of labor, dominance, and ecdysteroid levels in hemolymph and ovary of the bumble bee Bombus terrestris

To determine whether ecdysteroids are associated with reproductive division of labor in Bombus terrestris, we measured their levels in hemolymph and ovaries of queens and workers. Queens heading colonies had large active ovaries with high ecdysteroid content, whereas virgin gynes and mated queens before and after diapause had undeveloped ovaries with low ecdysteroid content. The hemolymph ecdysteroid titer was rather variable, but in a pooled analysis of mated queens before and after diapause versus colony-heading queens, ecdysteroid titers were higher in the latter group. In workers, agonistic behavior, ovarian activity, ovarian ecdysteroid content, and hemolymph ecdysteroid titers were positively correlated, and were lowest when a queen was present. In queenless workers, ecdysteroid levels were elevated in dominant workers, and were also influenced by the presence of brood and by group demography; hormone levels were higher in bees kept in larger groups. These findings are consistent with the premise that in B. terrestris the ovary is the primary site of ecdysteroid synthesis, and they show that ecdysteroids levels vary with the social environment.

Insulin signaling is necessary for vitellogenesis in Drosophila melanogaster independent of the roles of juvenile hormone and ecdysteroids: female sterility of the chico1 insulin signaling mutation is autonomous to the ovary

It has been suggested that insulin signaling mutations of Drosophila melanogaster are sterile and long-lived because of juvenile hormone (JH) and ecdysteroid deficiency. However, female sterility of an insulin/IGF-like signaling mutant ( chico 1) of D. melanogaster is not mediated by downstream systemic signaling in terms of major alterations in JH or ecdysteroid levels. chico 1 is a null mutation in the insulin substrate protein (CHICO) gene of D. melanogaster. Homozygous chico 1 females are sterile and their oocytes do not mature beyond the last previtellogenic stage. Homozygous chico 1 females exhibit approximately wild-type rates of JH biosynthesis, ovarian release of ecdysteroids and haemolymph ecdysteroid levels, suggesting that these two major hormone systems play no role in producing the sterility. Previtellogenic wild-type ovaries transplanted into homozygous chico 1 females underwent vitellogenesis, showing that systemic factors present in mutant females are sufficient to support normal vitellogenesis. chico 1 ovaries transplanted into wild-type females did not undergo vitellogenesis indicating that CHICO is necessary in the ovary for vitellogenic maturation. The ovary transplant experiments corroborate the endocrine results and demonstrate that insulin/insulin-like signaling (IIS) is necessary for vitellogenesis even when sufficient levels of JH, ecdysteroids or other factors are present.

In vivoEffects of a Recombinant Molt-Inhibiting Hormone on Molt Interval and Hemolymph Ecdysteroid Level in the Kuruma Prawn, Marsupenaeus japonicus

In order to determine the function of molt-inhibiting hormone (MIH) in vivo, we examined the effects of injecting of a recombinant MIH on the molt interval and hemolymph ecdysteroid level in the kuruma prawn, Marsupenaeus japonicus. The injection of recombinant MIH significantly prolonged the molt interval (9.0 +/-0.4 days in the control group, 9.5+/-0.5 days in the 2500 ng/g-body weight/injection-group, mean+/-SD), and significantly decreased the hemolymph ecdysteroid level (ratio of levels between after and before injection: 1.94+/-1.09 in the control and 1.28+/-0.39 in the 3000 ng/g-body weight/injection-group, mean+/-SD). These results conclusively show the inhibitory effects of MIH on molting in vivo.

