Juvenile Hormone-like Activity Research Articles

Toxic effects of chemical dispersant Corexit 9500 on water flea Daphnia magna.

In 2010, approximately 2.1 million gallons of chemical dispersants, mainly Corexit 9500, were applied in the Gulf of Mexico to prevent the oil slick from reaching shorelines and to accelerate biodegradation of oil during the Deepwater Horizon oil spill. Recent studies have revealed toxic effects of Corexit 9500 on marine microzooplankton that play important roles in food chains in marine ecosystems. However, there is still little known about the toxic effects of Corexit 9500 on freshwater zooplankton, even though oil spills do occur in freshwater and chemical dispersants may be used in response to these spills. The cladoceran crustacean, water flea Daphnia magna, is a well-established model species for various toxicological tests, including detection of juvenile hormone-like activity in test compounds. In this study, we conducted laboratory experiments to investigate the acute and chronic toxicity of Corexit 9500 using D. magna. The acute toxicity test was conducted according to OECD TG202 and the 48 h EC50 was 1.31 ppm (CIs 0.99-1.64 ppm). The reproductive chronic toxicity test was performed following OECD TG211 ANNEX 7 and 21 days LOEC and NOEC values were 4.0 and 2.0 ppm, respectively. These results indicate that Corexit 9500 has toxic effects on daphnids, particularly during the neonatal developmental stage, which is consistent with marine zooplankton results, whereas juvenile hormone-like activity was not identified. Therefore, our findings of the adverse effects of Corexit 9500 on daphnids suggest that application of this type of chemical dispersant may have catastrophic impacts on freshwater ecosystems by disrupting the key food chain network. Copyright © 2016 John Wiley & Sons, Ltd.

Laboratory Evaluation of a Biorational Insecticide, Kinoprene, against Culex pipiens Larvae: Effects on Growth and Development

ABSTRACT Aims: In the present study, the objective was to estimate the toxicity of an insect growthregulator with juvenile hormone-like activity, kinoprene, on Culex pipiens, the mostabundant and investigated mosquito species. Effects of this compound on growth anddevelopment were also evaluated.Methodology: A commercial formulation (Enstar 65% EC) was tested at differentconcentrations ranging between 162.5 and 650µg/L on newly molted fourth-instar larvaethat were exposed for 24 h under standard laboratory conditions according to WorldHealth Organization recommendations.Results: Kinoprene exhibited insecticidal activity by direct action on the treated fourth-instar larvae but also by differed action on the other following stages of development.Mortality occurred after earlier inhibition of their development or by their inability tocomplete their ecdysis. The LC 50 values were 1287.4µg/L for the direct action on fourthinstar larvae, and 246.8µg/L for the differed action until adult emergence. Moreover, thecompound disturbed growth and development since several morphological types and anincrease in the duration of larval and pupal stages were recorded. In a second series ofexperiments, the effects of kinoprene were examined on morphometric measurements ofOriginal Research Article

Pyriproxyfen and House Flies (Diptera: Muscidae): Effects of Direct Exposure and Autodissemination to Larval Habitats

Pyriproxyfen is an insect growth regulator with juvenile hormone-like activity that has potential uses for dipterans that are difficult to manage with conventional insecticides, such as house flies (Musca domestica L.). The objectives of this study were to determine the efficacy of this insect growth regulator against house flies using variety of delivery systems and target life stages, including an evaluation of the potential for autodissemination by female flies to larval development sites. Adult female house flies exposed to filter paper (3.75% active ingredient) or sugar treated with pyriproxyfen (0.01-0.1%) produced significantly fewer F1 pupae than untreated flies. Adult emergence from pupae was unaffected. In contrast, treatment of larval rearing medium with 0.35 ml/cm2 of a 12 mg pyriproxyfen/liter preparation had no effect on the number of pupae developing from eggs but markedly inhibited adult emergence from those pupae. There was little difference in susceptibility between an insecticide-susceptible and a wild strain of house fly. The LC50 for inhibiting fly emergence of dust formulations in diatomaceous earth incorporating commercial pyriproxyfen products ranged from 8 to 26 mg/liter, with little difference among products. Compared with untreated flies, significantly fewer pupae were produced at concentrations > 0.5% and no adults were produced at concentrations > 0.05% pyriproxyfen. When gravid females were exposed for 1 h to treated fabric (6 mg pyriproxyfen/cm2) and allowed to oviposit in rearing media containing eggs, sufficient pyriproxyfen was autodisseminated to reduce adult emergence from those eggs by > 99%. Intermittent contact with treated fabric over 2 d reduced adult emergence by 63-76%.

