Cypermethrin induction of vitellogenesis and ovarian development in unfed adult female Ornithodoros moubata (Acari: Argasidae)

Summary

Vitellogenesis in ticks is known to be induced by engorgement and mating. In this paper, the synthetic pyrethroid cypermethrin (CyM) is shown to induce production of yolk protein precursor, vitellogenin (Vg), and ovarian development in unengorged mated adult female Ornithodoros moubata. The levels of Vg found in the hemolymph and ovarian development induced by CyM were dose-dependent. i.e., CyM doses of more than 0.2 and 1.0 μg/tick were needed for significant increase of Vg titer in the hemolymph and yolk deposition in oocytes, respectively. Immunological and electrophoretical analyses of Vg and Vitellin (Vn) induced by CyM were identical with those induced by engorgement. Vg titer induced by CyM in unengorged females followed approximately the same time course as that in the normal engorged females. However, Vg titer induced by CyM continued to increase after day 8 and reached a maximum (95 μg/μ1) on day 10 after treatment, while Vg titer induced by engorgement decreased again after reaching a maximum (60 μg/μ1) on day 6, correlated with yolk Vn deposition in oocytes. Ovarian development induced by even high doses (10 or 20 μg/tick) of CyM was slow compared to normal development stimulated by engorgement. Oviposition was not observed in females treated with CyM.     

Regulation of vitellogenesis in the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae)

Studies were undertaken to investigate vitellogenesis and its regulation in female adults of the fall armyworm, Spodoptera frugiperda. A single female-specific protein, likely to be the S. frugiperda vitellogenin (Vg), appeared approximately 5 h after adult eclosion in the hemolymph of virgin females. The concentration of the protein increased with age as sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed. A protein with the same relative molecular mass was also present in egg extracts, but absent from hemolymph samples from male moths. The relative molecular mass of the designated S. frugiperda Vg was determined as 164.5+/-2.5 kDa. Vitellogenic oocytes became visible 36-48 h after emergence and egg deposition began on day 3 of adult life. Vg could not be detected in the hemolymph of females decapitated directly after eclosion. When decapitated virgin females were injected with the JH-mimic methoprene (MP), the level of Vg was comparable to that in non-decapitated moths, indicating that vitellogenesis in S. frugiperda depends on juvenile hormone (JH). However, the number of vitellogenic oocytes was somewhat lower than in non-decapitated virgin females. Injection of 20-hydroxyecdysone (20E) promoted Vg production to a similar extent in decapitated female moths, but in contrast to methoprene injection, treatment with 20E never resulted in the production of vitellogenic oocytes. In vitro cultivated ovaries of adult females dissected directly after eclosion produced lower amounts of ecdysteroids than those isolated on day 1 after emergence. Our results suggest a crucial role for 20E in the induction of vitellogenesis in the noctuid S. frugiperda, while JH seems to be essential for the continued uptake of Vg by developing oocytes and may trigger 20E biosynthesis in the ovary.     

Cyanoprotein: Developmental stage,sex and diapause-dependent expression,and synthesis regulation by juvenile hormone in the bean bug,Riptortus clavatus

Cyanoprotein (CP) synthesis was studied in nymphal and nondiapause adult, diapause adult, and juvenile hormone (JH) treated adult bean bugs, Riptortus clavatus. Hemolymph collected from bugs injected with [³⁵S]-methionine was analyzed by native polyacrylamide gel electrophoresis (PAGE) and fluorography, and CP synthesis was also determined quantitatively by rocket immunoelectrophoresis of hemolymph and counting. In the nymphal stages synthesis of CP-1, 2, 3, and 4 (with CP-4 synthesis predominant) reached a maximum at mid-instar and was not detected at each ecdysis, so that the synthetic activity of CPs changed cyclically in each instar. During the nymphal stages CP synthesis showed the same pattern and level in both females and males, and both diapause and nondiapause oriented bugs. In the adult stage, however, CP synthesis differed in the two sexes and nondiapause or diapause conditions. In nondiapause males CP synthesis was not detected in the adult, but in nondiapause females CP (only CP-1) was synthesized through the reproductive stages. CP-1 accumulated in the egg yolk together with vitellogenin. In diapause adults (both females and males) CP-1 to 4 were synthesized at a very low rate for over 2 months and accumulated in the hemolymph. JH or JH analog (JHA) methoprene and also long day condition, which terminate diapause, switched the main CP synthesis CP-4 to CP-1 in females. CP synthesis in diapause males stopped after JH(A) treatment. The activities of CP synthesis, thus, changed in developmental stages, sexes, and diapause. This is an excellent system for study of specific gene expression and switching controlled by insect hormones and sex. © 1992 Wiley-Liss, Inc.     

