Juvenile Hormone Levels Research Articles

Effects of experience and juvenile hormone on the organization of the mushroom bodies of honey bees

There is an age-related division of labor in the honey bee colony that is regulated by juvenile hormone. After completing metamorphosis, young workers have low titers of juvenile hormone and spend the first several weeks of their adult lives performing tasks within the hive. Older workers, approximately 3 weeks of age, have high titers of juvenile hormone and forage outside the hive for nectar and pollen. We have previously reported that changes in the volume of the mushroom bodies of the honey bee brain are temporally associated with the performance of foraging. The neuropil of the mushroom bodies is increased in volume, whereas the volume occupied by the somata of the Kenyon cells is significantly decreased in foragers relative to younger workers. To study the effect of flight experience and juvenile hormone on these changes within the mushroom bodies, young worker bees were treated with the juvenile hormone analog methoprene but a subset was prevented from foraging (big back bees). Stereological volume estimates revealed that, regardless of foraging experience, bees treated with methoprene had a significantly larger volume of neuropil in the mushroom bodies and a significantly smaller Kenyon cell somal region volume than did 1-day-old bees. The bees treated with methoprene did not differ on these volume estimates from untreated foragers (presumed to have high endogenous levels of juvenile hormone) of the same age sampled from the same colony. Bees prevented from flying and foraging nonetheless received visual stimulation as they gathered at the hive entrance. These results, coupled with a subregional analysis of the neuropil, suggest a potentially important role of visual stimulation, possibly interacting with juvenile hormone, as an organizer of the mushroom bodies. In an independent study, the brains of worker bees in which the transition to foraging was delayed (overaged nurse bees) were also studied. The mushroom bodies of overaged nurse bees had a Kenyon cell somal region volume typical of normal aged nurse bees. However, they displayed a significantly expanded neuropil relative to normal aged nurse bees. Analysis of the big back bees demonstrates that certain aspects of adult brain plasticity associated with foraging can be displayed by worker bees treated with methoprene independent of foraging experience. Analysis of the overaged nurse bees suggests that the post-metamorphic expansion of the neuropil of the mushroom bodies of worker honey bees is not a result of foraging experience.

Effects of 2,2‐dimethylchromene derivatives on wing determination and metamorphosis in the pea aphid, Acyrthosiphon pisum

AbstractThe relationship between the structure of nineteen 2,2‐dimethylchromene derivatives and their effects on aphid morphogenesis were investigated in a pink clone of the pea aphid, Acyrthosiphon pisum (Harris). Three bioassay systems were used: (1) wing induction—the induction of winged (alate) progeny by winged adults that normally produce only wingless (apterous) daughters, (2) wing inhibition—the inhibition of production of winged progeny by wingless adults that had been crowd‐induced to promote the appearance of winged progeny, (3) the effect on metamorphosis—the production of precocious adults indicating a decrease in juvenile hormone titre or the induction of supernumerary moults indicating a juvenile hormone agonist effect. Compounds demonstrating wing‐promoting effects had short (≤2 carbon) side chains at the C6 and/or C7 positions while methylation of C5 tended to decrease this activity. Of the seven compounds inducing wing formation, three also inhibited the production of winged progeny. However, the compounds affecting metamorphosis, in particular promoting precocious adult development, were similar to those that promoted wing inhibition rather than those with wing inducing effects; they had alkoxy groups at C7 with lengths of ≥2 carbons.There is a stronger correlation between compounds interfering with metamorphosis (and therefore evidenced to be affecting juvenile hormone levels, a classic property of some 2,2‐dimethylchromene derivatives) and the promotion of wingless forms than the induction of winged forms. This finding is in contradiction to the idea that juvenile hormones are involved in promoting wingless forms. In addition, attempts to reduce the wing‐inducing properties of Precocene II (the most potent compound effecting wing induction) by subsequent treatment with juvenile hormone Ill or the juvenile hormone analogue, pyriproxyfen, were inconclusive and attempts to inhibit w ng formation with these two compounds atter crowding were also unsuccessful. The precise mode of action of the 2,2‐dimethylchromenes in relation to aphid wing induction remains unclear but it seems likely that the effect is not related to changes in juvenile hormone titres. © 1095 WiIey‐Liss, Inc.