Resistance Mechanisms of Lycopersicon pennellii Accessions to Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae)

Resistance mechanisms of 5 Lycopersicon pennellii (Corr.) D’Arcy accessions to Spodoptera littoralis (Boisduval) were compared with that of 2 commercial cultivars of L. Esculentum with the ultimate intent of using L. pennellii as a source of resistance to be incorporated into L. esculentum. First instars were trapped by the sticky exudate which covered the leaf surface of L. pennellii, but 2nd-5th instars overcame this physical barrier. Second and 3rd instars were influenced by an extractable substance present within, but not on, L. pennellii leaves, which had effects similar to juvenile hormone. The L. pennellii accession Sisicaya 751 had the highest apparent level of this juvenile hormone-like activity among those tested. Leaf feeding or incorporation of material from hexane or acetone extracts of L. pennellii leaves into artificial diet or application of extracts directly to larvae caused high larval mortality, adult morphological deformation, male sterility, and inhibited oviposition. Large larvae (4th and 5th instars) were not affected by this juvenile hormone-like substance. Collectively, the data suggest that certain accessions of L. pennellii could serve as sources of resistance to S. littoralis which could be incorporated into an L. esculentum background.

Studies on Novel 3(2H)-pyridazinone Derivatives with Juvenile Hormone-Like Activity

In the course of studies on 3(2H)-pyridazinone derivatives, the authors found that some compounds substituted with phenyl group at 2-position showed distinct JH-like activity (metamorphosis-inhibiting activity) on the green rice leafhopper, Nephotettix cincticeps. Following elaborate investigations of structure-activity relationships among the related compounds, NC-170 [4-chloro-5-(6-chloro-3-pyridylmethoxy)-2-(3, 4-dichlorophenyl)-pyridazin-3(2H)-one] was discovered as the most potent candidate, which strongly inhibited the metamorphosis in leafhoppers and planthoppers, but not in any other insects at all. Further studies showed that the substituent at the 2-position on the pyridazinone ring played an important role on this strict selectivity and that the introduction of halogenated alkyl groups into the position drastically expanded the biological spectrum. NC-184 [4-chloro-2-(2-chloro-2-methylpropyl)-5-{(6-iodo-3-pyridyl)methoxy}-pyridazin-3(2H)-one], one of the most potent compounds among 2-halogenated alkyl derivatives, exhibited JH-like activity not only in hoppers but in various species over 11 orders. In the field trials against the brown planthopper, Nilaparvata lugens, a single treatment of NC-184 in late-July suppressed the population growth during summer and prevented the ‘hopper-burn’ in autumn. The results suggested that these novel JH mimics are promising agents for future hopper-control programs in paddy fields.

Disruptive developmental effects of benzyl-1,3-benzodioxole derivatives on unparasitized and parasitized Manduca sexta larvae

Treatment of tobacco hornworm larvae with the benzyl-1,3-benzodioxole derivative J-2710 immediately after ecdysis to the fourth instar disrupted development either during the moult to the fifth instar or shortly thereafter. Larvae given topical applications of 100 μg J-2710 in 1 μl acetone suffered 100% mortality, often after secreting moulting fluid in large pockets between the epidermis and the cuticle later in the fourth instar. Larvae that successfully ecdysed had abnormalities of the mouthparts and cervix that interfered with normal feeding, inhibiting growth in the fifth instar. Larvae of the gregarious endoparasitic wasp Cotesia congregata (=Apanteles congregatus) frequently failed to emerge from host Manduca sexta larvae treated with high doses of J-2710, particularly when the host failed to feed normally. Less potent disruptive effects on Manduca and Cotesia were seen after treatment of larvae with the derivatives J-3370 and J-2581. No anti-juvenile hormone action of J-2710 was observed. J-2710-treated M. sexta larvae showed no precocious metamorphosis and the developmental effects of J-2710 were not prevented by co-application of the juvenile hormone analogue methoprene in doses ranging from 1 to 100 μg/larva. Moreover, J-2710 had no effect on the action of methoprene in the black larval assay for juvenile hormone-like activity, unlike results reported to occur using the Galleria wax wound assay.

