Role of juvenile hormone-esterase in mating-stimulated egg development in the moth Heliothis virescens

Novel roles for the corpus allatum hormone in the cost of sexual interactions in the linden bug Pyrrhocoris apterus

The cost of sexual interactions, usually expressed as a reduction of life-span, is a fundamental but poorly understood aspect of life. According to a widely accepted view, a rise in the "pro-aging" juvenile hormone (JH) might contribute to the decrease of life span caused by sexual interactions. We tested this hypothesis using the linden bug Pyrrhocoris apterus by removing the corpus allatum (CA), the source of JH. If JH is causally involved in the cost of sexual interactions, then the absence of CA (JH) should decrease the negative effect of sexual interactions on survival. As expected, ablating the CA significantly prolonged life-span of both virgin females and virgin males. Mated insects of both sexes lived significantly shorter than virgins. However, contrary to prediction, the decrease of life span by sexual interactions was similar in control and CA-ablated males, and was even enhanced in CA-ablated females. Another unexpected finding was that males paired with CA-ablated females lived almost as long as virgin males and significantly longer than did males paired with control females, although ablating the female CA did not cause any decrease in mating activity. On the other hand, females paired with CA-ablated males lived only slightly longer than did females paired with control males. These results highlight several important points. (1) In both genders, the negative effect of sexual interactions on insect's survival is not mediated by the insect's own CA. (2) The male CA has only minor effect on female survival, while (3) the female CA (JH) is principally responsible for the sex-induced reduction in the male survival.

Morph-associated JH titer diel rhythm in Gryllus firmus: Experimental verification of its circadian basis and cycle characterization in artificially selected lines raised in the field

Previous studies demonstrated a high-amplitude, diel cycle for the hemolymph JH titer in the wing-polymorphic cricket, Gryllus firmus. The JH titer rose and fell in the flight-capable morph (long-winged, LW(f)) above and below the relatively temporally invariant JH titer in the flightless (short-winged, SW) morph. The morph-specific JH titer cycle appeared to be primarily driven by a morph-specific diel cycle in the rate of JH biosynthesis. In the present study, cycles of the JH titer and rate of JH biosynthesis in the LW(f) morph persisted in the laboratory under constant darkness with an approximate 24h periodicity. The JH titer cycle also shifted in concert with a shift in the onset of the scotophase, was temperature compensated in constant darkness, and became arrhythmic under constant light. These results provide strong support for the circadian basis of the morph-specific diel rhythm of the JH titer and JH biosynthetic rate. Persistence of the JH titer cycle under constant darkness in multiple LW-selected and SW-selected stocks also provides support for the genetic basis of the morph-associated circadian rhythm. The morph-specific JH titer cycle was observed in these stocks raised in the field, in both males and females, in each of 3 years studied. The onset of the cycle in the LW(f) morph, a few hours before sunset, correlated well with the onset of the cycle, a few hours before lights-off, in the laboratory. The morph-specific JH titer cycle is a general feature of G. firmus, under a variety of environmental conditions, and is not an artifact of specific laboratory conditions or specific genetic stocks. It is a powerful experimental model to investigate the mechanisms underlying endocrine circadian rhythms, their evolution, and their impact on life history evolution.

Identification of genes expressed in the accessory glands of male Mediterranean Fruit Flies (Ceratitis capitata)

Genes expressed in the male reproductive system exhibit rapid evolutionary change and encode products that underlie striking, fitness-related phenotypes. Despite this, they have been characterised in detail in relatively few species. We report here an initial characterisation of the genes expressed in the male reproductive accessory glands of the Mediterranean Fruit Fly (Ceratitis capitata). We describe 13 independent expressed sequence tags (ESTs), of which 9 showed significant homology to known sequences and of which 4 represented novel sequences. The evidence suggests that our transcripts are not homologues of genes encoding known accessory gland proteins (Acps) in Drosophila melanogaster, but that they do encode proteins that fall into known functional categories for Acps (e.g. proteases, lipases, cysteine-rich secretory proteins [CRISPs]). Our results are consistent with the finding that among Acps there is considerable evolutionary lability at the sequence level, but evolutionary constraint at the functional level. The results highlight the extraordinary diversity of male reproductive genes.

