Haemolymph Trehalose Concentration Research Articles

Supplemental Sugar Is Required for Sex Pheromone Biosynthesis in Mythimna separata.

Supplemental nutrients of adult moths maximize moth fitness and contribute to the pollination of many plants. Previous reports have revealed that sugar feeding promotes to sex pheromone biosynthesis by increasing the haemolymph trehalose concentration in mating moths. Here, Mythimna separata adults were employed as a model to investigate the effect of sugar feeding on sex pheromone biosynthesis. Results showed that in virgin females, sugar feeding markedly increased the concentrations of trehalose, pyruvic acid, and acyl-CoA in pheromone glands (PGs), which in turn led to an increase in sex pheromone titer, female ability to attract males and successfully mating frequency in sugar-fed females. Consistently, sugar-fed females laid more eggs than water-fed females. Furthermore, the refeeding of starved females also caused significantly increase in the concentrations of trehalose, pyruvic acid, and acyl-CoA in PGs, thus facilitating a significant increase in sex pheromone production. Most importantly, RNAi-mediated knockdown of trehalase (leading to PG starvation) resulted in an increase in trehalose content, and decrease in the concentrations of pyruvic acid, and acyl-CoA in PGs, which in turn led to a decrease of sex pheromone titer, female ability to attract males and successful mating efficacy. Altogether, results revealed a mechanism by which sugar feeding contributed to trehalose utilization in PGs, promoted to significantly increased sex pheromone precursor by increasing the concentrations of pyruvic acid and acyl-CoA, and facilitated to sex pheromone biosynthesis and successful mating.

Rapid Cold-Hardening of a Subtropical Species, Maruca vitrata (Lepidoptera: Crambidae), Accompanies Hypertrehalosemia by Upregulating Trehalose-6-Phosphate Synthase.

A subtropical insect, Maruca vitrata (F.) (Lepidoptera: Crambidae), is invasive to temperate zones, in which low temperatures during winter would be a serious challenge for colonization. This study assessed cold tolerance and cold-hardening of M. vitrata to understand its overwintering mechanism. Supercooling capacity was confirmed in all developmental stages exhibiting body freezing points at lower than -10°C, in which supercooling points (SCPs) were significantly different among developmental stages, with eggs having the lowest SCP (at -22.5°C). However, all developmental stages suffered significant mortality after being exposed to low temperatures much higher than SCPs. Furthermore, nonfreezing injury increased with elapsed time at 25°C after cold shock. One of the nonfreezing symptoms was a darkening on thorax, which was explained by uncontrolled prophenoloxidase activation. Pre-exposure to 8°C for 1 h significantly increased the survival of both young and old larvae to a low-temperature treatment (-5°C for 1 h). Rapid cold-hardening (RCH) was accompanied by significant increase in hemolymph trehalose concentration. During RCH, trehalose-6-phosphate synthase was significantly upregulated in its expression level. These results suggest that M. vitrata is a freeze-susceptible species and becomes cold-hardy via hypertrehalosemia.

Identification of a hypertrehalosemic factor in Spodoptera exigua.

Trehalose is a major blood sugar in insects with a range of physiological functions, including an energy source and a cryoprotectant. Hemolymph trehalose concentrations are tightly regulated according to physiological conditions. An insulin-like peptide, SeILP1, downregulates hemolymph trehalose concentrations in Spodoptera exigua. Here, we identified a factor that upregulates hemolymph trehalose concentration in S. exigua. Hemolymph trehalose concentrations were significantly increased after immune challenge or under starvation in a time-dependent manner. To determine endocrine factors responsible for the upregulation, stress-associated mediators, such as octopamine, serotonin, or eicosanoids were injected, but they did not upregulate hemolymph trehalose. On the other hand, injection with Schistocerca gregaria adipokinetic hormone (AKH) significantly increased hemolymph trehalose concentration in S. exigua. During upregulation of hemolymph trehalose by AKH injection, trehalose degradation appeared to be inhibited because expression of trehalase and SeILP1 were significantly suppressed while that of trehalose phosphate synthase was not significantly changed. Interrogation of a Spodoptera genome database identified an S. exigua AKH-like gene and its expression was confirmed. During starvation, its expression concentrations were increased, although RNA interference specific to the AKH-like hypertrehalosemic factor (SeHTF) gene significantly prevented the upregulation of hemolymph trehalose concentrations during starvation. A synthetic peptide of SeHTF was prepared and injected into S. exigua larvae. At nanomolar concentration, the synthetic SeHTF peptide effectively upregulated hemolymph trehalose concentrations. Here we report a novel hypertrehalosemic factor in S. exigua (SeHTF).