Juvenile hormone and hemolymph juvenile hormone binding protein titers and their interaction in the hemolymph of fourth stadium Manduca sexta

A driving force in the initiation of an endocrine response is the modulation of hormone titers surrounding the responsive tissue. For nonpolar hormones, titer fluctuations are, in part, regulated by specific circulatory transport proteins that bind, protect and convey the hormones to the responsive tissues. In the present study, juvenile hormone (JH), hemolymph juvenile hormone binding protein (hJHBP), and total hemolymph protein in the fourth larval stadium of Manduca sexta were quantified from similarly staged insects to assess whether JH is bound or unbound when it interacts with the target. JH levels, as determined by radioimmunoassay, were highest, 12.87 nM, 4 h after ecdysis to the fourth stadium, and declined 6-fold to the lowest titer, 2.28 nM, at 44 h after ecydsis, i.e. 8 h after head critical period. Conversely, hJHBP titers peaked at 11.95 μM 44 h after ecdysis and dropped 5-fold by the time of ecdysis to the fifth stadium. Total hemolymph protein also reached its highest level, 19.83 mg/ml, at 44 h; however, hJHBP titers did not follow fluctuations in the total hemolymph protein. Calculations of bound and unbound JH indicated that >99% of the hormone was bound by hJHBP. In contrast, <1% of the binding protein was hormone-loaded at any time during the stadium. Due to the rapid metabolism of JH in the hemol the hemolymph is improbable at certain times during development. Thus, the rate limiting step in JH uptake at these times may be the interaction of hJHBP with the target cell.

Physiological correlates of division of labor among similarly aged honey bees.

Hormone analyses and exocrine gland measurements were made to probe for physiological correlates of division of labor among similarly aged adult worker honey bees (Apis mellifera L.). Middle-age bees (ca. 2 weeks old) performing different tasks showed significant differences in both juvenile hormone (JH) biosynthesis rates and hemolymph titers; guards and undertakers had high JH, and wax producers and food storers, low JH. Guards and undertakers had similar hormone levels to foragers, even though they were 10 days younger than foragers. No differences in JH were detected among young bees (1-week-old queen attendants and nurses) or older bees (3-4 week-old pollen foragers, non-pollen foragers, and soldiers). Hypopharyngeal gland size was inversely correlated with worker age and rate of JH biosynthesis, but soldiers had significantly larger hypopharyngeal glands than did foragers, despite their similar age and JH level. Results from soldiers indicate that exocrine gland development is not always linked with age-related behavior and endocrine development; they also support the recent claim that soldiers constitute a group of older bees that are distinct from foragers. Hormonal analyses indicate that the current model of JH's role in honey bee division of labor needs to be expanded because high levels of JH are associated with several other tasks besides foraging. JH may be involved in the regulation of division of labor among similarly aged workers in addition to its role in age-related division of labor.

Effects of allatectomy and ovariectomy on cuticular hydrocarbons in Calliphora vomitoria (diptera)

AbstractThe relationships between female attractiveness, cuticular hydrocarbons, and levels of juvenile hormone and ecdysteroids were studied in Calliphora vomitoria. The experiments were conducted at 48 and 72 h post‐emergence, according to attractiveness appearance and increase. The 48‐h‐old allatectomized females were less attractive than the control females, whereas no changes occurred either in cuticular hydrocarbons total mass production or in the different hydrocarbon families. However, the 72‐h‐old allatectomized females were more attractive than the control females, and, in relative proportions, allatectomy led to an increase in monomethylalkanes and a decrease in n‐alkanes.Only at 48 h were the ovariectomized females less attractive than the control females and did ovariectomy increase the relative proportions of monomethylalkanes. At 72 h, ovariectomy did not influence female attractiveness, but it decreased the total cuticular hydrocarbon production. Allatectomy and ovariectomy significantly decreased ecdysteroids levels at 48 and 72 h. Ovariectomy did not affect juvenile hormone production.These results suggest that attractiveness and cuticular hydrocarbon synthesis could be under the direct control of ecdysteroids and the indirect influence of juvenile hormone. © 1994 Wiley‐Liss, Inc.

