Rates Of Juvenile Hormone Synthesis Research Articles

Neuropeptide regulators of the juvenile hormone biosynthesis (in vitro) in the beetle, Tenebrio molitor (Coleoptera, Tenebrionidae)

The genome of Tribolium castaneum encodes two allatostatin [AS type B; W(X)(6)Wamide and AS type C; PISCF-OH] and one allatotropin (AT) precursor, but no AS type A (FGLamide) (Tribolium Genome Sequencing Consortium, 2008: Nature 452:949-955). Here we studied the activity (in vitro) of peptides derived from these precursors on the synthesis/release of juvenile hormone (JH) III. The corpora cardiaca-corpora allata (CC-CA) complexes of adult females of another tenebrionid beetle, the mealworm Tenebrio molitor, were used. Incubating the gland complexes in a medium containing Trica-AS B3 peptide, we showed that the peptide has allatostatic function in T. molitor. The activity of the type C AS depended on the age of the test animals and their intrinsic rate of JH III biosynthesis. The Trica-AS C peptide inhibited the JH release from CA of 3-day-old females with a high intrinsic rate of JH synthesis, but activated JH release from the CA of 7-day-old females with a lower intrinsic rate of JH production. The allatotropin peptide (Trica-AT) also activated the JH release from the CA of 7-day-old females in a dose-dependent and reversible manner. Unexpectedly, a type A AS derived from the precursor of the American cockroach Periplaneta americana (Peram-AS A2b) inhibited the JH release from the CA of younger and older females in the concentration range of 10(-8) to 10(-4) M, and the effects were fully reversible in the absence of peptide. These data suggest a complex role of allatoactive neuropeptides in the regulation of JH III biosynthesis in beetles.

Target of Rapamycin (TOR) Mediates the Transduction of Nutritional Signals into Juvenile Hormone Production

Anautogeny is a reproductive strategy by which females do not reproduce until they feed. Therefore, nutritional signals must inform the reproductive tissues, and cells that the organism has reached a nutritional status suitable for triggering reproductive processes. One of the possible pathways involved in anautogeny is the "target of rapamycin" (TOR) pathway, which has been described as connecting the nutritional status with growth, proliferation, and cancer. The German cockroach, Blattella germanica, is an anautogenous species whose vitellogenesis is governed by juvenile hormone. In the present report, we describe the cloning of TOR cDNA from B. germanica (BgTOR). Expression studies showed that BgTOR is expressed in adult female corpora allata and fat body. BgTOR knockdown using systemic RNAi in vivo produced a severe inhibition of juvenile hormone synthesis in adult female corpora allata, together with a reduction of mRNA levels corresponding to 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase-1, HMG-CoA synthase-2, and HMG-CoA reductase. In addition, there was a reduction of vitellogenin mRNA in the fat body, and ovaries did not grow. Analysis of TOR expression in corpora allata of fed and starved females suggested that TOR is not regulated at the transcriptional level. Nevertheless, there was a reduction in HMG-CoA synthases and reductase mRNA in corpora allata (but not in the fat body) of starved females, together with a dramatic reduction of juvenile hormone production and ovary development. Taken together, our results indicate that TOR knockdown mimics starvation in terms of corpora allata activity, and suggest that nutritional signals that activate juvenile hormone biosynthesis and vitellogenin production are mediated by the TOR pathway.

Identification of Phe-Gly-Leu-amide type allatostatin-7 in Reticulitermes flavipes: Its localization in tissues and relation to juvenile hormone synthesis

The allatostatins (ASTs), with a Tyr/Phe-Xaa-Phe-Gly-Leu/Ile-amide C-terminus, are neuropeptides that occur in many orders of insects, but are known to inhibit juvenile hormone (JH) synthesis by corpora allata (CA) only in cockroaches, crickets, and termites. 5 AST peptides with similar sequences to those of 6 species of cockroaches have been isolated and sequenced from extract of brain tissue of the termite Reticulitermes flavipes. The amino acid sequence of a 6th peptide, R. flavipes AST-7, determined by LC–MS/MS following HPLC fractionation of brain extract, is S-P-S-S-G-N-Q-R-L-Y-G-F-G-L-NH 2. The 8 terminal amino acids are identical to AST-7 of the cockroach Diploptera punctata. R. flavipes and D. punctata AST-7s inhibited JH synthesis by CA of both species equally and their affinity for antibody against D. punctata AST-7 is similar. Immunoreactivity of termite tissue with this antibody indicates neuro- and myomodulatory activity of the peptide in addition to its demonstrated allatostatic function. The density of AST immunostaining in axons within the CA of R. flavipes and the rate of JH synthesis by similar glands were negatively correlated. This is evidence that when AST is abundant in the glands it is being released in vivo to limit JH production.