Juvenile hormone analog and injection effects on locust hemolymph protein synthesis

In adult female Locusta migratoria, at about day 8 after eclosion, when vitellogenin (Vg) is first produced as a result of induction by juvenile hormone (JH), the intensity of hemolymph protein electrophoretic bands at about 75 kDa and 20 kDa increases sharply, suggesting that JH may induce additional proteins. A major component of the elevated protein is persistent storage protein (PSP; subunit 74 kDa). Administration of the JH analog, methoprene, to precocene-treated adult locusts was followed by a rise in hemolymph levels of PSP but not in apolipophorin III (19 kDa), identified immunochemically and electrophoretically. The synthesis of PSP in adult fat body was confirmed by incorporation of [³H]leucine. At 48 h after treatment with methoprene, Vg synthesis was induced in females (as previously observed) and synthesis of PSP in both sexes was elevated above controls, while synthesis of apolipophorin III was not stimulated. We conclude that in adult locust fat body the synthesis of several proteins responds in different ways to the JH analog: Vg (and a 21 kDa protein described elsewhere) is induced de novo solely in females; PSP (and a 19 kDa protein described elsewhere) is stimulated in both sexes but is not fully JH-dependent; apolipophorin III is not stimulated. In these experiments, methoprene was administered both by injection in mineral oil and topically in acetone. After injection of mineral oil as a vector control, incorporation into secreted proteins was stimulated at 24 h, presumably due to a wound effect; topical application of acetone avoids this effect and is a preferred route for administration of JH analog. © 1992 Wiley-Liss, Inc.     

JH III production, titers and degradation in relation to reproduction in male and female Anthonomus grandis

Juvenile hormone (JH) is necessary for the production of vitellogenin (Vg) in the boll weevil, Anthonomus grandis. Occurrence of Vg in this species is typically restricted to reproductively competent females, and is not detected in untreated males. However, the JH analog, methoprene stimulates Vg production in intact males and in the isolated abdomens of both male and female boll weevils (where in each case no Vg is detected without treatment), suggesting that males are competent to produce Vg but are normally not stimulated to do so. Preliminary work indicating that male boll weevil corpora allata (CA) produced little or no JH in vitro suggested that failure of males to produce Vg might be due to very low JH levels compared to females. This study re-examines the question of JH in male boll weevils by determining in vitro production of JH III by male CA during the first 10 days after adult emergence, determining hemolymph JH esterase activity during this same time period and hemolymph JH III titers in adults of both sexes. We also re-examine the ability of isolated male abdomens to produce Vg in response to hormonal stimulation, analyzing the effect of a wide range of methoprene and JH III dosages. Results indicate that male A. grandis have circulating JH titers and JH production similar to females. JH esterase activity is slightly but significantly higher in males than females. Vg production by isolated abdomens of both sexes after stimulation with methoprene or JH III was confirmed. Dose response studies indicated that high levels of methoprene were less effective than intermediate doses in stimulating Vg synthesis in both sexes. We conclude that the sexually dimorphic effect of JH on Vg synthesis is not due to differences in JH production or differences in JH titer between the sexes.     

