Fertility and life expectancy of the predator Supputius cincticeps (Heteroptera: Pentatomidae) exposed to sublethal doses of permethrin

The stinkbug Supputius cincticeps (St?l) (Heteroptera: Pentatomidae) can be found in agricultural and forest ecosystems feeding primarily on larvae of Coleoptera and Lepidoptera, where it can be exposed to insecticide applications. This study therefore aimed to evaluate the reproductive potential of S. cincticeps after exposition to sublethal doses of permethrin (5.74 x 10(-3), 5.74 x 10(-2), 5.74 x 10(-1), 5.74 and 57.44 ppb) through the use of a fertility life table. The development cycle of this predator was determined in order to calculate its net reproductive rate (R0), the infinitesimal (rm) and finite (lambda) rates of increase in addition to mean generation time (T). The net reproductive (18.31), infinitesimal (rm) (0.050) and finite (lambda) (1.051) rates of increase were higher, while generation time (57.93 days) was shorter for S. cincticeps exposed to 5.74 x 10(-1) ppb of permethrin than in the control. This indicates a higher rate of population increase of this predator when exposed to this permethrin dose.     

Susceptibility of the predatory stinkbug <Emphasis Type="Italic">Picromerus bidens</Emphasis> to selected insecticides

The Palaearctic stinkbug Picromerus bidens L. (Heteroptera: Pentatomidae) has been considered as a potential biocontrol agent of several defoliator pests in various agricultural and forest ecosystems. It may therefore be a valuable alternative for the Nearctic pentatomid Podisus maculiventris (Say) (Heteroptera: Pentatomidae), the augmentative use of which has largely been abandoned in Europe given its possible environmental impact as an exotic polyphagous predator. However, no study has yet documented the impact of insecticides on P. bidens, which is essential to evaluate the possible combination of this predatory pentatomid with current insecticide applications in integrated pest management (IPM) programmes. This study reports on laboratory experiments investigating the susceptibility of P. bidens to five insecticides with different modes of action: the pyrethroid deltamethrin, the diacylhydrazine methoxyfenozide, the juvenile hormone mimic pyriproxyfen, the spinosyn spinosad, and the neonicotinoid imidacloprid, all of which are used to control defoliator pests. Fourth-instar nymphs and female adults of the predator were exposed to formulated materials of the insecticides by residual contact. Methoxyfenozide and spinosad did not cause significant mortality to 4th instars and female adults of P. bidens. In contrast, deltamethrin and imidacloprid were harmful to nymphs and adults of the predator, with LC₅₀ values ranging between 1.5 and 9.9 mg a.i./l. Pyriproxyfen was toxic to 4th instars with an LC₅₀ value of 13.9 mg a.i./l but did not affect female adults. Reproduction and longevity of P. bidens were not adversely affected when the predator was exposed to field concentrations of spinosad, methoxyfenozide, or pyriproxyfen, or sublethal concentrations (around LC₁₀) of deltamethrin and imidacloprid. The results from residual contact experiments suggest that methoxyfenozide, spinosad, and to a lesser extent, pyriproxyfen may be compatible with P. bidens in an IPM programme. Further experiments assessing food chain toxicity of these compounds should offer a more complete picture of their selectivity.     

