Precocious metamorphosis of the aphid Myzus persicae induced by the precocene analogue 6-methoxy-7-ethoxy-2,2-dimethylchromene

For up to three days after being treated with the precocene analogue 6-methoxy-7-ethoxy-2,2-dimethylchromene, adult green peach aphids (Myzus persicae) gave birth to offspring (alate and apterous virginoparae, males) which underwent precocious metamorphosis. Only a few precocious gynoparae and no precocious oviparae were recorded. The precocious aphids became adultoid in the third or fourth-instar as a result of corpus allatum destruction. They were able to develop mature embryos, but could not deposit them because of incomplete differentiation of the reproductive tract. The treatment did not induce the production of alate virginoparae in the experimental clone of Myzus persicae. However, a few males were born late in the reproductive sequence of treated apterae. The corpora allata of the treated adults appeared on histological examination to be unaffected by precocene.     

Photoperiodic determination of the male and female sexual morphs of Myzus persicae

The chronology of the photoperiodic determination of sexual morphs in holocyclic Myzus persicae was studied in the laboratory by transfer of synchronized batches of aphids between long-day (16 hr) and short-day (10 hr) régimes at a constant temperature of 20°C. The length of exposure to the short-day régime was measured in terms of the number of long dark-periods received by the aphids. The photoperiodic response extended over four generations (P, G₁, G₂, and G₃ respectively). When P generation aphids were given short days from the fourth instar, alate viviparae and males appeared successively in generation G₂, oviparae in G₃. Increasing the number of long dark-periods received during the development of G₂ embryos had a cumulative effect on the number which developed into alate viviparae. Determination of all the first-born G₂ aphids as alatae occurred only if their mothers had been exposed to the short-day régime throughout larval development. Alate viviparae gave birth to oviparae if they received a minimum of 4 long dark-periods, starting from a late stage in their embryonic development. The critical stage for ovipara determination in the G₃ embryo was on the sixth or seventh day after ovulation, more than half-way through embryonic development. G₂ aphids were determined as males before ovulation if their parents received 4 (in some circumstances only 3) long dark-periods. In the clones studied, male determination, once initiated in the G₁ parent, could not be reversed by later back-transfer to the long-day régime.     

The activity of the corpora allata in the fourth and fifth larval instars of the migratory locust

The presence of juvenile hormone in the haemolymph of larvae of Locusta has been detected by a modified Galleria bioassay and these results are compared with indirect methods of estimating corpus allatum activity. Juvenile hormone is present in the haemolymph during the fourth larval instar except on the last day of the instar, and is absent from the haemolymph of the fifth and final larval instar except on the last day of the instar. Changes in the volumes of the corpora allata simply reflect changes in the growth of the whole insect and are of no value in predicting endocrine activity. Changes in the size of the cells of the corpora allata can be correlated with the presence of juvenile hormone in the haemolymph in the fourth larval instar, but similar changes in cell size occur in the fifth larval instar when no juvenile hormone is present in the haemolymph. The effects of the implantation of corpora allata are unreliable as estimates of corpus allatum activity as isolated corpora allata from fifth instar larvae release juvenile hormone. Indirect methods of measuring corpus allatum activity are thus shown to be unreliable. The R_f value of Locusta juvenile hormone as determined by thin-layer chromatography differs from that of Roeller's juvenile hormone, suggesting that the two hormones might be chemically distinct.     

Precocene sensitivity of corpora allata in adult female Locusta migratoria after electrocoagulation of the pars intercerebralis neurosecretory cells