On the functional significance of juvenile hormone in the accessory sex glands of male Heliothis virescens

The storage of large quantities of juvenile hormone (JH) in male abdomens is a phenomenon known from some species of moths. Juvenile hormone, stored in male accessory sex glands (ASG), may be transferred to the female during copulation, but the physiological significance of the JH transfer remains unclear. Here, using the moth Heliothis virescens as a model, we show that JH transferred from male to the promiscuous female promotes JH synthesis and egg development in the female. We propose that this explains the functional significance of JH transfer in species that exhibit last male sperm precedence, and that this hormone acts as a bioactive substance which the first male to mate uses for co-opting and regulating the female's gonadotropic mechanisms, thereby ensuring that despite last male sperm precedence he will sire a significant number of viable offspring.

Role of juvenile hormone esterase and epoxide hydrolase in reproduction of the cotton bollworm, Helicoverpa zea

The role of juvenile hormone (JH) esterase (JHE) and epoxide hydrolase (EH) in reproduction of the cotton bollworm, Helicoverpa zea, was investigated. Peak emergence of male and female bollworm adults occurred early in the scotophase. Female adults were added to males in a 1:2 ratio, respectively, at the beginning of the first photophase after emergence (d0). The highest oviposition rates for mated females were noted on d 2-4. The in vitro JH III esterase and JH III EH activity was measured in whole body homogenates of virgin and mated females from d0 to d8 post-emergence. Maximal JHE activity for virgin females occurred on d2 (1.09+/-0.14(+/-1 SEM) nmol of JH III degraded/min/mg protein), which was approximately twice that of mated females on the same day. The same results were observed for EH where the activity peaked on d2 at 0.053+/-0.003 as compared to 0.033+/-0.003 nmol of JH III degraded/min/mg protein, respectively. By d4, both JHE and JH EH activities declined significantly in virgin and mated females and were the same through d7. The developmental changes and effects of mating on JH degradation were similar when measured per insect. The highest levels of JHE and JH EH activity/min/mg protein in d2 virgin and mated females was found in ovaries followed by the carcass and then haemolymph; no EH activity was found in haemolymph as expected. For ovary, the JHE and JH EH activity was highest in virgin compared to mated females. The role of both enzymes in the regulation of reproduction is discussed.

Effects of starvation and mating on corpora allata activity and allatotropin (Manse-AT) gene expression in Manduca sexta

The levels of three alternatively spliced mRNAs from the Manduca sexta allatotropin (Manse-AT) gene were determined following physiological manipulations during the larval, pupal and adult stages; starvation of larvae, induction of pupal diapause and adult mating experience. The juvenile hormone biosynthetic activity of the corpora allata (CA) was also determined in starved larvae and in mated and unmated females. Starvation of early fifth instar larvae specifically increased the amount of one Manse-AT mRNA that is predicted to encode Manse-AT and two related peptides, Manse-ATL-I and -II. The normal rapid decrease in the activity of the CA in last instar larvae was not observed in starved insects which maintained a relatively high rate of JH biosynthesis for at least 3 days. Diapause induction resulted in a small increase in one Manse-AT mRNA, but levels were much lower compared to those observed in larvae or adults. During the first 4 days of adult life, Manse-AT mRNA levels were not changed as a result of mating. However, in mated females, the rate of JH biosynthesis gradually increased, in sharp contrast to the relatively low level of CA activity seen in virgin females. These observations suggest the elevated activity of the CA in mated females is not simply due to the increased level of Manse-AT mRNA.

Regulation of JH epoxide hydrolase versus JH esterase activity in the cabbage looper, Trichoplusia ni, by juvenile hormone and xenobiotics