Stimulation of vitellogenin production by methoprene in prepupae and pupae of manduca sexta

Denaturing electrophoresis of hemolymph from prepupae of M. sexta showed trace amounts of polypeptides with mobilities corresponding to those of vitellogenin (Vg) apoproteins from adult females. Absence of the polypeptides in allatectomized insects suggested regulation by juvenile hormone (JH). Daily administration of 10 μg of the JH analog methoprene from day 4 of the fifth stage to day 0 of the pupal stage caused accumulation of these polypeptides. They were identified as apovitellogenins (apoVgs) immunochemically with Vg antiserum. Stimulation of Vg in response to methoprene varied with age. In all cases, day 0 female pupae were highly responsive. Vg synthesis was not stimulated when pupae were injected with 20-hydroxyecdysone (20-HE) in addition to methoprene. Methoprene-stimulated Vg synthesis was also abolished by inhibitors of mRNA or protein synthesis (α-amanitin, actinomycin, cycloheximide). This result indicated that methoprene-stimulated Vg accumulation requires gene expression. A Vg cDNA (2.1 kb) obtained by immunoscreening of the λgt 11 library, when used as a radiolabelled probe, hybridized with a 5.1 kb mRNA from total RNA of female fat body. It also hybridized with fat body RNA of normal prepupae and methoprene treated day 0 pupae but not with that of early fifth instars or solvent control pupae. The results indicate that the trace amounts of Vg found in prepupal stages are due to a weak expression of the Vg gene, which is stimulated by JH and repressed by 20-HE. © 1994 Wiley-Liss, Inc.     

Effects of precocenes on vitellogenesis in the adult female tick,Ornithodoros moubata (Acari: Argasidae)

Vitellogenin (Vg) concentrations in the hemolymph and ovarian development were studied inOrnithodoros moubata after treatment with precocenes 1 (P1) and 2 (P2). Precocene was dissolved in acetone or DMSO and topically applied to the dorsal surface of ticks: (1) at adult ecdysis; (2) 24 h before engorgement; (3) immediately after engorgement; and (4) 24 h after engorgement. Subsequently, P1 and P2 were dissolved in olive oil and injected through the gonopore into the body cavity 24 h after engorgement. Vitellogenin concentration was measured on days 5 and 10 after engorgement and ovarian development was scored on day 10, 20 or 30. Oviposition was also recorded and the average weight of eggs laid by females was determined. No differences in concentration of Vg in the hemolymph occurred between the control ticks and ticks treated topically or by injection with P1 and P2. Precocene did not suppress the synthesis of Vg inO. moubata. However, oviposition was reduced in ticks that survived repeated treatment with high doses of P2 dissolved in acetone.     

In vivo role of 20-hydroxyecdysone in the regulation of the vitellogenin mRNA and egg development in the American dog tick, Dermacentor variabilis (Say)

Injection of the hormone 20-hydroxyecdysone (20-E) into partially fed (virgin) female adults of the American dog tick, Dermacentor variabilis, while they are attached and feeding on the rabbit host, initiated the expression of the vitellogenin (Vg) gene, and Vg protein secretion and uptake by the ovary. The induction of egg production by 20-E in this bioassay was dose dependent in the range of 1-50 times the concentration normally found in a replete, vitellogenic female. Ticks examined 4 d after the 50 x treatment were still attached to the host, had numerous enlarged vitellin-filled (brown) oocytes in their ovaries, but had not engorged to repletion. The ovaries reached weights similar to those found in untreated, replete (mated) females (pre-oviposition) while solvent-injected controls demonstrated no increase in oocyte size or increase in ovary weight. An increase in the levels of a putative Vg protein was observed in hemolymph samples collected 1, 2 and 3d post-20-E injection but was not observed in the corresponding solvent controls as determined by native PAGE. Analysis of the ecdysteroid-induced protein by tryptic digestion-mass fingerprinting and BLASTP found that the putative Vg had the strongest match to GP80 (U49934), the partial sequence for the vitellogenin protein from Boophilus microplus. A partial Vg cDNA was cloned and sequenced from replete females of D. variabilis with a high similarity to GP80. Using this message as a probe, Northern blots conducted with RNA collected from partially fed, virgin females 1, 2 and 3d post-20-E injection showed upregulation of the Vg mRNA on all 3 days. Controls injected with solvent only showed no Vg mRNA. Injections with juvenile hormone III did not stimulate Vg expression, oocyte growth or full engorgement. These studies indicate that ecdysteroids and not JH can initiate expression of the Vg gene, Vg protein synthesis and release into hemolymph, and Vg uptake into developing oocytes under bioassay conditions mimicking normal feeding on the host.     