Destruction, by electrocoagulation, of the median neurosecretory cells of the pars intercerebralis of 2-day old adult female Locusta migratoria completely suppressed normal juvenile hormone-biosynthetic activity of the corpora allata in most animals. For example, 6 days after electrocoagulation the rates of spontaneous juvenile hormone biosynthesis, measured by radiochemical assay of freshly isolated glands, showed a median value of less than $\text{1}\text{100}$ that of the corresponding sham operated controls, which were then in mid-vitellogenesis. Injection of graded doses (200–1600 μg) of precocene I at this time, followed by assays five days later, resulted in a similar decline of both corpus allatum volume and precocene epoxidase activity (measured by radiochemical assays of precocene I dihydrodiol formation in vitro) in pars intercerebralis-coagulated and sham-operated animals, when expressed as a percentage of their own zero precocene controls. Electrocoagulation of the pars intercerebralis largely prevented the normal increase in both corpus allatum volume and its epoxidase activity, so that by age 13 days these parameters were about 2.5-fold lower in coagulated vs control (sham operated) animals. In fact, electrocoagulation had no marked effect on the value of epoxidase activity per unit corpus allatum volume. It is concluded that the corpora allata from this species and stage are sensitive to precocene irrespective of whether they are active in biosynthesis of juvenile hormone.     

Probable mechanism of sexual dimorphism in insulin control of Drosophila heat stress resistance

Adult males of Drosophila species (Drosophila melanogaster L. and Drosophila virilis) show a lower tolerance to heat stress compared with females. The present study investigates the effects of RNA interference (RNAi) knockdown of the insulin‐like receptor in the corpus allatum of D. melanogaster males on dopamine metabolism and content, heat stress resistance and juvenile hormone metabolism. In male flies, the knockdown of insulin‐like receptor in the corpus allatum is shown to change metabolism of juvenile hormone but not dopamine. It is also shown that knockdown of the insulin‐like receptor in the corpus allatum results in a decrease of heat stress resistance in females but not males, and that juvenile hormone rescues this decrease. The results suggest that at least one of the ways in which insulin‐like growth factors affect heat stress resistance is by successive mediation through juvenile hormone and dopamine, which could lead to sexual dimorphism in the trait.     

The role of endocrines in flight-muscle degeneration in Dysdercus cingulatus (Heteroptera: Pyrrhocoridae)

In Dysdercus cingulatus, extirpation of the median neurosecretory cells inhibits flight-muscle breakdown. However, implantation of median neurosecretory cells or corpus allatum into females lacking these neurosecretory cells induces muscle histolysis. Median neurosecretory cells stimulate the corpus allatum to produce juvenile hormone which in turn induces muscle degeneration. Topical application of kinoprene induces muscle breakdown, even in males and starved virgin females. The direct participation of juvenile hormone in muscle degeneration is further confirmed by observations on the effect of precocene II which inhibits muscle histolysis in many individuals. The endocrine basis of vitellogenesis and flight-muscle degeneration could be identical; vitellogenesis however appears to require a higher threshold concentration of juvenile hormone.     

Effects of prococene II on the nutritional physiology of last instar Heliothis zea larvae

When precocene II was fed to last instar larvae of Heliothis zea, it caused significant reductions in the calculated rate of growth, rate of nutrient assimilation, and conversion of ingested and digested food to body mass. No change in the rate of food consumption occurred but respiration was significantly higher. Transport of the nutrient [1-¹⁴C] linoleic acid across midgut tissue was hindered when larvae were fed precocence II. There was also a precocene-induced change in the apical (luminal) morphology of midgut cells, including absence of the glycocalyx and loss of the microvillar absorptive surface. The influence of precocene II on the midgut physiology and metabolic processes in last instar larvae of H. zea may account for the observed reduced growth and delayed development. © 1992 wiley-Liss, Inc.     

The effects of corpus allatum implantation on the development of flight muscles and fat body in Locusta migratoria

Implantation of corpora allata early in the fifth instar of female larvae of Locusta migratoria results in a faster development both during the last instar and the adult somatic growth period. The adult locusts attain a significantly higher maximum wet weight. The increase in dry weight, however, is smaller than in control insects. So the high titer of corpus allatum hormone results in a considerably higher water content.In CA-implanted locusts the growth of the indirect dorsal longitudinal flight muscles is inhibited and the protein content is lower as compared with control specimens. Especially the differentiation of these muscles is strongly inhibited. A hypothesis for a regulation of the indirect flight muscle development by the changing titer of the corpus allatum hormone is proposed.During the second part of the adult period investigated the high titer of the corpus allatum hormone strongly diminishes the growth of the fat body, but the protein content is not altered in comparison with the normal developing fat body. The data reveal that the influence of an induced high titer of corpus allatum hormone on protein metabolism in the flight muscles is different from that in the fat body.

