Mobilization of lipid and carbohydrate reserves in the migratory grasshopper Melanoplus sanguinipes

Abstract. The North American migratory grasshopper Melanoplus sanguinipes Fabricius (Orthoptera: Acrididae) exhibits heritable variation in predisposition to make long-duration flights, and performance of long-duration flight enhances reproductive output. As a first step in understanding the physiological basis of these phenomena, we examined the mobilization of lipid and carbohydrate reserves during flight and in response to injection of extracts of the corpora cardiaca. Extract of conspecific corpora cardiaca elevates the concentration of haemolymph lipid. Both synthetic locust adipokinetic hormone I (AKH I) and synthetic Locusta migratoria AKH II raise the concentration of lipid in the haemolymph. However, although AKH I is more active than AKH II in locusts, dose-response curves for the two peptides are similar in M.sanguinipes. Neither extract of conspecific corpora cardiaca nor locust AKH I affects haemolymph carbohydrate in this species. Haemolymph carbohydrate and total glycogen reserves are Diminished by tethered flight; in contrast, haemolymph lipid is elevated by flight. Grasshoppers identified as presumptive migrants or non-migrants do not differ significantly in body composition. Total lipid reserves did not decrease measurably after extended flight, even though total reserves of carbohydrate do not appear to be sufficient to maintain the durations of flight performed.     

Flight performance of the malaria vectors Anopheles gambiae and Anopheles atroparvus.

The flight potential and metabolism of two malaria vectors, Anopheles gambiae s.str. and An. atroparvus, were analyzed on flightmills. The flight distance, the flight time, and individual flight activities of females were recorded during 22 h flight trials. The glycogen and lipid before flight, after flight, and of unflown controls were measured for starved, sugar-, or blood-fed females. Maximal flight distances of An. gambiae were 9 km when sugar-fed and 10 km when blood-fed, while in starved females it was below 3 km and the average speed was around 1 km/h. In Anopheles atroparvus, the maximal flight distances were 10-12 km when sugar-fed, 4.5 km when blood-fed, and below 3.5 km when starved, with an average speed of 1.3 km/h. Flight performances consisted of 1-4 h intervals of continuous flights, but mainly of bouts shorter than one h, randomly distributed during the long flight trials in both species. An. gambiae utilized an average of 47% of its pre-flight carbohydrate reserves for survival and 38% for flight at a rate of 0.07 cal/h/female. After a blood meal they utilized 11% for survival and 61% for flight at a rate of 0.04 cal/h. At the same time, 25% of the pre-flight lipid was mobilized for flight at a rate of 0.09 cal/h when sugar-fed and 22% when blood-fed at a rate of 0.06 cal/h; lipid was barely mobilized for survival. An. atroparvus differed: carbohydrate mobilization was 28% for survival and 41% for flight at a rate of 0.15 cal/h when sugar-fed; lipid mobilization for flight was only 13% at a rate of 0.06 cal/h. After a blood meal only 2% of the pre-flight lipid was used (0.02 cal/h). The contribution of carbohydrate reserves for flight metabolism at the high rate of 0.21 cal/h could not be fully elucidated because its decrease coincided with a pronounced resynthesis from the blood meal. An. atroparvus always depended on sugar meals for its flight activities and barely utilized lipid reserves. An. gambiae was independent of sugar sources for strong flights due to its early blood feeding and because of its equicaloric lipid mobilization during flights. Strong evidence for lipid oxidation during its flight is discussed.     

The effect of Metarhizium anisopliae var acridum on haemolymph energy reserves and flight capability in the desert locust, Schistocerca gregaria

Adult desert locusts, Schistocerca gregaria , 3 days after inoculation with the entomopathogenic fungus Metarhizium anisopliae var acridum , had significantly less carbohydrate and lipid in the haemolymph than controls. This was not due to reduced food intake as 3 days of complete starvation had no effect on haemolymph titres of energy reserves in controls. Furthermore injection of an extract of the corpora cardiaca (the source of adipokinetic hormone, AKH) caused a large significant increase in haemolymph lipid in mycosed locusts, indicating the availability of significant quantities of lipid in the fat body, the target for AKH. Haemolymph carbohydrate declined significantly during tethered flight of control locusts but not in mycosed individuals. An injected supplement of trehalose significantly boosted flight performance of mycosed insects but not controls. The results are discussed in the light of the hypothesis that the poor flight capability of mycosed locusts is due in part to a fungus-induced reduction in mobile energy reserves.     

