A method for rearing the yellow-spotted longicorn beetle, <Emphasis Type="Italic">Psacothea hilaris</Emphasis> (Coleoptera: Cerambycidae), to stabilize the last larval instar

The larvae of Psacothea hilaris (Pascoe) grown continuously under a long day in the laboratory pupate after the 4th, 5th, or 6th instar. This developmental polymorphism has complicated studies on the control of metamorphosis in P. hilaris. Since pupation in P. hilaris is known to be suppressed under a short day, a change in the photoperiod from a short to a long day with appropriate timing may assist in obtaining physiologically homogeneous larvae that pupate at the next molt. When the photoperiod was changed from 12-h light:12-h dark to 15-h light:9-h dark at the beginning of the 5th instar, the pupation rate at the next (5th) molt reached 90%, which was significantly higher than the proportion of larvae that pupated after the 5th instar when the larvae were grown continuously under a long day (52%). This rearing technique will expedite studies on the control of metamorphosis in P. hilaris.     

Food availability controls the onset of metamorphosis in the dung beetle Onthophagus taurus (Coleoptera: Scarabaeidae)

In nature, larvae of the dung beetle Onthophagus taurus (Schreber 1759) are confronted with significant variation in the availability of food without the option of locating new resources. Here we explore how variation in feeding conditions during the final larval instar affects larval growth and the timing of pupation. We found that larvae respond to food deprivation with a reduction in the length of the instar and premature pupation, leading to the early eclosion of a small adult. To achieve pupation, larvae required access to food for at least the first 5 days of the final instar (= 30% of mean third‐instar duration in control individuals), and had to exceed a weight of 0.08 g (= 58% of mean peak weight in control individuals). Larvae that were allowed to feed longer exhibited higher pupation success, but increased larval weight at the time of food deprivation did not result in increased pupation success except for larvae weighing > 0.14 g. Larvae responded to food deprivation by initiating and undergoing the same sequence of developmental events, requiring the same amount of time, as ad libitum‐fed larvae once those had reached their natural peak weight. Our results reveal a striking degree of flexibility in the dynamics and timing of larval development in O. taurus. They also suggest that premature exhaustion of a larva's food supply can serve as a cue for the initiation of metamorphosis. Premature metamorphosis in response to food deprivation has been documented in amphibians, but this is, to the best of our knowledge, the first time such a behaviour has been documented for a holometabolous insect. We discuss our findings in the context of the natural history and behavioural ecology of onthophagine beetles.     

Effects of starvation on larval growth, survival, and metamorphosis of Manila clam Ruditapes philippinarum

The effects of starvation on larval growth, survival, and metamorphosis of Manila clam Ruditapes philippinarum at the temperature of 19.6–21.6 °C, the salinity of 34‰ and pH of 8.0 were investigated from May 18 to July 18, 2006. In this study, the early, middle and late umbo-veliger larvae with the shell lengths of 100, 140, and 190 μm were subject to temporary food deprivation for up to 4.5, 20, and 25d at 0.5, 4, 5d intervals, followed by refeeding for the remaining of a 24, 20, 25d period, respectively. The results suggested that the larvae should have shown considerable tolerance to starvation due to their endogenous and exterior nutrition material, for larvae and time to the point-of-no-return (PNR: the threshold point during starvation after which larvae could no longer metamorphose even if food is provided) were calculated to be 4.25, 17.54, and 22.17d. As the starvation period prolonged, the mean shell length of larvae starved got close to constants at 1.5, 4, and 15d after starvation, which were different for larvae at different stages when starvation began, survival of larvae decreased, and was lower in treatments starved earlier in development than those starved later, for the early, middle and late umbo-veliger larvae, after 4.5, 20 and 25d of starvation period, few larvaes were alive. After starvation period, the alive larvaes were able to metamorphose and had a capability of compensatory growth when refeeding was given. Starvation not only affected metamorphosis rate, but also caused the delay in the time to metamorphosis and the decrease in the metamorphosed sizes. For example, for the continuously-fed larvae, duration to metamorphosis was 20.7d, for larvae with a size of 100-μm starved for up to 4d, larvae with a size of 140-μm starved for up to 16d, larvae with a size of 190-μm starved for up to 20d, duration to metamorphosis were 29.7, 31.7, and 37.7d, the delay in duration to metamorphosis were 9, 11, and 17d, respectively. Furthermore, importance of nutrition material for maintaining larval survival during starvation and the compensatory growth on larvae at the same feeding time were discussed.     

