The influence of juvenile hormone on the feeding behaviour of last instar larvae of the codling moth,Laspeyresia pomonella (Lep., Tortricidae), reared under different photoperiods

Summary Duration of the feeding stage and corresponding weight increase during the last larval instar of the codling moth,Laspeyresia pomonella, are controlled by JH. Larvae reared under short day conditions have a relatively high titer of JH during the last larval instar and enter diapause as mature larvae. They feed longer and become heavier than larvae reared under long day conditions, which have no JH during the last larval instar and pupate when mature. By application of the JH mimetic Altosid^® during the first 2 or 3 days of the last larval instar, the duration of feeding activity of larvae reared under respectively long and short day conditions was prolongated and the larvae became significantly heavier. The feeding behaviour could only be influenced by the juvenoid as long as the feeding activity of the larvae had not yet ceased.     

Effects of a juvenile hormone mimetic,fenoxycarb, on post-embryonic development of the European corn borer,Ostrinia nubilalis Hbn.

Summary The effect of a juvenile hormone mimetic, fenoxycarb, Ro 13-5223, was tested on the larval instars of the European corn borer,Ostrinia nubilalis, by dipping or topical application. When larvae were treated in instars 2, 3 or 4, the duration of the fifth instar was modified. More permanent and fewer supernumerary larvae were obtained when treatment occurred in the early instars. This non-neurotoxic compound exhibited a strong dose-dependent juvenile hormone type of activity when it was applied to last instar larvae. Fenoxycarb prevented the onset of pupation and produced supernumerary larvae and intermediates. Permanent larvae were obtained if fenoxycarb was applied on day 0 or day 1 of the last instar. The use of such a JH mimetic in the understanding of endocrine control of diapause is discussed.     

Age-dependent tolerance toBaculovirus in last larval instars of the codling moth,Cydia pomonella,L., induced either for pupation or for diapause

Summary LD₅₀ values as well as time-dependent parameters of granulosis virus infections were determined at different times during the last larval instar (L₅) of the codling moth,Cydia pomonella L., induced either for pupation or for diapause. A significant increase of tolerance to virus was found in 48-h-old L₅ induced for pupation, and 24 h later in L₅ induced for diapause.     

Juvenile hormone titers in penultimate and last instar larvae ofPieris brassicae andBarathra brassicae,in relation to the effect of juvenoid application

Summary JH titer was determined in the haemolymph of penultimate and last instar larvae ofPieris brassicae L. andBarathra brassicae L. The differences we observed were consistent with physiological differences between the two species.The authors feel indebted to Prof.V. J. Brookes for useful comments.     

The alteration of juvenile hormone titre inSpodoptera litura (F.) due to a baculovirus infection

Summary The haemolymph juvenile hormone levels ofSpodoptera litura were remarkably low (540 Galleria units (GU)/ml) at the last larval moult as well as prior to pupation (194 GU/ml). During the last intermoult period this was 2600 GU/ml for a 24 h-period. On the other hand, the JH level in the haemolymph of NPV-infected last instar larvae was initially 1740 GU/ml but was maintained at 2400–2600 GU/ml during the next 48 h. Finally, the JH titre fell to 1393 GU/ml, but only prior to death. The failure of the diseased larvae to undergo the larval pupal moult is ascribed to the alteration of the JH titre in the haemolymph.     

Oenocyte and prothoracic gland activity inManduca sexta under varying photoperiod and light conditions

Summary Manduca sexta larvae were subjected to diapause-inducing and diapause-preventing photoperiods, using two types of fluorescents (Indorsun and Blacklight-blue). The oenocytes, prothoracic glands (PTG) and ecdysone levels were examined in 3-day-old 5th instar larvae, 2-day-old and 10-day-old pupae. Our results indicate that oenocytes and PTG cells tend to be more active under long photoperiods while oenocytes only are active under short photoperiods in pupae in diapause. UV light has a definite effect on oenocytes while PTG cells seem to be unaffected. Ecdysone and ecdysterone levels vary with PTG and oenocyte activity at the pupal stage. The significance of these findings is discussed.This work was supported by a research associateship to L.M. by the People's Republic of China and a grant from NSERC to B.J.R.P.     