Fat body is the site of vitellogenin synthesis in the soft tick,Ornithodoros moubata

Summary Vitellogenin (Vg) synthesis in cultured tissues was analysed biochemically in a soft tick,Ornithodoros moubata. Nine tissue fractions dissected from reproductive females were incubated in vitro in a specially designed Ringer containing³⁵S-methionine. The synthesis of total protein and Vg was assayed by the radioactivity incorporated into precipitates with trichloroacetic acid and antivitellin (Vn)-serum, respectively. Fat body was the most active tissue in Vg synthesis, which comprised 46% of the Vg synthesis by all tissues and 42% of total protein synthesis by fat body. Protein synthesized by the fat body and precipitated with anti-Vn-serum was shown by electrophoresis and fluorography, to consist of six radioactive polypeptides corresponding to the components of Vg. Vg synthesized in cultured fat body was first accumulated in the tissue and secreted into the medium during incubation. Some tissues other than fat body showed low Vg synthesis (in each, less than 12% of total protein synthesis) which, however, may be due to contamination by fat body cells as seen with the scanning electron microscope (SEM). SEM also showed that fat body cells in the active stage of Vg synthesis expanded about 10-fold in length. Immunohistochemical analysis showed a very strong reaction with anti-Vn-IgG in the cytoplasm of fat body from reproductive females. Fat body from unfed females and other tissues including midgut, did not show any specific fluorescence. A positive reaction was obtained with developing oocytes. These results indicate that the fat body is the only site of Vg synthesis in this tick.Abbreviations Vg vitellogenin - Vn vitellin - SDS sodium dodecyl sulfate - PAGE polyacrylamide gel electrophoresis - SEM scanning electron microscopy - TCA trichloroacetic acid     

Juvenile hormone biosynthesis,oocyte growth and vitellogenin accumulation in Choristoneura fumiferana and C. rosaceana: a comparative study

We assessed the effects of age and mating status on in vitro juvenile hormone (JH) biosynthesis, oocyte growth, egg production and vitellogenin (Vg) accumulation in the tortricid moths, Choristoneura fumiferana and C. rosaceana. To determine whether vitellogenesis is dependent on the presence of JH, we also examined the effects of decapitation and JH analog treatments on egg production. In both species, the corpora allata (CA) of adult females released fmol quantities of JH, with JH II being the major homolog produced. The CA began producing detectable quantities of JH around the time of emergence. Full activation of the CA was observed a few hours sooner in C. fumiferana than in C. rosaceana. In pharate adults and young virgin females of both species, growth of the basal oocyte reflected changes in CA activity. Decapitation of newly emerged females significantly reduced egg production, but treatment of decapitated females with the JH analog methoprene resulted in egg production that was similar to (C. fumiferana) or greater than (C. rosaceana) that of controls, indicating that JH is required for oocyte maturation. Vg was first observed in the hemolymph before the presumptive time of CA activation, suggesting that the synthesis of this protein is not dependent on JH. The presence of normal quantities of Vg in the hemolymph of pupae decapitated before CA activation confirmed this hypothesis. The Vg titer underwent a transient decline following CA activation and was significantly lower in mated than in virgin females of both species 3 and 5 days after copulation. Since CA activation at emergence and mating are both expected to cause a rise in the JH titer, we suggest that the declines in the levels of Vg result from JH-enhanced Vg uptake by the developing oocytes. Mating induced a significant increase in egg production but had no measurable impact on rates of JH biosynthesis in vitro.     

