Juvenile Hormone-like Compounds Research Articles

Effect of Pyriproxyfen, a Malaria Vector Larvicide, on the Growth and Mortality of Vannamei Shrimp

Anopheles mosquito shared a breeding site with the vannamei shrimp (Litopenaeus vannamei). Anopheles mosquito larvae commonly live in both stagnant fresh and brackish water. The potential breeding habitat of Anopheles mosquito larvae may be rice fields, pools or ponds, swamps, ditches, and slow-current streams. One of the effective strategies to control malaria is to apply chemical insecticides. Pyriproxifen is a larvicide that contains juvenile hormone-like compounds. Juvenile hormone-like compounds can affect mosquito morphogenesis, characterized by the failure of the larvae to develop into pupae. With a completely randomized design, the shrimp fry was divided into 4 groups, 6 repetitions, 20 individuals each. Shrimp fry in each experimental unit was placed and maintained in plastic jars containing 2.5 L of brackish water. The results showed that the insect growth regulator (IGR) with the active ingredient pyriproxyfen at various concentrations had no significant effect on the growth, mortality, and survival of vannamei shrimp fry. It can be concluded therefore that pyriproxifen larvicide was safe to be used for controlling malaria mosquito vectors in hatcheries and breeding ponds of vannamei shrimp.

Dietary methyl farnesoate, a potential growth inducer in male crab Oziothelphusa senex senex

Insect juvenile hormone-like compound methyl farnesoate (MF), identified through ‘reverse endocrinology’ in crustaceans is a sesqui-terpenoid and plays crucial role in growth well proved by direct administration into the animals at laboratory conditions. However, these studies are not reached to the cultural ponds. Moreover, dietary supplementation of MF and its effects on growth in crustaceans is still at infancy. The present study tested MF (concentration of 10−9, 10−8 and 10−7 moles/crab added to commercial shrimp pellet diet) in the growth of male crab Oziothelphusa senex senex (Oss) supplemented every alternative day for about 40 days. Along with experimental group control and eyestalk removed (ESX) groups are maintained. Dietary MF induced significant enhancement in the growth of male crab. The most effective group MF 10−8 moles/crab supplemented. The frequency of growth induction found in this study is MF 10−8>10−9>10−7 moles/crab ≤ ESX and molted percentage is 27.5%, 17.5%, 10%, 10% in each group, respectively. The dietary supplementation of MF effective in inducing growth in cultured crustaceans thereby increases the yield of crustacean protein.

Methyl Farnesoate through Feed: a Growth Manipulator in Female Crab Oziothelphusa Senex Senex

Methyl farnesoate (MF), the predominant juvenile hormone-like compound found in crustaceans. In crustaceans, MF mediated growth was reported and succeeded in the laboratory, but was not done successfully at the field level. The present investigation is aimed to test the role of dietary MF on growth of crustaceans in the semi-controlled environment. To test this, MF was supplemented through commercial shrimp pellet diet to female freshwater crab Oziothelphusa senex senex (Oss) with a concentration of 10-9, 10-8 and 10-7 moles/crab in an every alternative day for about 40 days along with eyestalk ablated (ESX) and control groups. Dietary supplementation of MF enhanced the growth of female crab by inducing molt. The molt induction frequency found in this study as MF concentration 10-8 moles/crab > 10-9 moles/crab > 10-7 moles/crab ≤ ESX and recorded molt percentage of 25%, 12.5%, 10%, 7.5% respectively. Evidencing that the dietary MF supplementation induces growth in cultured crustaceans thereby increases the yield of the culture.

Methyl farnesoate synthesis in the lobster mandibular organ: The roles of HMG-CoA reductase and farnesoic acid O-methyltransferase

Eyestalk ablation (ESA) increases crustacean production of methyl farnesoate (MF), a juvenile hormone-like compound, but the biochemical steps involved are not completely understood. We measured the activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) and farnesoic acid O -methyl transferase (FAOMeT), an early step and the last step in MF synthesis. ESA elevated hemolymph levels of MF in male lobsters. Enzyme activity suggested that increased MF production on day one was due largely to elevated HMGR activity while changes in FAOMeT activity closely paralleled changes in MF levels on day 14. Transcript levels for HMGR and FAOMeT changed little on day one, but both increased substantially on day 14. We treated ESA males with a partially purified mandibular organ-inhibiting hormone (MOIH) and observed a significant decline in MF levels, FAOMeT activity, and FAOMeT–mRNA levels after 5 h. However, no effect was observed on HMGR activity or its mRNA indicating that they must be regulated by a separate sinus gland peptide. We confirmed that lobster HMGR was not a phosphoprotein and was not regulated by reversible phosphorylation, an important mechanism for regulating other HMGRs. Nevertheless, molecular modeling indicated that the catalytic mechanisms of lobster and mammalian HMGR were similar.