Flight fuel related differences between solitary and gregarious locusts (Locusta migratoria migratorioides)

Abstract. Flight fuel relations of crowded and isolated Locusta migratoria migratorioides were investigated in younger (12–16 days after fledging) and older (27–30 or 27–32 days after fledging) adult males.No phase polymorphism dependent differences were found in resting haemolymph carbohydrate levels of the younger locusts.In the older age group, resting haemolymph carbohydrate levels were slightly though significantly higher in the isolated than in the crowded locusts.Injection of various doses of synthetic adipokinetic hormones (AKHs) did not induce marked changes in haemolymph carbohydrate levels and no differences were found between crowded and isolated locusts.A 30 min flight led to the same decrease in haemolymph carbohydrate levels of isolated and crowded locusts, 43.3% and 44.6% of the resting levels, respectively.We concluded, therefore, that the results do not seem to indicate that isolated locusts rely more heavily on carbohydrates as flight fuel than crowded locusts.Hyperlipaemic responses to flight were less intense in isolated than in crowded locusts, but phase polymorphism dependent differences in flight-induced increase of haemolymph lipid levels were not parallel in 12–16-day-old and 27–32-day-old males.In the younger age group the difference was mainly in the duration of flight needed to induce full response which appeared already after 20 min of flight in the crowded locusts, but only after 45 or 60 min of flight in the isolated ones.In contrast, the older isolated locusts showed markedly lower haemolymph lipid elevations than the crowded locusts even after 30, 45 or 60 min of flight.The hypothesis is forwarded that isolated locusts have a rather coarse adipokinetic strategy focused on a single long-distance migratory flight, whereas gregarious locusts possess a fine adipokinetic balance for reiterative migratory flights and saving fuel reserves for unpredictable long-distance migrations.     

Carbohydrate and fatty acid titres during flight of the migrant noctuid moth,Anticarsia gemmatalis Hübner

Haemolymph concentrations of total carbohydrate and fatty acids were determined in velvetbean caterpillar (Anticarsia gemmatalis Hübner, Lepidoptera: Noctuidae) adult females throughout a 4-hr period of tethered flight. Total carbohydrate concentration decreased from approx. 30 to 10 μg/μl during the first 45 min of flight. Total fatty acid concentration increased from approx. 20 to 40 μg/μl during the first 60 min of flight and then declined to and stabilized at preflight levels. The decrease in wet weight (from approx. 97 to 80 mg/moth) during flight was probably due to defecation since no change in dry weight or haemolymph volume occurred. After 4 hr of flight, no apparent change in whole body lipid content (approx. 12 mg/moth) was observed but the much smaller carbohydrate content was reduced approx. 80% (from approx. 0.6 to 0.1 mg/moth). Approximately equal amounts (approx. 360–550 μg) of carbohydrate and lipid were removed from the haemolymph during 4 hr of flight. Changes in the haemolymph concentrations of palmitic, oleic and linoleic acids correspond to the changes in total fatty acid concentration of the haemolymph, indicating that these are the major components of the lipid mobilized and utilized during flight of A. gemmatalis.     

Dynamics of energy substrates in the haemolymph of Locusta migratoria during flight

In the two-fuel system for flight of the migratory locust, the haemolymph carbohydrate concentration falls during flight periods of up to 1 hr, the decrease being greater in case the pre-flight carbohydrate level is higher. The increase in the lipid concentration from the onset of flight is virtually independent of the initial lipid concentration. Flight intensity affects these changes in substrate concentrations: the carbohydrate level decreases more rapidly if flight speed is higher, whereas the increase in lipid concentration is delayed at higher flight speeds. Respiratory carbon dioxide production is elevated rapidly during flight and reaches over eight times the resting level. From the rate of ¹⁴CO₂ production after labelling of the haemolymph diglyceride pool it is concluded that diglycerides contribute to providing the energy for flight from the earliest stage of flying activity; diglyceride oxidation increases until maximum utilization is attained after some 45 min of flight. The decline in haemolymph carbohydrate concentration due to flying activity results in a decrease of haemolymph osmolarity. Free amino acids, particularly taurine, increase markedly in the haemolymph during flight; yet their concentration only partially counterbalances the fall in haemolymph osmolarity.     