Hemolymph proteins in ticks

In comparison to insects and Crustacea, our knowledge of the predominant hemolymph proteins in ticks is minimal. The hemolymph protein most studied in ticks has been vitellogenin (Vg). Vg is synthesized by the tick fat body after female adults obtain a blood meal, is released into the hemolymph and is absorbed by developing oocytes as vitellin (Vn). Much of what we know about Vg is from studies of Vn. In general, the carbohydrate, lipid and amino acid composition is similar to insects except that in the tick, Vg contains heme, most likely from the digestion of host hemoglobin. In the American dog tick, Dermacentor variabilis, Vg is comprised of two native proteins and seven subunits on SDS-PAGE. Vg has been characterized in five tick species but the amino acid sequence is not yet available. Another predominant hemolymph protein, apparently a carrier protein (CP), has recently been studied in two tick species. This protein is found in the hemolymph of both male and females adults, in adult tissues outside of the hemolymph in some tick species, in coxal fluid of soft ticks and in whole body homogenates from eggs, larvae and nymphs. CP from the hard tick, D. variabilis, contains cholesterol, phospholipids, monoacylglycerides, triacylglycerides, free fatty acids, carbohydrate and heme. Under identical assay conditions, the analogous protein in the soft tick, Ornithodoros parkeri, did not contain heme. CP in the American dog tick consists of two subunits, one of which has 61% identity to the biliprotein, artemocyanin, from the fairy shrimp. CP is identical to a heme-lipoprotein (HeLp) from Boophilus microplus. The exact roles of CP and HeLp have not yet been fully determined, but they apparently are important in heme sequestration and as a storage depot for protein and lipid. Macroglobulin, lectin, antimicrobial, JH binding, JH esterase, and other tick hemolymph proteins are also discussed.     

Vitellogenin and egg production in the moth,Heliothis virescens

The characteristics of vitellogenin (Vg) and the relationship between Vg production and egg production in the tobacco budworm, Heliothis virescens, were studied. The relationship between Vg production and juvenile hormone (JH) and the impact of mating on Vg and egg production were also investigated. Vg appears in the hemolymph of H. virescens about 6 h after moth eclosion. Vg may be separated into two apoproteins (ApoVg-I and ApoVg-II) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The molecular weights were calculated to be 156,065 ± 800 for ApoVg-I and 39,887 ± 323 for ApoVg-II. SDS-PAGE analysis revealed that the female hemolymph Vg polypeptides appear to be identical to those from eggs but are absent in male hemolymph. Vg concentration was significantly higher in mated females than in virgin females of the same age at 48 h after emergence. Rates of egg production increased as Vg production increased; rates of egg production in mated females were significantly higher than those of virgin females at 48, 72, 96, and 120 h postemergence. Vg production is dependent on JH, because hemolymph from decapitated females lacked Vg while that of decapitated females treated with synthetic JH had Vg at levels comparable to similarly aged, normal H. virescens females. Hemolymph JH titers in mated females were significantly higher compared with those in virgin females at all sampling periods. The high JH level in mated females may explain the high Vg and egg production in mated H. virescens. Arch. Insect Biochem. Physiol. 34:287–300, 1997. © 1997 Wiley-Liss, Inc.     

Purification and characterization of biliverdin-binding vitellogenin from the hemolymph of the common cutworm,Spodoptera litura

Biliverdin-binding vitellogenin (Vg) was purified from adult female hemolymph of the common cutworm, Spodoptera litura, by using gel filtration and ion exchange chromatographies. The molecular mass of the protein was 490 kDa and it was composed of two 188-kDa subunits. Three internal amino acid sequences obtained by digestion of the protein with lysylendopeptidase showed high similarity to those of Bombyx mori Vg, supporting the purified blue protein to be vitellogenin. latroscan analyses demonstrated the presence of biliverdin in Vg that occupied 2.4% of total lipid components. Among the lipids of Vg (9.5 micrograms total lipids per 100 micrograms protein), diacylglycerol was the most predominant, followed by phospholipid, hydrocarbons, and then triacylglycerol, while in biliverdin-binding proteins (BPs) purified from larval hemolymph (3.1 micrograms total lipids per 100 micrograms protein), phospholipid was the most abundant lipid followed by diacylglycerol; hydrocarbons and triacylglycerol were minor components. Vg was first detected in the hemolymph of female pupae one day before eclosion, but injection of 5 micrograms of methoprene into a 3-day-old pupa induced Vg in the hemolymph 4 days earlier than in the control. Methoprene also induced a faster decline in BP-A and BP-B titers in the hemolymph with a corresponding increase of the Vg titer. These results suggest that juvenile hormone (JH) induces not only vitellogenesis but also the uptake of these proteins by stimulating the metamorphosis of fat body during the pupal stage.     

