Methyl palmitate: a novel product of the Medfly (Ceratitis capitata) corpus allatum

The corpus allatum (CA) of adult female Ceratitis capitata produces methyl palmitate (MP) in vitro, in addition to JHB₃ and JH III. Biosynthesized MP migrates on TLC and co-elutes from RP-18 HPLC with synthetic MP. Its identity is verified herein by GCMS. MP production is up-regulated twofold by mevastatin, an inhibitor of mevalonic acid-dependent isoprene biosynthesis. Fosmidomycin, an inhibitor of mevalonic acid-independent isoprene synthesis in graminaceous plants, up-regulates MP synthesis by about fourfold. However, it does not depress JHB₃ biosynthesis concurrently. This suggests that the initial enzyme(s) in the conversion of 1-deoxy-xylulose 5-phosphate to isoprene is presumably present in C. capitata, but is inhibited by fosmidomycin, and this inhibition diverts precursors to MP synthesis. Phytol, an acyclic diterpene, might be suppressing isoprene biosynthesis by CA, thereby resulting in a fourfold increase in the MP biosynthesis. Linolenic acid is an end-product and its presence in incubation media up-regulates MP biosynthesis by twofold, presumably due to the feedback diversion to biosynthesis of C_16:0 and its methyl ester. Biosynthesis of MP is markedly depressed after mating, while otherwise maintained at significantly higher levels in virgin females. MP biosynthesis is significantly reduced in virgin females by direct axonal control but is less consistent after mating.     

Presence and titer of methyl palmitate in the Medfly (Ceratitis capitata) during reproductive maturation

The relative amounts of methyl palmitate (MP) during the first 10 days post-eclosion were determined in whole-body extracts of adult female Ceratitis capitata by SIM monitoring of the 74 m/z fragment. MP peaks in receptive 3-day-old virgin females coincide with previously reported production of Juvenile Hormone (JH) by the corpus allatum (CA). Mating in the Medfly induces female non-receptivity. Indirect evidence suggests that the mevalonate pathway to sesquiterpene biosynthesis is underdeveloped in newly eclosed females. We propose that the pathway leading to synthesis of JH is markedly diverted in non-receptive virgin females to fatty acid synthesis, and partly so-in non-receptive mated females, leading to production of palmitic acid, presumably methylated thereafter. MP is depressed and remains marginal thereafter for the 7 days examined in the virgin female but goes through an apparent second cycle in the mated female. This contrasts with the consistent increase of allatal biosynthesis of MP of virgin and mated females previously reported and suggests additional control mechanisms in vivo. During the period of reduced receptivity following the first mating a second apparent peak of MP is observed. MP is a metabolic default metabolite of reproductively immature females whose putative role in reproductive physiology remains to be defined.     

Regulation of juvenile hormone biosynthesis in Heliothis virescens by Manduca sexta allatotropin

In Heliothis virescens, reproduction is strictly dependent on juvenile hormone (JH). In females, mating induces a sharp increase in JH titers, which stimulates increased vitellogenin biosynthesis and higher rates of egg production. JH biosynthesis is presumably stimulated by production and/or release of stimulatory neuropeptides such as allatotropins. There is evidence that allatotropin of H. virescens may be structurally related to Manduca sexta allatotropin (Manse-AT). In a radiochemical in vitro assay, synthetic Manse-AT stimulated JH biosynthesis by corpora allata (CA) of virgin H. virescens females in a dose-dependent manner, but had no effect on CA activity in H. virescens males. In females, the CA showed a transient increase in sensitivity to Manse-AT shortly after mating. Several structurally related peptides stimulated CA activity to a similar extent as Manse-AT. Corpora allata activity was stimulated by a Ca2+ ionophore, A23187. A membrane-permeable Ca2+ chelator, BAPTA/AM, antagonized the stimulatory effects of Manse-AT, suggesting that Manse-AT may enhance CA activity by increasing intracellular Ca2+ concentration.     