A comparative study of flight performance and fuel utilization as a function of age in females of Florida mosquitoes

Sugar-fed females of 7 species of Florida mosquitoes were flown for 4·5 hr on a flight-mill system twice a week during their life span and analysed for flight performance (speed of flight during the first hour, the distance flown at the end of 4·5 hr flight period, and per cent reduction in flight speed of the fourth hour as compared to the first hour) and for utilization of haemolymph sugars, glycogen, and triglycerides reserves.Species-specific differences occurred in 50 per cent survival age and flight performance. Aedes taeniorhynchus, Mansonia titillans, Culex nigripalpus, Psorophora confinnis, and A. sollicitans exhibited maximum flight potential during 2 to 8 weeks after emergence, as compared with only 1 to 2 weeks in A. aegypti and Anopheles quadrimaculatus. This suggested that the former group of mosquitoes possessed a greater potential for dispersal by searching flights during their life span when compared with the latter group. Glycogen was the only energy reserve utilized during sustained tethered flight in all species. The energy requirements as calculated from depletion of glycogen during sustained flight for 4·5 hr in different species varied from 0·06 to 0·09 cal/1000 m or 16 to 32 cal/hr per g. The considerably lower values of energy expended, on the average of 16 to 22 cal/hr per g in C. nigripalpus, P. confinnis, A. sollicitans, and A. aegypti, compared with 30 to 32 cal/hr per g in A. taeniorhynchus and M. titillans, is most probably due to the substantially lower speed of the former group of mosquitoes, 1000 to 1500 m/hr, than in the latter group of mosquitoes, 1500 to 2000 m/hr. A. sollicitans and M. titillans started to show wing abrasion and distinct signs of senescence during the last 2 to 3 weeks of their life span.Non-flown females of different species maintained on sugar ab lib. achieved maximum levels of glycogen and triglycerides reserves during the second week and they maintained these levels for the major portion of their life span, after which the levels of these reserves showed a distinct decline. It is suggested that this stabilization and decline of the energy reserves control longevity and flight potential in each mosquito species.     

Quantitative studies on the release of locust adipokinetic hormone

Fractionation of methanolic extracts of haemolymph on Sephadex LH-20 made possible the measurement of the titre of adipokinetic hormone in the haemolymph of locusts. Experimentally produced high concentrations of haemolymph carbohydrate caused a delay in the mobilization of lipid during flight, and very low titres of the hormone were present in the haemolymph of locusts injected with trehalose immediately before a 25 min flight. In these locusts flight speed was higher than saline-injected controls. Although delayed lipid mobilization during flight was also seen in locusts injected with sucrose, sucrose is not utilized for flight metabolism and flight speed was not increased by the injection. Tentative estimates of the release rate (c. 1000pg/20min flight) and half life (c. 20 min) of adipokinetic hormone during flight are made. The results described suggest that during flight the rate at which trehalose disappears from the haemolymph does not play a major role in the initiation of the release of adipokinetic hormone.     

Endocrine control of TAG lipase in the fat body of the migratory locust, Locusta migratoria