Isolation of cockroach Phe–Gly–Leu–amide allatostatins from the termite Reticulitermes flavipes and their effect on juvenile hormone synthesis

Immunoreactivity to cockroach Diploptera punctata allatostatin-7 (Dippu AST-7) has been demonstrated previously in axons innervating the corpora allata of the termite Reticulitermes flavipes. This peptide and Dippu AST-11 inhibited juvenile hormone (JH) synthesis by corpora allata (CA) of brachypterous neotenic reproductives (secondary reproductives) of termites. The present study shows that R. flavipes CA are also inhibited by Dippu AST-2, AST-5, AST-8, and AST-9 at approximately the same rank order of potency as demonstrated in D. punctata. Another allatostatin from Periplaneta americana (Peram AST-12) also inhibits JH synthesis by R. flavipes CA. Sensitivity to the allatostatins is higher in glands with low rates of JH synthesis than in those with relatively high JH synthetic rates as has been demonstrated in CA from male and female secondary reproductives as well as in those from non-egg-laying and egg-laying females. The identical inhibitory effects of R. flavipes brain extract on CA from both D. punctata and R. flavipes and the isolation and identification of five cockroach allatostatins (Dippu AST-1, AST-2, AST-5, AST-8, and Peram AST-12) from termite brain extract reflect the close relationship between cockroaches and termites.

Changes in juvenile hormone synthesis in the termite Reticulitermes flavipes during development of soldiers and neotenic reproductives from groups of isolated workers

Workers of Reticulitermes flavipes were isolated in groups of increasing numbers to determine the in vitro rates of juvenile hormone (JH) synthesis by individual pairs of corpora allata (CA) as other castes differentiated. Only neotenic reproductives developed in groups of 12. Mean JH synthesis rates increased after 5 weeks but only a few individuals had significantly higher rates, about 0.4pmol/pair/h, which occurred at about 3 weeks before neotenics developed. Soldiers and neotenics developed in groups of 50. Mean rates increased to a peak at week 6 after isolation, but only a few individuals had rates approaching 1pmol/pair/h, which occurred at the same time after isolation as the development of pre-soldiers. JH synthesis by CA of pharate pre-soldiers and soldiers was low compared to that of pharate workers and neotenics. CA of pre-soldiers attained a peak mean rate of JH synthesis of 0.9pmol/pair/h at 6 days of age, whereas CA of soldiers attained only a peak mean rate of 0.3pmol/pair/h. These measurements of JH synthesis by individual pairs of CA suggest that the few workers destined to become pre-soldiers have 2.5-fold higher JH synthesis than the few that would develop into neotenic reproductives, and show that a cycle of synthesis accompanies the development of pre-soldiers into soldiers.

Juvenile hormone synthesis as related to egg development in neotenic reproductives of the termite Reticulitermes flavipes, with observations on urates in the fat body

The relationship between juvenile hormone (JH) synthesis and egg development, which is well documented in cockroaches, is much less studied in their close relatives, the termites. In this study of neotenic reproductives of the subterranean termite Reticulitermes flavipes, in vitro rates of juvenile hormone (JH) synthesis by corpora allata (CA) are related to vitellogenic egg development and the size of CA. The first study compared brachypterous and apterous neotenics in their first cycle of egg development and a second study compared physogastric and non-physogastric brachypterous and apterous neotenics. In both studies, rates of JH synthesis correlated with the size of CA as indicated by their length. Unlike the cockroach in which all basal oocytes are in the same stage of development, those in termites are in various stages. In brachypterous and apterous in the first cycle of egg development, CA with high rates of JH synthesis were from females with early vitellogenic basal oocytes, whereas CA with low rates of JH synthesis were from females with either pre-vitellogenic or mature basal oocytes. This pattern of JH synthesis is similar to the cycle of JH synthesis correlated with oocyte development in several cockroach species. In later oocyte maturations, CA from physogastric apterous females with ovaries containing mature, as well as growing oocytes, showed a wide range of JH production; the CA with the highest rates of JH synthesis were from females with the highest proportion of early vitellogenic oocytes suggesting that both mature and early vitellogenic oocytes interact to regulate JH synthesis. Rates of JH synthesis were related to the number of vitellogenic ovarioles. Physogastric brachypterous neotenics, compared to the other classes of neotenic females, had CA with 2- to 4-fold higher rates of JH synthesis and ovaries with 2.5- to 8-fold greater number of vitellogenic ovarioles. However, both physogastric brachypterous and apterous neotenics had more vitellogenic basal oocytes and less urate in their fat bodies than the respective non-physogastric neotenics. These results demonstrate the similarities and differences between the classes of neotenic termites and between reproductive females in cockroaches and termites.