Biochemical and developmental alterations of Heliothis virescens (F.) (lepidoptera, noctuidae) larvae induced by the endophagous parasitoid Cardiochiles nigriceps viereck (Hymenoptera, braconidae)

AbstractAll larval stages of Heliothis virescens (F.) parasitized by the endophagous larval parasitoid Cardiochiles nigriceps Viereck, a braconid species belonging to the subfamily Microgasterinae, exhibit developmental arrest at last instar and fail to pupate. The major part of larval development of the parasitoid is synchronized with the arrested host last larval instar and the parasitoid first molt is never observed before the host attains the late digging stage. At this time, the total ecdysteroid titer of the hemolymph of parasitized hosts is very low and subsequently shows a slow and gradual increase, characterized by a low titer of 20‐hydroxyecdysone (20‐HE) associated with consistent amounts of inactive ecdysteroid polar metabolites. Juvenile hormone esterase (JHE) activity is high in both control and parasitized host larvae at the early digging stage of development, and juvenile hormone analogs (JHA) applied to parasitized host last instar larvae appear to suppress the parasitoid molt. Concurrent with these changes was an increase in the hemolymph titer of proteins which was maintained at a high level in parasitized larvae in contrast to the observed decrease in control larvae at the cell formation stage of development. Neck‐ligation of newly molted host 5th instar parasitized larvae, prior to both JHE release and the increase in protein titers, inhibited growth and molting of the parasitoid. In contrast, ligation after JHE release and with high hemolymph protein titers resulted in parasitoid molting and growth. These data suggest that the host ecdysteroid hormones are not directly involved in the regulation of the parasitoid molt, although high juvenile hormone (JH) levels probably prevent it. More likely, molting is triggered by other biochemical changes, such as proteins or other factors occurring in the hemolymph. Molting of C. nigriceps larvae in vitro into an ecdysone‐free semidefined medium further supported the view that host ecdysone is not necessary for the molt. Teratocytes of C. nigriceps seem to play an important role in the inactivation of 20‐HE through its conversion to inactive polar metabolites, and along with female calyx fluid and venom which depress the secretory activity of the host prothoracic glands, they are the most important sources of host regulatory factors. © 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.

Hormonal regulation and properties of a new group of basic hemolymph proteins expressed during insect metamorphosis.

Two abundant basic proteins, and arylphorin, that are expressed during metamorphosis of Trichoplusia ni were isolated, their cDNAs cloned, and regulation of their expression assessed. According to the criteria of encoded protein sequence, positions of sequence coinitiation and cotermination, amino acid compositions, nonsex-specificity, and immunological analyses, the related yet distinct basic proteins do not correspond to any previously established group of insect proteins, each of which can be distinguished on the basis of such criteria, although they appear to be within the arthropod hemocyanin superfamily. The basic proteins can be separated under native isoelectric focusing conditions, indicating that they do not preferentially form heteromeric complexes under such conditions. While the transcripts for both basic proteins and a coexpressed acidic protein (Jones, G., Brown, N., Manczak, M., Hiremath, S., and Kafatos, F. (1990) J. Biol. Chem. 265, 8596-8602) appeared in both sexes on the day prior to ecdysteroid-driven metamorphic commitment, and persisted at high abundance for the next 24 h, the arylphorin mRNA appeared 1 day earlier and declined immediately after metamorphic commitment. The dynamics of suppression of the appearance and abundance of transcripts in response to maintenance of a high juvenile hormone titer was different for the acidic versus the two basic proteins. Another regulatory difference in response to juvenile hormone was shown by a decreased translatability of the mRNAs for the two basic proteins, but not for the acidic protein. In contrast, the abundance and translatability of arylphorin mRNA was insensitive to a high juvenile hormone level. A further difference in regulation was shown by the maintenance of a high level of both arylphorin and the acidic protein in the hemolymph after disappearance of their transcripts, while the basic proteins instead disappeared from the hemolymph and persisted in the fat body. These results establish at least three qualitatively different effects of juvenile hormone on the abundance of transcripts for these representatives of three groups in the hemocyanin superfamily, and also establish mRNA translatability as another differential level of regulation among them. Given these differences in mechanisms of regulation of evolutionarily related proteins, this system of metamorphosis-associated proteins in T. ni should prove to be a valuable tool in studies of mechanisms of hormonal regulation of gene expression during the metamorphic transformation of larval tissues.