Activity of the corpora allata of adult female Aedes aegypti: effects of mating and feeding

The synthesis of juvenile hormone III (JH III) by the isolated corpora allata (CA) of Aedes aegypti adult female was studied using an in vitro radiochemical assay. We dissected the corpora allata-corpora cardiaca (CA-CC) complex attached to a piece of aorta. The complex was left connected to the intact head capsule to facilitate the visualization and transfer of the glands. A linear increase in the cumulative amount of biosynthesized JH III was found for at least the first 6 h of incubation; approximately 45% of the synthesized JH III was present in the medium. There was a dependence of JH III synthesis on exogenous methionine supply. Using reversed phase high performance liquid chromatography two major labeled products biosynthesized by the CA were separated. They co-migrated with JH III and methyl farnesoate (MF). The identity of the biosynthesized JH III was confirmed by gas chromatography-mass spectrometry. JH III synthesis was only 2.0 fmol/pair gland/h immediately after adult emergence, but increased to 32.6 fmol/ pair gland/h 18 h later in sugar-fed females. Two days after emergence, the CA biosynthetic activity slowly started to decrease, and reached values of around 5.3 fmol/pair gland/h by one week after emergence. Synthesis of JH was similar from either sugar-fed females mated or unmated. A blood meal resulted in a decrease of JH III synthesis in CA from mated females by 12 h after feeding and from virgin females by 24 h after feeding. JH III biosynthesis remained low for at least 96 h in mated females, but was back to higher levels 72 h after feeding in virgin females. Rates of JH III biosynthesis closely reflected the hemolymph levels of JH III both after emergence and after a blood meal described by Shapiro et al. (1986). The activity of the CA in Aedes aegypti females seems to be regulated by developmental changes and nutritional signals, and to be independent of mating stimulus.     

Biosynthetic maturation of the corpus allatum of the female adult medfly,Ceratitis capitata,and its putative control

The major juvenile hormone (JH) homolog synthesized in vitro by the adult female Medfly (Ceratitis capitata) corpus allatum (CA) is JHB(3), with JH-III the minor homolog. Methyl-incorporation in vitro in post-eclosion virgin females is age-dependent. Basal activity occurs during the first four days post-eclosion and increases significantly thereafter, peaking at five days. Biosynthetic maturation of the mated female CA is delayed by one day and reduced considerably. The delayed response may be due to direct cerebral or neural inhibition. Synthetic Drosophila melanogaster sex peptide depresses JH biosynthesis by the Medfly female CA in vitro. Male-derived accessory gland peptides of the Medfly are transferred to the female during mating and a Medfly SP-analog may be responsible for down-regulation of JH synthesis by the CA in mated Medfly females. Mevinolin, an inhibitor of the mevalonate pathway, significantly reduces the biosynthesis of JHB(3), while farnesoic acid, a proximate precursor of JHIII, significantly stimulates the biosynthesis of both JHB(3) and JHIII in vitro.     

Activity of the corpora allata of adult female Leucophaea maderae: effects of mating and feeding

Juvenile hormone III biosynthesis by corpora allata of adult female Leucophaea maderae was measured by an in vitro radiochemical assay. In fed females, JH III synthesis increases more than 20-fold after mating to a peak of 55 pmol/pair/h on day 9 and then rapidly declines. This increase in JH III synthesis concomitant with rapid oocyte growth in mated females is not observed in virgin females. The corpora allata from starved, virgin females appear to be inactive. The addition of 150 microM 2E,6E-farnesol (a) JH III precursor) to the incubation medium stimulates the corpora allata from starved, virgin females less than the corpora allata from starved, mated females. Both feeding and mating are necessary for the expression of a normal cycle of JH III synthesis in this cockroach.     

Juvenile hormone biosynthesis and oocyte development in adult female Blattella germanica: Effects of grouping and mating

The roles of grouping and mating in modulating the activity of the corpora allata (CA) in adult female cockroaches were investigated using the in vitro radiochemical assay of juvenile hormone (JH) biosynthesis. Isolated virgin females have longer, asynchronous cycles of CA activity and oocyte maturation than do isolated females mated on day 8. Three factors were identified as the major contributors to this difference: (1) an experimental artifact of selection for sexually receptive females, (2) a positive effect of grouping on JH synthesis and oocyte maturation, and (3) a positive effect of copulation on oviposition and retention of the ootheca. Mated females constitute a subpopulation of receptive females that differ significantly from other females by having higher rates of JH synthesis prior to mating. The relative importance of such selection is substantial when the rate of mating is low, as in experiments with isolated females that are exposed to males for a short period of time. Long-term exposure of females to males introduces a grouping effect, which obscures any additional effect of mating on CA activity and oocyte development. However, mating influences ootheca formation and its retention. The effect of grouping can be mimicked in isolated females by transection of the nerves connecting the CA–corpora cardiaca complex to the brain, suggesting that in this insect isolation causes brain inhibition of the CA, and grouping provides disinhibitory stimuli that release the CA from brain inhibition.     