Juvenile hormone titres and metabolism during starvation-induced supernumerary larval moulting of the tobacco hornworm, Manduca sexta L.

When tobacco hornworm (manduca sexta) larvae are starved for 5 days immediately after ecdysis to the 5th instar, then fed normal diet, they undergo a supernumerary moult instead of metamorphosis. During starvation the titre of juvenile hormone in the haemolymph increased to a maximum of 3 ng juvenile hormone I equivalents/ml (determined by the black Manduca larval bioassay) on the fourth day of starvation, then began a decline which continued through the subsequent feeding period. The changes in juvenile hormone titre were not attributable to changes in haemolymph volume during starvation (only a 5% decrease) and subsequent feeding. During starvation the esterase activity of the haemolymph declined 4-fold with a 2-fold larger decrease in the DFP-insensitive, presumably juvenile hormone specific, esterase activity. Both the total and the juvenile hormone-specific esterase activity then increased as a function of larval weight during the subsequent feeding period. As growth was slow in the prolongedly starved larvae, sufficient juvenile hormone was present at the time of prothoracicotropic hormone (PTTH) and ecdysteroid release at the beginning of the fourth day of feeding to prevent metamorphosis.     

Evidence for the presence of a threshold weight for entering diapause in the yellow-spotted longicorn beetle, Psacothea hilaris

Under long-day conditions larvae of Psacothea hilaris (Coleoptera: Cerambycidae) pupate after the 4th or 5th instar, while under short-day conditions they undergo 2-4 nonstationary supernumerary molts and eventually enter diapause. To explore the possibility of a threshold weight for entering diapause, P. hilaris larvae were deprived of food on days 0 (day of ecdysis), 4 or 8 of the 4th, 5th and 6th instars under short-day conditions. Within the first 40 days of starvation, 60% of the larvae starved starting on day 0 of the 4th instar died, but all the larvae starved at later stages survived. The incidence of diapause in these survivors was determined by the occurrence of pupation after a temporary chilling at 15 degrees C for 15 days. Diapause incidence increased as the onset of starvation was delayed; from 11% in the larvae starved on day 0 of the 5th instar to 100% in the larvae starved on day 4 and day 8 of the 6th instar. Analysis of the relationship between the initial weight of a respective larva at the onset of starvation and its pupation success revealed that none of the larvae weighing 690 mg did. This finding suggests the presence of a threshold weight (about 600 mg), below which larvae are incapable of entering diapause. We discuss these findings with reference to the life history of P. hilaris.     

Change in significance of feeding during larval development in the yellow-spotted longicorn beetle, Psacothea hilaris

Larvae of the west-Japan type yellow-spotted longicorn beetle, Psacothea hilaris (Coleoptera: Cerambycidae), show a long-day type photoperiodic response at 25 degrees C; under long-day conditions, larvae pupate after the fourth or fifth instar, while under short-day conditions, they undergo a few nonstationary supernumerary molts and eventually enter diapause. In the present study, the effect of food on the development and photoperiodic response of the larvae was examined with special reference to molting and pupation. Although the pupal body size was greatly affected by the food quality and the length of feeding, the critical day length for induction of metamorphosis at 25 degrees C was always between 13.5 and 14 h. Exposure to starvation of larvae reared on the standard diet revealed that the capability to pupate is acquired after a few days of feeding in the fourth instar. In the larvae that had acquired the capability to pupate, premature pupation was induced by exposure to starvation, indicating that feeding becomes dispensable long before it is normally terminated.     

Food‐availability dependent premature metamorphosis in the bean blister beetle Epicauta gorhami (Coleoptera: Meloidae), a hypermetamorphic insect that feeds on grasshopper eggs in the larval stage

Larvae of the bean blister beetle, Epicauta gorhami, feed on only grasshopper eggs and undergo hypermetamorphosis with pseudopupal diapause in the fifth instar. Whether E. gorhami larvae enter pseudopupal diapause or pupate directly from the fourth instar is controlled by temperature and photoperiod. In nature, larvae are confronted with a significant variation in the availability of food, suggesting the possibility that feeding conditions may also affect the diapause incidence. Here, we addressed this issue by changing the feeding conditions in the fourth instar under conditions of 16 h light : 8 h dark (LD 16 : 8) at 25°C. Food deprivation reduced the length of instar and increased the tendency to pupate, leading to the early eclosion of a small adult. Even non‐feeding fourth‐instar larvae pupated. Regardless of the timing of food deprivation, the post‐feeding larval period was constant and equivalent to that of ad libitum‐fed larvae, suggesting that premature exhaustion of the food supply triggers the initiation of pupation. In agreement with these results, when larvae were fed on intact grasshopper egg pods of various sizes from four species, those that fed on smaller egg pods had a decreased tendency to pseudopupate (i.e., to enter diapause). Food‐deprived larvae showed a clearer photoperiodic response and had a shorter critical day‐length. Thus, in E. gorhami, feeding conditions do not affect pupation success, but do affect the tendency to pupate or pseudopupate. This is the first report of the occurrence of premature pupation in carnivorous insects. We discuss our findings in the context of the natural history and behavioral ecology of E. gorhami.     