Impact of trehalose transporter knockdown onAnopheles gambiaestress adaptation and susceptibility toPlasmodium falciparuminfection

Anopheles gambiae is a major vector mosquito for Plasmodium falciparum, the deadly pathogen causing most human malaria in sub-Saharan Africa. Synthesized in the fat body, trehalose is the predominant sugar in mosquito hemolymph. It not only provides energy but also protects the mosquito against desiccation and heat stresses. Trehalose enters the mosquito hemolymph by the trehalose transporter AgTreT1. In adult female A. gambiae, AgTreT1 is predominantly expressed in the fat body. We found that AgTreT1 expression is induced by environmental stresses such as low humidity or elevated temperature. AgTreT1 RNA silencing reduces the hemolymph trehalose concentration by 40%, and the mosquitoes succumb sooner after exposure to desiccation or heat. After an infectious blood meal, AgTreT1 RNA silencing reduces the number of P. falciparum oocysts in the mosquito midgut by over 70% compared with mock-injected mosquitoes. These data reveal important roles for AgTreT1 in stress adaptation and malaria pathogen development in a major vector mosquito. Thus, AgTreT1 may be a potential target for malaria vector control.

Alteration of carbohydrates metabolism and midgut glucose absorption in Gromphadorhina portentosa after subchronic exposure to imidacloprid and fenitrothion

This study was undertaken to test the hypothesis that following exposure to insecticides, changes take place in the metabolism of carbohydrates and absorption in the midgut of insects. The Madagascar hissing cockroach (Gromphadorhina portentosa) was chosen for the experiment as a model organism, due to it being easy to breed and its relatively large alimentary tract, which was important when preparing the microperfusion midgut bioassay. In each group of cockroaches treated with imidacloprid and fenitrothion, absorption of glucose, expressed as the area under the curve (AUC), was elevated compared to the control group. Glucose in the hemolymph of the examined insects was present in a vestigial amount, often below the threshold of determination, so the determinable carbohydrate indices were: hemolymph trehalose concentration and fat body glycogen content. The level of trehalose found in the hemolymph of insects when exposed to fenitrothion, and irrespective of the level of concentration mixed into food, were significantly lower when comparing to the control samples. Imidacloprid acted analogically with one exception at the concentration of 10 mg·kg−1 dry food where trehalose concentration did not differ from the control values. Coupling with fat body glycogen concentration was less visible and appeared only at the concentrations of 5 and 10 mg imidacloprid·kg−1 dry food. As described in this study changes in the sugar distribution and midgut glucose absorption indicate that insects cover the increased energy needs induced by insecticides; also at the gastrointestinal tract level. The result indicates that the midgut glucose absorption parameters could be considered as a non-specific biomarker of insecticide toxicity.

Signal Honesty through Differential Quantity in the Female-Produced Sex Pheromone of the Moth Heliothis virescens

Over the last 50 years, female-produced sex pheromones of moths have been subjected to intensive study. Most work has focused on their role in mate recognition, and little on any role they may have in mate assessment. This is largely because it has been assumed that female, rather than male, moths are "choosy", and invest larger amounts of carbon in eggs than in pheromone. Recently, we found that pheromone production in the moth Heliothis virescens depended on hemolymph trehalose concentration, and that sugar-stressed females produced less pheromone than unstressed ones. In this paper, we demonstrate, for the first time in moths, that a female-produced pheromone signal can allow H. virescens males to assess sugar resources (quality) of a female. This signal honesty is based on quantitative, rather than qualitative (component ratio), differences in pheromone, produced and released by sugar-stressed and unstressed females. Increasing marginal cost of pheromone production, as sugar resources are depleted, may ensure signal honesty.