The chorion genes of the medfly. II. DNA sequence evolution of the autosomal chorion genes s18, s15, s19 and s16 in Diptera

We present a total of approximately 15 kb of DNA sequences, encompassing four chorion genes Ccs18, Ccs15, Ccs19, Cc16 and their flanking DNA in the medfly C. capitata. Comparison of coding regions, introns and intergenic sequences in five Dipteran species, D. melanogaster, D. subobscura, D. virilis, D. grimshawi and C. capitata documented an extensive divergence in introns and coding regions, but few well conserved elements in the proximal 5′ flanking regions in all species. These elements are related to conserved regulatory features of three of the genes, including tissue- and temporal regulation. In the fourth, gene s15, significant alterations in the 5′ flanking region may be responsible for its changed temporal regulation in C. capitata. One long intergenic sequence, located in the distal 5′ flanking region of gene s18, is homologous to ACE3, a major amplification control element and contains an 80-bp A/T-rich sequence, known to stimulate strong binding of the origin recognition complex (ORC) in D. melanogaster. Analysis of the nucleotide composition of all chorion genes in C. capitata and D. melanogaster showed that C. capitata exhibit less biased representation of synonymous codons than does D. melanogaster.     

Juvenile hormone biosynthesis in larval and adult stick insects,Carausius morosus

Corpora allata (CA) from adult egg-carrying Indian stick insects, Carausius morosus, synthesise and release juvenile hormone (JH) III in vitro. No JH biosynthesis was observed in larvae, young adults, and old adult females that do not carry sclerotised eggs. In females, which bear sclerotised eggs, a consistent JH biosynthesis was observed. Supplementation of precursors of JH biosynthesis (farnesol, mevalonic acid lactone) greatly enhanced JH biosynthesis in a stage-, age-, and dose-dependent manner, but CA from the last larval instar retained the biosynthesised JH within the gland. Elevated calcium concentration in the incubation medium stimulated JH biosynthesis by CA from older adults but had either no or a poor effect on CA from young adults and larvae. The results obtained with farnesol, mevalonic acid lactone, and calcium indicate that the rate-limiting steps of JH biosynthesis very likely occur before the formation of mevalonic acid and that these early steps cannot be stimulated by elevated calcium concentrations in larvae and young adults. In older adults, in which spontaneous JH biosynthesis occurs, elevated calcium concentration can markedly stimulate JH biosynthesis. A pre-purified extract from brains of adult females had a stimulating effect on JH biosynthesis by CA from adult females. The results indicate that JH biosynthesis in C. morosus may require food-derived farnesol and may be regulated by allatotropic signals from the brain, possibly triggered by sclerotised oocytes in the ovary.     

Drosophila melanogaster sex peptide stimulates juvenile hormone synthesis and depresses sex pheromone production in Helicoverpa armigera

Previous studies demonstrate that virgin female adult Helicoverpa armigera (Lepidoptera: Noctuidae) moths exhibit calling behaviour and produce sex pheromone in scotophase from the day after emergence, and that mating turns off both of these pre-mating activities. In the fruit fly Drosophila melanogaster, a product of the male accessory glands, termed sex peptide (SP), has been identified as being responsible for suppressing female receptivity after transfer to the female genital tract during mating. Juvenile hormone (JH) production is activated in the D. melanogaster corpus allatum (CA) by SP in vitro. We herein demonstrate cross-reactivity of D. melanogaster SP in the H. armigera moth: JH production in photophase virgin female moth CA in vitro is directly activated in a dose-dependent manner by synthetic D. melanogaster SP, and concurrently inhibits pheromone biosynthesis activating neuropeptide (PBAN)-activated pheromone production by isolated pheromone glands of virgin females. Control peptides (locust adipokinetic hormone, AKH-I, and human corticotropin, ACTH) do not inhibit in vitro pheromone biosynthesis. Moreover, SP injected into virgin H. armigera females, decapitated 24 h after eclosion, or into scotophase virgin females, suppresses pheromone production. In the light of these results, we hypothesize the presumptive existence of a SP-like factor among the peptides transmitted to female H. armigera during copulation, inducing an increased level of JH production and depressing the levels of pheromone produced thereafter.     

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.     

