Hormonal control of pupal coloration in the painted lady butterfly Vanessa cardui

Pupae of the painted lady butterfly Vanessa cardui exhibit pupal color polyphenism consisting of white, dark and intermediate types. We investigated environmental factors affecting pupal coloration and the physiological mechanisms underlying the control of pupal color polyphenism in this species. Over 80% of larvae reared at 16 °C developed into pupae of dark types, whereas over 82% of larvae at 32 °C developed into pupae of white types irrespective of long/short-day photoperiod conditions. When mature larvae reared at 32 °C were ligatured between thoracic and abdominal parts at three different pharate pupal stages, all of the head-thoracic parts developed into white pupae regardless of pupal stage, but all abdominal parts ligatured at the early pharate pupal stage only developed into dark pupae. These results indicate that temperature during larval stages is an important element affecting pupal coloration as an environmental cue in V. cardui, and that a factor(s) inducing white pupae is released from head-thoracic parts under conditions of high temperature. Additionally, when ligatured abdomens destined to develop into dark pupae were treated with crude extracts prepared from the central nervous system, all of the ligatured abdomens developed into white pupae at a level dependent on dose and pupal stage. These results suggest that the factor inducing white pupae is a key molecule controlling pupal color polyphenism in V. cardui.     

Über den Einfluß der Kulturdauer im larvalen Wirt auf die Entwicklungsleistungen implantierter männlicher Genitalimaginalscheiben vonEphestia,kuehniella Z.

Summary Complete and bisected male genital disks (HO) from full-grown (T9) larvae were transplanted either into larvae and pharate pupae of different age (T4, T7, T9 larvae, A1–A5 pharate pupae) or repeatedly transferred into full-grown larvae before being implanted into a final larval host. After metamorphosis of the hosts, most of the complete transplants and regenerated HO halves showed normal morphological features, but the implanted genitals from old pharate pupae (A4 and A5) were abnormally differentiated. Frequency of Regeneration. After transplanting both halves of the bisected HO into T9 hosts, three groups of results were observed: (1) each of the two halves regenerated into a complete genital organ; (2) only one half regenerated; (3) neither of the two halves regenerated. In the pharate pupae no regeneration of the implanted halves took place. If the lapse of time between the transplantation and, the onset of metamorphosis (=onset of pharate pupae phase) was long enough by transplanting into young larvae (T4) or by repeatedly transferring into old larvae and subsequent transplantation into a final larval host, all the implanted halves were able to regenerate. Size of the Implanted Genital Organs After prolonging the in vivo culture in larval hosts by implanting into young larvae or repeatedly transferring into old larvae, it was found that the regenerated genitalia grew to the same size as the complete transplants, but the size of the complete transplants increased, if at all, only insignificantly. Duration of Development of the Hosts. Regeneration of one HO half implanted into a full-grown larva caused an average delay of further development of about 2 days. An additional delay was recorded when both halves had regenerated. However, no delay was observed when HO halves implanted into young (T4) larvae regenerated, and no delay occurred in the final hosts when the repeatedly transferred halves had reached a certain stage of regeneration.The developmental capacities of the tranplanted disks and the control of metamorphosis by regenerating disks are discussed.

     

Radiation biology and inherited sterility of light brown apple moth (Lepidoptera: Tortricidae): developing a sterile insect release program

The radiation biology of two geographically isolated populations of the light brown apple moth [Epiphyas postvittana (Walker)] was studied in Australia and New Zealand as an initiation of a SIT/F1 sterility program. Pharate and < or = 2 d pre-emergence pupae were exposed to increasing radiation doses up to a maximum dose of 300 Gy. Fertility and other life history parameters were measured in emerging adults (parental) and their progeny (F1-F3 adults). Parental fecundity was significantly affected by increasing irradiation dose in pharate pupae only. For both populations, parental egg fertility declined with increasing radiation. This was most pronounced for the irradiated parental females whose fertility declined at a higher rate than of irradiated males. At 250 Gy, females < or = 2 d preemergence pupae produced few larvae and no adults at F1. No larvae hatched from 250 Gy-irradiated female pharate pupae. At 300 Gy, males still had residual fertility of 2-5.5%, with pharate pupae being the more radio-sensitive. Radiation-induced deleterious inherited effects in offspring from irradiated males were expressed as increased developmental time in F1 larvae, a reduction in percent F1 female survival, decreased adult emergence and increased cumulative mortality over subsequent generations. Males irradiated at > or = 150 Gy produced few but highly sterile offspring at F1 and mortality was > 99% by F2 egg.     

