Juvenile hormone-dependent vitellogenin synthesis in Locusta migratoria fat body: inducibility related to sex and stage

Juvenile hormone (JH)-dependent vitellogenin (Vg) synthesis in the fat body of Locusta migratoria is normally limited to sexually mature adult females. As a step toward examining the basis of this limitation, we have tested female and male locusts in a series of stages after the third larval molt for inducibility of Vg synthesis by the synthetic JH analog, methoprene. We find that in the fourth and fifth larval instars fat body of both sexes can be induced to produce Vg, but in the adult stage females respond strongly while no more than trace amounts can be induced in males. Quantitative assays show relative responsiveness in the order: adult female greater than fifth instar female greater than fifth instar male much greater than adult male. During the fifth instar of both sexes, maximal vitellogenic response was obtained in midinstar. After the larval-adult ecdysis, female fat body was unresponsive during the first 4 days, then responsiveness increased and by Day 8 after ecdysis fat bodies were fully as competent to produce Vg as at Day 14, the usual maximum of the first vitellogenic cycle due to endogenous JH. Larval and adult female fat bodies implanted into male larvae are competent for Vg synthesis after metamorphosis, so that the differences between adult male and female cannot be imposed by the male milieu intérieur during the larval-adult molt. In male and female precocious adults, produced by treatment of fourth instars with precocene, fat body responded to methoprene as in normal adults. We conclude that factors intrinsic to the fat body cells, determined early in development, are responsible for differential gene programing in males and females, which is partially expressed by the fifth instar but fully manifest only after a molt in the absence of JH.

Replication of Drosophila chromosomes. IX. Stimulation of initiation of polytene replication cycles in vitro by juvenile hormone

A greater proportion of polytene nuclei show [3H]thymidine incorporation when third instar larval salivary glands of Drosophila nasuta are pulse-labelled after in vitro culture (3-24 h) in the presence of a juvenile hormone mimic, ZR 515. In glands chronically labelled with [3H]thymidine in the presence of ZR 515, more nuclei are seen to have entered new polytene replication cycles. Similarly, when salivary glands from larvae fed on 5-fluorodeoxyuridine to block polytene replication cycles at intersynthetic periods were cultured in vitro, new polytene replication cycles were initiated more quickly in the presence of ZR 515. These results suggest a stimulatory effect of juvenile hormone on new polytene replication cycles.

Vitellogenin mRNA in locust fat body: identification, isolation, and quantitative changes induced by juvenile hormone

Change in RNA during the juvenile hormone (JH) stimulated synthesis of vitellogenin (Vg) in the fat body of adult female Locusta migratoria have been studied. Total RNA from mature females, but not that from males or prereproductive females, shows a 6300 nucleotide component, which has been isolated by binding to oligo(dT)-cellulose and sucrose gradient centrifugation, and identified as Vg mRNA by translation in Xenopus oocytes. It has been assayed quantitatively by photometric scanning after electrophoresis. During a gonotrophic cycle, Vg mRNA increased rapidly from 0 up to about 1% of the total fat body RNA, or more than 10(6) copies per cell. After destruction of the corpora allata (the source of JH) by treatment with ethoxyprecocene, Vg synthesis was stimulated by injection of 150 micrograms of the JH analog, methoprene. In primary stimulation, Vg mRNA was first detected at 24 h and showed a marked lag in accumulation; in secondary stimulation by methoprene after decay of the primary effect, Vg mRNA was detected after only 12 h and accumulation was much more rapid. Both in the natural cycle and in experimental stimulation, Vg mRNA did not disappear in correlation with declining Vg synthesis, which suggests conservation of mRNA in untranslated form. Total (chiefly ribosomal) RNA showed a different pattern, accumulating markedly during primary and only slightly during secondary stimulation. The data indicate that JH acts selectively (though not necessarily directly) on transcription of the Vg genes.

Growth of mouse fibroblast cells in the presence of an insect growth regulator or a synthetic C18 juvenile hormone

1. Mouse fibroblast L-cells susceptible to methoprene and to a synthetic C18 juvenile hormone were cultivated for several months in the medium with one of these compounds at a subeffective concentration (10 microgram/ml) then allowed to grow in the medium with the particular compound at an effective concentration (20 microgram/ml). 2. This resulted in establishing the cells whose mitotic activity, morphology, pattern of growth and the rate of macromolecular biosynthesis (even after cultivation for several months in the presence of methoprene or the hormone at originally effective concentration) did not differ from those for control cells.