Mutual pheromonal inhibition among queens in polygyne colonies of the fire ant Solenopsis invicta

Decrease in individual reproductive output with increasing numbers of reproductives is a general feature of social insect colonies. The previously described negative relationship between the fecundity of individual queens and number of resident queens in polygyne (multiple-queen) colonies of the fire ant Solenopsis invicta appears to result from mutual pheromonal inhibition. In an experimental test for the presence of fecundity reducing pheromones, corpses of functional (egg-laying) queens were found to effectively inhibit the fecundity of functional queens, suggesting that queen-produced pheromones suppress egg production in such queens. Evidence concerning a possible mechanism mediating this inhibition was also obtained. Treatment of queens with methoprene, a juvenile hormone (JH) analog, increased ovary development, suggesting that fecundity in functional queens may be mediated by the level of endogenous JH. These findings are consistent with the occurrence of mutual pheromonal inhibition among queens achieved by suppression of endogenous JH titers.

Comparative metabolism of isoleucine by corpora allata of nonlepidopteran insects versus lepidopteran insects, in relation to juvenile hormone biosynthesis

AbstractWe studied the metabolism of [U‐14C]isoleucine by intact and homogenized corpora allata (CA) from various insect species to determine how this substrate is converted to precursors of juvenile hormone (JH). CA homogenates of the lepidopterans Manduca sexta, Hyalophora cecropia, and Samia cynthia metabolize [U‐14C]isoleucine to several products including 2‐keto‐3‐methyl‐valerate, 2‐methylbutyrate, CO2, propionate, and acetate. Intact CA of male H. cecropia produce particularly high levels of 2‐keto‐3‐methylvalerate, indicating a highly active branched‐chain‐amino acid transaminase. In contrast, CA homogenates from the nonlepidopterans Periplaneta americana, Schistocerca nitens, Tenebrio molitor, and Diploptera punctata barely metabolize [U‐14C]isoleucine. However, P. americana CA homogenate metabolizes [U‐14C]2‐keto‐3‐methylvalerate, the transamination product of [U‐14C]isoleucine, more rapidly than does a homogenate of M. sexta CA. Furthermore, intact CA from P. americana incubated with [U‐14C]2‐keto‐3‐methylvalerate incorporate low levels of 14C into JH III, but do not metabolize this substrate to JH II or JH I. Intact CA from female Diploptera punctata produce very high levels of JH III, but are also unable to incorporate radiolabel from [U‐14C]isoleucine into JH III, which substantiates our findings with other nonlepidopteran CA. The results suggest that CA of nonlepidopteran insects lack an active branched‐chain amino acid transaminase and, consequently, are unable to utilize these substrates for JH biosynthesis.