Feeding and hemolymph trehalose concentration influence sex pheromone production in virgin Heliothis virescens moths

Previously, we demonstrated that sex pheromone production in mated female Heliothis virescens moths is dependent upon hemolymph trehalose concentration (HTC), which is influenced by activities such as the feeding of adults on sucrose. In this paper we demonstrate, for the first time, that this effect also occurs in starved (i.e., sugar-stressed) virgin females. Females allowed to feed on sugar for 6 days, following eclosion, had significantly greater titers than females that had fed only on water (i.e., were starved). No differences in pheromone titer were observed between sugar- and water-fed females at shorter (1 or 3 days) periods following eclosion. The relatively short-term effects of HTC on sex pheromone titer of virgins, were demonstrated by feeding experiments, in which starved (for 4 days) virgins fed on 10% sucrose solution had significantly greater HTC and pheromone titers than ones fed only on water; an increase in HTC was apparent within an hour, while the increase in pheromone titer was apparent within 2.5 h, of sugar feeding. Starvation also showed similar effects on titers of pheromone gland fatty acids (pheromone intermediates) and HTC. Over 6 days of starvation, fatty acid titers and HTC declined gradually. After feeding on sucrose, titers of hexadecanoic, ( Z)-9-hexadecanoic, ( Z)-11-hexadecanoic and ( Z)-9-octadecanoic, acids, as well as HTC, increased significantly 24 h later, but titers of octadecanoic and (Z, Z)-9,12-octadecanoic (linoleic) acids did not. Lepidoptera cannot biosynthesize polyunsaturated acids, but the lack of change in octadecanoic acid titer suggests this acid may not participate in pheromone biosynthesis. In addition to these short-term changes in pheromone and fatty acid production, mediated by HTC, a longer-term effect of age, regardless of HTC, on pheromone titer was observed. Overall, these results are consistent with hemolymph trehalose and glandular fatty acids acting as twin metabolite reservoirs for pheromone biosynthesis. Hemolymph trehalose, able to be refilled through feeding on exogenous sugars, has a one-way flow of metabolites for synthesis of glandular free fatty acids (FFAs) and pheromone, while glandular glycerolipids provide a reversible reservoir for metabolites, accepting surplus FFAs when glandular concentrations are high, and providing FFAs for pheromone biosynthesis when concentrations are low.

Sugar feedingviatrehalose haemolymph concentration affects sex pheromone production in matedHeliothis virescensmoths

Long-distance, female-produced sex pheromones are widespread among moths. Larval feeding provides most of the nutrients for development of these insects but is not thought to influence the de novo production of the fatty-acid derived compounds used as pheromones by most species. Feeding on plant nectar (sugar) by adult moths is important for increasing female fitness and also for the pollination of many plant species. In this paper, I show that feeding on sucrose solution, as opposed to water, increases sex pheromone titre in mated, but not virgin, female Heliothis virescens. Mating caused a rapid decrease in haemolymph trehalose concentration, which was restored to near-virgin levels by sugar ingestion. When isolated mated female abdomens were cultured with different concentrations of trehalose, pheromone titre increased with increasing trehalose concentration. This effect was not observed when abdomens were cultured on saline containing the sugar rhamnose, which insects cannot metabolise to glucose. Virgins injected with the juvenile hormone (JH) analogue, methoprene, showed the same effects as mated females with respect to pheromone titre and haemolymph trehalose concentration. Thus, following mating increases in JH titre increase demand for, and lowering of, blood sugar to develop oocytes, which can be compensated for by sugar ingestion. Haemolymph trehalose concentration probably influences glycolysis in gland cells and, consequently, levels of cytosolic citrate and acetyl-CoA for pheromone biosynthesis. This increase in pheromone titre in sugar-fed, mated females may facilitate further mating and increased fecundity. Thus, exogenous sugar feeding is behaviourally and physiologically integrated with endogenous JH titre to maximise female fitness.