Effect of Eyestalk-Ablation on Circulating Ecdysteroids in Hemolymph of Snow Crabs, Chionoecetes opilio: Physiological Evidence for a Terminal Molt

Bering Sea snow crabs (Chionoecetes opilio) are a commercially important crab harvested in the Bering Sea. Optimal management of this species requires an understanding of the biology of this crab that is currently incomplete. Fisheries managers apply a continuous growth model in their management of snow crab, which assumes that male crabs increase in size throughout their lifespan. Male snow crabs undergo a morphometric molt that leads to a disproportionate increase in chelae size and it is still debated whether this molt is associated with a terminal molt. This study was conducted to determine whether adult male C. opilio are anecdysic. Using current knowledge of the hormonal regulation of crustacean growth, snow crab physiology was manipulated to induce an increase in molting hormones (ecdysteroids). Since female snow crabs are known to undergo a terminal molt after attaining reproductive maturity, we compared ecdysteroid levels in eyestalk-ablated terminally molted females, small-clawed males and large-clawed males. Snow crabs were collected from the Bering Sea and maintained in circulating seawater at approximately 6°C. Animals were either eyestalk-ablated or left intact. Ecdysteroid levels in hemolymph were quantified using an enzyme-linked immunosorbant assay (ELISA). Circulating ecdysteroids were significantly higher in small-clawed male crabs when compared to large-clawed males or terminally molted females. Eyestalk-ablation increased circulating ecdysteroids in small-clawed males, but had no significant effect on circulating ecdysteroids in large-clawed males or in terminally molted females.

In vitro secretion of ecdysteroid by Y-organ during molt cycle and evidence for secretion of 3-dehydroecdysone in the giant freshwater prawn, Macrobrachium rosenbergii (Crustacea: Decapoda: Caridea)

Summary In crustaceans, a molting gland, the Y-organ, is known to secrete ecdysteroids. In the present study, we examined the products and the in vitro secretory activity of the Y-organ in the giant freshwater prawn, Macrobrachium rosenbergii. Ecdysteroids present in the Y-organ incubation media were determined by high-performance liquid chromatography and radioimmunoassay systems. Ecdysone (E), 3-dehydroecdysone (3DE), 20-hydroxyecdysone (20E) and high polarity products (HPP) were detected. The detection of 20E and HPP is probably due to the hydroxylation and conjugation activities in the epidermal tissue introduced into the incubation medium along with the Y-organ. The predominant products were E and 3DE in M. rosenbergii. The in vitro secretory activities of the Y-organ fluctuated in a similar manner to the ecdysteroid levels in the hemolymph: the secretory activities were the highest in the late premolt stage in which hemolymph levels also peaked. The present study is the first report that determines the Y-organ products in a caridean species. The close relationships between Y-organ activities and hemolymph ecdysteroid levels suggest that the Y-organ activity directly affects the hemolymph ecdysteroid levels in M. rosenbergii.

Corazonin reduces the spinning rate in the silkworm, Bombyx mori

The insect neuropeptide, [Arg 7]-corazonin was injected into larvae of the silkworm, Bombyx mori to investigate its influence on development and behavior. A single injection of 50 pmol of corazonin into the fourth and fifth instar larvae induced prolongation of the spinning period in all experimental groups except for those injected on day 10 of the fifth instar. The injection also caused a prolongation of the pupal period in some experimental groups, while it had no effect on the timing of larval ecdysis and the length of feeding period of the fifth instar. The spinning period was significantly prolonged even at a low dose of 1 pmol. Both the spinning rate and the rate of increase in hemolymph ecdysteroid level during the spinning stage were reduced by injection of corazonin. However, corazonin injection during days 5–7 of the fifth instar reduced the spinning rate without influencing the ecdysteroid level until the end of day 8, thereafter the rate of increase in hemolymph ecdysteroid level was slower in the corazonin-injected larvae than in the control larvae. Therefore, the suppressed ecdysteroid level observed in the corazonin-injected larvae appears to be a result rather than a cause of the reduced spinning rate. This study is the first published report for the corazonin effect on the behavior in insects.

Artificial diets for rearing the Colorado potato beetle, <italic>Leptinotarsa decemlineata</italic>