Hmgcr in the Corpus Allatum Controls Sexual Dimorphism of Locomotor Activity and Body Size via the Insulin Pathway in Drosophila

The insulin signaling pathway has been implicated in several physiological and developmental processes. In mammals, it controls expression of 3-Hydroxy-3-Methylglutaryl CoA Reductase (HMGCR), a key enzyme in cholesterol biosynthesis. In insects, which can not synthesize cholesterol de novo, the HMGCR is implicated in the biosynthesis of juvenile hormone (JH). However, the link between the insulin pathway and JH has not been established. In Drosophila, mutations in the insulin receptor (InR) decrease the rate of JH synthesis. It is also known that both the insulin pathway and JH play a role in the control of sexual dimorphism in locomotor activity. In studies here, to demonstrate that the insulin pathway and HMGCR are functionally linked in Drosophila, we first show that hmgcr mutation also disrupts the sexual dimorphism. Similarly to the InR, HMGCR is expressed in the corpus allatum (ca), which is the gland where JH biosynthesis occurs. Two p[hmgcr-GAL4] lines were therefore generated where RNAi was targeted specifically against the HMGCR or the InR in the ca. We found that RNAi-HMGCR blocked HMGCR expression, while the RNAi-InR blocked both InR and HMGCR expression. Each RNAi caused disruption of sexual dimorphism and produced dwarf flies at specific rearing temperatures. These results provide evidence: (i) that HMGCR expression is controlled by the InR and (ii) that InR and HMGCR specifically in the ca, are involved in the control of body size and sexual dimorphism of locomotor activity.

Glutamate-gated chloride channels inhibit juvenile hormone biosynthesis in the cockroach, Diploptera punctata

Juvenile hormone (JH) synthesized and released from endocrine gland corpus allatum (CA) plays an important role in insect metamorphosis, vitellogenesis and reproduction. Glutamate is a major neurotransmitter in the nervous system and its activated receptors possess excitatory and inhibitory forms in muscle fibers of invertebrates. Previously, we have shown that the rise of intracellular calcium through excitatory glutamate receptors, N-methyl- d-aspartate (NMDA) and non-NMDA-type channels stimulates JH synthesis in the cockroach, Diploptera punctata. Here, we demonstrate the occurrence of inhibitory chloride permeable glutamate (GluCl) receptors on CA cell membranes. Application of the GluCl channel activators, ibotenic acid (Ibo) and ivermectin, but not γ-aminobutyric acid caused a decline in JH synthesis in glands of either high or low activity during the gonadotrophic cycle. Also, while recording the membrane potential of the isolated whole CA glands intracellularly, Ibo induced a hyperpolarizated response. Both changes in the membrane potential and inhibition of JH synthesis could be abolished by the application of the chloride channel blocker picrotoxin. Finally, we found both excitatory and inhibitory glutamate receptors cause antagonistic effects on rates of JH synthesis. These results indicate a novel function of GluCl channels in the inhibition of JH synthesis that could be a potential pathway for developing a new generation of insecticides.