Laboratory testing of a lethal ovitrap for Aedes aegypti

Laboratory tests were conducted to determine the feasibility of making the mosquito ovitrap lethal to Aedes aegypti (L.) when they attempt to oviposit in the trap. Heavy-weight velour paper strips (2.54 x 11 cm) were used as an alternative to the wooden paddle normally provided as a substrate for mosquito oviposition. The paper strips were pretreated with insecticide solutions and allowed to dry before being used in oviposition cups of 473 ml capacity, filled with water initially to within 2.5 cm of the brim. Insecticides chosen for their quick knock-down efficacy were bendiocarb 76% WP (1.06 mg a.i./strip) and four pyrethroids: permethrin 25% WP (0.16 mg a.i./strip), deltamethin 4.75% SC (0.87 mg a.i./strip), cypermethrin 40% WP (2.81 mg a.i./strip), and cyfluthrin 20% WP (0.57 mg a.i./ strip). For experimental evaluation, two oviposition cups (one with an insecticide-treated strip and one with an untreated strip) were placed in cages (cubic 30 cm) with gravid female Ae. aegypti mosquitoes (aged 6-8 days) from a susceptible laboratory strain. Mortality-rates of female mosquitoes were 45% for bendiocarb, 47% for permethrin, 98% for deltamethrin, 100% for cypermethrin, and 100% for cyfluthrin. Young instar larvae added to the treated cups died within 2h. After water evaporation from the cups for 38 days, fresh mosquito females had access to previously submerged portions of the velour paper paddle, and mortality rates of 59% or more occurred. Cups that had water (360 ml) dripped into them, to simulate rain, produced female mosquito mortality rates of > 50% and all larvae died within 3 h of being added. These tests demonstrate that the ovitrap can be made lethal to both adults and larvae by insecticidal treatment of the ovistrip. Field efficacy trials are underway in Brazil to access the impact of this simple, low-cost, environmentally benign approach on populations of the dengue vector Ae. aegypti.     

Toxicity of diflubenzuron, pyriproxyfen, imidacloprid and diafenthiuron to the predatory bugOrius laevigatus (Het.: Anthocoridae)

The susceptibility of the predatory bugOrius laevigatus (Fieber) to the insect growth regulators diflubenzuron, pyriproxyfen, the nitroguanidine insecticide imidacloprid and the thiourea compound diafenthiuron was investigated in the laboratory. Fifth-instar nymphs were exposed to formulated materials of each compound and adults were exposed to formulated materials of diafenthiuron and imidacloprid. In each case, exposure via ingestion and residual contact was tested. Pyriproxyfen was harmless toO. laevigatus nymphs by both ways of exposure. The respective LC₅₀-values of diflubenzuron via ingestion and residual contact were 229.9 and 391.1 mg a.i./l. Diafenthiuron did not cause significant mortality to fifth-instar nymphs and adults via ingestion but was toxic by residual contact with LC₅₀-values of 329.4 mg a.i./l and 125.9 mg a.i./l for nymphs and adults respectively. Imidacloprid proved to be the most toxic compound with LC₅₀-values of 1.1 and 0.04 mg a.i./l for nymphs and 2.1 and 0.3 mg a.i./l for adults, via ingestion and residual contact, respectively. The results suggest that use of pyriproxyfen in an integrated pest management programme will not cause any problems but that imidacloprid, and to a lesser extent, also diflubenzuron and diafenthiuron could be harmful to the predator.     

Permethrin resistance ratios compared by two methods of testing nymphs of the German cockroach, Blattella germanica

For the German cockroach, Blattella germanica L. (Dictyoptera: Blattellidae), the permethrin resistance ratio (RR) was assessed by topical application and by tarsal contact tests, using first-instar nymphs of five strains from Tehran, Iran. Each test was replicated three or four times with 10 nymphs aged 2-3 days; mortality was scored 24h post-treatment. The reference susceptible strain showed LD50 permethrin 0.0175 microl/nymph from topical application, KT50 of 8.41 min and LT50 of 12.82 following tarsal contact with permethrin 15 mg/m2. In four wild strains (F1 generation) the RR varied from 4.14 to 4.7 for mortality after topical application, from 4.2 to 6.45 for mortality and 17-27 for knockdown following tarsal contact tests. Hence, overall knockdown results gave much higher RRs than for mortality data. Resistance ratios based on both methods of treatment were very similar: one strain showed a slightly higher value by topical application (RR 4.6 vs. 4.2, i.e. 1.1-fold difference) whereas the other three strains gave slightly greater RR (1.2-1.4 fold) by tarsal contact. Resistance was abolished by cotreatment with the synergist piperonyl butoxide plus permethrin (ratio 3:1 required for full efficacy), indicating that mixed-function oxidases were inhibited as a major metabolic pathway in all four resistant strains.     