Juvenile hormone in Drosophila melanogaster: Identification and titer determination during development

Juvenile hormone (JH) III was identified in whole-body extracts of eggs, larvae, pupae, pharate adults and adults of Drosophila melanogaster. Titers of the hormone varied according to stage of development. Highest levels were found in post-feeding (wandering) larvae and adults; only low levels were found in feeding last-stadium larvae and in pupae. None of the other known JHs were detected (limit of detection ≈0.01 ng/g). These results are discussed in the light of the known physiological roles of JH in the development of Drosophila and other insects.     

THE GENETICS AND EVOLUTION OF CANNIBALISM IN FLOUR BEETLES (GENUS TRIBOLIUM)

Cannibalism plays a major role in population regulation in Tribolium confusum, accounting for up to tenfold differences in population size between different genetic strains. I characterized the within- and between-strain genetic variation for cannibalism using standard quantitative-genetic methods. The four laboratory strains studied have similar birth and death rates but differ in their strain-specific cannibalistic tendencies. The cannibalism rates of the strains were stable for more than 60 generations of laboratory husbandry. I found considerable genetic variation for cannibalism within each strain. A genetic analysis of the between-strain differences in each of three types of cannibalism (larvae eating eggs, adults eating eggs, and adults eating pupae) showed that all three cannibalism pathways are autosomally inherited and exhibit minor degrees of dominance. Adult cannibalism of eggs and larval cannibalism of eggs appear to be genetically correlated. The differences between the “high” and “low” cannibalism strains appear to be polygenic for two kinds of cannibalism, larvae eating eggs and adults eating pupae. However, strain differences in adult cannibalism of eggs may be due to only two loci. The stability of the between-strain differences for more than 60 generations, the additive nature of inheritance, and the demonstration of considerable within-strain genetic variation suggest that cannibalism may be selectively neutral or under stabilizing selection with many adaptive peaks.     

Hormonal control of seasonal morph determination in the swallowtail butterfly, Papilio xuthus L. (Lepidoptera: Papilionidae)

Seasonal morphs (spring and sumer forms) of Papilio xuthus L. are determined coincidentally with diapause and non-diapause in pupae by larval exposure to short days and long days respectively. The neuroendocrine principle underlying seasonal-morph determination was studied using surgical operations in P. xuthus.When recipient 0-day old or chilled diapause pupae were joined to donor 0-day old non-diapause pupae, the recipients developed into summer or intermediate morphs. When the same kinds of recipients used above were joined to 0-day old or chilled diapause pupae, there were no significant effects on the adult morph. In contrast, recipient non-diapause pupae all developed into summer morphs, regardless of groups of the type of donors.Furthermore, when the brain of 5th-instar larvae, pharate pupae or pupae, predetermined to be diapause, was transplanted into the abdomen of 0-day old, 30-day old or chilled diapause pupae, the recipients developed into summer or intermediate morphs.The results indicate that the brain of non-diapause pupae secretes a humoral factor producing the summer morph. In non-diapause pupae, the factor may be secreted at about the stage of larval-pupal ecdysis coincidentally with that of prothoracicotropic hormone.     

Haemocytes of the pink bollworm, Pectinophora gossypiella, during larval development and diapause

Seven types of haemocytes were observed in the last larval instar of the pink bollworm, Pectinophora gossypiella (Saunders): prohaemocytes, plasmatocytes, granular haemocytes, spherule cells, adipohaemocytes, oenocytoids, and podocytes. Total and differential haemocyte counts made from diapausing and non-diapausing larvae showed that during diapause there was a significant reduction in the numbers of all haemocyte types. Upon termination of diapause, the haemocyte level increased. There were no significant differences in the level of haemocytes in the pharate pupae that developed from diapause or non-diapause type larvae, except in the case of adipohaemocytes, which were three times as prevalent in pharate pupae from diapausing larvae. Functional aspects of various types of haemocytes are discussed, and it is suggested that the lower haemocyte level observed during diapause is the result of lower metabolic activity.     