Molecular analysis of nutritional and hormonal regulation of female reproduction in the red flour beetle, Tribolium castaneum

Female reproduction includes maturation of oocytes and the synthesis of yolk proteins (vitellogenin, Vg) in the fat body and their deposition into the oocytes. Our recent studies showed that juvenile hormone (JH) regulates Vg synthesis and 20-hydroxyecdysone (20E) regulates oocyte maturation in the red flour beetle (Tribolium castaneum). Here, we report on the role of nutritional signaling on vitellogenesis and oogenesis. Comparison of gene expression between fed and starved beetles by microarray analysis showed the up-regulation of genes involved in energy homeostasis and down-regulation of genes involved in egg production in the starved beetles. The RNA interference (RNAi) aided knock-down in the expression of genes involved in insulin and TOR signaling pathways showed that both these signaling pathways play key roles in Vg synthesis and oocyte maturation. Starvation of female beetles resulted in a block in Vg synthesis but not in the progression of primary oocyte development to the resting stage. Feeding after starvation induced Vg synthesis and the progression of primary oocytes from the resting stage to the mature stage. However, in the beetles where JH or 20E synthesis or action was blocked by RNAi, both Vg synthesis and oocyte maturation were affected suggesting that both these hormones (JH and 20E) and nutritional signaling and their cross-talk regulate vitellogenesis and oogenesis.     

Juvenile hormone regulation of vitellogenin synthesis in the red flour beetle,Tribolium castaneum

To elucidate the endocrine regulation of vitellogenin (Vg) synthesis in the red flour beetle, Tribolium castaneum, the titers of juvenile hormone (JH) and ecdysteroids in the whole body of female beetles were measured and compared with Vg mRNA levels. Juvenile hormone levels remained high while the ecdysteroid levels declined steadily during 1–5 days post adult emergence (PAE). The Vg mRNA levels began to increase by the end of 3rd day PAE and peaked by the 4th–5th day PAE. Gene expression profiling by microarray and quantitative real-time PCR analyses of RNA isolated from 1 to 5 days PAE beetles revealed that the genes coding for proteins involved in JH biosynthesis and action, but not those involved in 20-hydroxyecdysone (20E) biosynthesis and action had similar expression patterns as the genes coding for Vg. RNA interference (RNAi)-aided knock-down in the expression of these genes showed that both JH and 20E were required for Vg gene expression. However, Vg mRNA was induced by the application of JH III but not by the injection of 20E into the previtellogenic females. These data suggest that JH is required for Vg synthesis in the fat body and 20E influences Vg synthesis through its action on oocyte maturation.     

Relationship between feeding,mating, vitellogenin production and vitellogenesis in the tickDermacentor variabilis

Anti-vitellin IgG directed againstDermacentor variabilis egg vitellin was used in sodium dodecyl sulfate polyacrylamide (SDS-PAGE) gradient gel immunoblots to detect the presence of vitellin and its precursor, vitellogenin, in the organs of feeding adults and in the immature stages of this tick. Vitellin polypeptides were found in the egg, larvae, nymph, and in the unfed adult stages of both sexes. Vitellin polypeptides were first detected in the ovary of mated females during the rapid-engorgement feeding, period. These polypeptides were also present in the ovaries of ovipositing females, unmated females fed for extended periods, and fed unmated females that were detached from the host and held for 12 h before dissection. The same anti-vitellin antibody was used in immunoblots to monitor the appearance of vitellogenin in the organs and hemolymph of female ticks. Immunoreactive peptides of vitellogenin were found in the fat body, midgut, and hemolymph of pre-rapid-engorging mated and unmated females. These polypeptides were not found in fed males nor in Malpighian tubes of feeding or ovipositing females Our data supported the following conclusions: 1) presence of immunoreactive vitellogenin in the adult female fat body, hemolymph, and midgut was, dependent upon feeding; 2) in mated feeding females, we could not detect the uptake of vitellogenin by the ovary until rapid engorgement; 3) in unmated females, vitellogenesis did not, begin unless prolonged feeding occurred; and 4) during the early developmental stages of this tick, vitellin served as an embryonic nutrient reserve and as a reserve against starvation between feedings.     