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Die wirkung von corpora allata-implantation auf die entwicklung der flugmuskeln und des fettkörpers bei Locusta migratoria

Zusammenfassung Nach Corpora allata-Implantation am Anfang des L₅ von weiblichen Larven von Locusta migratoria folgt eine schnellere Entwicklung sowohl im letzten Larvenstadium als auch in der adulten somatischen Wachstumsperiode. Die adulten Heuschrecken erreichen ein signifikant höheres Frischgewicht-Maximum. Die Zunahme des Trockengewichts ist jedoch geringer als bei Kontrollen. Der hohe Titer an Corpus allatum-Hormon resultiert also in einem beträchtlich höheren Wassergehalt.Der Zuwachs der indirekten dorsalen Flugmuskeln ist in mit Corpora allata implantierten Heuschrecken gehemmt und der Eiweißgehalt ist niedriger als bei Kontrollen. Besonders die Differenzierungsphase der Muskeln ist stark gehemmt. Es wird eine Hypothese über die Regulation der Entwicklung indirekter Flugmuskeln durch den sich ändernden Titer des Corpus allatum-Hormons aufgestellt.Während des zweiten Teils der untersuchten adulten Periode nimmt das Wachstum des Fettkörpers unter dem Einfluss des hohen Hormontiters ab, aber der Proteingehalt dieses Gewebes ändert sich im Vergleich zu dem sich normal entwickelnden Fettkörper nicht.Diese Daten zeigen, daß der Einfluss eines induzierten hohen Titers an Corpus allatum-Hormon beim Proteinstoffwechsel in den Flugmuskeln anders ist als im Fettkörper.

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Abbreviations CA corpus allatum - CAH corpus allatum hormone - LFM indirect dorsal longitudinal flight muscle - Tris tris (hydroxymethyl)aminomethane     

A pharmacological and endocrinological study of female insemination inPhormia regina (Diptera: Calliphoridae)

Injections of octopamine, dopamine, and the octopaminergic agonists, clonidine and naphazoline, into the thoracic hemocoel enhanced female insemination in sugar-fed (sexually unreceptive)Phormia regina. Topical applications of the juvenile hormone (JH) analogue, methoprene, also enhanced female insemination in sugar-fed (sexually unreceptive)P. regina. Since JH plays a role in receptivity in protein-fed females, it was originally hypothesized that one agonist, clonidine, enhanced female insemination by acting on the corpus allatum (CA) to increase JH biosynthesis. Two or three doses of the antiallatal agent, precocene II, prior to administration of clonidine, did not inhibit clonidine-enhanced female insemination. Removal of the corpus allatum also did not have a significant effect on clonidine-enhanced female insemination. Measurement of juvenile hormone (JH) biosynthesis/release in corpora allata, which were removed at 1, 3, 5, and 7 h postinjection, revealed that clonidine does not affect JH biosynthesis/release. Our study reveals a possible role for the biogenic amines in female insemination in insects. We suggest that the octopaminergic agonist, clonidine, acts downstream from the corpus allatum on the regulatory mechanisms involved in female insemination.     

Precocene causes male determination in the aphid Myzus persicae

When adult apterous viviparous females of Myzus persicae, reared in short night conditions at 21–23°C, are treated with the precocene analogue 6-methoxy-7-ethoxy-2,2-dimethylchromene, they deposit males towards the end of their reproductive lives. The first-born normal daughters of the treated females also deposit some males at various times in their reproductive lives. Karyotypic analysis was used to investigate the sequence of male and female embryos in the ovarioles of precociously metamorphosed aphids. The experiments support the hypothesis (Mittler et al., 1979) that juvenile hormone level controls the sex determination process in aphids. Since male aphids have an XO sex chromosome constitution, this implies that juvenile hormone level influences the behaviour of the X-chromosomes at or before the single maturation division of the egg. At this division one X-chromosome is eliminated from eggs which will develop as males. Aphids provide the first example of a specific endocrine influence on chromosome behaviour in sex determination.     