Colorado potato beetles have been reared successfully through 12 generations on artificial diets containing either 2.5% potato leaf powder or 2.5% lettuce leaf powder/0.75% potato leaf powder. For all but one of the treatment groups, the mean duration of each of the four larval stages was between 0.8 and 1.5 days longer than the durations exhibited by control beetles that had been fed on potato leaves. Maximum weights of prepupae, newly emerged adults and day 5 - 9 adults were approximately 78, 80 and 82%, respectively, of the weights for comparable stages of control beetles. Mean percent mortality for 1 st instars was two to six times higher for artificial diet-fed CPBs than for leaf-fed beetles. However, since pupal mortality was four times higher for control beetles than for beetles reared on artificial diet, mean percent total mortality (newly hatched through the 9 day old adult) was equivalent for leaf-fed beetles and for later generations of potato and Lettuce+Potato diet-fed CPBs. Hemolymph ecdysteroid levels and fluctuations in mature 4 th instar larvae and prepupae were similar in controls and experimental groups. Number of hatchlings produced per adult pair per day (fertility) was approximately eight times greater in control beetles than in later generations of artificial diet-fed beetles, primarily because fewer egg masses were laid per day, percent hatch was lower and cannibalism of eggs was higher in these latter groups. Interestingly, the mean percent hatch, although only 68% of the control value, was 1.5 times greater for beetles reared on diet containing lettuce-leaf powder, and a small percentage of potato leaf powder, than on diet containing only potato leaf powder. Percent hatch was equal for beetles fed on diet containing only lettuce-leaf powder and those fed on potato leaves. Finally, it is noteworthy that the quality of eggs, as judged by the ability of the wasp parasitoid, Edovum puttleri , to parasitize and develop in the eggs, was similar for eggs produced by control beetles and for those produced by beetles fed on potato and Lettuce+Potato diets. The diets and rearing system described here will be useful for providing beetles on a year-round basis for experiments designed to evaluate the effects of potential insect control agents, to investigate the mechanism(s) by which insects become resistant to control agents and for other applied and fundamental studies related to the control of this serious pest. The use of lettuce leaf powder in place of most of the potato leaf powder is especially advantageous because of the much reduced cost and greater availability of lettuce as compared to potato leaves.

Artificial diets for rearing the Colorado potato beetle, Leptinotarsa decemlineata

Colorado potato beetles have been reared successfully through 12 generations on artificial diets containing either 2.5% potato leaf powder or 2.5% lettuce leaf powder/0.75% potato leaf powder. For all but one of the treatment groups, the mean duration of each of the four larval stages was between 0.8 and 1.5 days longer than the durations exhibited by control beetles that had been fed on potato leaves. Maximum weights of prepupae, newly emerged adults and day 5-9 adults were approximately 78, 80 and 82%, respectively, of the weights for comparable stages of control beetles. Mean percent mortality for 1(st) instars was two to six times higher for artificial diet-fed CPBs than for leaf-fed beetles. However, since pupal mortality was four times higher for control beetles than for beetles reared on artificial diet, mean percent total mortality (newly hatched through the 9 day old adult) was equivalent for leaf-fed beetles and for later generations of potato and Lettuce+Potato diet-fed CPBs. Hemolymph ecdysteroid levels and fluctuations in mature 4th instar larvae and prepupae were similar in controls and experimental groups. Number of hatchlings produced per adult pair per day (fertility) was approximately eight times greater in control beetles than in later generations of artificial diet-fed beetles, primarily because fewer egg masses were laid per day, percent hatch was lower and cannibalism of eggs was higher in these latter groups. Interestingly, the mean percent hatch, although only 68% of the control value, was 1.5 times greater for beetles reared on diet containing lettuce-leaf powder, and a small percentage of potato leaf powder, than on diet containing only potato leaf powder. Percent hatch was equal for beetles fed on diet containing only lettuce-leaf powder and those fed on potato leaves. Finally, it is noteworthy that the quality of eggs, as judged by the ability of the wasp parasitoid, Edovum puttleri, to parasitize and develop in the eggs, was similar for eggs produced by control beetles and for those produced by beetles fed on potato and Lettuce+Potato diets. The diets and rearing system described here will be useful for providing beetles on a year-round basis for experiments designed to evaluate the effects of potential insect control agents, to investigate the mechanism(s) by which insects become resistant to control agents and for other applied and fundamental studies related to the control of this serious pest. The use of lettuce leaf powder in place of most of the potato leaf powder is especially advantageous because of the much reduced cost and greater availability of lettuce as compared to potato leaves.