JH III esterase and JH III epoxide hydrolase (EH) in vitro activity was compared in whole body Trichoplusia ni homogenates at each stage of development (egg, larva, pupa and adult). While activity of both enzymes was detected at all ages tested, JH esterase was significantly higher than EH activity except for day three of the fifth (last) stadium (L5D3). For both enzymes, activity was highest in eggs. Adult virgin females had 4.6- and 4.0-fold higher JH esterase and EH activities, respectively, than adult virgin males. JH III metabolic activity also was measured in whole body homogenates of fifth stadium T. ni that were fed a nutritive diet (control) or starved on a non-nutritive diet of alphacel, agar and water. With larvae that were starved for 6, 28 and 52 h, EH activity per insect equivalent was 48%, 5% and 1%, respectively, of the control insects. At the same time points, JH esterase activity levels in starved T. ni were 29%, 4% and 3% of that of insects fed the nutritive diet. Selected insect hormones and xenobiotics were administered topically or orally to fifth stadium larvae for up to 52 h, and the effects on whole body EH and JH esterase activity analyzed. JH III increased the JH III esterase activity as high as 2.2-fold, but not the JH III EH activity. The JH analog, methoprene, increased both JH esterase and EH activity as high as 2.5-fold. The JH esterase inhibitor, 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP), had no impact on EH activity. The epoxides trans- and cis-stilbene oxide (TSO and CSO) in separate experiments increased the EH activity approximately 2.0-fold. TSO did not alter JH esterase levels when topically applied, but oral administration reduced activity to 70% of the control at 28 h, and then increased the activity 1.8-fold at 52 h after the beginning of treatment. CSO had no effect on JH esterase activity. Phenobarbital increased EH activity by 1.9-fold, but did not change JH esterase levels. Clofibrate and cholesterol 5alpha,6alpha-epoxide had no effect on EH. JH esterase activity also was not affected by clofibrate, but cholesterol 5alpha,6alpha-epoxide reduced the JH esterase activity to 60-80% of the control. The biological significance of these results is discussed.

A morph-specific daily cycle in the rate of JH biosynthesis underlies a morph-specific daily cycle in the hemolymph JH titer in a wing-polymorphic cricket

A previous study documented a high amplitude, morph-specific daily cycle in the hemolymph JH titer in the wing-polymorphic cricket, Gryllus firmus. The JH titer rose and fell 10-20 fold in the flight-capable [LW(f), long-winged] morph during the late-photophase-early scotophase, while it was relatively constant during that time in the flightless (SW, short-winged) morph. In the present study we documented a dramatic morph-specific daily cycle in the in vitro rate of juvenile hormone (JH) biosynthesis that was tightly correlated with the hemolymph JH titer on days 5-7 of adulthood. Biosynthetic rates rose and fell 1-2 fold between the late photophase-early scotophase on each of days 5-6 and 6-7 of adulthood in the LW(f) morph, while biosynthetic rates were relatively constant during this period in the flightless, short-winged morph (SW), except for a slight dip in the rate of biosynthesis late in the photophase on these days. Similar morph-specific patterns of JH biosynthesis were observed whether rates were measured on corpora allata attached to corpora cardiaca in males or females, or on corpora allata alone. Hemolymph juvenile hormone esterase activity was significantly higher in the LW(f) vs. the SW morph during the beginning of scotophase, when the JH titer is decreasing rapidly in the LW(f) morph. Results indicate that the morph-specific daily cycle in the JH titer in G. firmus is primarily regulated by a morph-specific daily cycle in the rate of JH biosynthesis and to a lesser degree by hemolymph JH esterase activity. This is the first documentation of a diurnal cycle in the rate of JH biosynthesis in any insect, or a daily cycle in the rate of JH biosynthesis that is correlated with a specific morph in a polymorphic species. Results have important implications for the endocrine regulation of dispersal polymorphism, circadian rhythms of insect hormone titers and their regulators, and general studies of the JH titer and its regulation in insects.

The hemolymph JH titer exhibits a large-amplitude, morph-dependent, diurnal cycle in the wing-polymorphic cricket, Gryllus firmus

The hemolymph juvenile hormone (JH) titer was measured in over 500 flight-capable and flightless, adult female Gryllus firmus at 3-6 h intervals during each of days 2-8 of adulthood. The flight-capable morph exhibited a large-amplitude daily cycle in the hemolymph JH titer, while the flightless morph exhibited a barely perceptible cycle. The JH titer cycle was observed on all days in the flight-capable morph, but the large amplitude cycle (>15-20 fold increase in mean titer; >100-fold increase in some individuals), began on day 5. For both the large and small amplitude cycles, the JH titer peaked near the end of the photophase-beginning of the scotophase. The hemolymph ecdysteroid titer did not exhibit a corresponding large amplitude daily cycle, although a low amplitude cycle (1-3-fold change) was seen in both morphs. The large magnitude rise in the JH titer in the flight-capable morph during the photophase was not due to decreased hemolymph volume or JH degradation. Daily cycles in the JH titer may be common, but may have gone unnoticed in other insect species due to restricted temporal sampling. Failure to identify these cycles can result in substantial errors in inferring biological roles for JH. Because JH regulates flight behaviors, morph-specific daily cycles in the JH titer may be especially common in dispersal-polymorphic insects, in which flight is restricted to one morph during a limited period of the day or night. However, because JH regulates numerous biological traits, analogous cycles may be common in insects exhibiting other types of complex (e.g. caste or phase) polymorphism, in which morphs differ in a biological characteristic that is restricted to a specific period of the photophase or scotophase.