Regulation of juvenile hormone synthesis in wild-type and apterous mutant Drosophila

Juvenile hormone (JH) is a major regulator of insect development and reproduction and its titer is determined largely by central nervous system regulation of JH synthesis by the corpora allata. To establish the basis for a molecular genetic dissection of the neuroendocrine system responsible for modulating JH titer, a radiochemical assay was utilized to examine JH synthesis in vitro by the isolated corpus allatum as well as the regulation of this synthesis by brain extracts of wild-type and apterous mutant Drosophila melanogaster females during reproductive maturation. JH production by glands of wild-type females increases in parallel with the progress of ovarian maturation, the major product of the adult corpus allatum being juvenile hormone 3 bis-epoxide (JHB 3). Gland activity appears to be regulated by both the availability of JH precursors and the level of terminal oxidase(s) in the JH biosynthetic pathway. The brain contains an allatostatic factor, that is transmitted to the glands via nervous connections. Allatostatin production in the brain appears to be positively regulated by JHB 3. Adult corpora allata from the mutants ap 4 and ap 56f synthesize very low levels of JH; additionally, brains of ap 56f homozygotes lack allatostatic activity.

Female sexual receptivity is defective in juvenile hormone-deficient mutants of theapterous gene ofDrosophila melanogaster

During reproductive maturation of female insects, the acquisition of sexual receptivity is coordinated with ovarian development. Juvenile hormone regulates vitellogenesis in the ovaries, but the action of this hormone in the development of sexual behavior is less well-understood. A strain of Drosophila melanogaster carrying a mutation in the apterous gene (ap4) was known to exhibit arrested vitellogenesis (rescuable by applying exogenous juvenile hormone), sterility of both sexes, and a deficiency of juvenile hormone. In this study, we examined the effects of mutations of ap on female receptivity and its relationship to juvenile hormone. We observed abnormally low female receptivity in homozygous ap strains, and heteroallelic combinations of ap mutations exhibited low receptivity. For female receptivity, ap showed no dominance (i.e., ap/ap+ was intermediate between ap/ap and ap+/ap+). Low receptivity mapped genetically to the ap locus. The reduction in female receptivity in these mutants is positively correlated with levels of juvenile hormone synthesized by their corpora allata.

Circulation is required for egg production in the insect,Rhodnius prolixus

Summary Egg production in the blood-feeding insect, Rhodnius prolixus, was inhibited by transecting the dorsal vessel (DV) in abdominal segment III immediately after feeding, or ligaturing the DV in the same location, 3 to 6 days post-emergence. Juvenile hormone (JH), applied topically to operated animals after feeding, removed this inhibition indicating that a functioning DV is required to maintain the appropriate levels of JH in the abdomen. Reduced JH levels in the abdomen may result from failure to transport JH from the corpus allatum (CA) in the head to the abdomen, or from a reduction in activity of the CA. The present study examined the flow of material from the head to the abdomen in DV-severed animals, and found that: 1) methyl-blue injected into the head of DV-severed animals accumulated in nephrocytes in the abdomen 1 to 2 h after injection; 2) radiolabelled 14C inulin injected into the head of DV-severed animals diffused to the abdomen within 90 min. of injection; 3) egg toying, which depends ...

Ovaries and regulation of juvenile hormone titer in Acheta domesticus L. (Orthoptera)

A study was performed on females Acheta domesticus to examine the effects of various experimental conditions on the ovarian physiology. Using a radioimmunoassay to determine juvenile hormone (JH) titers as well as in vitro JH biosynthesis, we observed that retention of mature follicles in egg-retaining females, i.e., virgins or mated females not provided an egg-laying substrate, inhibits JH production and consequently oocyte development. Mating in intact as well as ovariectomized females does not affect corpora allata activity. It is only when mating is associated with egg laying that JH biosynthesis and hemolymph titers increased and oocyte development and fecundity are stimulated. Despite lower JH biosynthesis, ovariectomized females present enlarged corpora allata and the levels of JH observed in their hemolymph were intermediate between those of intact egg-laying and virgin females. In intact females, the hemolymph JH titers as well as the JH esterase activities were related to ovarian development. JH esterase activity was very high in ovariectomized animals. Several factors involved in ovarian development of A. domesticus are discussed.