Fluctuations in hemolymph ecdysteroid levels during the reproductive and non-reproductive molt cycles in the giant freshwater prawn Macrobrachium rosenbergii

SUMMARY: Hemolymph ecdysteroid levels were traced during the molt cycle in female giant freshwater prawn, Macrobrachium rosenbergii. Levels were compared between the reproductive molt cycle, accompanied by ovarian development and oviposition following ecdysis, and the non-reproductive molt cycle, marked by the absence of ovarian development, to examine the involvement of ecdysteroids in ovarian development. Total ecdysteroid levels determined by radioimmunoassay (RIA) showed similar fluctuation patterns between both molt cycles. Levels were low during postmolt stages A–B and gradually decreased to low basal levels at intermolt stages C0–C1. Levels then increased during premolt stages D0–D2, reached a large peak at the early D3 stage, and declined sharply prior to ecdysis. In addition, ecdysteroids in the hemolymph were analyzed using high-performance liquid chromatography combined with RIA in order to identify individual ecdysteroid species. During both molt cycles, 20-hydroxyecdysone, ecdysone and high polarity immunoreactive products were detected, and 20-hydroxyecdysone was the most predominant ecdysteroid. Fluctuations in all ecdysteroid species during each type of molt cycle paralleled those of total ecdysteroid levels, and did not show significant differences between the reproductive and non-reproductive molt cycles. These results suggest that ecdysteroids are not involved in ovarian development but in the molting process only.

Manipulation of fifth-instar host ( Manduca sexta) ecdysteroid levels by the parasitoid wasp Cotesia congregata

Although 5th (last) instar parasitized Manduca sexta larvae undergo developmental arrest and do not wander, they exhibit a small hemolymph ecdysteroid peak (300–400 pg/ μl) which begins one day prior to the parasitoid's molt to the 3rd (last) instar and concomitant emergence from the host. Ecdysteroids present in this peak were 20-hydroxyecdysone, 20,26-dihydroxyecdysone and one or more very polar ecdysteroids, as well as small amounts of 26-hydroxyecdysone and ecdysone. In parasitized day-1 and -2 5th instars ligated just behind the 1st abdominal proleg, hemolymph ecdysteroid levels increased in both anterior and posterior portions (100–500 pg/ μl), while in unparasitized larvae, hormone levels only increased in the anterior portion (100–350 pg/ μl). Thus, the ecdysteroid peak observed in host 5th instars was probably produced, at least in part, by the parasitoids. It may serve to promote Cotesia congregata's molt from the second to the third instar and/or to facilitate parasitoid emergence from the host. In parasitized day-1 and -2 5th instars ligated between the last thoracic and 1st abdominal segments, hemolymph ecdysteroid titers reached much higher levels (500–3500 pg/ μl) in the anterior portion (no parasitoids present) than in the posterior portion (150–450 pg/ μl). Therefore, it appears that the parasitoid's regulation of hemolymph ecdysteroid titers occurs at two levels. First, parasitization neutralizes the host's ability to maintain its normal hemolymph ecdysteroid levels. Second, in a separate action, the parasitoid manipulates the ecdysteroid-producing machinery so that hemolymph levels are maintained at the 200–400 pg/ μl characteristic of day 3–4 hosts. This is the first report of a parasitoid's ability to interfere with the normal inhibitory mechanisms which prevent prothoracic gland production of ecdysteroid at inappropriate periods of insect growth and development.

Molt-Inhibiting Hormone mRNA Levels and Ecdysteroid Titer during a Molt Cycle of the Blue Crab,Callinectes sapidus

Synthesis of ecdysteroid molting hormones by crustacean Y-organs is believed to be regulated by a neuropeptide, molt-inhibiting hormone (MIH), produced in eyestalk neural ganglia. In the present study, steady-state MIH mRNA and hemolymph ecdysteroid levels were determined by Northern blot and radioimmunoassay, respectively, during the molt cycle of the blue crab,Callinectes sapidus.The level of MIH mRNA dropped steadily during premolt (D1–D4), reaching a minimum in D3/D4, then increased by 10-fold in postmolt (A/B) and remained elevated during intermolt (C4). These stage-specific changes in MIH mRNA levels were accompanied by significant fluctuations in the hemolymph ecdysteroid titer. The ecdysteroid titer increased steadily to a peak of 377.0 ng/ml in D3 of premolt, then dropped to 120.0 ng/ml in D4 (just prior to molting), and was low during postmolt (A/B, 4.4 ng/ml) and intermolt (C4, 3.3 ng/ml). The results represent the first report of developmental changes in MIH gene expression and are generally consistent with the hypothesis that MIH negatively regulates ecdysteroid synthesis in crustaceans.