Production of lipophorin in the fat body of adult Locusta migratoria: comparison with vitellogenin

The lipid-transport lipoprotein, lipophorin (Lp), an abundant plasma protein of insects, is synthesized in the fat body of Locusta migratoria as a polypeptide of relative mass (Mr) = 85 000. No posttranslational modification could be detected. Precipitation of this protein leads to formation of a product of Mr about 240 000, which fails to dissociate under treatment with sodium dodecyl sulfate and beta-mercaptoethanol. In adult female locusts, synthesis and secretion of protein by the fat body increases three- to four-fold from emergence until day 7 of adult life, Lp representing 15-30% of the total. In the subsequent vitellogenic stage (days 7-14 or later), a further impressive increase in protein output up to five times the previtellogenic rate is observed, followed by a decrease to the previtellogenic level at the end of the cycle. This fluctuation is mainly due to production of the yolk precursor protein, vitellogenin (Vg), which makes up some 60% of the secreted protein at the peak of the cycle. Production of Lp does not follow these dramatic changes. Inactivation of the corpora allata, the source of juvenile hormone (JH), by treatment with precocene, prevents the synthesis of Vg in females, and diminishes the production of other proteins, including Lp, in both sexes. Normal secretion patterns can be restored by application of the JH analog, methoprene. It is concluded that, whereas the synthesis of Vg is dependent upon and intensely stimulated by JH, the synthesis of Lp is stimulated only to a minor extent, in common with other proteins.

The delayed effects and the basal follicle numbers developed by females of Culex pipiens L. Emerged from treatments of larvae with partially-lethal concentrations of Altosid and Dimilin

The possible juvenilizing effects of Dimilin and Altosid against larvae of Culex pipiens L. were studied. Apart from delayed lethal action, possible effect on the mean number of basal follicles developed per female has been considered. A baseline exposure was found which caused only low mortalities of the early 4th larval instar. Results showed a correlation between the overall deaths during development and the sex ratio. Higher mortality increases the proportion of females. Treatments with 0.00001, 0.0001 and 0.001 ppm Dimilin caused 9.6%, 33.6% and 18.6% increase in the mean basal follicle numbers developed per female, respectively. In the case of Altosid, these levels of increase were 23.1%, 26.5% and 23.8%, respectively, after treatments with the same concentrations.

Effects of Ecdysterone and the juvenile hormone analogue methoprene on protein, RNA and DNA synthesis in wing discs of Calliphora vicina

The protein, RNA and DNA content of wing discs increase exponentially during the last larval instar. Biosynthesis of protein, RNA and DNA was studied by injecting labelled precursors into larvae or white prepupae and measuring the incorporation in the wing discs dissected out after an appropriate time. Protein synthesis is stimulated by ecdysterone, methoprene has no effect. Biosynthesis of rRNA is increased in wing discs of white prepupae after ecdysterone or methoprene injection. Methoprene inhibits the synthesis of mRNA, while ecdysterone has no clear-cut effect within the limits of our method (gel electrophoretic analysis). Ecdysterone and methoprene have no detectable influence on incorporation of thymidine into DNA, but the incorporation label from uridine into DNA is diminished; this effect may be due to changes in the precursor pool.

Insect growth regulators and insect control: a critical appraisal

Insect growth regulators (IGRs) of the juvenile hormone type alter physiological processes essential to insect development and appear to act specifically on insects. Three natural juvenile hormones have been found in insects but not in other organisms. Future use of antagonists or inhibitors of hormone synthesis may be technically possible as an advantageous extension of pest control by IGRs. A documented survey of the properties, metabolism, toxicology, and uses of the most commercially advanced chemical, methoprene, shows it to be environmentally acceptable and toxicologically innocuous. Derivation of its current use patterns is discussed and limitations on these are noted. Residue levels and their measurement in the ppb region have allowed exemption from the requirement of tolerances in the EPA registered use of methoprene for mosquito control. Tolerances for foods accompany its fully approved use for control of manure breeding flies through a cattle feed supplement. The human health effects of using this chemical appear to be purely beneficial, but further advances through new IGR chemicals appear unlikely without major changes in regulatory and legislative policy.

Insect growth regulators and in vitro volatile fatty acid production

Three insect growth regulators were tested for their effects on in vitro volatile fatty acid production. Each material was tested at 100 and 200 ppm of feed in a triplicated trial. At the concentrations used, there was a trend toward lowered acetate:propionate ratios with inconsistent effects on total volatile fatty acid production for all materials. Of the individual acids, only the relative production of valeric was affected significantly.

Suppression of pupal esterase activity in Aedes aegypti (Diptera: Culicidae) by an insect growth regulator

Changes in non-specific esterases of Aedes aegypti were noted during pupal development. One esterase band was found to increase markedly within 3 h of pupation and this increase in activity was suppressed by prior treatment of larvae with an insect growth regulator, ZR 515. It is suggested that the esterase activity may help to reduce endogenous levels of juvenile hormone during metamorphosis and that the growth regulator may prevent this normal regulation.