Possible involvement of proteinaceous and non-proteinaceous trehalase inhibitors in the regulation of hemolymph trehalose concentration in Bombyx mori

The midgut of the silkworm Bombyx mori contains two types of trehalase: soluble and membrane-bound. The trehalose concentration in larval hemolymph remains substantially high through the feeding period of the last (fifth) larval instar, despite appreciable trehalase activity through this period. We found that B. mori larval hemolymph contains two types of trehalase inhibitor, a proteinaceous inhibitor (inhibitor-P) and an inhibitor that is extractable with methanol and ethanol (inhibitor-M). Both inhibit the two types of trehalase, but with different sensitivities. Inhibitor-P inhibited soluble trehalase (ST) more effectively than membrane-bound trehalase (MT), while inhibitor-M inhibited MT slightly more than ST. The inhibitory activity of inhibitor-M was high during the early to middle feeding period, followed by a sudden decrease during the late feeding period. Inhibitor-P activity increased throughout the feeding period, and markedly decreased 2 days after gut purge. Thus, the two inhibitors exhibited stage-specific changes in the hemolymph, indicating coordinated inhibitory activity. Therefore, trehalose concentration regulation in the hemolymph appears to be complex, consisting of at least two inhibitors and two types of trehalase.

Regulation of soluble and membrane-bound trehalase activity and expression of the enzyme in the larval midgut of the bamboo borer Omphisa fuscidentalis

Diapausing larvae of Omphisa fuscidentalis contain soluble and membrane-bound trehalase in the midgut. Soluble trehalase activity accounts for three-fourths of the total trehalase activity in midgut homogenates. The exposure of diapausing larvae to juvenile hormone analog (JHA) induced pupation, accompanied by an increase in soluble trehalase activity at the beginning of the prepupal period. Injection of 20-hydroxyecdysone (20E) increased the level of soluble trehalase activity 5 days postinjection in a dose-dependent manner. In contrast, no increase in membrane-bound trehalase activity was observed under the same conditions. We cloned the cDNAs that encode the soluble and membrane-bound forms of trehalase in O. fuscidentalis trehalase-1 ( OfTreh-1) and trehalase-2 ( OfTreh-2), respectively. Treh-1 encodes a 581-aa protein while Treh-2 encodes a 648-aa protein with one putative transmembrane domain near the C-terminus. The mRNA expression level of Treh-1 was 27-fold higher than that of Treh-2 in diapausing larval midgut. Following the exposure of diapausing larvae to JHA, Treh-1 mRNA expression increased gradually until the prepupal period whereupon it increased dramatically; in contrast, the mRNA expression of Treh-2 remained at its initial level. Similarly, 20E upregulated Treh-1 expression but had no effect on Treh-2 expression. Taken together, these results suggest that an increase in the soluble trehalase activity at pupation is caused by upregulation of Treh-1 gene. Moreover, membrane-bound trehalase does not appear to be involved in the dynamic changes in the hemolymph trehalose concentration that occur during the larval–pupal transformation.

Involvement of adipokinetic hormone in the homeostatic control of hemolymph trehalose concentration in the larvae of Bombyx mori.