Mode of action of the venom of the ectoparasitic wasp,Euplectrus comstockii, in causing developmental arrest in the European corn borer,Ostrinia nubilalis

Euplectrus comstockii Howard (Hymenoptera: Eulophidae), is an ectoparasitic, gregarious wasp which parasitizes the larval stage of several important lepidopteran pests. Parasitization of both natural and unnatural hosts prevents molting in the parasitized instar. Here we report the effect of wasp venom on the European corn borer (unnatural host), an important pest of corn and other vegetables. Venom collected from venom glands of adultE. comstockii, when injected intoO. nubilalis 5th instars, inhibited the growth rate, development and molting of the injected larvae. The observed effect on molting was dose and age dependent. When 3rd, 4th and 5th instarO. nubilalis were envenomated by adult wasps, the larvae also were developmentally arrested and failed to undergo a molt. However, 3rd and 4th instars underwent apolysis (separation of the epidermis from the old cuticle) and produced new cuticle. Fifth instars did not. A premolt hemolymph ecdysteroid peak was not observed in these experimental 5th instars, but injections of 20-hydroxy-ecdysone induced apolysis and new cuticle formation. Envenomated 4th instars (on becoming pharate 5th instars) exhibited a premolt hemolymph ecdysteroid peak. HPLC/RIA revealed that 20-hydroxyecdysone was present in the hemolymph of these pharate 5th instars. Thus, in the European corn borer, the mode of action of the venom depended upon the instar parasitized. Our results support the presence of a venom component(s) that, in 4th instar hosts, inhibited ecdysis, but did not prevent hemolymph ecdysteroid levels from increasing sufficiently to stimulate apolysis. In 5th instars, the same, or perhaps, a different component(s) ofE. comstockii venom prevented the synthesis/release of ecdysteroid by inhibiting a previously unknown molt-regulating physiological event that occurs between days 3 and 4 of the instar.

Effects of Parasitism by the Braconid Wasp Cotesia congregata on Metabolic Rate in Host Larvae of the Tobacco Hornworm, Manduca sexta

We examined growth rates, gas exchange patterns and energy metabolism of tobacco hornworm (Manduca sexta) larvae parasitized by the braconid wasp Cotesia congragata. Larvae parasitized at the beginning of the fourth-instar had reduced growth compared to unparasitized larvae of the same age and short-term differences in metabolism (measured as rates of CO 2 production, V ̇ CO 2) were apparent almost immediately after wasp oviposition. However, over the growth period between parasitization and the last part of the fifth-instar, there was no significant difference between parasitized and unparasitized hosts as seen in the relationship between mass and V ̇ CO 2. One day prior to parasitoid emergence, host larvae stopped eating, ceased spontaneous locomotor activity and showed a dramatic decline in metabolism. The 60% decline of V ̇ CO 2 at this time is consistent with lack of specific dynamic action because the animals were not feeding. Gas exchange became highly cyclical on the day of parasitoid emergence, but the cause and significance of this phenomenon, which disappeared by the third day following emergence, are not clear. This pattern of cycling was not induced by starving nonparasitized larvae for 6 days, nor by immobilizing nonparasitized larvae with tetrodotoxin. Ecdysteroid levels in the host's hemolymph significantly increased on the day when parasitoids completed their L2–L3 molt and began emerging, but not during the wasps' L1–L2 molt which occurred a few days earlier. Contrary to our initial expectation that hemolymph ecdysteroid titers might be linked to alterations in the host's metabolic rate, we observed no such correlation.