An ultrastructural and developmental analysis of the corpus allatum of juvenile hormone deficient mutants ofDrosophila melanogaster

Summary The ultrastructure of the corpus allatum of theapterous mutantsap ⁴ andap ^56f ofDrosophila melanogaster during larval-pupal-adult metamorphosis and adult life was correlated with the gland's ability to synthesize juvenile hormone in vitro. During the early wandering period of the third instar of both mutants, a high concentration of smooth endoplasmic reticulum, mitochondria and mitochondrion-scalariform junction complexes are typical features of an active corpus allatum cell. Juvenile hormone biosynthesis by the glands is high at that time and, in fact, only slightly lower than that of wild type glands. In contrast to the wild type gland, the cells of the pupal and pharate adult corpus allatum of both mutants contains highly electron dense mitochondria with tubular cristae but no whorls of smooth endoplasmic reticulum nor glycogen clusters. The frequency and size of the lipid droplets, putatives depots of the juvenile hormone precursors, in cells of theap ^56f gland is a function of the insect's age, but both are lower than in wild type gland cells. Juvenile hormone biosynthesis by both mutant glands remains at the basal level when compared to increased synthesis by the wild type gland. The frequency and density of lipid droplets in cells of theap ⁴ corpus allatum are much lower than in theap ^56f glands. During adult life, the ultrastructural profile of theap ^56f corpus allatum is similar to that of the wild type gland although the in vitro production of juvenile hormone by the former is much lower than that of the wild type gland. The ultrastructural features of the adult corpus allatum ofap ⁴ homozygotes reveal precocious degeneration and support the view that this non-vitellogenic mutant is a juvenile hormone deficient mutation.     

Functional response of different stages of Hippodamia variegata (Col.: Coccinellidae) to Diuraphis noxia (Hemiptera: Aphididae) on two wheat cultivars

As one of the most important natural enemies of aphids, lady beetles have been widely used for the control of pest aphids. Important to the efficiency of natural enemies is their functional response to varying prey densities. In this study, the functional response of Hippodamia variegata Goeze (Col.: Coccienllidae) to different densities of Diuraphis noxia Mordvilko was examined on two wheat cultivars with different resistance levels under laboratory conditions (25 ± 1°C, 65 ± 5% RH and 16:8 L:D photoperiod). Our results revealed that all stages of H. variegata exhibited a type II functional response, in that predation decreased with increasing prey density. Searching efficiency (a) and handling time (T_h) of third instar larvae on the Sardari cultivar were 0.0285/h and 0.0079 h, while for fourth instar larvae these values were 0.0561/h and 1 × 10^?8 h, for males these values were 0.0412/h and 0.0173 h and for females were 0.059/h and 0.0168 h. The corresponding values for the back cross cultivar for third instar larvae were 0.0475/h and 0.0782 h, for fourth instar larvae were 0.0753/h and 0.0529 h, for males were 0.045/h and 0.0060 h and for females were 0.0516/h and 0.0077 h. This study demonstrated that these wheat cultivars do not have a significant effect on the functional response parameters of H. variegata life stages, except for the searching efficiency of third instar larvae and the handling time of male adults. The possible application of this species against Russian wheat aphids in an integrated pest management programme is also discussed.     

Precocious metamorphosis and wing formation in the pea aphid,Acyrthosiphon pisum,induced by precocene analogue 7-ethoxy-6-methoxy-2,2-dimethylchromene

Maternal treatment with 5 μg of the precocene analogue 7-ethoxy-6-methoxy-2,2-dimethylchromene influenced offspring development in the pea aphid, Acyrthosiphon pisum. Under conditions favoring the production of apterous offspring, virginoparous aphids produced a significant proportion of alates and precocious adultoids; the precocious adultoids were sterile. The effect of precocene on offspring development was temporary. Some implications of precocene treatment for aphid control are discussed.     