Prior to wandering, 5th instar larvae of the silkworm, Bombyx mori, maintain constant hemolymph titers of trehalose. Head ligation of day 3, 5th instar larvae significantly decreased the hemolymph trehalose concentrations, but the concentrations did not decrease in starved larvae. After being diluted by replacement of larval hemolymph with insect Ringer's solution, the trehalose concentrations recovered the initial levels in 90 min in the non-ligated larvae, while they were not restored in 90 min in the neck-ligated larvae. These results suggest that a head factor(s) with hypertrehalosemic activity is involved in the homeostatic control of hemolymph trehalose concentration. When adipokinetic hormone (AKH) was injected into neck-ligated larvae, the trehalose concentrations increased in 2 h and decreased thereafter. Repeated injections of AKH every 4 h maintained the concentrations for 12 h. These findings suggest that AKH induces a hypertrehalosemic response and is involved in the homeostasis of hemolymph trehalose concentration in the larval feeding period.

Role of Ecdysteroids in the Dynamics of Insect Haemolymph Sugar

Abstract In Bombyx 5th instar larvae, haemolymph trehalose concentrations were maintained in a range of 8-14 mM during the feeding period and then decreased to approximately half the level concomitantly with the occurrence of a gut purge. The decrease occurred as well in larvae that were starved for 29 hr before the gut purge and those that were ligated around the neck. In contrast, ligation between the thorax and abdomen suppressed such a decrease in trehalose concentrations. These results indicated that thoracic factor(s) was involved in the decrease in the haemolymph trehalose concentration. Injections of ecdysteroids into the isolated abdomens of day 5 larvae resulted in a decrease in haemolymph trehalose concentrations. These findings suggest that an increase in the haemolymph ecdysteroid titer at the wondering stage brings about a decrease in the haemolymph trehalose concentrations. Ecdysteroids thus appear to play an important role in the changes in the carbohydrate metabolism at the larval-pupal t...

Regulation of compatible solute accumulation in larvae of the mosquito Culex tarsalis: osmolarity versus salinity.

In this study, we demonstrate that two of the osmolytes utilized in the osmoconforming strategy of larval Culex tarsalis are regulated by two fundamentally different signals. When the external osmolality was increased using salinity (sea salts), hemolymph NaCl, proline and trehalose concentrations increased significantly. When sorbitol was used to increase the external osmolality without an elevation in salt concentration, hemolymph NaCl and proline concentrations decreased, whereas hemolymph trehalose concentration increased. The results suggest that proline accumulation was cued by increases in salinity, whereas trehalose levels followed increases in osmolality. Interestingly, we found that C. tarsalis larvae accumulated the exogenous sorbitol in the hemolymph in an osmoconforming manner. We conducted further studies in which changes in hemolymph NaCl concentrations were manipulated using changes in environmental salinity. The results suggested that hemolymph proline accumulation was cued by the proximal signal of hemolymph NaCl levels. Regardless of which solute (sea salts, sorbitol or mixtures thereof) was used to raise the external osmolality, trehalose accumulation tracked the increase in total osmolality of the medium. These findings indicate that the synthesis and accumulation of these two osmolytes are regulated by two independent signals.

Carbohydrate metabolism during starvation in the silkworm Bombyx mori.

The effect of starvation on carbohydrate metabolism in the last instar larvae of the silkworm Bombyx mori was examined. Trehalose concentration in the hemolymph increased slightly during the first 6 h of starvation and decreased thereafter, whereas glucose concentration decreased rapidly immediately after diet deprivation. Starvation-induced hypertrehalosemia was completely inhibited by neck ligation, suggesting that starvation stimulates the release of a hypertrehalosemic factor(s) from the head. The percentage of active glycogen phosphorylase in the fat body increased within 3 h of starvation and its glycogen content decreased gradually. These observations suggest that production of trehalose from glycogen is enhanced in starved larvae. However, hypertrehalosemia during starvation cannot be explained by the increased supply of trehalose into hemolymph alone, as similar changes in phosphorylase activity and glycogen content in the fat body were observed in neck-ligated larvae, in which hemolymph trehalose concentration did not increase but decreased gradually. When injected into larvae, trehalose disappeared from hemolymph at a rate about 40% lower in starved larvae than neck-ligated larvae. The hemolymph lipid concentration increased during starvation, suggesting that an increased supply of lipids to tissues suppresses the consumption of hemolymph trehalose and this is an important factor in hypertrehalosemia.

