Induction of autotomy in the American bird grasshopperSchistocerca americana (Drury) by the ecdysone agonist RH-5849 and investigation of its mode of action

The non-steroidal ecdysone agonist RH-5849 (1,2-dibenzoyl-l-tert-butylhydrazine) was found to be an effective neurotoxicant on injection into the American bird grasshopper,Schistocerca americana (Drury). Treated grasshoppers became immediately hyperactive, followed by loss of coordination, paralysis and eventually death. We also discovered that this compound induced bilateral autotomy of the metathoracic legs during the early stages of intoxication. However, no evidence of ecdysonergic or morphogenetic activities was observed. Synergism studies with neurotoxins of known mode of action suggested that RH-5849 has a mechanism of action similar to that of 4-amino pyridine, which blocks potassium channels.     

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.     

Precocene-induced metamorphosis in the desert locustSchistocerca gregaria

Summary 50–100% of the 2nd, 3rd and 4th instar nymphs ofSchistocerca gregaria exposed to precocene 2 by contact method metamorphosed precociously from the instar treated. The corpora allata of the precocious adults were degenerate. Topical application of a juvenile hormone analogue (ZR-512) induced in the precocious adults the colouration characteristic of sexually mature adults.This research was supported by the N.S.E.R.C. grant No.A4669.We thank Dr G. B. Staal, Zoecon Corporation, Palo Alto, California, for the generous gift of precocene 2 and ZR-512, M. Hota for rearing the insects, R. G. Long, for the photographs, and Jann Aitken for technical assistance.     

Titers of ecdysone, 20-hydroxyecdysone and juvenile hormone III throughout the life cycle of a hemimetabolous insect,the ovoviviparous cockroachNauphoeta cinerea

Summary Titers of ecdysone, 20-hydroxyecdysone and juvenile hormone III were measured in whole body extracts or hemolymph of embryos, first, penultimate and last stadium nymphs, and adult females ofNaupoheta cinerea. We used a gas-chromatography/mass spectrometry method for quantifying juvenile hormone and a radio-immunoassay for ecdysteroid determination. Juvenile hormone III is particularly abundant in the embryonic stage (up to 960 ng/g), at a low level in first and penultimate stadium nymphs (2–10 ng/ml) and almost absent in the last nymphal stadium; in the adult female the juvenile hormone titer rises to 180 ng/ml in hemolymph during rapid oocyte growth. The titers of ecdysone and 20-hydroxyecdysone undergo similar fluctuations in the embryonic and nymphal stages, being highest at the time of cuticle formation in the embryo and a few days before the nymphal and adult molts (around 100–200 ng/ml for exdysone and 2–4 g/ml for 20-hydroxyecdysone).Acknowledgments. We thank Mrs A. Tschan for rearing the cockroaches, Mr M. Kaltenrieder for drawing the graphs, Mr G.C. Jamieson and Mrs C. Reuter for GC/MS analyses. We are also grateful to the Swiss National Science Foundation (grant no. 3.291-0.82 to B. Lanzrein) and the United States National Science Foundation (grant no. PCM 82-08665 to D.A. Schooley) for their financial support.     

Effects of the pyrimidine-containing cytochrome P-450 inhibitor,fenarimol, on the formation of 20-OH ecdysone in flies

Summary The effect of fenarimol, a pyrimidine-containing cytochrome P-450 inhibitor, was tested in vitro on brain-ring gland complexes ofCalliphora vicina (Dipt., Calliphoridae), and on microsomes prepared from the fat body of 0-h wandering stage larvae ofNeobellieria bullata (Dipt., Sacrophagidae). Fenarimol had no influence on the formation of ecdysone, but it was an effective inhibitor of cytochrome P-450-dependent ecdysone 20-monooxygenase.     

Activité protéosynthétique des glandes prothoraciques et titre d'ecdysone chez des larves permanentes deLocusta migratoria obtenues par irradiation sélective du tissu hématopoïétique

Summary The prothoracic glands of permanent fifth instar larvae ofLocusta migratoria (moulting blocked by selective X-ray treatment of the hemocytopoietic tissue) are in a state of high activity as evidenced by the rate of incorporation of a labelled amino-acid into the proteins synthesized in these glands. Such permanent larvae apparently synthesize no ecdysone nor ecdysterone.     

Instar-specific defensive secretions of stink bugs (Heteroptera: Pentatomidae)

Defensive secretions (allomones) from first-instar nymphs of stink bugs in the subfamily Pentatominae contain (E)-4-oxo-2-decenal as a major constituent, whereas this compound is absent from later instars. In contrast, first instars ofEdessa meditabunda (Edessinae) produce allomones like those of later instars. The C₆ and C₈ (E)-4-oxo-2-alkenals are common, characteristic exocrine compounds of nymphal and adult Heteroptera, but (E)-4-oxo-2-decenal is previously unknown as a major natural product for which a biological role has yet to be established.     

Effects of the adenylate cyclase activator forskolin and its inactive derivative 1,9-dideoxyforskolin on insect cytochrome P-450 dependent steroid hydroxylase activity

The adenylate cyclase activator forskolin and its pharmacologically inactive derivative 1,9-dideoxyforskolin were found to inhibit in a dose-dependent fashion the ecdysone 20-monooxygenase activity associated with wandering stage larvae ofDrosophila melanogaster and fat body and midgut from last instar larvae of the tobacco hornworm,Manduca sexta. The concentrations of these labdane diterpenes required to elicit a 50% inhibition of the cytochrome P-450 dependent steroid hydroxylase activity in the insect tissues ranged from approximately 5×10^–6 to 5×10^–4 M.     

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.     