Juvenilizing effect of ecdysone mimic RH 5849 inGalleria mellonella larvae

The response of the final instar larvae ofG. mellonella to topical application of the non-steroidal ecdysone mimic, RH 5849, was age-related as well as dose-dependent. In young final instar larvae, moderate doses of RH 5849 induced perfect supernumerary larval moults, but doses equal to and higher than 8.5 μg per larva caused premature formation of larval cuticle and were lethal. Application of RH 5849 significantly increased allatotropic activity of the brain, and also activated synthesis of juvenile hormone (JH) by the corpora cardiaca/corpora allata complex. Simultaneous application of RH 5849 and FMev, a potent inhibitor of JH synthesis, to young final instar larvae lowered the incidence of perfect supernumerary larval moults. We conclude that the effect of RH 5849 on the developmental programme inG. mellonella is mediated by the corpora allata.     

Reversible juvenile hormone inhibition of ecdysteroid and juvenile hormone synthesis by the ring gland ofDrosophila melanogaster

Juvenile hormone bisepoxide (JHB₃) and juvenile hormone III (JH III) both inhibited the in vitro production of ecdysteroids by ring glands and brain-ring gland complexes from third instar post-feeding larvae ofDrosophila melanogaster in a reversible manner, although JHB₃ had greater efficacy. The JH III and JHB₃ precursor, methyl farnesoate, did not affect ecdysteroid production. The in vitro synthesis of total detectable JH (JHB₃+JH III+methyl farnesoate) by the corpus allatum portion of the isolated ring gland was also inhibited reversibly in the presence of exogenous JHB₃ and JH III, but not by methyl farnesoate. These data indicating negative feedback are in agreement with the accepted dogma of endocrine gland regulation.     

Juvenile hormone I is the principal juvenile hormone in a hemipteran insect,Riptortus clavatus

Juvenile hormone I (JH I) was identified by combined gas chromatography/mass spectrometry as the predominant JH in the hemolymph of female adults of the bean bug,Riptortus clavatus (Thunberg) (Hemiptera: Alydidae). Among JH I, II, and III, JH I was the most effective hormone for inducing the synthesis of yolk proteins in diapause adults.     

Role of low ecdysteroid levels in the early last larval instar ofBombyx mori

The relationship between juvenile hormone and ecdysteroid titers during the early stage of the last larval instar of the silkworm,Bombyx mori, was examined in this study. When larvae were fed 20-hydroxyecdysone-supplemented mulberry leaves throughout the last larval instar, 100% underwent supernumerary larval molting instead of metamorphosis. The application of juvenile hormone mimic during the early last instar did not induce supernumerary larval molting, but did delay metamorphosis. Temporal and quantitative ecdysteroid titer measurements revealed that in normal larvae the titers maintained very low levels (3–12 ng/ml) during the early stage of the last instar; however, in 20-hydroxyecdysone-treated larvae, levels ranging from 24 to 45 ng/ml were detected, and a major peak (246 ng/ml) was observed on day 6. These results show that very low ecdysteroid titer levels during the early stage of the last larval instar may play an important role in initiating decreases in juvenile hormone titers as well as in directing metamorphosis.     

La croissance cellulaire de quelques tissus au cours des trois derniers stades larvaires dePieris brassicae L. (Lepidoptera: Pieridae)

Summary The cellular growth of certain tissues in last 3 instar larvae ofPieris brassicae L. was studied in relation to moult, body growth and also with variations in the size of prothoracic gland.     

Head critical period and juvenile hormone titre during the last larval instar of the cockroach,Periplaneta americana

From neck ligation experiments with last instar larvae of the cockroachPeriplaneta americana it was concluded that the head critical period is reached around day 17, which corresponds to 59% of the last larval stage. At the same stage the juvenile hormone III titre in the hemolymph dropped to undectable levels.     

Tissue distribution of juvenile hormone hydrolytic activity inGalleria mellonella larvae

Summary Juvenile hormone (JH) hydrolytic activity was determined in different tissues of day-4 last instar larva ofGalleria mellonella. Midgut, gonad, imaginal wing discs and fat body contain higher JH hydrolytic activity than hemolymph, while silk gland and body wall have lower activity. JH esterase activity in imaginal wing discs exhibits a pattern of age-related changes different from that of the hemolymph.We acknowledge the support of this research by the National Institutes of Health (GM 22429) and the Johnson Wax Foundation. Address to which reprint requests may be sent.     