Effect of macromolecule supplementation during in vitro maturation of goat oocytes on developmental potential

In vitro maturation (IVM) of goat oocytes with serum-supplemented media results in oocytes with reduced developmental potential. The objective of this study was to develop a defined medium for IVM of goat oocytes that better supports subsequent embryonic development. Cumulus oocyte complexes (COC) were matured for 18-20 hr in: Experiment (1), tissue culture medium 199 (TCM199) with 10% (v/v) goat serum or modified synthetic oviduct fluid maturation medium (mSOFmat) with 2.5, 8.0, or 20.0 mg/ml bovine serum albumin (BSA); Experiment (2), mSOFmat with 4.0, 8.0, 12.0, or 16.0 mg/ml BSA; or Experiment (3), 1.0 mg/ml polyvinyl alcohol (PVA; control), 4.0 mg/ml BSA, 0.5 mg/ml hyaluronate plus 0.5 mM citrate, or hyaluronate, citrate, and BSA. Mature COC were coincubated for 20-22 hr with 12-15 x 10(6) sperm/ml in modified Brackett and Oliphant (mBO) medium. Embryos were cultured for a total of 7 days in G1/2, and evaluated for cleavage, and blastocyst development, hatching, and total cell numbers. In the first experiment, more (P < 0.05) blastocysts developed per cleaved embryo following maturation in mSOFmat with 2.5 or 8.0 mg/ml BSA than with 20.0 mg/ml BSA or TCM199 with 10% goat serum. The various concentrations of BSA used in the second experiment did not affect (P > 0.05) any of the developmental endpoints examined. In the third experiment, developmental potential of oocytes matured with PVA or hyaluronate with citrate was not different (P > 0.05) from oocytes matured in the presence of BSA. These results demonstrate that developmentally competent goat oocytes can be matured under defined conditions.     

Effect of cotton cultivar on performance of Aphis gossypii (Homoptera: Aphididae) in Iran

Cotton aphids, Aphis gossypii Glover (Homoptera: Aphididae), obtained from cotton, Gossypium hirsutum L., fields in the Gorgan region of northern Iran, were colonized on 'Varamin' cotton plants in a growth chamber. The development, survivorship, and life table parameters of the cotton aphid were evaluated at 27.5 +/- 1 degrees C, 65 +/- 10% RH, and aphotoperiod of 14:10 (L:D) h of artificial light on five commonly growing cotton cultivars: Varamin, 'Sealand' (relatively resistant cultivar), 'Bakhtegan', 'Sahel' (both relatively susceptible cultivars), and 'Siokra' [resistant to Bemisia tabaci (Gennadius)]. The developmental times of immature stages ranged from 4.6 d on Bakhtegan and Varamin to 6.3 d on Sealand, whereas the immature survival was 97.5 to 65% on Sahel and Siokra, respectively. On average, there were 28.7, 28.3, 23.5, 20.1, and 16.8 nymphs produced per female on Sahel, Bakhtegan, Varamin, Sealand, and Siokra, respectively. The intrinsic rate of natural increase (r(m)) for cotton aphids on Sahel was the highest, whereas the values for r(m) varied from 0.284 (nymphs per female per d) on Siokra to 0.368 on Sahel. Jackknife estimates of generation times (T), net reproductive rate (R(0)), doubling time (DT), and finite rate of increase (lambda) on these cultivars were as follows: 9.79-10.84 d for T, 9.23-23.81 nymphs per female for R(0), 2.17-3.19 d for DT, and 1.28-1.38 nymphs per female per d for lambda. Cotton aphid performance was at its highest on Sahel and lowest on Siokra.     