Brood Guarding by an Adult Parasitoid Reduces Cannibalism of Parasitoid-Attacked Conspecifics by a Caterpillar Host

Adult female bethylid parasitoids (Hymenoptera: Bethylidae) commonly guard their offspring until they develop into later immature stages to protect them from competing parasitoids and predators. Another possible mortality factor is from caterpillar larvae that cannibalize parasitized conspecific larvae. This study determined the effect of brood guarding on the occurrence of host cannibalism by using a brood guarding bethylid parasitoid Goniozus legneri and a non-guarding braconid parasitoid Habrobracon gelechiae (Hymenoptera: Braconidae), both are gregarious ectoprasitoids that attack the obliquebanded leafroller Choristoneura rosaceana (Lepidoptera: Tortricidae). When a C. rosaceana larva parasitized by G. legneri was presented to a live conspecific larva, the frequency of cannibalism on the parasitized conspecific was lower in the presence than in the absence of a guarding female G. legneri. In contrast, when a C. rosaceana larva parasitized by H. gelechiae was presented to a live conspecific larva, the presence or absence of H. gelechiae did not affect cannibalism frequency. Cannibals did not gain a fitness advantage in terms of larval survival, developmental time, or body mass of developed pupae; therefore, cannibalism by the host larva may be a group defense against increased parasitism in subsequent population generations. We suggest that brood guarding by parasitoids can act as a broad defense strategy to protect offspring from the cannibalism of parasitized conspecifics by the host larvae.     

Effect of Monochamus carolinensis on the Life History of the Pinewood Nematode,Bursaphelenchus xylophilus

The development of Bursaphelenchus xylophilus in pine wood infested with and free of Monochamus carolinensis was investigated. Formation of third-stage dispersal juveniles occurred in the presence and absence of pine sawyer beetles. The proportion of third-stage dispersal juveniles in the total nematode population was negatively correlated with moisture content of the wood. Formation of nematode dauer juveniles was dependent on the presence of the pine sawyer beetle. Dauer juveniles were present in 3 of 315 wood samples taken from non-beetle-infested Scots pine bolts and 81 of 311 samples taken from beetle-infested bolts. Nematode densities were greater in wood samples taken adjacent to insect larvae, pupae, and teneral adults compared with samples taken from areas void of insect activity. Nematodes recovered from beetle larvae, pupae, and teneral adults were mostly fourth-stage dauer juveniles, although some third-stage dispersal juveniles were also recovered. Dauer juvenile density was highest on teneral adult beetles.     

Carbohydrate metabolism during the pupal molt of the tobacco hornworm,Manduca sexta

During the pupal molt of the tobacco hornworm, Manduca sexta, the percentage of active fat body glycogen phosphorylase increased from 5–10 to 20%, but only for a period of 5 h prior to the molt. From the time of the appearance of two sclerotized dorsal bars to the time of the molt, the concentration of total hemolymph carbohydrates doubled to 100 mM trehalose. Initially, the glucose level was high (16 mM) when compared with feeding larvae (approximately 1 mM) but decreased to zero just prior to the molt. The amount of cuticular chitosan decreased from approximately 100 mg to 10 mg at pupation; the exuvia contained approximately 7 mg. While the levels of total lipids in hemolymph were not affected, the lipid content of the fat body decreased significantly prior to the molt but increased sharply thereafter. Fat body glycogen phosphorylase in pharate pupae and pupae of M. sexta was substantially activated by the Manduca adipokinetic peptide hormone, which in pharate pupae, produced the same response at 2 and 20 pmol per insect as in ligated larval abdomens. In pupae the response was clearly reduced. Using chilling to stimulate glycogen phosphorylase, it was found that the enzyme in pharate pupae and pupae responded both in vivo and in vitro as in ligated abdomens of larvae. Thus, a transition to the adult response seems to occur during the pupal and pharate adult development. © 1995 Wiley-Liss, Inc.     