Effects of starvation on moult cycle and hepatopancreas of Stage I lobster(Homarus americanus) larvae

Effects of feeding and starvation on the moult cycle and on the ultrastructure of hepatopancreas cells were studied in Stage I lobster larvae (Homarus americanus Milne-Edwards). The relative significance of yolk and first food was quite different in larvae originating from two females. This difference was evident also in the amounts of stored lipid in the R-cells of the larval hepatopancreas. Most larvae from one hatch were, in principle, able to develop exclusively with yolk reserves (without food) to the second instar. The larvae from the second hatch showed lecithotrophic development only to the transition between late intermoult and early premoult (Stages C/D₀ of Drachs's moult cycle) of the first larval instar. When initial starvation in this group lasted for 3 days or more, the point of no return (PNR) was exceeded. After the PNR, consumption of food was still possible, but development ceased in the transition C/D₀ or in late premoult (D_3–4). It is suggested that these stages of the moult cycle are critical points were cessation of development and increased mortality are particularly likely in early larval lobsters under nutritional stress. Examination of hepatopancreas R-cells suggested that the PNR is caused by an irreversible loss of the ability to restore lipid reserves depleted during initial starvation. Initial periods of starvation ending before the PNR prolonged mainly Stage D₀ of the same instar (I). During this delay, structural changes in the R-cells caused by the preceding period of starvation were reversed: reduced lipid inclusions, swollen mitochondria, an increased number of residual bodies indicating autolysis, and a reduction of the microvillous processes. Continually starved larvae which showed lecithotrophic development throughout the first instar and were then re-fed after moulting successfully, had later a prolonged intermoult (Stage C) period in the second instar. This shows that, despite occasional lecithotrophy, food is an important factor in early larval development of the lobster.     

Photoperiodic response of larvae of the yellow-spotted longicorn beetle Psacothea hilaris after removal of the stemmata

The role of the stemmata in photoperiodism has been examined in holometabolic insects, but the only reliable results in Coleoptera have been obtained in Leptocarabus kumagaii (Carabidae), the larvae of which do not respond to photoperiod without stemmata. In the present study, photoperiodism was examined in another coleopteran, Psacothea hilaris (Pascoe) (Cerambycidae), after surgical removal of the stemmata. Larvae reared under short-day conditions and transferred to long-day conditions on day 2 of the 5th instar pupated without further larval molts, whereas those continuously reared under short-day conditions underwent supernumerary molts and did not pupate. When the stemmata were removed on day 2 of the 5th instar, the larvae pupated under long-day conditions but did not do so under short-day conditions. However, under long-day conditions some underwent supernumerary molts before pupation. Larvae from which the sensilla trichodeum were removed showed a similar response to that of stemmata-deficient larvae, and larvae from which stemmata were removed at a younger stage (day 2 of the 4th instar) responded to photoperiod similarly to intact larvae. Thus, supernumerary molts under long-day conditions after removal of the stemmata were attributed to injury due to surgery, rather than a change in photoperiodic photoreception. Therefore, we conclude that larvae of P. hilaris show a photoperiodic response after removal of stemmata, in contrast to larvae of L. kumagaii.     

Effects of food availability on larval development in the slipper limpet Crepidula onyx (Sowerby)