Brain factor fromGalleria mellonella (Lepidoptera) stimulating silk gland activity

Brain extracts from day 1–4 last instar larvae ofGalleria mellonella (Lepidoptera) stimulate RNA synthesis in cultured silk glands from day 3 last instar larvae. When the fibroin-synthesizing posterior parts of silk glands were incubated for 3 h in vitro in the presence of brain extract (0.1 brain equivalent), [³H]-uridine incorporation into RNA was stimulated more than twofold. The stimulating effect of brain extract showed a dose response relationship. It is suggested that the heat-resistant and protease-sensitive brain factor is a peptide.     

Mixed life cycles in the transitional zone between voltinisms in the fall webworm,Hyphantria cunea

The fall webworm,Hyphantria cunea Drury, was introduced from North America into Japan at half a century ago. At present, the populations north of 36° N are bivoltine and those south of 36° N are trivoltine. In the present study, the life cycle in the transitional zone between voltinisms was clarified in Tsukuba (36.1° N). When fourth instar larvae of the second generation were collected in the field and maintained in the laboratory, the incidence of pupal diapause increased when the sampling date was delayed from 16 August to 5 September. The fact that some developed without diapause inidcates the occurrence of a trivoltine life cycle in this locality, where a bivoltine life cycle is predominant. The critical photoperiod for diapause induction at 20 and 25°C was 14 h 13 min and 14 h 10 min, respectively. The photoperiodic response may explain the rapid increase in diapause incidence in late summer. In laboratory-reared diapause pupae, the time and period of chilling (5°C) greatly influenced the time required for adult emergence at the final incubation temperature of 25°C. However, diapause pupae chilled for a sufficiently long period developed to adulthood rapidly, irrespective of the conditions before chilling. Therefore, the difference in timing of entering diapause between pupae of the second and third generations would not result in their temporal reproductive isolation in the following spring. It is concluded that the mixed voltinism in Tsukuba is not a result of a mixture of genetically distinct bivoltine and trivoltine populations, but a result of the phenotypic plasticity in a genetically rather homogeneous population.     

Existe-t'il une action particulière des différentes longueurs d'onde du spectre visible sur la physiologie des chrysalides et prénymphes dePieris brassicae conditionnées à la diapause?

Summary Pieris brassicae larvae were reared under 9 h/24 h white light and 20°C (conditions determining the diapause status). From the pupal moult they were exposed for 20 days under different wavelengths (absorbed or not by the green integumentary pigment: pterobilin). This treatment has no effect on diapause.     

Influence of oxygen concentration on development ofDrosophila melanogaster

Summary 1st, 2nd, and early 3rd instarDrosophila larvae are extremely sensitive to 100% O₂ or 75% O₂/25% N₂ (at atmospheric pressure) whereas eggs, late 3rd instar larvae, and pupae are relatively insensitive under our exposure conditions. Eclosing flies exposed to an O₂ enriched environment consistently possessed 2 eye abnormalities: dark eye color and altered eye shape.Supported by NSF-URP grant SP1782684 and a Summer Faculty Fellowship to Harry Nickla.     

Juvenile hormone catabolism inManduca sexta: Homologue selectivity of catabolism and identification of a diol-phosphate conjugate as a major end product

We studied time-dependent metabolism of (10R)-[³H] juvenile hormone (JH) III and (10R, 11S)-[³H]JH I injected intoManduca sexta larvae; the hormones are metabolized to polar metabolites, expecially the JH acid-diol, and an unknown. Products were analyzed using a reversed-phase liquid chromatography assay. (10R)-JH III is metabolized much more rapidly than (10R, 11S)-[³H]JH I, whether injected seperately or as a mixture of hormones. The unknown metabolites of JH I and JH III were identified as phosphate conjugates of JH I and JH III diol by tandem mass spectral analysis of isolated samples. The phosphate conjugate of JH I diol is the principle end product of JH I metabolism.     

Zuchtmethode und semisynthetische Nährmedien für Apfelwickler

Summary A method for the individual rearing of the codling mothLaspeyresia pomonella is described. The method allows the collection of exactly dated eggs and the rearing of a large number of larvae in a small space. By using the second medium described, it is possible to watch all developmental stages at any time without disturbing them. The average larval survival rate is 70–80%.     

Protein content of various developmental stages of three strains of the pink bollworm,Pectinophora gossypiella

Summary Comparison of the total body protein of male and female larvae, pupae, and adults of a diapause and 2 nondiapause strains of the pink bollwormPectinophora gossypiella indicated that the protein content of larvae of the diapause strains was significantly higher than of the non-diapause strain.I thank Drs D.R. Nelson and R.A. Bell of the U.S.D.A. Metabolism and Radiation Research Laboratory, Fargo, for facilities and guidance.