Maternal provisioning and possible joint breeding in the burrower bug Adomerus triguttulus (Heteroptera: Cydnidae)

Subsocial burrower bugs (Heteroptera: Cydnidae) provide unique opportunities to investigate evolutionary ecological questions regarding parental provisioning and family dynamics. Observations and marked nutlet‐setting experiments in the field showed that Adomerus triguttulus females progressively delivered mint nutlets into nests harbouring nymphs under the litter. More than one female often attended nymphs, but not eggs, in a nest in the field. The number of nymphs aggregating in a nest with a single female was usually smaller than that in a nest with two females, suggesting the joining of different families and facultative joint parental care. There was a positive correlation between the number of nutlets delivered and the number of nymphs in a nest. The number of attendant females also affected the amount of provisioning; more nutlets were found for second‐instar broods with more females. The effect of brood size on provisioning was confirmed for families under laboratory rearing. Maternal provisioning also varied with the developmental stage of offspring; second‐instar broods received more nutlets than first‐instar broods, with a temporal decrease in provisioning during the moulting of nymphs. Considering the growing evidence of food solicitation signals of young in subsocial insects, the observed finely tuned supply of food by the female could be induced by begging signals from the nymphs.     

Density-mediated indirect effects of a common prey tadpole on interaction between two predatory bugs: <Emphasis Type="Italic">Kirkaldyia deyrolli</Emphasis> and <Emphasis Type="Italic">Laccotrephes japonensis</Emphasis>

This paper suggests that the nymphs of a specialist predator, Kirkaldyia (=Lethocerus) deyrolli (Belostomatidae: Heteroptera), are indirectly affected by their tadpoles’ prey. K. deyrolli nymphs and the predator Laccotrephes japonensis (Nepidae: Heteroptera) adults coexist in rice paddy fields. It was predicted that the difference in tadpole density may influence the K. deyrolli nymph survival rate. We first compared survival rates of the first instar nymphs of K. deyrolli in June (high tadpole density period) and July (low tadpole density period). Secondly, we investigated the survival rate of K. deyrolli nymphs at different tadpole densities and under the presence or absence of L. japonensis adults to examine whether higher tadpole density moderates predation pressure from L. japonensis adults to K. deyrolli nymphs, e.g., density-mediated indirect effects. As a result of the comparison, the survival rate of K. deyrolli nymphs in June was higher than that in July. For the field experiment, the slopes between the survival rate of K. deyrolli nymphs and tadpole density were positive under both predator presence and absence. However, the slope under the presence of a predator was steeper than that under absence of the predator (“predator-by-tadpole density interaction” was significant). These results suggest that a higher tadpole density in June provides an abundant food resource for K. deyrolli nymphs and also moderates predation pressure from L. japonensis.     

Social suppression of ovarian cyclicity in captive and wild colonies of naked mole-rats, Heterocephalus glaber

To investigate the endocrine cause of reproductive suppression in nonbreeding female naked mole-rats, animals from 35 colonies were studied in captivity. Urinary and plasma progesterone concentrations were elevated in pregnant females (urine: 10.0-148.4 ng/mg Cr, 27 samples from 8 females; plasma: 3.6-30.0 ng/ml, 5 samples from 5 females; Days 21-40 of pregnancy) and cyclic breeding females (urine: 0.5-97.8 ng/mg Cr, 146 samples from 7 females; plasma: less than 1.0-35.4 ng/ml, 25 samples from 7 females). The latter group showed cyclic patterns of urinary progesterone, indicating a mean ovarian cycle length of 34.4 +/- 1.6 days (mean +/- s.e.m.) with a follicular phase of 6.0 +/- 0.6 days and a luteal phase of 27.5 +/- 1.3 days (19 cycles from 9 breeding females). In non-breeding females urinary and plasma progesterone values were undetectable (urine: less than 0.5 ng/mg Cr, 232 samples from 64 females; plasma: less than 1.0 ng/ml, 7 samples from 6 females). Breeding females had higher (P less than 0.001) plasma LH concentrations (3.0 +/- 0.2 mi.u./ml, 73 samples from 24 females) than did non-breeding females (1.6 +/- 0.1 mi.u./ml, 57 samples from 44 females). Urinary and plasma progesterone concentrations in non-breeding females from wild colonies situated near Mtito Andei, Kenya, were either below the assay sensitivity limit (urine: less than 0.5 ng/mg Cr, 11 females from 2 colonies; plasma: less than 1.0 ng/ml, 25 females from 4 colonies), or very low (plasma: 1.6 +/- 0.6 ng/ml, 15 females from 4 colonies). In captivity, non-breeding females removed from their colonies (i.e. the dominant breeding female) and either paired directly with a non-breeding male (N = 2), or removed and housed singly for 6 weeks before pairing with a non-breeding male (N = 5) may develop a perforate vagina for the first time in as little as 7 days. Urinary progesterone concentrations rose above 2.0 ng/mg Cr (indicative of a luteal phase) for the first time 8.0 +/- 1.9 days after being separated. These results suggest that ovulation is suppressed in subordinate non-breeding female naked mole-rats in captive and wild colonies, and show that plasma LH concentrations are significantly lower in these non-breeding females. This reproductive block in non-breeding females is readily reversible if the social factors suppressing reproduction are removed.     