Biological effects of paragonial substances PS-1 and PS-2, in females of Drosophila funebris

The paragonial substances of Drosophila funebris, PS-1 and PS-2, elicit two typical responses after injection into virgin females. Females that have received PS-2, exhibit increased oviposition and higher incorporation rates of (¹⁴C) into ovarian proteins. As shown by decapitation experiments these two observations appear to be under control of the brain. Injection of PS-1, on the other hand, reduces the receptivity of virgin females. Implanted paragonial glands influence the fecundity and receptivity only when they have been disrupted prior to implantation. Natural transfer of in vivo labelled paragonial substances showed that one third of the gland content is delivered in a single mating. Transferred substances were detectable in all body parts of the mated females. PS-1 and PS-2 exhibit relatively short half-lives.     

Mating in Heliothis virescens: Transfer of juvenile hormone during copulation by male to female and stimulation of biosynthesis of endogenous juvenile hormone

Studies were undertaken to determine whether adult males of Heliothis virescens transfer juvenile hormone (JH) to females during copulation, and an in vitro radiochemical assay was used to determine whether mating causes an allatotropic effect, i.e., stimulation of JH biosynthesis by corpora allata (CA). In vitro, CA from 3-day-old mated females synthesized and released approximately 2.5 times total JH as that of CA from comparably aged virgin females. Of the homologues, JH II exhibited significant increase in mated females; JH I also increased but not significantly. JH III remained similar to that of virgin females. This is the first demonstration of an allatotropic effect of mating in moths. In contrast to the female, CA of virgin males did not produce any JH, but accessory sex glands (ASG) in 3-day-old males synthesized small amounts of JH. Immediately after adult emergence, male ASG contained approximately 1.5 ng JH I and II, which increased by 12 h after emergence and remained at this high level up to 54 h after emergence. JH III was barely detected in ASG. JH in ASG of mated male immediately after uncoupling was depleted almost completely, and 24 h later recovered to levels comparable to that of 54-h-old virgin male. Virgin female bursa copulatrix did not contain any JH, but mated female bursa, immediately after uncoupling, had JH at levels comparable to that observed in virgin male ASG. By 6 h after uncoupling, JH levels decreased dramatically in mated female bursa. These data suggest the transfer of JH to females by the male. Arch. Insect Biochem. Physiol. 38:100–107, 1998. © 1998 Wiley-Liss, Inc.     

Control of reproduction in female cockroaches with special reference to Nauphoeta cinerea—I. First pre-oviposition period

Prior to the first oviposition, a receptivity centre, perhaps neurosecretory cells in the brain, controls the female's acceptance of courting males. In L. maderae this centre is affected by starvation. A brief exposure to food can induce mating but is inadequate for oöcyte development. Before the first ovulation starvation has no effect on receptivity in N. cinerea.

In N. cinerea mechanical stimulation caused by the firm insertion of the spermatophore in the bursa copulatrix releases stimuli via the nerve cord to the brain which render the female unreceptive and, at the same time, increases the activity of the corpora allata resulting in rapid development of the oöcytes.

The mechanical presence of the oötheca in the uterus also has two principal effects. Like spermatophore insertion, it inhibits mating. But its effect on the corpora allata is inhibitory, rather than stimulatory, and, consequently, the oöcytes remain underveloped for almost the entire gestation period. The effectiveness of inhibitory stimulation from the stretched uterus depends upon the period in the reproductive cycle in which it occurs-i.e. on the physiological state of the female. In N. cinerea uterine stretching inhibits mating and oöcyte development after oviposition or during gestation but is not effective when exerted during the first pre-oviposition period. In P. surinamensis, uterine stretching does not inhibit the corpora allata prior to the first ovulation but does prevent oöcyte development during gestation.

In fed L. maderae and N. cinerea there appears to be a synergistic action of nutrition and mating in controlling the rate of oöcyte development. Mating (mechanical) and feeding (chemical) stimuli are both usually required for activating the corpora allata to their fullest extent so that the oöcytes mature at their maximum rate. There is some indication that mating stimuli in N. cinerea and L. maderae are effective in further stimulating the corpora allata only if the corpora allata have reached a certain level of activity, if activating stimuli have begun to occur in the brain, or if the mating stimulus occurs in combination with nutritional factors. Thus, the corpora allata in starved virgin females of N. cinerea become sufficiently active so that some yolk is deposited in the oöcytes but these oöcytes do not mature; mating is effective in further stimulating the endocrine glands in these starved females and oviposition occurs in about the normal period. In starved virgins of L. maderae the corpora allata are virtually inactive and yolk is not deposited in the oöcytes; mating has no effect on oöcyte development in starved females. D. punctata differs from both the above species in that the corpora allata in the virgin female usually remain inactive whether she feeds or starves. Mating stimuli alone can activate the corpora allata, in fed or starved females, and consequently the oöcytes mature.     