Workshop on rotifers in ecotoxicology

The aim of the workshop on rotifers in ecotoxicology was to stimulate discussions on new developments in the field. Discussions about the use of biomolecular tools indicate that gene expression analysis with rotifers should be available in the next few years. Such analyses will be a great asset as they enable ecotoxicologists to study molecular mechanisms of toxicity. Rotifers also appear as useful tools in the risk assessment of pharmaceuticals and their metabolites that find their way into aquatic ecosystems because their sensitivity to some of these substances is higher than that of cladocerans and algae. The nature and extent of the impact of potential endocrine disruptors on aquatic invertebrates is another poorly resolved issue for which rotifers are a promising tool. Indeed, rotifers seem to be particularly sensitive to androgenic and anti-antiandrogenic substances, whereas copepods and cladocerans are typically more affected by estrogens and juvenile hormone-like compounds. Besides their usefulness in these emerging fields of aquatic ecotoxicology, it was emphasized that research with rotifers on basic issues like, e.g., toxicant interference with predation, competition, or interspecific and interclonal variation in ecotoxicological tests is still needed.

Physiological effects of methyl farnesoate and pyriproxyfen on wintering female crayfish Cherax quadricarinatus

Methyl farnesoate (MF), the predominant juvenile hormone-like compound of crustaceans, was found in the hemolymph of female Cherax quadricarinatus crayfish. Administration of MF to C. quadricarinatus females during their winter reproductive arrest period had no effect on reproduction; however, it did have a tendency to accelerate molting. However, since MF caused increased mortality (∼47% survival in the high MF treatment), we were not able to draw definitive conclusions regarding its physiological affect. In contrast, administration of pyriproxyfen, a juvenile hormone analog, did not cause significant mortality (95% survival in the high pyriproxyfen treatment), although it accumulated in high quantities in the hepatopancreas and, to a lesser extent, muscle tissue, ovaries and gills. The highest dose of pyriproxyfen used in this study, 20 μg/gram animal body weight/week, caused a delay in spawning, which became statistically significant from the seventeenth week. This dose of pyriproxyfen caused a tendency of acceleration of molting without any effect on molt increment. The results of this study show that pyriproxyfen does not seem to be toxic to the crayfish, even in relatively high doses, and might affect the energetic balance between molt and reproduction.

Occurrence of vertebrate steroids, estradiol 17β and progesterone in the reproducing females of the mud crab Scylla serrata

In crustaceans, vitellogenesis is known to be controlled by eyestalk neuropeptides, biogenic amines, ecdysteroids and a juvenile hormone-like compound, methyl farnesoate. In recent years, the occurrence of vertebrate steroid hormones, estradiol 17β (E 2) and progesterone (PG) has also been reported in a few decapods, although their precise role in female reproduction is yet to be determined. The levels of E 2 and PG in the ovary, hepatopancreas and the hemolymph of the red mud crab, Scylla serrata were analyzed in different vitellogenic stages in order to establish a correlation between hormone profile and stages of vitellogenesis. It was observed that the levels of both the steroids increased steeply in the tissues at the onset of vitellogenesis (vitellogenic stage I). Maximum levels of estradiol were present in the hepatopancreas whereas the highest concentration of progesterone was seen in the ovary, suggesting dichotomous roles for these hormones in vitellogenesis. Furthermore, levels of these hormones were estimated in different embryonic stages of the eggs of the sand crab Emerita asiatica and mud crab S. serrata. Their levels fluctuated, following a definite pattern in the different stages, suggesting a possible functional role as morphogenetic hormones. This study, in addition, also reports the presence of E 2 and PG on lipovitellin purified from ovary and eggs as well as vitellogenin purified from the hemolymph implicating a role for these lipoproteins as steroid carriers.

A Neurohormone Regulating both Methyl Farnesoate Synthesis and Glucose Metabolism in a Crustacean

Methyl farnesoate (MF) has been identified as a juvenile hormone-like compound in crustacea which has central roles in the regulation of development and reproduction. To study the regulation of MF synthesis, we isolated a neuropeptide which inhibits MF synthesis from the neurohemal organ--sinus gland X-organ complex of the spider crabLibinia emarginata.The primary structure of this neuropeptide has been determined. It has 72 amino acid residues (deduced molecular mass 8490.5 Da) with pyroglutamic acid at the N-terminus and NH2at the C-terminus. It shares a high percentage of sequence identity with other sinus gland neuropeptids which form the unique family of CHH neuropeptides of crustacea. Activity studies showed that this neurohormone has dual effects: it inhibited MF synthesisin vitroand had hyperglycemic activity when injected into crabs.