Developmental changes in the ability to synthesize juvenile hormone in vitro by corpora allata from the Eri silkworm, Samia cynthia ricini (Lepidoptera: Saturniidae)

A radiochemical assay (RCA) has been used for the measurement of juvenile hormone (JH) synthesis in vitro by corpora allata (CA) from the Eri silkworm, Samia cynthia ricini. Using CA from newly emerged female adults for the bioassay, the most suitable incubation conditions were determined. A high rate of JH synthesis was found in medium TC199 at pH 6.5, 30°C and 4 mM Ca2+. The time course of JH synthesis showed a steady decrease during the first 6 hours of incubation.Under optimal incubation conditions, CA from the 4th and 5th larval instars, pupae and adults were used for measuring JH synthesis in vitro. The highest rates of JH synthesis were found on the 1st day of both larval stages, and then JH synthesis decreased steadily during the following two days of each instar. From the 4th day of the 5th larval instar to the 2nd day after pupation, CA could still synthesize small amounts of JH. However, from the 3rd day of the pupal stage to 12 hours before adult emergence, no JH release was observed. About 6 hours before emergence, CA of both female and male pharate adults regained the ability to synthesize JH. JH synthesis increased to a maximum shortly after emergence and then decreased again during the following two days. During this period, JH synthesis in vitro by CA from females was always higher than that of males. This is the first report on JH synthesis in vitro by CA from both female and male pharate adults and adults of a lepidopteran species, where the adults do not feed, are relatively short-lived, mate only once, and ovarian maturation and vitellogenesis are completed before emergence.

Ionotropic glutamate receptors mediate juvenile hormone synthesis in the cockroach, Diploptera punctata

By monitoring changes in the cytosolic [Ca 2+] i and rates of juvenile hormone (JH) synthesis in response to l-glutamate agonists and antagonists, we identified and characterized glutamate receptor subtypes in corpus allatum (CA) cells of the cockroach, Diploptera punctata. During the first ovarian cycle, corpora allata exhibited a cycle of changes in sensitivity to l-glutamate correlated to cyclic changes in rates of JH synthesis. When exposed to 60 μM l-glutamate in vitro, the active corpora allata of day-4 mated females produced 60% more JH, while inactive corpora allata at other ages showed 10–20% stimulatory response. Pharmacological characterization using various l-glutamate receptor agonists and antagonists indicated that several ionotropic subtypes of l-glutamate receptors were present in the CA. The CA showed an increase in rates of JH synthesis in response to NMDA, kainate, and quisqualate, but not to AMPA in both L-15 medium and minimum incubation medium. In contrast, applications of the metabotropic receptor-specific agonist trans-ACPD failed to elicit a change in the cytosolic [Ca 2+] i and JH production. An elevation of cytosolic calcium concentration, followed by 20–30% rise in JH production, was observed when active CA cells were exposed to 10–40 μM kainate. Kainate had no stimulatory effect on JH synthesis in calcium-free medium. The kainate-induced JH synthesis was blocked by 20 μM CNQX but was not affected by 20 μM NBQX. Kainate-stimulated JH production was not suppressed by MK-801 (a specific blocker of NMDA-receptor channel), nor was NMDA-stimulated JH production affected by CNQX (a specific antagonist of kainate receptor). These data suggest that active CA cells are stimulated to synthesize more JH by a glutamate-induced calcium rise via NMDA-, kainate- and/or quisqualate-sensitive subtypes of ionotropic l-glutamate receptors. The metabotropic-subtype and ionotropic AMPA-subtype l-glutamate receptors are unlikely to be present on active CA cells.

Release of neurosecretory granules within the corpus allatum in relation to the regulation of juvenile hormone synthesis in Diploptera punctata

The release of neurosecretory granules within the corpora allata (CA) of the viviparous cockroach Diploptera punctata has been compared in glands with intact nerves from the brain (Brain–CA) and those detached from the brain. Measurements of juvenile hormone (JH) synthesis in vitro, comparing these two conditions of the CA at several stages of vitellogenesis in adult females, showed lower production of hormone in Brain–CA complexes than in CA alone. Glands treated with tannic acid to trap exocytotic granules before fixation for electron microscopical examination showed, in sample sections, 10 times more exocytotic profiles in the glands with intact nerves to the brain than in the isolated glands. Sections treated with antibody against allatostatin I (Dip 7), a member of the neuropeptide family that inhibits JH synthesis by CA in vitro, showed neurosecretory granules in allatostatin immunoreactive nerves to be 75±4% of the granules in the sample of sections of CA. Because the total quantity of allatostatin in CA was found by ELISA not to vary significantly with changes in JH synthesis, it is concluded that the lower rates of JH synthesis by glands with intact nerves to the brain are most likely due to the release of small amounts of allatostatin within the CA.