Effects of food availability on the larval survival and development of Crepidula onyx were studied in four experiments by feeding the larvae with different concentrations of the chrysophyte Isochrysis galbana and by starving the larvae for different periods of time. Food concentration had a clear impact on the survival, growth and development time of C. onyx veligers. Larval development occurred only at 10⁴ cells ml⁻¹ and higher algal concentrations. No shell increment was detected in the veligers cultured for 12 days at 10² cells ml⁻¹I. galbana or the blank control. At 10³ cells ml⁻¹, there was only a slight increase in shell length over 12 days. At 10⁴ cells ml⁻¹, about 40% of the larvae became competent in 18 days. At 10⁵ and 10⁶ cells ml⁻¹, more than 90% of the larvae reached competence in 7 days. Initial starvation negatively affected the larval development, but the sensitivity differed among parameters measured on day 5: lower survivorship was detected only for larvae that had suffered 3 days or longer initial starvation, whereas one-day initial starvation caused shorter shells and lower percentage of competent larvae. Three days of continuous feeding was required for 50% of the larvae to reach competence. After feeding for 3 days, most larvae could become competent to metamorphose even under starvation. The time of starvation was also critical: larvae that suffered 1-day food deprivation in the first 2 days of larval release had shorter shells and lowered percent competent larvae than those that suffered the same length of food deprivation in later stages of development. Our study thus indicates that both food concentration and short-term starvation have detrimental effects on the larval development of this species, and that once the larva has consumed certain amount of food, starvation may induce metamorphosis.     

The effects of starving versus fasting on blood composition in larval house crickets

Larval crickets (Acheta domesticus) starved for 2 days during the growth phase of the instar consumed twice as much water as larvae that ceased feeding of their own accord during the last 2 days of the last instar. The behaviour of drinking more water during starvation may compensate for dry weight loss and prevent the larvae from missing the critical weight required to initiate the next moult. During starvation the plasma volume increased while the tissue volume remained constant, which produced a shift in both organic and inorganic solutes from the tissues into the plasma. During fasting there was no change in tissue or plasma volume, therefore large osmotic adjustments were unnecessary, and the only change in plasma solutes noted was a decline in plasma proteins.The titres of proteins, lipids and amino acids remained constant during 2 days of starvation, though the amount of each increased because of the increased plasma volume. Although both the titre and the amount of plasma sugar sharply declined during starvation, there was no change in the sugar titre when the insects fasted. There was some evidence that prior to fasting the programmed gradual decline in food intake matched the decline in metabolic rate, which permitted a plasma sugar stability not evident in starved larvae. The decline in plasma proteins during the fasting phase appeared due to the removal of a larval specific protein and not a direct result of fasting.     

Stage-dependent effects of starvation on the growth, metamorphosis, and ecdysteroidogenesis by the prothoracic glands during the last larval instar of the silkworm, Bombyx mori

The stage-dependent effects of starvation on the growth, metamorphosis, and ecdysteroidogenesis of the prothoracic glands during the last larval instar of the silkworm, Bombyx mori, were studied in the present study. When last instar larvae were starved beginning on day 1 of that instar, all larvae died between days 5 and 7 of the instar. Although the prothoracicotropic hormone (PTTH) release from the brain-corpus cardiacum-corpus allatum (BR-CC-CA) did not significantly change during starvation, a deficiency in PTTH signal transduction was maintained, which led to very low levels of hemolymph ecdysteroids after the beginning of starvation. However, when starvation began on day 3 of the last larval instar, the major hemolymph ecdysteroid peak, preceding larval-pupal transformation, occurred 1 day earlier than that in control larvae. Protein content of the prothoracic glands in day 3-starved larvae was maintained at a low level as compared to that of control larvae. The secretory activity of the prothoracic glands in day 3-starved larvae was maintained at a level similar to that of control larvae. However, the rate of ecdysteroidogenesis, expressed per microgram of glandular protein, was greatly enhanced in these starved larvae, indicating that upon starvation, larvae increased the ecdysteroid production rate to enhance the rate of survival.     

Factors influencing juvenile hormone esterase activity in the wax moth, Galleria mellonella

The effects of juvenile hormone, antiallatotropins, selected surgical procedures and starvation on the juvenile hormone esterase levels in Galleria larvae and pupae were investigated. JH reduced JH esterase activity in larvae but induced the enzyme in 1-day-old pupae. In vitro studies confirmed that the peak of synthesis and/or release of JH esterase from the fat body of last instar larvae occurred 4 days after ecdysis. These studies also showed that fat body from JH-treated larvae released much less enzyme than controls. Antiallatotropins, precocene 2 and ZR 2646 also reduced JH esterase levels in larvae, but ZR 2646 induced JH esterase in pupae. In starved larvae, JH esterase did not increase during the first five days. A minimum of 36 hr of feeding was necessary for the larval esterase activity to increase on schedule on day 4 of the last larval stadium. When day-l larvae were ligated behind the head or the prothorax, they had lower JH esterase levels and yet showed a slight increase in the enzyme when the larvae reached the age of 4 days. The significance of these results is discussed in relation to the possible control of esterase activity during metamorphosis.     