The methyl viologen-catalyzed mehler reaction and catalase activity in blue-green algae and Chlamydomonas reinhardi

1. The methyl viologen-catalyzed Mehler reaction was investigated in intact cells of five species of blue-green algae and Chlamydomonas reinhardi.

2. In the presence of methyl viologen, all the blue-green algae except Anabaena flos-aquae show a light-dependent O₂ consumption as well as a post-illumination O₂ evolution. The rate of O₂ consumption is stimulated by 1 mM KCN, an inhibitor of catalase, but the dark O₂ evolution becomes suppressed.

3. A. flos-aquae shows a light-dependent methyl viologen-catalyzed O₂ uptake which is not affected by 1 mM KCN. Furthermore, there is no release of O₂ in the dark following illumination.

4. With C. reinhardi, the cells do not show any net O₂ exchange during or after illumination. Addition of 1 mM KCN, however, results in an immediate O₂ uptake in the light.

5. Based on the mechanism postulated for the Mehler reaction in isolated chloroplasts, it was deduced that the differences in the kinetics of the O₂ exchange catalyzed by methyl viologen reflect differences in the endogenous catalase activity in these algae. Cells of A. flos-aquae are deficient in catalase activity whereas those of the other blue-green algae possess catalase, although at low activity. C. reinhardi, on the other hand, has high catalase activity in vivo.

6. These findings are corroborated by results obtained from O₂ electrode measurements of catalase activity in cell-free extracts of these algae.

7. The possible roles of catalase in algae and the implications of these results are also discussed.     

The effect of enforced virginity and subsequent mating on the activity of the corpus allatum of Periplaneta americana measured in vitro, as related to changes in the rate of ovarian maturation

ABSTRACT. Female P. americana, reared with males from the time of adult emergence, mated on the 4th–5th day after metamorphosis, produced the first ootheca on the 8th or 9th day, and then produced successive oothecae at intervals of 3.0 days, whereas, only 50% of virgin females had produced their first ootheca by the 28th day after adult emergence. Examination of the ovaries indicated that oocyte development is normal in virgins until shortly after the time when they first become receptive to males. When mating was not allowed there was a dramatic reduction in the rate of vitellogenic growth of the terminal batch of oocytes which persisted until mating was allowed, and was often accompanied by resorption of a percentage of the oocytes. Short-term, in vitro, radiochemical assay of juvenile hormone (JH III) biosynthesis by corpora allata (CA) showed that, in females reared with males, the cycles of ovarian development are accompanied by regular pulses of CA activity. There is a small, possibly preparatory peak of JH III biosynthesis before vitellogenesis of the first wave of oocytes, followed by a larger peak of JH III production during vitellogenesis of this batch of eggs and one peak of CA activity between ovulation of each subsequent wave of oocytes. Activities as low as 0.25 pmol C₁₆JH/CA pair/h and as high as 48.38 pmol/CA pair/h were observed in CA from mated females after the onset of cyclic activity. Stimuli received during mating are somehow responsible for the cyclic activity of the CA, for when females were subjected to enforced virginity the first small peak was normal but the second peak was not fully realized and there was then a gradual decline in CA activity until approximately 2 weeks post-emergence. Thereafter the glands exhibited a more or less constant rate of JH biosynthesis (mean = 3.45 ± 0.32 pmol/CA pair/h.) When females were mated after 21 days of enforced virginity the activity of the CA was enhanced. By 48 h after mating the mean glandular activity was at least four times that found in virgins of the same age, and by 72 h rates as high as 40 pmol/CA pair/h were observed. This was followed by normal cyclic activity of the CA. The increase in rate of JH biosynthesis appears to result in a recommencement of oocyte development in these ‘delayed-mated’ females.     