Aspects of the role and activation of the enzyme triacylglycerol lipase (TAG lipase) in the fat body of the migratory locust Locusta migratoria were investigated. TAG lipase is under the hormonal control of the three endogenous adipokinetic peptides of the migratory locust, Locmi-AKH-I, Locmi-AKH-II and Locmi-AKH-III. Injection of low doses (5-10 pmol) of each peptide causes an increase in lipase activity. The activation of lipase is time dependent: an elevated activity was recorded 15 min after injection of 10 pmol Locmi-AKH-I and maximum activation was reached after 45-60 min. The activation of TAG lipase is also dose-dependent. Doses of 2 pmol of each Locmi-AKH had no effect, whereas 5 pmol caused a significant activation. Maximum activation is reached with a dose of 10 pmol. Analogues of the second messengers cAMP (cpt-cAMP) and IP(3) (F-IP(3)) both activate the enzyme glycogen phosphorylase whereas only cpt-cAMP, but not F-IP(3), activates TAG lipase; cpt-cAMP elevates the lipid levels in the haemolymph. Activation of lipase is specific to the three endogenous AKH peptides: 5 pmol of the endogenous peptide Locmi-HrTH and 10 pmol of corazonin failed to activate lipase. High doses of octopamine did not activate lipase nor did they elevate the lipid concentration in the haemolymph. TAG lipase is stimulated by flight activity but activation is slower than that of glycogen phosphorylase: after 30 min of flight or after 5 min of flight plus 1h of subsequent rest, activity of TAG lipase is increased, but not immediately after 5 min of flight. In contrast, glycogen phosphorylase is activated significantly after 5 min of flight. These activation patterns of the two enzymes mirror-image the concentration of their substrates in the haemolymph: there is a significant decrease in the concentration of carbohydrates after 5 min of flight, whereas no change of the concentration of lipids can be measured after such short time of flight activity; however, a subsequent rest period of 1h is sufficient to increase the lipid concentration.     

Development of imaginal competence to adipokinetic hormone in Locusta: lipid and carbohydrate levels, and glycogen phosphorylase activity in precocene-induced adultiforms

Abstract. Adipokinetic responses to injection of synthetic adipokinetic hormone I (sAKH) were investigated in precocene-induced fifth-instar adultiforms and in chemically allatectomized but morphogenetically normal adults of Locusta migratoria (L.). The results were compared with data on normal fifth (=last)-instar nymphs and normal adults. Chemical allatectomy did not affect the resting level of lipid in the haemolymph, nor the slight decrease of haemolymph carbohydrate concentration induced by sAKH. The effects of chemical allatectomy on sAKH-induced hyperlipaemia, the resting level of haemolymph carbohydrate, total glycogen phosphorylase specific activity, as well as sAKH-induced phosphorylase activation in the fat body, were mostly minor and probably indirect. The concentrations of lipid and carbohydrate in the haemolymph, and sAKH-induced activation of fat body glycogen phosphorylase were more or less similar in normal fifth-instar nymphs, normal adults and fifth-instar adultiforms. Thus, precocious metamorphosis did not affect markedly those parameters which show no or slight changes during normal metamorphosis. In contrast, parameters which change substantially during normal metamorphosis (sAKH-induced hyperlipaemia, sAKH-induced changes in haemolymph carbohydrate level and total glycogen phosphorylase activity) showed similar changes in the course of precocious metamorphosis; the values for fifth-instar adultiforms were similar to those obtained for normal adults, but differed markedly from those found in normal fifth-instar nymphs. Thus, accelerated (precocious) morphological adult development is strongly correlated with accelerated imaginal target competence to AKH and with relevant physiological development.     

Role of methionine-enkephalin on the regulation of carbohydrate metabolism in the rice field crab Oziotelphusa senex senex

In the present study, the role of eyestalks and involvement of methionine-enkephalin in the regulation of haemolymph sugar level was studied. Bilateral eyestalk ablation significantly decreased the haemolymph sugar levels, whereas injection of eyestalk extract into ablated crabs significantly increased the haemolymph sugar levels. Total carbohydrate (TCHO) and glycogen levels were significantly increased in hepatopancreas and muscle of eyestalk-ablated crabs, with a decrease in phosphorylase activity. Injection of eyestalk extract into ablated crabs resulted in partial/complete reversal of these changes. Injection of methionine-enkephalin into intact crabs significantly increased the haemolymph sugar level in a dose-dependent manner. Total tissue carbohydrate and glycogen levels were significantly decreased, with an increase in phosphorylase activity in hepatopancreas and muscle tissues of intact crabs after methionine-enkephalin injection. Methionine-enkephalin injection did not cause any changes in haemolymph sugar, tissue total carbohydrate and glycogen levels and activity levels of phosphorylase in eyestalk-ablated crabs. These results suggest that the eyestalks are the main source of hyperglycaemic hormone and methionine-enkephalin induces hyperglycaemia through eyestalks.     