Inactivation of ecdysone and the possible feed back control of the titre during pupation of Sarcophaga peregrina

Radioactive β-ecdysone injected into mature larvae or pharate pupae of Sarcophaga peregrina was rapidly metabolized, but the decrease in moulting hormone activity in whole animal extracts was much faster than the decrease of radioactivity. The metabolites were extracted, examined by TLC and HPLC and shown to be conjugates of β-ecdysone in larvae (as shown by enzymatic hydrolysis) but 3-epi-β-ecdysone in pupae. These compounds did not exhibit appreciable activity. The process of inactivation by epimerization may be a mechanism of feed back control of ecdysone, since epimerization is induced by ecdysone itself.     

Ecdysteroid synthesis by testes of 5th instars and pupae of the European corn borer,Ostrinia nubilalis (Hubner)

Summary

Testes from young fifth instar Ostrinia nubilalis produced very small amounts of ecdysteroids while those from larvae that had purged their gut produced considerably more immunodetectable ecdysteroid in vitro. Larval testes that had fused produced 2.2 times more ecdysteroid than those that remained separate. It was the sheath of the testes rather than the contents that was physiologically active. Synthesis was questionable in testes from day-1 pupae and was not observed in testes from pharate pupae, from day-2 pupae or from pharate adults. Thus, synthesis only occurred at specific times in the life cycle. Ecdysteroid profiles for testes from wandering larvae whose testes had fused showed a net increase in all normally observed ecdysteroids, with the greatest increase being in 20-hydroxyecdysone. For testes from day-1 pupae, the nature of the ecdysteroid profile changed after 24 h of incubation, with some ecdysteroids showing increases and other decreases. There appear to be considerable differences among species regarding the times of testis synthesis and the amounts and nature of the ecdysteroids synthesized.     

Hormonal control of the orange coloration of diapause pupae in the swallowtail butterfly, Papilio xuthus L. (Lepidoptera: Papilionidae)

Diapause pupae of Papilio xuthus show color polymorphism, represented by diapause-green, orange, and brownish-orange types that are each associated with specific pupation sites. We investigated the role of the site of pupation on the induction of the development of orange types (or brownish-orange types), and the endocrine mechanism underlying the control of color polymorphism in short-day pupae. All short-day larvae of the wandering stage developed into orange or brownish-orange type pupae when they were placed in rough-surfaced containers after gut-purge. Utilizing a pharate pupal ligation between the thorax and abdomen, the endocrine mechanism underlying the control of color polymorphism was shown to involve a head-thorax factor (Orange-Pupa-Inducing Factor: OPIF) that induced orange types in short-day pupae. OPIF was bioassayed using the ligated abdomens of short-day pharate pupae. OPIF was extractable with 2% NaCl solution from 5th-instar larval ganglia complexes following the mesothoracic complex (TG(2,3)-AG(1-7)), but it could not be extracted with either acetone or 80% ethanol solution. OPIF may not exist in the brains of day-0 pupae or in brain-subesophageal ganglion and prothoracic ganglion complexes of 5th-instar larvae. The short-day pharate pupae responded to OPIF in a dose-dependent manner.     

Habitat choice as the defensive behavior of Calopteryx splendens Harris larvae (Odonata, Calopterygidae): Impact of the predator species and of the population density of damselflies

Laboratory experiments have demonstrated that the change in the height of dispersal of Calopteryx splendens Harris larvae on perches is a protective strategy in the presence of fish. Specificity of protective behavior of damselflies in the presence of pelagic or bottom-dwelling fishes, or of a complex of both types of fishes is described. The effectiveness of the habitat choice is reduced in the presence of the complex of fishes. The use of an optimal protective strategy by all the larvae was observed only in the case when their population density was the lowest. The increase in the population density resulted in the increased importance of intraspecies competition (cannibalism) and decreased effectiveness of protective behavior against heterospecific predators.     