Precocene I and II inhibition of vitellogenic oöcyte development in Drosophila melanogaster

Adult female Drosophila melanogaster were exposed to precocene I and II, antiallatropin compounds which result in juvenile hormone deficiency in many insects. The presence of juvenile hormone in Drosophila adults was evaluated by examining vitellogenic oöcyte development, a process regulated by juvenile hormone in these flies. Both precocenes reduced the number of vitellogenic oöcytes present 43 hr after exposure in a dose-dependent manner. Precocene I was effective when applied to either newly eclosed females prior to vitellogenic oöcyte development or to gravid females. Precocene I was also effective in decapitated females, indicating that the action of the compound is not mediated by the brain. Corpus allatum volume, presumably a reflection of secretory activity, increased between 0 and 24 hr after eclosion in control females but not in precocene-treated females even after 48 hr. However, when females were removed from precocene medium, gland volumes increased within 48 hr to approximately those of control flies. This result is consistent with the reversibility of the precocene effect on Drosophila adults. These results suggest that precocene acts on the corpus allatum of Drosophila adult females to produce juvenile hormone deficiency.     

The effects of juvenile hormone, 20-hydroxyecdysone and precocene II on activity of corpora allata and the mode of negative-feedback regulation of these glands in the adult Colorado potato beetle

When the titre of juvenile hormone III in female Leptinotarsa decemlineata was elevated by the implantation of supernumerary corpora allata or by the injection of the hormone, the rate of endogenous hormone production by the host glands was significantly restrained, as determined by the short-term in vitro radiochemical assay. From denervation studies, it is suggested that during phases of elevated juvenile hormone titre, the corpus allatum activity is regulated via humoral as well as neural factors requiring intact nerve connections. Restrainment of gland activity appears to be mainly via the neural pathway. Isolated corpora allata were not influenced by 10^?5 M juvenile hormone III added to the incubation medium in vitro.Studies with farnesenic acid revealed that the final two enzymatic steps in the biosynthetic pathway of juvenile hormone are also diminished during prolonged neural inhibition of the corpora allata.20-Hydroxyecdysone and precocene II had no apparent effect on the corpus allatum activity of Leptinotarsa decemlineata.     

Chemical allatectomy of late Locusta embryos by a synthetic precocene and its effect on hopper morphogenesis

The anti-allatin substance, 7-ethoxy-precocene II (= “precocene III”) was topically applied to eggs of Locusta migratoria migratorioides with fully grown embryos in stage XX (about 64 ± 4% of the whole period of egg development). A day after precocene application the eggs were washed for 10–15 s in acetone and then transferred to clean containers for removing precocene residues and for preventing contamination at hatching. The treatment induced prothetelic morphogenetic disturbances which became overt in the subsequent hoppers; the effect was dose dependent and the ED₅₀ (= effective anti-allatin dose 50%) was low, 20.5 μg precocene III per g fresh egg weight (= 0.37 μg per egg). Quite similar results were obtained following application of precocene III to eggs with embryos in stage XXI (73 ± 4% of the egg development). These findings and direct examination of histological sections of the embryonic corpora allata demonstrated that precocene chemically allatectomizes late Locusta embryos. The lethal effect of precocene III was dependent on the washing. When the eggs were washed in acetone a day after application, mortality did not occur in a dose-dependent way; even the highest dose applied, 256 μg precocene III per egg (= 14405 μg per g fresh weight), was less than the LD₅₀ (lethal dose 50%). In contrast, without washing mortality was dose dependent, but it occurred later, at or after hatching; the LD₅₀ was 1334.9 μg per g (= 22.7 μg/egg). The results show that the late embryos are highly susceptible to the anti-allatin effect of the precocene, but are extremely insusceptible to its lethal effect; toward hatching, however, susceptibility to the lethal effect becomes marked.With doses between 45–14405 μg precocene III per g fresh egg weight, the anti-allatin effect became overt by a quite-uniform belated morphogenetic response. All hoppers which hatched from precocenetreated eggs were morphogenetically normal in the 1st instar and in the beginning of the 2nd instar, but the duration of the 2nd instar was almost doubled and at the end of this instar over 96% of the locusts died in the moult, being unable to shed the exuvia. Artificial removal of the apolyzed old cuticle revealed 3rd instar prothetelic adultiforms. These results and some data in the literature indicate that allatectomy of the embryo does not result in prothetelic morphogenetic disturbances in the 1st and early 2nd instar larvae and may impose the question what is the role of the juvenile hormone in late embryos and early larvae.     