Cyclic AMP mediates the elevation of proline by AKH peptides in the cetoniid beetle, Pachnoda sinuata

The role of cyclic nucleotides in the transduction of the hyperprolinaemic and hypertrehalosaemic signal of the endogenous neuropeptide Mem-CC was investigated in the cetoniid beetle Pachnoda sinuata. Flight and injection of Mem-CC into the haemocoel of the beetle induce an increase of cAMP levels in the fat body of the beetle. This increase is tissue-specific and does not occur in brain and flight muscles. An elevation of cAMP levels was also found when in vitro preparations of fat body tissue were subjected to Mem-CC. Elevation of the cAMP concentration after injection of Mem-CC is time- and dose-dependent: the maximum response is measured after 1 min, and a dose of 25 pmol Mem-CC is needed. Injection of cpt-cAMP, a cAMP analogue which penetrates the cell membrane, causes a stimulation of proline synthesis but no mobilisation of carbohydrate reserves. The same is measured when IBMX, an inhibitor of phosphodiesterase, is injected. cGMP seems not to be involved in synthesis of proline nor carbohydrate release, because injection of cpt-cGMP has no influence on the levels of proline, alanine and carbohydrates in the haemolymph. Although glycogen phosphorylase of the fat body is activated by Mem-CC in a time- and dose-dependent manner, it cannot be stimulated by cpt-cAMP. The combined data suggest that cAMP is involved in regulation of proline levels by Mem-CC but not in regulation of carbohydrates. Octopamine has no effect on metabolites in the haemolymph and is not capable of activating glycogen phosphorylase, indicating that it is not involved in the regulation of substrates in this beetle. Furthermore, the requirements of the receptor of Mem-CC are different for eliciting a hypertrehalosaemic and a hyperprolinaemic effect, respectively, suggesting that differentiation in signal transduction begins at the receptor level.     

The role of the glandular lobes of the corpora cardiaca during flight in Locusta

ABSTRACT. Flight performance in Locusta is reduced following severance of the major afferent nerves to the corpora cardiaca or removal of the glandular lobes of the corpora cardiaca. These operations prevent the release of adipokinetic hormone and the consequent mobilization of stored lipid. However, locusts deprived of about 90% of their glandular lobe tissue, while flying poorly, did mobilize lipid. It is suggested that the remaining glandular parenchyma cells are capable of secreting enough hormone to stimulate lipid mobilization, but that the concentration may be inadequate to encourage lipid utilization. After removal of all the glandular lobe parenchyma, the blood carbohydrate concentration was temporarily depressed. Nevertheless flight performance was equally poor, both when haemolymph carbohydrate levels were low and when they had returned to normal. After the injection of trehalose into operated control locusts and locusts deprived of their glandular lobes, flight was still markedly poorer in the operated insects, even though the injection of trehalose prevented adipokinetic hormone release in the intact locust. It seems that the poor flight performance of locusts deprived of their glandular lobes cannot be fully explained by the simple absence of adipokinetic hormone.     

取食蜂蜜对棉铃虫齿唇姬蜂体内主要代谢物质的影响

为揭示食物在齿唇姬蜂Campoletis chlorideae Uchida生命中所起的作用,测定分析饱食蜂蜜和只取食清水的齿唇姬蜂体内糖类、脂肪和蛋白质随日龄增加的变化趋势。结果显示,取食蜂蜜对齿唇姬蜂体内主要代谢物质影响显著。10%蜂蜜水和清水饲养的齿唇姬蜂的雌蜂和雄蜂在刚羽化时体内都含有较高水平的糖原、总糖、脂肪和蛋白质。但随着日龄的增加,用清水饲养的雌、雄蜂体内的糖原和总糖含量迅速下降并达到最低水平;而用蜂蜜水饲养的雌、雄蜂随日龄的增加体内的糖原含量没有显著变化,并且与清水饲养的雌、雄蜂相比,其体内总糖含量反而有所上升。用蜂蜜水饲养的齿唇姬蜂的寿命显著长于用清水饲养的齿唇姬蜂。由于蜂蜜中含有丰富的果糖,所以冷蒽酮反应测定显示,用蜂蜜水饲养的齿唇姬蜂体内果糖含量较高,但却不能在清水饲养的齿唇姬蜂体内测出。2种食物处理的齿唇姬蜂在羽化后体内脂肪含量均有下降;并且随日龄的增加,清水饲养的齿唇姬蜂体内脂肪含量的下降速度明显快于蜂蜜水饲养的齿唇姬蜂。取食蜂蜜水的齿唇姬蜂体内蛋白质含量随日龄无显著变化;而用清水饲养的齿唇姬蜂在羽化后体内蛋白质含量随日龄的增长迅速下降并达到最低水平。     