Juvenile hormone catabolism and oviposition in the codling moth, Cydia pomonella, as functions of age, mating status, and hormone treatment

In vitro catabolism of juvenile hormone (JH) in haemolymph of adult female Cydia pomonella was ascribed mainly to juvenile hormone esterase (JHE) activity. No significant differences were noted between virgin and mated females 0-96 h post-emergence. Changes in JHE activity did not appear dependent upon fluctuations in JH titre; conversely, changes in JHE activity could not explain the changes in JH titres. Maximal JHE activity was recorded at 24 h (331.47 +/- 47.25 pmol/h/microl; 355.93 +/- 36.68 pmol/h/microl, virgin; mated insects, respectively) and preceded the peak in JH titres at 48 h. Topical application of JH II (10 ng-10 microg) or fenoxycarb (50 ng) enhanced JHE activity up to 640 and 56%, respectively. Treatment upon emergence with 10 microg JH II induced enzymic activity for less than 24 h, and when 10 microg JH II or 50 ng fenoxycarb were applied, circulating JH titres returned to control levels within 24 h. Oviposition was highly sensitive to exogenous JH and declined significantly with dosages >100 pg. To allow a degree of oocyte maturation before JH treatment, the hormone was administered at 6, 12, 24, or 48 h post-emergence and/or females were mated. Neither measure "protected" the system; oviposition declined immediately after JH application.

Male accessory gland derived factors can stimulate oogenesis and enhance oviposition in Helicoverpa armigera (Lepidoptera: Noctuidae)

In Helicoverpa armigera, female moths began to lay eggs on the third day after emergence. Mating stimulated earlier egg maturation/oogenesis (P = 0.002) and oviposition (P << 0.01). We established a suitable bioassay model for the influence of male accessory glands (MAG) on the physiology of virgin females: Crude extracts of MAG (2- to 3-day-old) were injected into 2-day-old virgin females, and the injected females were dissected 20 h after mating. It was shown that crude extracts of MAG stimulated earlier egg maturation (P < 0.001) and oviposition (the oviposition ratio was more than 2 times the ratio of the control). Proteinaceous components in crude extracts purified by fractionation and sub-fractionation in reverse phase high performance liquid chromatography also stimulated earlier egg maturation (P < 0.01) and ovipositon (more than 2 times the ratio of the control), and we called them the oogenesis and ovipostion factors (OOSF). With SDS-PAGE, the molecular mass of the bands from OOSF was estimated to be between 55-66 KD. Arch.

Genetic and diurnal variation in the juvenile hormone titer in a wing-polymorphic cricket: implications for the evolution of life histories and dispersal

The wing-polymorphic cricket, Gryllus firmus, contains (1) a flight-capable morph (LW(f)) with long wings and functional flight muscles, (2) a flightless morph with reduced wings and underdeveloped flight muscles (SW), and (3) a flightless morph with histolyzed flight muscles but with fully developed wings (LW(h)). The LW(f) morph differed genetically from the SW morph and phenotypically from the LW(h) morph in the size of flight muscles, ovarian growth during the first week of adulthood, and the hemolymph titer of juvenile hormone (JH). This is the first study to document that phenotypes that differ genetically in morphological aspects of dispersal capability and in ovarian growth also differ genetically in the titer of a hormone that potentially regulates those traits. The JH titer rose 9-100-fold during the photophase in the flight-capable LW(f) morph but did not change significantly during this time in either flightless morph. Prolonged elevation of the in vivo JH titer in flight-capable females, by topical application of a hormone analogue, caused a substantial increase in ovarian growth and histolysis of flight muscles. The short-term, diurnal rise in the JH titer in the dispersing morph may be a mechanism that allows JH to positively regulate nocturnal flight behavior, while not causing maladaptive histolysis of flight muscles and ovarian growth. This is the first demonstration of naturally occurring, genetically based variation for diurnal change in a hormone titer in any organism.