Effects of the insect growth regulator (S)-methoprene on survival and reproduction of the freshwater cladoceran Moina macrocopa

This study examines the acute and chronic effects of the insecticide (S)-methoprene on the survival and reproduction of the freshwater cladoceran Moina macrocopa. In laboratory toxicity tests, the 24- and 48-h LC50 values for (S)-methoprene were 0.51 and 0.34 mg litre −1, respectively. Survival, longevity and fecundity were reduced at 0.05 mg litre −1 and higher concentrations. At 0.005 and 0.01 mg litre −1, longevity and fecundity increased slightly as compared to control animals. If environmental concentrations of methoprene do not exceed 0.05 mg litre −1, as is generally the case, application of this insecticide is unlikely to induce detrimental effects on natural cladoceran populations. The stimulatory effect of very low levels of methoprene on reproductive performance is consistent with the hypothesis of a regulatory role of juvenile hormone-like compounds in crustacean reproduction.

Modified survival, growth and reproduction in an estuarine mysid ( Mysidopsis bahia) exposed to a juvenile hormone analogue through a complete life cycle

The influence of methoprene, a juvenile hormone analogue used in mosquito control, on survival, growth, and reproduction of the estuarine mysid, Mysidopsis bahia, was examined during exposure through a complete life cycle in the laboratory. Total lethality occurred among all juvenile mysids exposed to 125 μg methoprene/l for 4 days. Mysids reared at a sublethal concentration (62 μg/l) weighed significantly less than unexposed mysids as they matured after 15 days of exposure. Release of the first brood was significantly delayed by as much as 3 days in mysids exposed to low μg/l concentrations of methoprene. The total number of young produced by groups of mysids during their first brood was significantly reduced when mysids were reared in methoprene concentrations ≥8 μg/l. The most sensitive response of mysids to methoprene exposure was a significant reduction in number of young produced per female in concentrations ≥2 μg/l. Ecological concern exists because the responses of mysids in this study to very low concentrations of a synthetic pesticide resemble responses of insects to juvenile hormone and juvenile hormone analogues. Similarity in these responses suggest that methoprene may be interfering with an endogenous endocrine system in this crustacean which utilizes juvenile hormone-like compounds.

Identification of a Juvenile Hormone-Like Compound in a Crustacean

Juvenile hormone (JH) has central roles in the regulation of insect development and reproduction but has not previously been identified in other arthropod classes. The hemolymph of a crustacean, Libinia emarginata (Leach), has now been analyzed for JH-like compounds. Samples contained 0.003 to 0.030 nanogram of JH III per milliliter and 10 to 50 nanograms of methyl farnesoate per milliliter; methyl farnesoate is a compound structurally related to JH III that has JH bioactivity. Several tissues were examined for synthesis and secretion of JH-like compounds. Of these tissues, only the mandibular organs produced and secreted JH III and methyl farnesoate. However, microchemical analysis revealed that this JH III was racemic, and thus likely an artifactual oxidation product of methyl farnesoate. Secretion of methyl farnesoate was related to reproduction in females, with the highest rates observed in Libinia near the end of the ovarian cycle when oocyte growth and vitellogenesis are greatest. These results indicate that JH-like compounds such as methyl farnesoate have regulatory roles in crustaceans.

The effect on reproduction and morphometrics of females ofCulex pipiensL. of treatment of larvae with six insect growth regulators

SUMMARYSix compounds which show juvenile-hormone-like (JH) activity (TH6040, JH-25, Altosid, Altozar, ZR-777 and ZR-619) were tested on larvae ofCulex pipiens. The reproduction potential of the females obtained during two successive generations was not affected greatly, but there was a decline in pupation rate with some compounds. There seemed to be a direct relationship between the size of females of this species and treatment with JH compounds tested in the present investigation, since treatment with concentrations to inhibit the emergence of 10% or 50% of adults caused significant changes in the width of head, wing dimensions or length of hind legs.

Influences of some freshwater plants on the development and survival of mosquito larvae in British Columbia

Six species of freshwater aquatic plants and an alga (Characeae) collected in southern British Columbia markedly reduced the number of adult mosquitoes emerging from experimental tanks by influencing larval development and survival. One of the plants and the green alga apparently produce juvenile hormone-like compounds, one species ingests mosquito larvae, and two operate by facilitating the presence and activity of predators of the larvae.