Glutathione content and embryo development after in vitro fertilisation of pig oocytes matured in the presence of a thiol compound and various concentrations of cysteine.

The present study examined the effect of different concentrations of cysteine in the presence of a thiol compound, beta-mercaptoethanol (BME), during in vitro maturation (IVM) of pig oocytes on cumulus expansion, nuclear maturation, intracellular glutathione (GSH) level and subsequent embryonic development after in vitro fertilisation (IVF). In experiment 1, oocytes were matured in NCSU 23 medium containing 10% porcine follicular fluid, 25 microM BME, 0.5 microgram/ml LH, 0.5 microgram/ml FSH and 0, 0.1, 0.2 or 0.4 mg/ml cysteine for 20-22 h and then without hormonal supplements for an additional 20-22 h. After culture, cumulus cells were removed and a proportion of oocytes fixed to examine the rate of nuclear maturation. The remaining oocytes were co-incubated with spermatozoa for 5-6 h and putative zygotes were transferred to NCSU 23 medium containing 0.4% bovine serum albumin for 144 h. A proportion of putative zygotes were fixed 12 h after insemination to examine fertilisation parameters. In experiment 2, oocytes were matured as in experiment 1 and the GSH content was measured by a DTNB-GSSG reductase recycling assay. No mean differences among treatments were observed in nuclear maturation (78-89%). The mean differences in penetration rate (69-77%), polyspermy rate (31-40%), male pronuclear formation rate (93-96%) or mean number of sperm per oocyte (1.5-1.8) were not affected by the presence or absence of cysteine during oocyte maturation. Also no difference was observed in cleavage rates 48 h after insemination. However, compared with no addition (19%), the presence of 0.1-0.4 mg/ml cysteine during IVM increased (p < 0.001) the proportion of blastocysts (32-39%) at 144 h. In comparison with controls (5.6 pmol/oocyte), the GSH content of oocytes matured in the presence of cysteine was significantly (p < 0.001) higher (13-15 pmol/oocyte) with no mean differences among different cysteine concentrations. The results indicate that in the presence of a thiol compound, supplementation of IVM medium with cysteine can increase the GSH level and improve the developmental competence of pig oocytes following fertilisation. Further, no effect on either GSH level or embryo development was observed by increasing the levels of cysteine supplementation from 0.1 to 0.4 mg/ml.     

Effects of permethrin at different temperatures on pyrethroid-resistant and susceptible strains of Anopheles

The influence of temperature (16, 22, 28, 37 degrees C) on effects of permethrin was investigated for susceptible and pyrethroid-resistant strains of the mosquitoes Anopheles gambiae and An. stephensi (Diptera: Culicidae). Young unfed female adult mosquitoes were exposed to 0.25% permethrin test papers or to polyester netting treated with permethrin 500mg a.i./m2. The time to 50% knockdown (KT50) declined as temperature increased, i.e. there was a positive temperature coefficient of this effect of the pyrethroid. Resistance ratios (comparing KT50 values) between resistant and susceptible An. stephensi ranged between 2.5 and 4.4 at the different temperatures. Comparative tests of pyrethroid tolerance of different strains would be valid over the 22-28 degrees C range but, when using a discriminating dose to detect resistance, more precise temperature control is desirable. Mortality 24h after exposure to 0.25% permethrin of both susceptible and resistant strains of An. stephensi showed a negative correlation with temperature between 16 and 22 degrees C and a positive correlation at higher temperatures. In An. gambiae, however, the correlation was positive over the whole range. Irritancy of permethrin-treated netting to Anopheles females (measured as time lapse until first flight take-off, and the number of take-offs during 7.5 min exposure) was positively correlated with temperature in all four strains and was much greater for the susceptible than the resistant strains.     