Neural control of cell size in the corpora allata during the reproductive cycle of the cockroach Diploptera punctata (Dictyoptera: Blaberidae)

Summary Rising and subsequent falling rates of juvenile hormone (JH) synthesis occurred concurrently with synchronous growth and atrophy of CA cells during the ovarian cycle in mated adult females of Diploptera punctata. Ultrastructural observations revealed that growth of CA cells resulted from synchronous proliferation of cellular machinery required for JH synthesis. Cell growth was suppressed in CA of virgin females, in which rates of JH synthesis remained low, but was stimulated by mating or by severance of nerves leading from the brain to the CA. Atrophy of CA cells during declining rates of JH synthesis was due to synchronous autophagy of cellular organelles. While the mechanism initiating autophagy is unclear, it is independent of nervous connections between the CA and brain. We propose that under normal physiological conditions the quantity of JH synthesized by a corpus allatum is determined largely by the total amount of cellular machinery available for JH production. Therefore, the cycle of JH synthesis in mated adult females of D. punctata is regulated mainly through synchronous proliferation of cell components (under neural inhibition) followed by synchronous autophagy (nerve independent). In the course of this study, we have found that individual CA cells from D. punctata, like those from Blattella germanica, retain their ability to synthesize JH III following enzymatic dissociation of the CA.

Ultrastructural changes in corpora allata during a cycle of juvenile hormone biosynthesis in embryos of the viviparous cockroach, Diploptera punctata

We have observed changes with time in the fine structure of corpora allata (CA) during a known cycle of increasing and decreasing juvenile hormone (JH) synthesis in late embryos of Diploptera punctata. A previous report showed that rates of JH release were relatively low in 28-day-old embryos, but CA activity subsequently rose linearly to a peak on about day 42, and thereafter steadily declined to a low level on day 64 just before birth (Holbrook et al., 1997). We now show that, regardless of rate of JH synthesis, CA cells are large and replete with organelles which nevertheless exhibit variable morphology in embryos of different age. Highly active CA cells on day 40 contain abundant ring-form mitochondria, whereas CA cells of low activity on days 28 and 64 contain mitochondria that are rod-shaped or globular. Mitochondrial cristae were scarce and indistinct on day 28 but numerous and well developed on day 64. Endoplasmic reticula (ER) are rare on day 28 and appear in increasing numbers when CA activity rises. On day 40, ER are abundant and often exhibit a whorl-like appearance which is not observed on day 28. After day 44, when biosynthetic activity is declining, whorls of ER gradually decrease in number and are ultimately replaced by vesicular smooth ER on day 64. Neurosecretions are found only after day 38, by which time rates of JH synthesis have increased substantially from those of day 28. Except for membranous autophagic vacuoles, which are frequently found when ER whorls disintegrate as rates of JH synthesis decline toward birth, most autophagic vesicles such as multivesicular vesicles and dense bodies occur only sporadically among CA cells at all examined ages. We conclude that synchronous autophagy of exhausted organelles, which results in atrophy of CA cells and long-term arrest of JH synthesis in adult females of D. punctata, does not occur in embryos. The slow cyclic change in rate of JH synthesis in embryonic CA is most likely due to asynchronous autophagic activity and to alterations in certain unique features of intracellular organelles.

Role of the corpora allata and juvenile hormone in the control of imaginal diapause and reproduction in three species of locusts

To understand the hormonal regulation of imaginal diapause and ovarian development in three species of locusts, Nomadacris succincta, Nomadacris japonica and Locusta migratoria, juvenile hormone (JH) biosynthesis by the corpora allata (CA) in vitro and JH esterase activity in the hemolymph were measured. The two species of Nomadacris exhibited a positive correlation between oocyte growth and JH biosynthesis by CA in vitro, although the correlation was significant only in N. succincta. In contrast, L. migratoria showed a negative correlation, indicating a higher rate of JH synthesis associated with more suppressed ovarian development. In this species, however, the hemolymph JH titer was higher in reproductively active females than in sexually immature females, indicating a positive correlation between the hemolymph JH titer and ovarian development. The levels and temporal pattern of variation in mean hemolymph JH esterase activity were rather similar between reproductively active and inactive females in L. migratoria. It is thus unlikely that the hemolymph JH esterase plays an important role in the regulation of the hemolymph JH titers in this species. Topical application of 100 μg of methoprene stimulated ovarian development significantly in L. migratoria, whereas 450 μg failed to induce ovarian development or vitellogenesis in sexually immature females of N. succincta and N. japonica. Besides JH, there appear to be other factors present that are involved in the control of the termination of diapause in the two Nomadacris species.