Effects of energetic reserves on behavioral patterns of Mediterranean fruit flies (Diptera: Tephritidae)

The objective of this study was to associate levels of nutritional reserves (specifically lipids, sugars, and glycogen) in individual Mediterranean fruit flies, Ceratitis capitata (Diptera: Tephritidae), with observed patterns of behavior in the field. We collected females (n=255) and males (n=181) from the field, recording the time of collection and the activity they were engaged in when collected. Subsequently, we employed colorimetric biochemical techniques to determine the precise amounts of lipids, sugars, and glycogen in each individual. Lipid and sugar levels in males varied significantly according to the time of collection and the type of activity. Lipid and sugar levels in females did not vary in this manner. Sugar levels in both males and females were highest during the evening, when most feeding occurs. Males that engaged in sexual signaling in leks during the mid-afternoon had relatively low sugar and high lipid levels. Males engaged in the alternative mating tactic of fruit guarding had relatively high sugar and low lipid contents. Glycogen levels in males were high in the mornings, and a decline in glycogen content was associated with participation in leks; however, female glycogen levels did not vary significantly with time of day or activity. Our results provide quantitative evidence for the role nutrient reserves play in driving patterns of male reproductive behavior, yet suggest that factors other than sugar and lipid reserves constrain female behavior. Received: 8 April 1997 / Accepted: 23 June 1997     

Dependence of the life span of the honeybee (Apis mellifica) upon flight performance and energy consumption

Summary The life span of worker-honeybees is determined by the duration of the hive-period and of the foraging period (Figs. 1,2). The duration of the forgaing period is regulated in the following way: Total flight performance of the individual bee seems to be fixed. Daily flight performance strongly affects total flight duration. High daily flight performance decreases maximal flight duration and vice versa.Foragers accumulate the highest glycogen reserves in the flight muscles compared to other stages (Figs. 3, 4). They use these reserves to overcome starvation or when growing old. Young foragers are able to restore glycogen reserves after sugar intake, whereas old foragers were found to have a reduced glycogen synthesizing ability (Fig. 5).The results indicate that bees exhaust their energysupplying mechanisms after a definite total flight performance.     

The hormonal control of haemolymph lipid during flight in Locusta migratoria

Fractionation of methanolic extracts of haemolymph on thin layer chromatography, followed by bioassay, has been used to measure the titres of adipokinetic hormones I and II in the haemolymph of flown locusts. These titres have been correlated with the elevation in haemolymph lipid. Haemolymph lipid elevates in a biphasic manner during locust flight. A rise in lipid occurs during the first 10 min of flight. Lipid levels then plateau between 10 and 20 min. A second, more pronounced elevation begins at 20 min and continues for up to 60 min. The titre of adipokinetic hormone I elevates 10–15 min after flight commences while that of hormone II elevates between 15–30 min. Adipokinetic hormone I contributes 80% of the activity at 30 min but only 45% at 60 min. It is suggested that the elevation in haemolymph lipid during the first 10 min of flight may not be induced by adipokinetic hormone I or II. The role of octopamine in this initial elevation is proposed and discussed.     

Beetles' choice--proline for energy output: control by AKHs

Many beetle species use proline and carbohydrates in a varying ratio to power flight. The degree of contribution of either fuel varies widely between species. In contrast, dung beetle species investigated, thus far, do not have any carbohydrate reserves and rely completely on proline to power energy-costly activities such as flight and, probably, walking and ball-rolling. While the fruit beetle, Pachnoda sinuata, uses proline and carbohydrates equally during flight, proline is solely oxidised during endothermic pre-flight warm-up, as well as during flight after prolonged starvation. Thus, proline seems to be the essential fuel for activity in beetles, even in flightless ones and in those that use proline in combination with carbohydrates; the latter can be completely substituted by proline in certain circumstances. It is apparent from the rapid decline of energy substrates in flight muscles and haemolymph after the onset of flight that mobilisation of stored fuels of the fat body is necessary for prolonged flight periods. This task is performed by AKH-type neuropeptides. In beetles, like in other insects, these peptides mobilise glycogen via activation of glycogen phosphorylase. They also stimulate proline synthesis from alanine and acetyl-CoA in the fat body. Acetyl-CoA is derived from the beta-oxidation of fatty acids and we propose that the neuropeptides activate triacylglycerol lipase.     