Action of two juvenile hormone antagonists on lepidopteran epidermis

The juvenile hormone antagonist ETB (ethyl-4-2( t-butylcarbonyloxy)-butoxybenzoate) caused formation of precocious larval-pupal intermediates after the 4th (penultimate)-larval instar of the tobacco hornworm, Manduca sexta, when 50 μg were applied to any 3rd stage larvae or to 4th stage larvae within 12 hr after ecdysis. This dose was most effective within 12 hr after ecdysis to the 3rd stage. In the black mutant larval assay for juvenile hormone, ETB had activity, 0.75 μg per larva giving half-maximal score. In vitro ETB acted as a juvenile hormone to prevent the ecdysteroid-induced change in commitment at concentrations above 0.1 μg/ml with an ED 50 at 2.8 μg/ml and as a partial juvenile hormone antagonist to 0.1 μg/ml juvenile hormone I at concentrations between 10 −3 and 10 −2 μg/ml. By contrast, EMD (ethyl-E-3-methyl-2-dodecenoate) had little juvenile hormone-like activity in vitro up to its limits of solubility (100 μg/ml) and exhibited sporadic partial juvenile hormone antagonistic activity in vitro at concentrations between 1 and 100 μg/ml. Since these concentrations were 10–1000 times that of juvenile hormone I in the medium, EMD apparently is not an efficient competitor.

Biocidal activity of algal toxins against immature mosquitoes

Extracts of two species of green algae, filamentousRhizoclonium hieroglyphicum Kütz and a phytoplankton,Chlorella ellipsoidea Gerneck, obtained with solvents in the laboratory were assayed againstAedes aegypti L.,Culex quinquefasciatus Say, andCuliseta incidens (Thomson). On extraction with petroleum ether, groundR. hieroglyphicum yielded an active crude extract which was chromatographed on a neutral alumina column and eluted consecutively with petroleum ether, benzene, and methanol. All three eluted fractions were found to induce significant mortality in test mosquito species. The benzene-eluted fraction was the least toxic. The methanol-eluted fraction was the most toxic to all species and exhibited juvenile hormone-like activity; it also caused morphogenetic changes in emerging adults. All three fractions delayed the rate of development of mosquito larvae by 2-5 days. Three supernatants ofC. ellipsoidea obtained on different occasions were tested against first instars ofC. quinquefasciatus. After the confirmation of their activity, all supernatants were extracted with diethyl ether, combined, and assayed against first- and fourth-stage larvae of the three mosquito species. The first-stage larvae ofC. quinquefasciatus andC. incidens were approximately three times more suspectible than those ofA. aegypti. However, fourth-stage larvae of the former two species were about twice as susceptible to the extract as those of the latter species. Dead first-stage larvae of all the species had a shrunken appearance. In general,C. ellipsoidea extract was quicker acting than that ofR. hieroglyphicum.

A comparison of the juvenilizing effect of six juvenile hormone-like activity compounds on Egyptian Culex pipiens L.

SummaryTests were made to determine the juvenilizing effects of TH6040, JH-25, Altosid, Altozar, ZR-777 and ZR-619 on Culex pipiens L. using the IC50 value (dose to inhibit the emergence of 50% of adults) as a criterion. The descending order of activity was Altosid, TH6040, Altozar, ZR-777, JH-25 and ZR·619. Insignificant prolongations were recorded in the larval or pupal durations except in the case of TH6040 (Dimilin). The time lapse from larval treatment (early fourth instar) to adult emergence was prolonged by about 18·7% following treatment with 0·0001–0·1 μg/ml.Juvenilizing effects of the tested compounds applied to the early fourth instar extended to the adult stage of Culex pipiens L. and affected the duration of the first gonotrophic cycle. The concentrations of TH6040, JH-25, Altosid, Altozar, ZR-777 and ZR-619 tested caused prolongation of the time between emergence and first oviposition by about 20–50% (at 0·0001–0·1 μg/ml), 3–26% (at 0·001–5μg/ml), 0–15% (at 0·1 × 10-8–0·001 μg/ml), 3-–23% (at 0·1 × 10-8–0·001 μg/ml), 9–27% (at 0·1 × 10-7–0·01 μg/ml), and 11–32% (at 0·1 × 10-7–0·01 μg/ml), respectively.The results obtained indicated that the sex ratio of C. pipiensL. changed progressively in all treatments but with an inconsistent trend according to the concentration of each compound. This conclusion provides further evidence on the effect of juvenile hormone-like activity compounds on adults emerging from treated larvae. The numbers of females produced were increased by about 15–30%, 9–27%, 1–35%, 1–38%, 6–44% and 31–71% after treatment with 0·0001–0·1 μg TH6040, 0·001–5μg JH-25, 0·1x 10-8–0·001 μg Altosid, 0·1 x 10-8–0·001 μg Altozar, 0·1 x lO-7–O·Ol μg ZR-777 and 0·01 × 10-7–0·01 μg ZR-619‘sol;ml, respectively.