Synthesis and degradation of juvenile hormone III during the final two larval stages of female and male crickets, Gryllus bimaculatus de Geer (Ensifera, Gryllidae)

The rates of synthesis of juvenile hormone III were determined in female and male penultimate and final larval instars of the Mediterranean field cricket, Gryllus bimaculatus, using an in vitro radiochemical assay. Throughout the penultimate larval stadium, mean rate of juvenile hormone synthesis declines from about 4 pmol · hr−1 - pair corpora allata (CA)−1 on day 0 to less than 1 pmol · hr−1 · pair CA−1 on day 5, but increases again prior to the next larval moult (day 6). During the first 24 hr of the final larval stadium, mean rates of juvenile hormone synthesis are between 5–6 pmol · hr−1 · pair CA−1 and thereafter drop below 0.5 pmol · hr−1 · pair CA−1 by day 4. Immediately following imaginal ecdysis, the corpora allata of virgin females synthesize juvenile hormone III at higher rates than those observed throughout the final larval instar. The accumulation of methyl farnesoate within the corpora allata parallels the rates of juvenile hormone III synthesis, but at a lower level. Juvenile hormone III esterase activity in hemolymph, as measured in vitro, is moderate during the penultimate larval stadium (ca. 200 pmol · hr−1 · μl−1) and increases significantly to a high level from day 2 to the end of the final larval stadium. There is no sexual dimorphism in timing or magnitude of juvenile hormone III synthesis and juvenile hormone III esterase activity, respectively.

Sensitivity to Diploptera punctata allatostatin of male corpora allata following denervation, juvenile hormone analog treatment and ovary implantation

Allatostatins, brain neuropeptides, of Diploptera punctata inhibit the corpora allata in vitro, and the sensitivity of the corpora allata to allatostatins depends on the developmental state of the glands. This investigation demonstrates changes in rates of juvenile hormone synthesis and sensitivity of corpora allata of male D. punctata to allatostatin I (A-P-S-G-A-Q-R-L-Y-G-F-G-L-NH 2) in vitro as a result of experimental treatments which were shown previously to effect changes in hemolymph allatostatin. Sensitivity of male glands to allatostatin increased in the first 8 days of adult life. Severance of nerves to the corpora allata on day 1 resulted in increased sensitivity of corpora allata by day 5 compared to controls. Treatment of animals with juvenile hormone analog (7S-hydroprene) in addition to severance of nerves showed an increase in sensitivity to allatostatin by day 3. Implantation of vitellogenic ovarioles into males on day 2, after severance of corpora allata nerves and juvenile hormone analog application on day 1, resulted by day 4 in relatively lower sensitivities of corpora allata to allatostatin than for corpora allata from similarly treated males receiving non-vitellogenic ovarioles. These changes in sensitivity of corpora allata to allatostatin in vitro could only in part account for changes in rates of juvenile hormone synthesis observed following experimental treatments.

Effects of Diploptera punctata allatostatins on juvenile hormone biosynthesis and endogenous juvenile hormone III levels in virgin and mated female Periplaneta americana

Corpora allata from 4-day-old virgin and sexually mature female Periplaneta americana were tested for sensitivity to inhibition of juvenile hormone biosynthesis in vitro by four allatostatins from Diploptera punctata. Two of these allatostatins were also tested for their ability to lower juvenile hormone levels in vivo when injected in aqueous solution. In 4-day-old virgin females (showing comparatively low rates of juvenile hormone synthesis) corpora allata were sensitive to all four neuropeptides. Inhibition of juvenile hormone synthesis was roughly equivalent at the single dose tested (58–74% inhibition @ 10 −5 M). By contrast, corpora allata from mid-cycle sexually mature females (in which juvenile hormone synthesis approaches maximum rates) were sensitive only to D. punctata allatostatin 4. Investigation of the sensitivity of corpora allata to allatostatins 1 and 4 throughout the reproductive cycle revealed that at no stage did allatostatin 1 cause more than 25% inhibition of juvenile hormone synthesis. Allatostatin 4 however, caused a moderate inhibitory response early in the cycle (33–71%), rising to a highly significant response (81–97%) towards the end of maximal oocyte growth when endogenous (control) rates of juvenile hormone synthesis are naturally declining. The activities of the Diploptera allatostatins against Periplaneta corpora allata in vitro are matched by their actions in vivo. Injections of allatostatins 1 and 4 (100 μg/insect) into day-4 virgin P. americana were effective in bringing about a lowering of total body JH III levels 12 h post-injection. Similar injections of allatostatin 1 into mid-cycle mated females produced no apparent effect but injection of allatostatin 4 did result in a substantial reduction (50–70%) of endogenous total body JH III levels in these insects.