Neuroendocrine regulation of corpus allatum activity in Manduca sexta: The endocrine basis for starvation-induced supernumerary larval moult

When newly-ecdysed 5th instar larvae of Manduca sexta were starved for 3 days and thereafter fed on standard diet the majority (90%) of the surviving larvae moulted into 6th instars. Allatectomy prior to starvation abolished the supernumerary moult, while denervation of the corpora allata (CA) had no effect.Cautery of medial neurosecretory cells, but not of the lateral cells, prevented supernumerary moulting and pupation ensued. Transplantation of brains from young 5th instar donors into larvae, whose medial neurosecretory cells were cauterized prior to starvation, restored the extra larval moult. Neither CA nor corpora cardiaca (CC) could be substituted for the medial neurosecretory cells.For induction of the supernumerary moult the medial neurosecretory cells are required only until day 1 after refeeding whereas the CA are required until day 3 after refeeding. Allatectomy on day 3 after refeeding resulted in the production of black 6th instar larvae.We conclude that starvation-induced supernumerary moulting is due to activation of the CA by allatotropin produced by medial neurosecretory cells in the brain. The anteromedial cells (group II) appear to be the source of allatotropin.     

Effects of prehatching salinity and initial larval biomass on survival and duration of development in the zoea 1 of the estuarine crab, Chasmagnathus granulata, under nutritional stress

The effects of individual larval biomass, and salinity experienced during embryogenesis (i.e., prehatching salinity) on starvation tolerance and growth of zoea 1 of the estuarine crab (Chasmagnathus granulata) were evaluated in laboratory experiments. Freshly hatched zoeae 1 were obtained from broods maintained at three salinities (15‰, 20‰ and 32‰), and cultured at 20‰ under different initial feeding periods and subsequent food deprivation (“point of reserve saturation” experiment: PRS) or under initial periods of food deprivation and subsequent feeding (point of no return experiment: PNR). Another group of larvae were used for determination of biomass (dry weight, carbon, and nitrogen) of zoea 1.Larval survival and duration of development depended on the length of feeding period: no larvae reached the second instar under complete starvation; survival was higher and duration of development shorter as the feeding period lengthened. After different initial feeding periods (PRS experiment), zoeae 1 that hatched from eggs incubated at the prehatching salinities of 15‰ and 20‰ showed higher survival and shorter duration of development than those at 32‰. Prehatching salinity also affected the amount of reserves accumulated during the first 2 days after hatching, with larvae from 15‰ and 20‰ showing the highest percentage of total accumulation of carbon and nitrogen. Initial larval biomass did not affect survival, but it had a slight effect on duration of development, with larger larvae (in terms of biomass) developing faster. After different initial starvation periods (PNR experiment), prehatching salinity did not affect survival, but it affected duration of development: larvae from 15‰ and 20‰ reached the second instar earlier. Variability in survival and duration of development was explained in part by among-brood variability in initial larval biomass: larvae with higher biomass showed higher survival and shorter duration of development. Thus, C. granulata, survival and duration of development under food stress depend on the interaction between environmental conditions experienced before and after hatching (pre- and posthatching factors, respectively).     

Parameters influencing the acquisition of competence for metamorphosis in imaginal disks of Drosophila

When imaginal disks from first and early second instar larvae of Drosophila are transplanted into larval hosts that are ready to pupate, they are unable to differentiate adult structures. The disks gradually become competent to respond with imaginal differentiation towards the end of the second larval instar (Fig. 1). The first sign of imaginal differentiation is a light-orange pigment that appears in the presumptive eye region when eye-antennal disks from early second instar larvae were subjected to immediate metamorphosis. This pigment was identified as being composed of ommochromes and drosopterins.Incompetent eye-antennal disks from early second instar donors were cultured in adult females for 2 to 5 days, and then retransplanted into late third instar larval hosts. If the adult host flies were kept on standard food the disks grew by cell multiplication (Fig. 2c) and became competent to undergo imaginal differentiation (Fig. 3). If, on the other hand, the adult hosts were starved on a protein-free sugar diet, cell divisions were effectively blocked in the disks. These did not noticeably grow (Fig. 2b) and remained incompetent (Fig. 3). The block caused by starvation proved to be reversible. Based on these results the hypothesis is advanced that the acquisition of competence requires a minimum number of cell divisions to take place in the disk primordium.     