Regulation of female reproduction in mites: A unifying model for the Acari

It is well established in the literature that circulating high levels of juvenile hormone (JH) are responsible for the initiation of vitellogenesis and female reproduction in most insects studied so far. Exceptions include some Diptera, Lepidoptera and Hymenoptera. The current view is that JH also regulates yolk protein (vitellogenin, Vg) synthesis and female reproduction in mites. However, there is no published evidence that mites have the common insect JHs at any stage of their development. Also, research on the effects of exogenous applications of JH and JH analogs on the reproduction of mites is contradictory. Significant information is available on the life history of mite reproduction, and new information has become available on mite storage proteins including Vg. Although initial studies suggested that ticks may respond to exogenously applied juvenile hormone or anti-JHs, current research shows that ticks cannot synthesize the common insect JHs and have no detectable levels of these hormones in their hemolymph during female reproduction. In ticks, it appears that ecdysteroids, and not JH, regulate expression of the Vg gene and the synthesis and release of Vg protein into the hemolymph. In fact within the Arthropoda, JH has been found only in insects. Methyl farnesoate and not JH regulates Vg synthesis in the Crustacea, the sister group to the insects. Based on this evidence, a new working hypothesis is proposed, i.e., that ecdysteroids and not the JHs regulate vitellogenesis in the Acari including both ticks and mites. To the present, the role of neuropeptides in the regulation of female reproduction in mites is not known.     

Juvenile hormone-like substances can induce vitellogenesis in the tick Ornithodoros moubata (Acarina: Argasidae)

Topical application of different juvenile hormone analogs (JHA) or of a mixture of stereoisomers of insect juvenile hormone (JH) 1 and 3 to fed virgin female Ornithodoros moubata immediately after feeding induced vitellogenesis and egg-laying in up to 70% of treated females. In controls only 13.7% oviposited. The eggs were sterile, with abnormal shape, but their number versus the weight of engorged females was normal or sometimes greater than in mated females. However, preoviposition period was longer than in mated females.

It was more difficult to induce egg-laying by similar topical applications 100 days after feeding of virgin females. A maximum of 58% of ovipositing females was obtained with a very high dosage of JH mixture (500 fig). Injection of this mixture into the females was more potent; 15 to 50 fig induced oviposition in about 60% of the females. The preoviposition period was also longer than in control females.

Our results suggest the presence of a JH-like substance which is involved in the hormonal control of vitellogenesis. However, since natural isomers of JH were much less efficient than isomeric mixtures or JHA, we suppose that the natural tick hormone does not correspond to JH, but rather to a JH-like substance.     

HORMONAL CONTROL OF THE VITELLOGENESIS IN THE JAPANESE OAK SILKWORM, ANTHERAEA YAMAMAZ (LEPIDOPTERA: SATURNIIDAE)

Abstract Effects of ecdysteroid and juvenile hormone (JH) on vitellogenesis of the Japanese oak silkworm, Antheraea yamami are reported in this article. After topical treatment with 20-hydroxyecdysone alone or JH analog (i.e. methoprene) alone and combined treatment with these two chemicals, vitellogenin (Vg) titers in the fat body and haemolymph at the pupal stage were mostly higher than those of the control, indicating that both ecdysteroid and JH exerted a promoting effect on the synthesis of Vg. In contrast, the Vg uptake was markedly inhibited by JH while stimulating effect of the ecdysteroid could be shown that vitellin (Vt) titer in the ovary was lower after methoprene treatments, but higher after 20-hydroxyecdyson treatments. Meanwhile, effects of these two hormones on Vg synthesis in the fat body were also tested with the incubation in vitro with Grace medium containing H-leucine and the hormones. The results demonstrated that Vg synthesis was stimulated after treating with methoprene alone or 20-hydroxyecdysone alone and combined treating with these two chemicals, and particularly ecdysteroid had more marked positive effect. To comprehensively concluded our results, it could be regarded that ecdysteroid play the main role in the regulation of vitellogenesis for the Japanese oak silkworm.