Insect Growth Regulator Control of Longtailed Mealybug, Hemispherical Scale, and Phenacoccus solani on Ornamental Foliage Plants1

Four insect growth regulators with juvenile hormone-like activity (ZR-777, prop-2-ynyl-3,7,11-trimethyl-2,4-dodecadienoate, Ent. no. 70531; ZR-619, ethyl-11-methoxy-3,7,11-trimethyl-2,4-dodecadienethiolate, Ent. no. 70513; hydroprene, ethyl-3,7,11-trimethyl-2,4-dodecadienoate; and Ro 20-3600, 6,7 epoxy-3-methyl-7-ethyl-1-[3,4-(methylenedioxy) phenoxy ]-2- cis/trans -octene, Ent. no. 70357) were evaluated for effect on the longtailed mealybug, Pseudococcus longispinus (Targioni-Tozzetti), Phenacoccus solani Ferris, and hemispherical scale, Saissetia coffeae (Walker), major pests of ornamental tropical foliage plants. Foliar sprays at 1000 ppm effectively reduced populations of P. Longispinus and P. solani on Ardisia crenata Sims and Gynura sarmentosa D.C. ZR-777 provided control 5 days after 1 application. Repeated applications of ZR-619 and Ro 20-3600 were necessary. P. solani populations were still suppressed 1 month after treatment. Bioassays demonstrated ZR-777 to be toxic and to suppress reproduction of adult female P. longispinus and P. solani . All IGRs were equally effective as foliar sprays against S. coffeae when applied at monthly intervals at 2500 ppm.

The juvenile hormone-like effect of farnesol derivatives on the pupal development of Cerura vinula L.

The two synthetic farnesol derivatives, farnesyl methyl ether and the dihydrochloride of ethylfarnesoate were found to be morphogenetically effective in a distinguishable manner in the last larval instar of Cerura vinula L. by topical application assays. The juvenile hormone-like activity of the two substances correlates with the amount of applied substances and a critical time interval to the prepupal processes. In spite of the deficiency of some prepupal processes, it is possible, that the pupal moult occurs after a long period of delay. The time lapse of the pupal development is suggested to be dependent upon some balance of the hormones of the prothoracic glands, ecdysone, and the juvenile hormone of the corpora allata.

Inhibition of metamorphosis and of ecdysis in mosquitoes

A derivative of farnesoic acid (DFA), known to have juvenile hormone-like activity in silkworms, has been shown to inhibit development of Aedes aegypti and Culex pipiens larvae. Three types of abnormal development were noted after A. aegypti larvae were exposed to DFA during a brief period of development: some retained larval characteristics in the pupal stage; some failed to undergo adult ecdysis and instead hardened within the pupal skin; and some developed into adult males but with unrotated terminalia. The period of sensitivity of C. pipiens was less clear-cut. A. aegypti larvae, continuously exposed to DFA throughout the fourth instar, tended to produce non-viable ‘fifth-instar larvae’.

Juvenile Hormone Activity of Isomers of Farnesol

SINCE the juvenile hormone of insects was first extracted from the abdomens of male cecropia moths1, its presence or the presence of juvenile hormone-like activity has been demonstrated in other insects2, in invertebrates3, in bacteria, yeast, and higher plants4, in certain organs of mammals5, and in the faeces of the beetle Tenebrio molitor6. Recently, the active constituents of the faeces of T. molitor were isolated and identified as two related acyclic sesquiterpenes, farnesol (I) and farnesal7, and the activity of one of them, farnesol, was examined in detail on the assassin bug, Rhodnius prolixus8. Although the juvenile hormone activity of farnesol was demonstrated, its unit activity was far less than those of partially purified extracts of cecropia moths, and therefore it is not likely that farnesol is the true juvenile hormone of insects8,9. Nevertheless, interest is centred on these terpenes as possible precursors of the juvenile hormone.