The juvenile hormone titre during the penultimate and ultimate larval stadia of Trichoplusia ni

The juvenile hormone titre in penultimate and last-stadium larvae of Trichoplusia ni (Hübner) was determined by a method utilizing gas chromatography-mass spectrometry with selected ion monitoring. Juvenile hormone II was the predominant homologue detected; highest levels were only ⋍400 pg/g. The juvenile hormone titre was high during the fourth stadium and during apolysis of the last stadia then declined to barely detectable levels just before cocoon spinning, and peaked again during the prepupal stage. Prepupal levels of this hormone were similar to those detected in 4th and 5th larval stadia suggesting an important biological role for juvenile hormone in the prepupa. Starvation of day-1, 5th stadium larvae or inhibition of in vivo juvenile hormone esterase activity with O-ethyl- S-phenyl-phosphoroamidothioate (EPPAT) resulted in higher levels of juvenile hormone in mid last-stadium larvae. T. ni larvae undergoing precocious development caused by parasitization with Chelonus sp. showed greatly reduced levels of juvenile hormone II compared to control larvae, but contained a considerable level of juvenile hormone III. Separate analysis of the host carcass and the parasite larva supported the hypothesis that the hymenopterous parasite was the major source of the juvenile hormone III detected.

Ecdysteroids control vitellogenesis and egg maturation in pharate adult females of the Indianmeal moth, Plodia interpunctella

AbstractVitellogenesis occurs during the late pharate adult stage in the Indianmeal moth, Plodia interpunctella. Repeated treatment of pharate adult females with doses of 20‐hydroxyecdysone (20HE) from 10 to 250 ng per pupa suppressed oocyte growth and inhibited yolk protein accumulation in the oocytes. Treatment of the pharate adults with a biologically inactive ecdysteroid analogue, 22–isoecdysone, had no effect on egg maturation or yolk protein accumulation. The hormonal action of 20HE was not through the inhibition of the corpora allata or juvenile hormone levels, because treatment with a juvenile hormone analogue did not reverse the inhibition by 20HE treatment. Exposure of early vitellogenic ovaries to 20HE in organ cultures in vitro showed that 20HE had a direct effect on the ovarian synthesis of YP2. At 20HE concentrations below 10 nM, YP2 synthesis was minimal, at 10 nM 20HE YP2 synthesis was maximal, and at concentrations higher than 10 nM YP2 synthesis was suppressed to 35% of the maximal level. Synthesis of most other ovarian proteins remained constant with the changing 20HE concentrations. Ovarian RNA from treated females translated in a reticulocyte lysate demonstrated that the hormonal effect of 20HE on the ovarian tissues was on the specific accumulation of translatable YP2 transcript as well as transcripts for a few other polypeptides. This study shows that 20HE controls the rate of egg development during metamorphosis and that declining titers of 20HE regulate the expression of adult genes.

JH III levels in larvae and pharate pupae of Anastrepha suspensa (Diptera: Tephritidae) and in larvae of the parasitic wasp Biosteres longicaudatus (Hymenoptera: Braconidae)

AbstractThis is the first report of a juvenile hormone (JH) in the Caribbean fruit fly, Anastrepha suspensa (Diptera: Tephritidae). JH III was identified in whole body extracts of L3 (final instar) larvae and pharate pupae (PhP) by using a physicochemical method. JH III was also found in PhP superparasitized (up to 11.3 ± 3.5 S.D. parasites/host) by the solitary wasp Biosteres longicaudatus (Hymenoptera: Braconidae) and in first instars of the parasite. The levels of JH III in hosts were up to 15 × higher than those of the controls. The JH esterase (JHE) levels in the hemolymph of 1‐day‐old PhP controls were significantly (P &lt; 0.05) higher than those of superparasitized individuals. These results suggest that the elevated JH III levels induced by superparasitism may arise from JH buildup due either to decreased JHE activity to continued synthesis of JH by the ring gland or to secretion of JH III by the parasites into the host's hemocoel.