Genetic control of geographic variation for cannibalism in the southwestern corn borer,Diatraea grandiosella

The southwestern corn borer,Diatraea grandiosella Dyar, is a subtropical insect whose range has expanded northward within this century. Geographic variation exists between populations at the extremes of the range for a suite of morphological and behavioral characters, including cannibalism. Laboratory colonies established from a Missouri population (37°N lat.) with a high cannibalism rate and a Mexican population (19° N lat.) with a low cannibalism rate were used to examine the genetic basis of cannibalism by means of a controlled breeding design. When larvae were held in pairs on artificial diet in 30 ml plastic cups at 30° C 16L:8D, the highest incidence of cannibalism in both Missouri and Mexican populations was found in larvae 15 to 18 days-of-age (5th and 6th instars). Under these conditions, cannibalism was expressed in 33% of the pairs formed from Missouri larvae and 11% of the pairs formed from Mexican larvae. First and second generation crosses between Missouri and Mexican populations showed an intermediate level of cannibalism, whereas backcrosses to the parental generations showed a regression to the parental phenotypes. These results indicate that cannibalism is under additive genetic control. Larvae from the Missouri parental population were more likely to consume their victim (i.e., cannibalize) once intraspecific killing had occurred than were larvae from the Mexican parental population or from any of the crosses, and female larvae were cannibals more often than were males. Under the conditions employed, no advantage was detected for cannibalism over instraspecific killing for larval weight gain or growth rate.     

Fatty acid profile of the cabbage looper, Trichoplusia ni, and the effect of diet and rearing conditions

The fatty acids, palmitic (16:0), palmitoleic (16:1), stearic (18:0), oleic (18:1), linoleic (18:2), and linolenic (18:3) were measured by GLC in Trichoplusia ni (Hübn.) from larvae reared on three different diets. The effect of rearing temperature and humidity on the levels of these fatty acids in pupae and pharate adults was determined. T. ni tended to accumulate 18:3 somewhat in proportion to its level in the diet. The respective levels (relative percentage) of this fatty acid in the diet and in the pupae were: bean leaves, 73·6 and 56·7; the diet based on lima beans, 10·2 and 3·5; and a meridic diet containing wheatgerm oil, 5·6 and 1·8. Pupae from larvae reared on a diet marginal in 18:3 content produced adults with deformed wings when reared at 30°C and normal wings when reared at 23 or 24°C, but there was no difference in their tissue level of 18:3. The phospholipids of last instar larvae, pharate pupae, pupae, pharate adults, and emerged adults are made up mostly of 18:0, 18:2, and 18:3 while the triglycerides of these stages contain relative large quantities of 16:0, 16:1, and 18:1. Pupal rearing temperature did not appear to influence the level of 18:3 in these two fractions enough to account for the degree of deficiency expressed as adult wing deformity. Both high (95%) and low (20%) relative humidity have an adverse effect on wing development but this effect can be overcome by 18:3 supplementation of the larval diet.     

Neurohormones in developing embryos of the silkworm,Bombyx mori: The presence and characteristics of prothoracicotropic hormone B

The presence and fluctuation of prothoracicotropic hormone (PTTH) activity have been shown in brainless Bombyx mori pupae and in developing embryos. The embryonic PTTH is only effective in eliciting adult development of brainless pupae. PTTH activity first became detectable in embryos which had developed almost to the stage of differentiation of their neuroendocrine systems. The hormone was partially purified from pharate first-instar larvae (1 day before hatching) and approx a 300-fold purification was achieved. 0.2 μg of the partial purified hormone can evoke adult development in brainless pupae. The molecular weight of the hormone was estimated to be 20,000–30,000 daltons by gel-filtration on a Sephadex G-50. Two distinct forms of PTTH are present in developing embryos of B. mori.     