Dependence of ecdysteroid metabolism and development in host larvae on the time of baculovirus infection and the activity of the UDP-glucosyl transferase gene

Infection of fourth-instar gypsy moth ( Lymantria dispar, Lepidoptera: Lymantriidae) larvae with the wild-type (Wt) gypsy moth baculovirus, LdNPV on the first day post-molt, or infection of fifth instars on the fifth day post-molt, results in elevated ecdysteroid levels in both hemolymph and the media of cultured prothoracic glands, when examined by radioimmunoassay and compared to mock-infected controls. In contrast, insects infected with an ecdysteroid UDP-glucosyl transferase minus [ egt(-)] mutant virus show ecdysteroid levels and gland activity similar to that found in controls. UDP-glucosyl transferase causes sugar-conjugation of ecdysteroids containing a hydroxyl group at the C-22 position, and our ecdysteroid antiserum recognizes these conjugated ecdysteroids. Since we found that 20-hydroxyecdysone inhibits gland activity in culture and glucose-conjugated ecdysone, the major form of ecdysteroid in the hemolymph of Wt baculovirus-infected animals does not, the elevated level of hemolymph ecdysteroids and heightened gland activity in Wt virus-infected animals are most likely due to low levels of 20-hydroxyecdysone resulting from sugar conjugation of ecdysone by EGT. Interestingly, hemolymph ecdysteroid titer and gland activity of fifth-instar larvae infected with either the Wt or egt(-) virus on the first day post-molt remain at basal levels throughout the instar, with death occurring prior to pupation, suggesting that LdNPV may have a second, egt-independent mechanism for regulation of host ecdysteroid levels.

Testicular Ecdysteroids in the Silkmoth, Bombyx mori.

Testicular and haemolymph ecdysteroid levels in the silkmoth, Bombyx mori, were measured from the beginning of the last larval instar until 1 day before adult eclosion by Radioimmunoassay. The amount of ecdysteroids in testes just after the 4th ecdysis was about 150 pg/pair and rapidly decreased by Day 2. Afterwards, ecdysteroids titre increased gradually. An abrupt increase of ecdysteroids titre was observed during the wandering stage. After pupation, the level of ecdysteroids became increasingly detectable on Day 3 of the pupal stage and it decreased rapidly thereafter. The main component of ecdysteroids in larval testes was 20-hydroxyecdysone (about 2/3 of the total) and ecdysone. An unknown ecdysteroid which eluted at the same retention time as authentic 20-hydroxyecdysone-22-acetate was also detected. The fluctuation pattern of ecdysteroids in the haemolymph closely paralleled that of the testes, although the titres were much higher than those of testes.

Effect of nonsteroidal ecdysteroid agonists on ecdysteroid titer in Spodoptera exigua and Leptinotarsa decemlineata

In control last-instar larvae of Spodoptera exigua, and Leptinotarsa decemlineata, major hemolymph ecdysteroid peaks appeared around day 3–4, and 8–9, respectively, which is correlated with normal apolysis. Later on, hormone titers declined to a basal level. In Colorado potato beetle last-instars, a small rise was noted around day 4, which represents the time of digging. In last-instar larvae of S. exigua treated with either RH-5849 or tebufenozide, the ecdysteroid titer remained at a basal level without any elevation. Such larvae showed signs of untimely apolysis within 12–24 h after treatment followed by cessation of fresh weight gain. Likewise, hemolymph ecdysteroid levels and larval weight gain were reduced in last-instar larvae of L. decemlineata treated with RH-5849 as compared with controls. Otherwise, treatment of Colorado potato beetle larvae with tebufenozide caused no hormonal and physiological abnormalities as compared with controls. It is suggested that both nonsteroidal ecdysteroid agonists act via ecdysteroid receptor binding without an increase in ecdysteroid titer.