Bombyxin secretion in the adult silkmoth Bombyx mori: sex-specificity and its correlation with metabolism

Changes in the hemolymph bombyxin titer of the adult silkmoth Bombyx mori were investigated by time-resolved fluoroimmunoassay. Immediately after eclosion, hemolymph bombyxin titers were low in both males and females, and then increased steeply in males to a very high level and this high titer was maintained for at least 3 h, whereas the titer increment in females was small and transient. The difference in the change of bombyxin titer between males and females suggests that bombyxin is responsible for the regulation of physiological changes underlying sexually different activities of the adult moths. However, no evidence was obtained that bombyxin controls adult metabolism as far as the effects of bombyxin on the concentrations of carbohydrates and lipids in the hemolymph were investigated. The change in the hemolymph trehalose concentration was almost the same between sexes, and between intact and neck-ligated moths. Furthermore, bombyxin injection did not affect the hemolymph trehalose concentration nor trehalase activity in the muscle. Although the hemolymph lipid concentration rose after eclosion in males, it was not influenced by bombyxin. These results exhibit striking contrast to the results of our previous study, in which bombyxin showed hypotrehalosemic activity in the larval stage, thus indicating that the action of bombyxin changes during metamorphosis.

Dynamics of haemolymph sorbitol-6-phosphate and its control by ecdysteroid in the larvae of the silkworm, Bombyx mori

Developmental changes in the concentration of sorbitol-6-phosphate (S-6-P) and trehalose in the Bombyx haemolymph were determined from fourth larval stadium to adult eclosion by gas-liquid chromatography. In the fourth stadium, haemolymph trehalose concentration transiently decreased after ecdysis and then gradually increased from day 1 to day 3, followed by an abrupt increase immediately before the last larval ecdysis. The trehalose concentration decreased again after the last larval ecdysis, recovered to a level similar to that which was found on days 1–3 of the fourth stadium, and remained relatively constant during the feeding period of the fifth stadium. Concomitant with the onset of the wandering stage, the trehalose concentration decreased to a low level, but gradually increased again during the pupal period. Haemolymph S-6-P concentrations were always higher than trehalose concentrations during the feeding period of the fourth and fifth stadia and 2.5-fold higher immediately before spinneret pigmentation. S-6-P concentration began to decrease to a low level (less than 1 mM) concomitantly with the occurrence of spinneret pigmentation, one day earlier than the onset of the wandering stage. In contrast to the slow increase in the trehalose concentration after the wandering stage, the S-6-P concentration remained low throughout the pupal period. After the dilution of larval haemolymph by the replacement of larval haemolymph with insect Ringer's solution, or an artificial increase in haemolymph S-6-P and trehalose concentration by an injection of each of S-6-P and trehalose, S-6-P concentration did not recover to the level before manipulation, whereas trehalose concentration became similar to the initial level in a few hours, indicating that S-6-P concentration is not under homeostatic control, in contrast to trehalose. Injections of ecdysone or 20-hydroxyecdysone induced a decrease in the haemolymph S-6-P concentration in a dose-dependent manner. These findings suggest that S-6-P accumulates in the haemolymph during the feeding period, as a storage form of sugar and ecdysteroid is involved in the sharp decrease in haemolymph S-6-P concentration at the end of the feeding period in Bombyx larvae.