Neural and hormonal regulation of calling behavior in Blattella germanica females

Virgin females of the German cockroach, Blattella germanica, exhibit cycles of calling behavior in relation to the cycles of corpora allata activity and ootheca production. The roles of juvenile hormone, mating, and the ootheca in the regulation of calling behavior were investigated. The onset of calling in relation to increasing rates of juvenile hormone synthesis suggested involvement of the corpora allata. Allatectomy prevented the expression of calling behavior and treatment with the juvenile hormone analog fenoxycarb restored calling. Corpus allatum denervation through nervi corporis allati transection, which accelerates the synthesis of juvenile hormone by the corpora allata, also accelerated the onset of calling. Using castrated males, timed interruption of mating and ventral nerve cord transection, we demonstrated that, while insertion of the male genitalia and/or spermatophore in the bursa copulatrix caused an immediate suppression of calling behavior, presence of sperm and/or associated seminal fluid in the spermatheca was required for the complete inhibition of calling in the first as well as in the second ovarian cycle. Although inhibitory signals from the presence of an ootheca in the genital atrium would suppress calling behavior indirectly by inhibiting corpus allatum activity, treatment of gravid females with fenoxycarb suggested that signals from the ootheca also inhibit calling directly. The ventral nerve cord plays a critical role in the transmission of inhibitory signals from mating and from the presence of the ootheca.

Cyclic volumetric changes in corpus allatum cells in relation to juvenile hormone biosynthesis during ovarian cycles in cockroaches

AbstractDevelopment and activity of the corpora allata (CA) were investigated in adult female Blattella germanica and Supella longipalpa. These two cockroach species differ in their reproductive modes, with relatively uninterrupted cycles of oocyte development in S. longipalpa and discrete patterns of oocyte development which are interrupted by pregnancy in B. germanica. During ovarian cycles in both cockroach species, elevated rates of juvenile hormone (JH) synthesis closely coincide with synchronous volumetric growth of the CA. Declines in CA activity before ovulation coincide with synchronous declines in the size of CA cells. However, in adult females of both species the number of CA cells remains relatively constant. Quantitative studies in normal and ovariectomized adult B. germanica females show that the volumetric changes in CA cells are paced and synchronized by ovarian factors. Without the ovaries, the enlargement of CA cells in newly eclosed females is slower and relatively asynchronous. Without an ootheca in ovariectomized females, the volume of CA cells fails to decline synchronously, resulting in variable but high rates of JH synthesis. The precise relationship between volume of CA cells and‐JH biosynthesis in oviparous and viviparous cockroaches suggests that in cockroaches, cell volume, and not CA cell number, is a better predictor of JH biosynthetic activity. © 1994 Wiley‐Liss, Inc.

Role of juvenile hormone biosynthesis in dominance status and reproduction of the bumblebee, Bombus terrestris

In Bombus terrestris females, dominant status is correlated with high levels of juvenile hormone (JH) biosynthesis and rapid oocyte maturation. Queenright workers, which are inhibited by the dominant queen, complete the cycle of oocyte maturation while exhibiting a continuous low rate of JH production, but their egglaying is inhibited. Measurements in foundress queens suggest that the low JH titer during oogenesis is probably not responsible for the inhibition of egg-laying. Queenless workers, kept individually, are not activated either for JH production or oocyte maturation. In groups of three queenless workers, a dominance order becomes established and high rates of JH synthesis are observed in the dominant egg-laying workers, with low rates in subordinated workers. In groups of founder queens, also, a dominance order becomes established and results in a reduced rate of JH production in subordinated females.