In vitroproduction of ecdysteroids by Y-organs ofPenaeus vannamei(Crustacea, Decapoda). Correlation with hemolymph titers

Summary Ecdysteroids secreted in vitro by Y-organs of the white shrimp Penaeus vannamei were quantified at different stages of the molt cycle by enzyme immunoassay (EIA). The production was maximal during the first hour of incubation, and the highest values were obtained with Y-organs from animals at molt stages D1′″. and D2-D3. Ecdysteroid production increased in parallel with the rise in hemolymph ecdysteroid levels, which peaked at the late premolt stage D1′″. A preliminary characterization showed that 20-hydroxyecdysone was the major circulating ecdysteroid. Ecdysteroids present in the incubation median of Y-organs were measured after HPLC separation. Three major immunoreactive compounds comigrated with standard ecdysteroids, 20-hydroxyecdysone, ecdysone and 3-dehydroecdysone; a fourth, less polar immunoreactive product was also detected. 3-Dehydroecdysone appeared to be the predominant secretory product, and the other compounds could arise from its metabolism by contaminating epidermis cells in the Y...

THE ROLE OF ECDYSTEROIDS IN THE REPRODUCTIVE DIAPAUSE OF DERMACENTOR NIVEUS NEUMANN

Abstract The ecdysteroid levels in hemolymph, ovary, synganglion and whole body of diapausing female Dermacentor niveus were detected by HPLC, and compared with the results of nondiapausing female. It is revealed that the ecdysteroid levels in hemolymph and ovary of diapausing female are similar basically to that of nondiapausing female in the first few days after engorgement. From the 10th day after engorgement, the ecdysteroid levels of diapausing female decreased and even became distinctly lower than that of nondiapausing female. The paucity of ecdysteroids in these individuals would influence the normal development of oocytes. In order to explore the effect of ecdyateroids on the diapausing female, we injected 20‐hydroxyecdysone with different dosages at different time into the ticks, and found that after just complete engorgement the injection with large dosages (10000 and 1375 ng/tick) caused death of the ticks. From 10th to 20th day after engorgement the ecdysteroid levels of diapausing female are lower than that of nondiapausing one before oviposition, the injection with certain dosages 50, 70 and 100 ng/tick> of 20E can accelerate vitellogenesis and terminate reproductive diapause, but the amount of eggs produced by them is less than that produced by nondiapausing female. The termination of diapause in female of ixcdid tick by exogenous ecdysteroids is reported for the first time.

Ecdysteroid levels in haemolymph and reproductive organs of fourth and fifth nymphal instar and adult Melanoplus sanguinipes

Levels of ecdysteroids were determined by radioimmunoassay (RIA) in the haemolymph, testes, male accessory reproductive glands (MARG) and female reproductive system of fourth and fifth (final) nymphal instars and adults of the migratory grasshopper, Melanoplus sanguinipes. In nymphs, the haemolymph ecdysteroid levels were found to peak (60.5 ng/ml [males], 40 ng/ml [females] in the fourth instar and 446 ng/ml [males], 340 ng/ml [females] in the fifth instar) a little after the middle of the stadium. The ecdysteroid level in the testes of fifth instar nymphs also peaked on the same day as that of the haemolymph. However, ecdysteroid levels in the haemolymph of adults (peak values 5.3 ng/ml [males] and 4.3 ng/ml [females]) were much lower than those of final instar nymphs. Ecdysteroids also occur in the testes, MARG and female reproductive system of adults. In mated males, the levels of ecdysteroids in the testes and MARG were greater than those in unmated males of the same age. In contrast, in females that had mated or oviposited, ecdysteroid levels in the reproductive system and haemolymph were lower than those in virgins.

Ecdysteroid profiles and vitellogenesis inPenaeus monodon(Crustacea: Decapoda)

Summary Ovarian and haemolymph ecdysteroid levels in adult female Penaeus monodon at various stages of vitellogenesis have been studied. The concentration of free ecdysteroids, predominantly 20-hydroxyecdysone, was maximal in animals with immature (stage 0) ovary, decreased gradually during early vitellogenesis (stage 0 to stage I) and fell sharply during later vitellogenesis (stage I to stage IV). 20-hydroxyecdysone 22-phosphate was identified in stage 0 ovary and in stage 0 and I–II haemolymph, and 20-hydroxyecdysonoic acid was observed in stage 0 ovary and haemolymph. Low levels of 20-hydroxyecdysone 22-fatty acyl esters were detected in stage 0 ovary but did not occur in the haemolymph. A major component of the stage IV haemolymph ecdysteroids was 20-hydroxyecdysone 22-acetate. The significance of the results is discussed.