Juvenile hormone-III biosynthesis in presumptive long-winged and short-winged Gryllus rubens: Implications for the endocrine regulation of wing dimorphism

In vitro rates of juvenile hormone-III biosynthesis were quantified for corpora allata from nascent long-winged and short-winged Gryllus rubens. Rates were measured during the penultimate and last stadia, two juvenile-hormone-sensitive periods of wing morph determination. This was done to assess the contribution of differences in rates of hormone biosynthesis to juvenile-hormone-mediated morph determination. Corpora allata from individuals of the same morph, sex and stage of development exhibited low variability in juvenile hormone-III biosynthetic rates. Developmental profiles of these biosynthetic rates for each sex and morph were U-shaped during each stadium. Rates varied from 1 to 5 and 0 to 5 pmol juvenile hormone-III/h/pair corpora allata during the penultimate and last stadium, respectively. Juvenile hormone-III biosynthetic rates did not differ significantly between morphs of the same sex on any day in development, except for a few cases at the beginning or end of each stadium. In general, developmental patterns of juvenile hormone-III biosynthesis were similar between the sexes of each morph. These data (1) provide no evidence that morph-specific differences in rates of juvenile hormone-III biosynthesis underlie juvenile-hormone-mediated morph determination, and (2) further implicate previously documented variation in juvenile hormone esterase activity in morph determination. Data on juvenile hormone biosynthesis, degradation and titre also collectively implicate cessation of biosynthesis rather than elevation of juvenile hormone esterase activity in producing the steep decline in the juvenile hormone titre early in the last stadium; this decline presumably initiates metamorphosis. Alternate morph development appears to result at least in part from differential clearance of low levels of juvenile hormone following the steep decline.

Control of growth and ultrastructural maturation of a cricket flight muscle.

The metathoracic dorsal longitudinal muscle (DLM) in the cricket Teleogryllus oceanicus increased in mass and rapidly acquired interfibrillar tracheoles and an increased proportion of mitochondria around the time of the adult molt. Both neural input and juvenile hormone levels were investigated as possible factors controlling this rapid maturation. Motor axons to the muscle were cut early in the last nymphal instar, and muscle growth slowed but ultrastructural maturation continued; the percentage of muscle volume occupied by mitochondria tripled and tracheoblasts invaded the fibers in both the denervated and contralateral innervated muscles. Newly molted last instar nymphs were treated with methoprene, a juvenile hormone analog, and examined four days following the next molt. Muscle growth was slowed but not stopped. Both mitochondrial proliferation and tracheoblast formation were completely blocked by hormone treatment. This study shows that both neural input and low levels of juvenile hormone are required for muscle growth. However, ultrastructural maturation seems to depend exclusively on low levels of juvenile hormone.

Relationship between haemolymphatic levels of juvenile hormone and the duration of the spermatophore in the bursa copulatrix of the cockroach Blaberus craniifer Burm

first gonadotrophic cycle, oviposition occurs about 1 wk earlier in mated females. As ovarian activity is essentially under the control of juvenile hormone (JH), haemolymphatic hormone levels were measured by radioimmunoassay in both virgin and mated females. In the latter, the duration of the spermatophore in the bursa copulatrix was manipulated. Matings were performed with single pairs : a 7-day-old virgin female was allowed to mate with a virgin male, and the spermatophore was extirpated from the bursa copulatrix just after completion of mating, or 24 h after pairing. The females were then isolated, and JH levels were measured from the 8th to the 12th post-imaginal day. The results show that the haemolymphatic level of JH (JH 111) remained low in virgin females for 12 d after the imaginal molt (< 16 ng/ml). The juvenile hormone titre following mating was higher when the spermatophore was left in the bursa for around 22 h after copulation, reaching a peak of 239 ng/ml. The longer the spermatophore remained in the bursa copulatrix, the sooner oviposition took place. The results show for the first time that there is a relationship between the duration of the spermatophore in the bursa copulatrix and haemolymphatic levels of juvenile hormone and basal oocyte growth during the first gonadotrophic cycle. The stimulating effect of the spermatophore from the bursa is discussed.