引入新型异戊二烯醇利用途径促进解脂耶氏酵母中β-胡萝卜素的合成*

目的:微生物体内异戊二烯类化合物的前体物异戊烯焦磷酸酯的天然合成路径受到严格的代谢调控,因此限制了异戊二烯类化合物的高效生物合成,而新型异戊二烯醇利用途径独立于生物体内源性代谢路径,通过在微生物中引入IUP能够进行异戊烯焦磷酸酯的大量合成,从而促进异戊二烯类化合物的大量合成。方法:在油脂酵母解脂耶氏酵母中引入IUP,强化异戊烯焦磷酸酯生物合成,促进β-胡萝卜素的高效积累。结果:通过生物信息学的方法预测IUP中两个关键蛋白酿酒酵母来源的胆碱激酶ScCK和拟南芥来源的异戊烯磷酸激酶AtIPK,均为酸性亲水性蛋白,无跨膜区和信号肽,二者都具有疏松不稳定的结构特征,显著富集于磷酸类物质的合成通路中。在解脂耶氏酵母中利用同源重组技术引入外源β-胡萝卜素合成关键基因carRP和carB,强化甲羟戊酸途径的关键基因thmgR和ggs1,使工程菌株中积累2.68 mg/L β-胡萝卜素。通过Cre-loxP系统回收基因组上的ura标签,再将IUP进一步整合到工程菌株染色体上。当培养基中含有20 mM异戊二烯醇作为底物、碳氮比为4/3且发酵96 h后,重组解脂耶氏酵母中β-胡萝卜素的产量提高到410.2 mg/L,较原始工程菌的产量提高了近200倍。结论:IUP能够促进解脂耶氏酵母中β-胡萝卜素的高效积累,为利用IUP开展β-胡萝卜素和其他异戊二烯类化合物的高效生物合成提供新思路。     

Leaf isoprene emission rate as a function of atmospheric CO2 concentration

There is considerable interest in modeling isoprene emissions from terrestrial vegetation, because these emissions exert a principal control over the oxidative capacity of the troposphere. We used a unique field experiment that employs a continuous gradient in CO₂ concentration from 240 to 520 ppmv to demonstrate that isoprene emissions in Eucalyptus globulus were enhanced at the lowest CO₂ concentration, which was similar to the estimated CO₂ concentrations during the last Glacial Maximum, compared with 380 ppmv, the current CO₂ concentration. Leaves of Liquidambar styraciflua did not show an increase in isoprene emission at the lowest CO₂ concentration. However, isoprene emission rates from both species were lower for trees grown at 520 ppmv CO₂ compared with trees grown at 380 ppmv CO₂. When grown in environmentally controlled chambers, trees of Populus deltoides and Populus tremuloides exhibited a 30–40% reduction in isoprene emission rate when grown at 800 ppmv CO₂, compared with 400 ppmv CO₂. P. tremuloides exhibited a 33% reduction when grown at 1200 ppmv CO₂, compared with 600 ppmv CO₂. We used current models of leaf isoprene emission to demonstrate that significant errors occur if the CO₂ inhibition of isoprene is not taken into account. In order to alleviate these errors, we present a new model of isoprene emission that describes its response to changes in atmospheric CO₂ concentration. The model logic is based on assumed competition between cytosolic and chloroplastic processes for pyruvate, one of the principal substrates of isoprene biosynthesis.     

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.     

The effect of ventral nerve cord severance and male castration on female mating behavior, clutch size, and maternal care in the ring-legged earwig

Mating is critical for the expression of oviposition and maternal care in the earwig, Euborellia annulipes; additionally, mating diminishes receptivity to additional mating and promotes a decline in juvenile hormone synthesis at the end of the gonadotrophic cycle (in contrast to most insect species wherein mating stimulates juvenile hormone production). We report here that severance of the ventral nerve cord of virgin females similarly promoted egg deposition and maternal care of eggs, diminished mating receptivity, and elicited a timely decline in juvenile hormone biosynthesis. Mating of intact females to adult males that were castrated as larvae did not abolish oviposition; however, clutch size was reduced, and no eggs developed. Such castrated males had smaller seminal vesicles than did intact males, presumably attributable to lack of sperm in castrated males. In contrast, mating of intact females to males castrated on day 1 of adult life did not reduce clutch size compared with those of sham-operated animals and did not abolish fertilization; in fact, these castrated males produced viable offspring after six matings. These results are consistent with the notion that ventral nerve cord severance mimicked mating in intact animals. Following mating, the ventral nerve cord likely is a conduit to release the brain from inhibiting oviposition and maternal care. The presence of sperm in the spermatheca is not necessary for release of this inhibition but may modulate clutch size.