Effects of sperm concentrations and culture media on fertilization and development of in vitro matured pig oocytes

This study was carried out to investigate the effects of sperm concentrations and culture media on fertilization and development of in vitro matured pig oocytes. The concentrations of frozen-thawed sperm were 0.2 x 10(7), 2 x 10(7), 20 x 10(7) and 200 x 10(7)/ml, respectively. Culture media were NCSU-23, HEPES-buffered (25 mM) NCSU-23, PZM-3 and PZM-4, respectively. Increasing the sperm concentration from 0.2 x 10(7) to 2 x 10(7)/ml, significantly increased the penetration rate. Also, increasing the sperm concentration from 20 x 10(7) to 200 x 10(7)/ml increased the penetration rate from 62.1% to 69.9%, respectively, with no differences between these two concentrations. A similar pattern was observed for polyspermic penetration and male pronucleus formation. The mean number of sperm per oocyte significantly increased in the 20 x 10(7)/ml and again in the 200 x 10(7)/ml sperm concentrations. The percentage of blastocysts from cleaved oocytes at the 2 x 10(7)/ml sperm concentration was significantly higher than that at the 0.2 x 10(7), 20 x 10(7) and 200 x 10(7)/ml sperm concentrations. The percentage of blastocysts from cleaved oocytes and the cell numbers per blastocyst were significantly higher in the HEPES-buffered NCSU-23 culture medium than in the NCSU-23, PZM-3 and PZM-4 culture media under a gas atmosphere of 5% CO2 in air.     

Influences of zinc on fertilisation and development of bovine oocytes in vitro.

The effects of zinc (as ZnCl2) on in vitro production of bovine embryos (IVMFC) and components of the procedure, that is in vitro oocyte maturation (IVM), fertilisation (IVF) and embryo development in culture (IVC), and the effect of added zinc on sperm motility were studied. Immature cumulus oocyte complexes (COCs) were aspirated from ovarian follicles (2-5 mm diameter) at slaughter, and matured, fertilised and cultured in chemically defined conditions. The presence of zinc (10, 100 or 1000 micrograms added per millilitre) throughout IVMFC inhibited fertilisation. After addition of 10 micrograms zinc per millilitre separately to media for IVM and IVF, fertilisation was inhibited only when zinc was present for IVM. When present for IVF, 80% of oocytes selected for IVM reached 2- to 4-cell stages by 46 h after insemination whereas 67% of control oocytes (inseminated without added zinc) cleaved. Higher zinc concentrations (100 and 1000 micrograms added per millilitre) for IVF inhibited fertilisation. Sperm motility was reduced with addition of 10 micrograms per millilitre of zinc for sperm preparation (i.e. capacitation interval). Addition of 1.0 microgram zinc per millilitre to media used through IVMFC, or to the IVC medium alone, resulted in inhibition of development after 2- to 4-cell stages. When added to IVM or to both IVM and IVF media 1.0 microgram/ml of zinc compromised development to the morula stage and beyond. Maturing bovine oocytes may be more sensitive to 1.0 microgram ml of zinc in vitro than in vivo because a concentration of 3.0 micrograms/ml has been reported for bovine follicular fluid. Fertilisation was not adversely affected by 10 micrograms/ml of zinc; however, higher concentrations were inhibitory.     