Morphogenetic effect of precocene I and II onSchistocerca gregaria (Forsk)

Summary 4th instar nymphs ofSchistocerca gregaria exposed to precocene I and II by topical application metamorphosed precociously. The ED₅₀ of both compounds were evaluated and, unexpectedly, precocene I was found to be more active than precocene II. All adultiforms were identical and in an advanced form.Acknowledgments. This work was supported by grants from the Natural Sciences and Engineering Research Council of Canada and the Ministère de l'Education du Québec. We are grateful to Gaston Grégoire for rearing the insects.     

Inhibition of Y-chromosome loop formation in primary spermatocyte nuclei ofDrosophila hydei by trimethylphosphate

Summary Primary spermatocyte nuclei of either late 3 instar larvae or newly eclosed adult males ofD. hydei contain lampbrush loops which are associated with Y-chromosome fertility factors. Formation of the loops is inhibited by continual larval development on food medium containing 0.008 M, or more, trimethylphosphate (TMP) and is accompanied by disruption to spermiogenesis.     

Moult inhibition in the insectDysdercus cingulatus (Insecta: Heteroptera) by the cerebral glands of the millipedeJonespeltis splendidus (Myriapoda,Diplopoda)

Summary Implantation of 2 pairs of cerebral glands of the diplopodJonespeltis into the newly-moulted 4th or 5th instar nymphs of the insectDysdercus delayed the moulting of these insects for a fairly long time. Implantation of cerebral glands into 1-day old 5th instars postponed the subsequent moult for a shorter period, whereas implantation of cerebral glands into 2-day old 5th instars had no effect. These observations suggested that a neurosecretory factor from the cerebral glands inhibited moulting in this insect, and in the case of 5th instar nymphs there was a critical period before which implanted glands were effective in moult inhibition.Acknowledgments. Prof. V.K.K. Prabhu is thanked for suggesting the topic and for guidance. The University of Kerala is thanked for the fellowship awarded. The laboratory facilities afforded are also gratefully acknowledged.     

Sexual behavior without adult morphogenesis inLocusta migratoria

Summary Injection of azadirachtin into young Vth (=last) instarLocusta hoppers inhibits molt and a considerable portion of the animals survice for more than 40 days as over-aged nymphs; in contrast, the duration of the Vth instar is 8–10 days in normal controls. Males of over-aged nymphs exhibit adult sexual behavior, and injection of juvenile hormone intensifies this behavior. The results demonstrate that the terminal molt leading to morphogenetic adult differentiation is not necessary for an adult behavioral pattern to develop, and/or to become overt, in a hemimetabolous insect.We thank Prof. H. Rembold for a generous gift of azadirachtin and Mr Y. Toren for keeping the locust culture.     

Variations des taux d'ecdystéroïdes au cours du développement deBombyx mori; rapport entre ces variations et les phases de croissance et de morphogenèse

Summary During the development ofBombyx mori (monovoltin race) ecdysteroid levels were determined in oocytes, eggs, and haemolymph of larvae, and in the haemolymph of pupae. In haemolymph, the only RIA reactive materials are ecdysone and ecdysterone. In oocytes and eggs, other ecdysteroids are also detected. During larval instars, the ecdysteroid levels are low whereas they are very high during morphogenetic periods. During embryonic diapause, the ecdysone titer decreases during the cessation of morphogenesis.     

Biological activity of flucycloxuron,a novel benzoylphenylurea derivative,onTenebrio molitor: comparison with diflubenzuron and triflumuron

Flucycloxuron, a novel benzoylphenylurea (BPU) derivative, exhibited insecticidal activity when injected into newly ecdysed pupae ofTenebrio molitor. Mortality occurs because of defective adult ecdysis. Treatment caused a reduction in both cuticle thickness and incorporation of¹⁴C-labelled precursor into chitin, although it had no significant effect on the protein synthesis. The potencies of other BPU compounds as inhibitors of chitin biosynthesis have been examined and results showed that diflubenzuron was less effective than either flucycloxuron or triflumuron.     

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.     

Effets de l'intoxication par le lindane sur les corpora allata deLocusta migratoria (Orthoptère)

Summary The corpora allata of adult and 5th instar nymphs of the migratory locust exhibit several ultrastructural alterations after lindane intoxication. The type of cell degeneration observed here is very similar to ultrastructural changes obtained after the administration of precocene.     

Juvenile hormone in larval diapause of the codling moth,Laspeyresia pomonella L. (Lepidopterae,Tortricidae)

Summary Whereas in last instar larvae ofL. pomonella kept under long-day-conditions (LD), the JH-titer is temporarily reduced to zero, it stays relatively high in short-day-conditioned (SD) larvae which enter diapause. Application of JH or a juvenoid to LD-larvae results in diapause, if the treated insects are kept under SD-conditions. From these results it is concluded that inL. pomonella diapause is initiated by a relatively high titer of JH during the last larval instar.     

Preliminary observations of a bacteriophage infectingXenorhabdus luminescens (Enterobacteriaceae)

A bacteriophage infective toXenorhabdus luminescens, a bacterial symbiont of heterorhabditid nematodes, was recovered from insects that supported poor nematode development. Plaque tests showed the phage particles to be infective only to primary and not secondary colonies ofX. luminescens. The phage was not infective toX. nenatophilus primaries or secondaries. The bacteriophage particles ranged 80–90 nm in length, with the head ranging from 40 to 50 nm in diameter. Restriction analysis was performed on isolated bacteriophage DNA. This first report of a bacteriophage fromXenorhabdus species has pratical implications since it could be detrimental to cultures ofHeterorhabditis nematodes that are being produced throughout the world for the biological control of insects.