Ecdysteroids and diapause in pupae of Heliothis punctiger

Most pupae of H. punctiger enter diapause when reared at 19°C, 12L:12D. When pharate pupae were treated for only 12 hr at 28°C about 50% developed at 19°C. The proportion of non-diapausing pupae increased as the temperature at which the pharate pupal stage was spent increased.The quantity of injected 20-hydroxyecdysone necessary to promote development in diapausing pupae varied from about 1 μg g^?1 soon after pupation to about 4 μg g^?1 after 50 days. It fell somewhat after 150 days.Removing brains from non-diapausing pupae showed that the brain secreted its hormone at the time of pupation (or just before). However, if the pupae were kept at 19°C development did not occur unless the brain remained in situ for at least 20 hr at 28°C. Implanting brains from non-diapausing pupae into diapausing ones had no measurable effect.These results may be explained by postulating that the prothoracic gland is ‘activated’ by exposure to high temperature, but that it reverts to inactivity over a period at 19°C. The ‘active’ gland must then be stimulated by brain hormone for a long period to trigger secretion of its hormone, which results in development. Diapause is thus the result of the failure of the prothoracic gland to secrete.     

Haemolymph ecdysteroid titre and epidermal cell commitment of the female southwestern corn borer larvae

The epidermal cell commitment (to pupation or formation of immaculate larvae) and related haemolymph ecdysteroid titres of the southwestern corn borer, Diatraea grandiosella were studied in both nondiapause-bound and diapause-bound last-instar female larvae. Cell commitment was estimated by examining the characteristics of new cuticle secreted in response to an injection of 20-hydroxyecdysone. Haemolymph ecdysteroid titres were determined by radioimmunoassay. Juvenile hormone effect on epidermal cell commitment was studied by applying a juvenile hormone mimic (ZR-515) to last-instar non-diapause-bound larvae and examining the resulting cuticle.In non-diapause-bound larvae, the epidermis of different body regions was committed to pupal development at different times. When pupal cuticular characteristics were evaluated by a scoring system, it appeared that the development of normal pupal cuticle is discontinuous. Three sudden increases in pupal characteristics were observed at 1.67, 2.67 and 3.67 days into the last-larval instar. Haemolymph ecdysteroid titre changes were correlated with the sudden increases in pupal characteristics. Peak ecdysteroid titres were found at 1.67, 2.33, and 3.33 days into the final instar. A fourth ecdysteroid peak (138.8 ng/ml of haemolymph) occurred in pharate pupae. In contrast, the commitment of diapause-bound larvae to produce immaculate integument was made in a fast and continuous fashion. Full commitment was made by 50% of the individuals 4 days (ca. first quarter) into the stadium. Haemolymph ecdysteroid titres fluctuated during the first 2 weeks of the stadium but no significant peaks were observed prior to pharate stage. An ecdysteroid peak (29.8 ng/ml of haemolymph) was identified in pharate immaculate larvae.Pupal development could be completely prevented in 26.7% of nondiapause-bound larvae as late as 4 days into the last instar by topical application of ZR-515. This indicates that the commitment to pupation as revealed by 20-hydroxyecdysone injection is reversible.     

Comparative studies on ecdysone metabolism between mature larvae and pharate pupae in the fleshfly,Sarcophaga peregrina

Metabolites of radioactive ecdysone or 20-hydroxyecdysone in larvae and pharate pupae of Sarcophaga peregrina were separated and identified by using thin-layer chromatography, high-performance liquid chromatography, and chemical methods. At the larval stage ecdysone was metabolized to biologically less active ecdysteroids predominantly through 20-hydroxyecydsone, at the pharate pupal stage, to other ecdysteroids which were tentatively identified as 26-hydroxyecdysone, 3-epi-26-hydroxyecdysone, and 3-epi-20,26-dihydroxyecdysone. Ecdysteroid acids were found in the polar metabolites during pharate pupal-pupal transformation, but scarcely detected in the larval metabolites. These acids were presumed to be ecdysonoic acid, 20-hydroxyecdysonoic acid, and their epimers. The conjugates of ecdysteroid that released the free ecdysteroids by enzymatic hydrolysis were produced more in larvae than in pupae, whereas the very polar ecdysteroids that were not affected by the enzyme were found more in pupae. Therefore, there are different metabolic pathways of ecdysone between these two successive developmental stages, and the alteration of the metabolic pathway may serve as one of the important factors in a regulatory mechanism of molting hormone activity which is responsible for normal development of this insect.