Juvenile hormone synthesis by ring glands of the blowfly Lucilia cuprina

The major radiolabelled product released from ring gland and brain-ring gland complexes of third instar larval and pre-pupal stages of the sheep blowfly Lucilia cuprina upon incubation with L-[methyl-³H]methionine corresponded to one diastereomer of juvenile hormone III bisepoxide (JHB₃). Endocrine glands incubated with the juvenile hormone precursor 2E,6E-farnesoic acid released increased quantities of JHB₃, together with significant amounts of juvenile hormone III but not the isomeric methyl 2E-6,7-epoxyfarnesoate. Synthesis of JHB₃ was developmentally and neurally regulated. Ring glands and brain-ring gland complexes from third instar larvae released more JHB₃ than comparable preparations from pre-pupae, while isolated corpus allatum segments of the gland were more active than intact brain-gland complexes. These results reinforce the emerging status of JHB₃ as the characteristic juvenile hormone of dipteran insects. Arch. Insect Biochem. Physiol. 34:239–253, 1997. © 1997 Wiley-Liss, Inc.     

Juvenile hormone biosynthesis by corpus cardiacum-corpus allatum complexes of larval Lymantria dispar

• 1.1. A radiochemical assay was used to examine juvenile hormone (JH) synthesis and secretion in vitro by incubating two pairs of larval corpus cardiacum-corpus allatum complexes (CC-CA) from, Lymantria dispar, in 50 μl of osmotically balanced Grace's medium containing 1 μC1 [³H-methyl]-methionine for 6 hr.
• 2.2. For CC-CA of fourth instar female larvae, maximal incorporation of ³H-methyl was 0.15 pmol/pr/hr between days 2 and 3. High pressure liquid chromatographic (HPLC) analysis suggested that the biosynthetic products are mainly JH III with a little JH II at times.
• 3.3. For CC-CA of last instar female larvae, incorporation of ³H-methyl was 0.48 pmol/pr/hr at the beginning of the stadium and decreased to negligible levels by day 10. HPLC analysis suggested that CC-CA of last instar larvae produced only JH III. Volume increases in CA during the last instar were associated with declining activities of JH secretion.
• 4.4. Comparisons of maximal rates of ³ H-methyl incorporation by each unit volume of CA revealed that in the last instar each unit volume (μm³) of glandular tissue secreted 50% more JH than in the fourth instar.

     

Effects of precocene II on female-specific hemolymph polypeptides in Oncopeltus fasciatus

Using polyacrylamide gel electrophoresis (PAGE) under denaturing conditions, two major polypeptides of 200,000 and 170,000 daltons were detected in the hemolymph of mature female Oncopeltus fasciatus, but they were not found in the hemolymph of males or newly emerged females. Those polypeptides constituted the two major bands of early vitellogenic oocytes; however, they were absent from the yolk of mature eggs. The slower-migrating band (200,000 daltons) appears to correspond to a vitellogenic protein already identified in O. fasciatus, whose synthesis has been suggested to be independent of juvenile hormone (JH). Treatment of newly emerged adult females with the corpus allatum cytotoxin precocene II prevented the appearance of the female-specific bands and induced an important accumulation of other proteins in the hemolymph. Yolk deposition was also inhibited in those animals. Topical application of JH to precocene-treated females restored the appearance of the 200,000 and 170,000 dalton polypeptides in the hemolymph. These results suggest that JH is required for the synthesis of female-specific polypeptides in O. fasciatus.     

Precocene-induced degeneration of the corpus allatum of adult females of the bug Oncopeltus fasciatus

Application of precocene II, either topically or by contact method, to newly emerged adult females of O. fasciatus inhibits egg maturation and induces degeneration of the corpus allatum (CA). Seven days after precocene-treatment the CA were very small. Ultrastructural studies revealed a number of disintegrating nuclei, degenerating mitochondria, lysosome-like bodies and autophagic vacuoles. Fifteen days after precocene treatment the CA showed further reduction in the size and number of cells, and the degenerative changes were much more pronounced. It appears that the effect of prococene on the CA is irreversible.