Physiological and biochemical aspects of flight metabolism in cocoon-enclosed adults of the fruit beetle,Pachnoda sinuata

We studied several aspects of flight metabolism in cocoon-enclosed adults of the fruit beetle Pachnoda to investigate their flight capability. The majority of adults which were forcefully removed from their pupal cocoon flew off within 5 min of exposure to bright sunlight. Most of the beetles which did not fly voluntarily were, however, capable of flight. Compared with 2-4 week old adults of the same species, cocoon-enclosed adults have higher reserves of glycogen in flight muscles and fat body, whereas the level of total carbohydrates in the haemolymph and the concentration of proline in haemolymph, flight muscles and fat body were similar.Enzymes involved in carbohydrate breakdown (MDH, GAPDH) were more active in flight muscles and fat body of cocoon-enclosed adults compared with adults, while enzymes of proline metabolism in the flight muscles (AlaT, NAD-ME) and fat body (AlaT, NADP-ME) had similar activities in cocoon-enclosed adults and adults. An enzyme of the beta-oxidation of fatty acids (HOAD) had similar activities in flight muscles and fat body of cocoon-enclosed adults and adults.Mitochondria isolated from flight muscles of adults removed prematurely from their cocoon favour the oxidation of proline and pyruvate. Pyruvate, however, is oxidized at higher rates than by mitochondria isolated from flight muscles of adults.During a short lift-generating flight, cocoon-enclosed adults proved that their flight muscles are capable of strong flight performance. During these flights, cocoon-enclosed adults consume proline and carbohydrates at a similar rate to that of adults.The endogenous AKH peptide, Mem-CC, has hyperprolinaemic and hypertrehalosaemic activity in cocoon-enclosed adults. The hypertrehalosaemic effect, however, is stronger in cocoon-enclosed adults than in adults.The content of Mem-CC in corpora cardiaca of larvae (3rd instar), cocoon-enclosed adults and 1 day-old adults is similar at 5-6 pmol per pair of corpora cardiaca, whereas it is higher in 10 day-old adults and 20 day-old adults (37 and 15 pmol per pair corpora cardiaca, respectively).From these results we conclude that cocoon-enclosed adults comply with all the prerequisites for flight performance before they leave their pupal cocoon. Furthermore, cocoon-enclosed adults have a more pronounced carbohydrate-based metabolism before they leave their cocoon compared with adults, which suggests that carbohydrate breakdown is mainly involved in such activities as leaving the cocoon and burrowing activity thereafter.     

Proline can be utilized as an energy substrate during flight of Aedes aegypti females

In order to determine whether proline can be utilized as fuel during flight of Aedes aegypti, proline, alanine, and glutamine concentrations were monitored at 0, 30 and 60 min after flight using sugar-fed males and females, and blood meal-fed females. In sugar-fed and blood meal-fed females, flight lead to a significant decrease in proline and a significant increase in glutamine concentration in both hemolymph and thorax. Only during flight after a blood meal was a significant increase in the alanine concentration observed in hemolymph. After flight, the proline alanine and glutamine levels in the hemolymph and thorax from males did not change significantly. In addition, activities of enzymes related to amino acid metabolism were assayed in homogenates of cephalothorax and thorax from both sexes, and in fat body and midgut from females. In both sexes, the activities of all the enzymes studied were significantly higher in thorax than in cephalothorax. The levels of the enzymes involved in proline oxidation were higher in thorax than in fat body and midgut. These results suggest that proline can be used as an energy substrate for flight muscle of Ae. aegypti females. However, the elevation in glutamine levels observed in hemolymph and thorax after flight has not been reported in other insects that fuel flight using proline and may suggest an additional mechanism for shuttling ammonia between flight muscle and fat body is present in mosquitoes.