Analysis of molecular markers for metamorphic competency and their response to starvation or feeding in the mosquito, Aedes aegypti (Diptera: Culicidae)

The nutritional condition of fourth instar larvae of the yellow fever mosquito, Aedes aegypti, governs female longevity and egg production, both are key determinants of pathogen transmission. As well, nutrition provisions larval growth and development and attains its greatest pace in the last larval instar in preparation for metamorphosis to an adult. These developmental processes are regulated by a complex endocrine interplay of juvenile hormone, neuropeptides, and ecdysteroids that is nutrition sensitive. We previously determined that feeding for only 24 h post-ecdysis was sufficient for fourth instar Ae. aegypti larvae to reach critical weight and accumulate sufficient nutritional stores to commit to metamorphosis. To understand the genetic basis of metamorphic commitment in Ae. aegypti, we profiled the expression of 16 genes known to be involved in the endocrine and nutritional regulation of insect metamorphosis in two ways. The first set is a developmental profile from the beginning of the fourth instar to early pupae, and the second set is for fourth instars starved or fed for up to 36 h. By comparing the two sets, we found that seven of the genes (AaegCYP302, AaegJHE43357, AaegBrCZ4, AaegCPF1-2, AaegCPR-7, AaegPpl, and AaegSlif) were expressed during metamorphic commitment in fourth instars and in fed but not starved larvae. Based on these results, the seven genes alone or in combination may serve as molecular indicators of nutritional and metamorphic status of fourth instar Ae. aegypti larvae and possibly other mosquito species in field and laboratory studies to gauge sub-lethal effects of novel and traditional cultural or chemical controls.     

Comparison of nutritional status of field and laboratory reared Balanus amphitrite Darwin (Cirripedia: Thoracica) larvae and implication of starvation

Experiments were carried out to evaluate the influence of rearing temperature and food concentration (20 and 30 °C, 1×10⁵ and 2×10⁵ cells ml⁻¹) on the starvation threshold and nucleic acid content of the larvae of Balanus amphitrite. The larvae were also field-reared using micro-enclosures. Laboratory-reared larvae were larger in size than the field-reared larvae. An increase in size, DNA content and instar index of the starved II instar larvae was observed indicating that the absence of food may not be fatal to this early instar. The temperature at which larvae were raised and the food concentration had variable influence on the capacity to withstand starvation. Exposure to increased temperatures during starvation eliminated the effect of doubling food concentration during their feeding period prior to starvation. The larvae reared at 20 °C had comparatively lower nucleic acid content. The laboratory-reared larvae had ca. 1.7 times greater RNA:DNA ratio than larvae raised at comparable temperature in the field.     

Feeding glucose or sucrose, but not trehalose, suppresses the starvation-induced premature pupation in the yellow-spotted longicorn beetle, Psacothea hilaris

Under 25 degrees C and a long-day photoperiod, starvation induces premature pupation in 4th instar Psacothea hilaris larvae exceeding a threshold weight of 180 mg, resulting in the formation of small but morphologically normal adults. To investigate possible mechanisms underlying this phenomenon, we first measured the hemolymph trehalose and glucose levels of starved larvae. When larvae were starved after 4 days of feeding (attaining the threshold weight), glucose levels decreased 4-fold within the next 24 h, while trehalose levels, after a temporary slight decrease, increased remarkably to reach a peak just before the prepupa stage. The effects of ingesting various nutrients on the developmental fate and the hemolymph sugar titers of starving larvae were then examined. Feeding on agar blocks containing sucrose or glucose totally suppressed the occurrence of premature pupation, while trehalose, fructose, casein and starch were ineffective. Feeding on glucose or trehalose resulted in a 6-fold decrease in hemolymph glucose levels and remarkably elevated trehalose levels. Since feeding on glucose and trehalose induced similar changes in hemolymph sugar titers but trehalose was not effective in suppressing premature pupation, glucose may have exhibited its effects via gustatory mechanisms.     

The effects of starvation and 20-hydroxy-ecdysone on feeding and pupariation of early 3rd-instar Calliphora vicina larvae

At a larval body weight of 15–16 mg, young 3rd-instar Calliphora vicina larvae pass from the obligatory feeding phase, when starvation results in cessation of growth or development, to the facultative feeding phase when starvation leads to subsequent pupariation. During normal larval development the transition from obligatory to facultative feeding phase appears to be independent of 20-hydroxyecdysone but absence (or insufficiency) of the hormone is the likely reason why starved larvae in the obligatory feeding phase fail to pupariate. 20-Hydroxy-ecdysone induces termination of feeding by normal, facultative phase larvae and is the probable signal for larval commitment to pupariation.