Effect of a Trehalase Inhibitor, Validoxylamine A, on Oocyte Development and Ootheca Formation in Periplaneta americana (Blattodea, Blattidae)

Injection of a specific trehalase inhibitor, validoxylamine A(VAA), suppressed oocyte development in the American cockroach, Periplaneta americana. Ootheca formation was also affected by the same treatment. Inhibition of trehalases of ovaries and thoracic muscles in P. americana in vitro by VAA was very strong; I50 values were 5.0×10-9 M and 1.4×10-8 M, respectively. When the inhibition of trehalase activity was measured after injection of VAA(5 and 50 μg/insect) into cockroaches, more than 90% of the activity in the ovaries was inhibited. The high level of inhibition lasted 2 weeks at the higher dosage, but recovery activity was observed in the second week following the injection of the lower dosage. VAA injection also inhibited the muscular trehalase but to a lesser degree than the ovarian trehalase. Enhancement of haemolymph trehalose concentration and the maintenance of its higher level after the injection of VAA suggested strong inhibition of trehalase in various tissues of the cockroach. It is speculated that the uptake of materials required for oocyte development as well as the energy supply was prevented through the inhibition of trehalase.

Physiological states affect metabolic response to high temperature in Morimus funereus larvae

The metabolic response (fat body glycogen and haemolymph trehalose concentration, midgut amylolytic and proteolytic activities) of Morimus funereus to a high stressful temperature has been studied in larvae from two physiological states (0–6 hr after moulting, “non-feeding” larvae; 7 days after moulting “feeding” larvae), during the intermoult period. The results obtained reveal differences in the response of the larvae from each group to a constant temperature of 35°C. These differences are most prominent for fat body glycogen and midgut protease activity. Glycogen concentration in the fat body and midgut protease activity increase significantly in “non-feeding” larvae at the beginning of exposure of the larvae to 35°C. At the end of the experimentally induced stress, the glycogen concentration was significantly above the control value, while midgut protease activity was close to that of the control. In the “feeding” larvae, glycogen was nearly exhausted on the fourth day of exposure, while proteolytic activity decreased below the control level. During thermal stress, various types of metabolic responses dependent on physiological states were observed at the level of the metabolic parameters studied.

Effect of dietary regime and stressful temperatures on Morimus funereus larval metabolism

The effects of high and low constant temperatures on the survival and certain metabolic changes in the 7-day exposed larvae of Morimus funereus, dependent on dietary regime, have been studied. In the larvae fed the natural diet (ND), midgut protease activity dropped down to a lower level at all the temperatures investigated, whereas only at the temperature of 23°C in the larvae fed the artificial diet (AD), did midgut protease activity decrease, and this was nearly identical to that in the larvae fed the natural diet. Midgut amylase activity in the larvae fed the natural diet was nearly the same as that in the larvae from a natural habitat (NC), except at the temperature of 13°C, when it increased. In the larvae fed the artificial diet, midgut amylase activity significantly decreased at all the temperatures investigated when compared with that of the larvae from a natural habitat. Maximal increase in the fat body glycogen concentration was observed in the larvae on both diets at the temperature of 13°C. In the larvae fed the artificial diet, haemolymph trehalose concentration significantly increased at the temperature of 3°C and decreased linearly with the temperature rise of 13 and 23°C, respectively; the natural diet did not affect trehalose concentration at any temperature regime.

雑草ヒエを寄主とするヒエホソメイガＥｎｏｓｉｍａ ｌｅｕｃｏｔａｅｎｉｅｌｌａの生態学的研究 Ｘ．越冬幼虫の血液のトレハロース濃度および血液量の季節変化

Haemolymph and whole-body trehalose contents in overwintering larvae of Enosima leucotaeniella were measured by gasliquid chromatography. The volume of haemolymph (Vμl) was determined by the following relationship: V=(T2/T1)×1, 000, where, T1 is the haemolymph trehalose concentration (mg/ml) and T2 is the whole-body trehalose content (mg). This estimate was comparable in accuracy with the 14C-inulin-dilution method. During October to March 1993 and 1994, the trehalose concentration in haemolymph was controlled by ambient temperature. However, the volume of haemolymph barely changed (55% to 65%) during October to February, but decreased markedly in March. Physiological changes such as decreased body glycogen and increased glucose content were also noticed in March. Therefore, the decreased haemolymph volume may be one phenomenon in a series of physiological changes of overwintering larvae in the late post-diapausing stage.