Foam separation of Escherichia Coli with a cationic surfactant

An experimental investigation of the foam separation of E. coli from distilled water suspension using a cationic surface-active agent, ethylhexadecyldimethyl-ammonium bromide (EHDA-Br) is presented. Results are evaluated in terms of total cell count, using a membrane filtration technique. Cell concentrations in the initial suspensions are varied from 5.0 × 10⁵ to 1.0 × 10⁸ cells/ml. Surfactant concentrations in the initial cell suspensions are varied from 0.015 to 0.040 mg./ml., and foaming times are varied from 2 to 20 min. The residual quantity of cells decreases exponentially with foaming time to about 0.02% of the initial quantity after 20 min. The cell enrichment ratio, varying from 10 to 1,000,000, is an inverse power function of the initial surfactant concentration and an exponential function of foaming time. Foaminess decreases with increasing initial cell concentrations, and for an initial surfactant concentration of 0.030 mg./ml., the residual cell concentration is a linear function of the initial cell concentration.     

Experiences with the dominant lethal test in female mice: effects of alkylating agents and artificial sweeteners on pre-ovulatory oocyte stages.

Pre-ovulatory oocytes are especially sensitive to mutagenic influences. Since post-dictyotene oocytes are not subject to selection and elimination before fertilization, they may reveal mutagenic effects directly and unrestrictedly. Presuming that a chemical is administered at pro-estrus to female mice one can conclude that the substance or its active metabolite has the chance to reach the gamete during the sensitive pre-fertilization stages. We proved the usefulness of the test system by investigating the effects of alkylating agents. A second step was to investigate other substances. The following treatments induced dominant lethal effects: methyl methanesulfonate 100 mg/kg i.m., cyclophosphamide 200 mg/kg per os, triaziquone 0.25 mg/kg i.p. In contrast, the following agents were ineffective and can be classified as not mutagenic in this method: sodium cyclamate 10 000 mg/kg per os, saccharine sodium, 10 000 mg/kg per os, cyclohexamine sulfate 150 mg/kg per os, ethanol 5 ml/kg per os.     

Effects of a GnRH agonist on oocyte number and maturation in mice superovulated with eCG and hCG

The objective was to investigate the effects of a gonadotropin-releasing hormone agonist (GnRH) on ovulation rate and the number and maturation of oocytes in mice superovulated with equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG). Thirty 3-month-old BALB/C female mice (weight: 25-30 g) were assigned to three experimental groups: control, superovulated, and superovulated with GnRH pretreatment (n=10 per group). Control mice received an i.p. injection of 0.1 ml physiological saline solution. Superovulation was induced with 5 IU eCG (i.p.) and 5 IU hCG 48 h later. Mice in the superovulated with GnRH pretreatment group were given GnRH (20 mg/kg Fertirelin, i.m.), 24 h before superovulation. Thirteen hours after hCG administration, mice were sacrificed by cervical dislocation and blood samples were collected to determine serum progesterone concentration (by radioimmunoassay). Ovaries and oviducts were also harvested to enumerate corpora lutea and cumulus-enclosed oocytes. Progesterone concentrations were not significantly different among groups. The oocyte number and the maturation, ovulation rate, and the number of corpora lutea were higher in GnRH-treated mice than both controls and superovulated mice. In conclusion, GnRH given 24 h before superovulation with eCG-hCG increased the number and maturation of oocytes and the rate of ovulation in mice.     

Characterization of the maturational changes induced by a GnRH analogue in the rat ovarian follicle

The GnRH analogue [D-Ser(t-Bu)6]des-Gly10-GnRH-N-ethylamide (GnRHa, 2 micrograms/rat) or hCG (4 i.u./rat) was administered to hypophysectomized, PMSG-primed immature female rats. Oocyte maturation was initially detected by 2 h after GnRHa administration but the response to hCG was observed only after 4 h. Initiation of GnRHa-induced ovulation also preceded the response to hCG by 2 h. Maximal response to both these hormones was obtained at 10 and 14 h after hormone administration for oocyte maturation and ovulation respectively. The number of oocytes ovulated after GnRHa was significantly lower than that with hCG (29 +/- 4 and 50 +/- 7 per rat respectively; P less than 0.05). Expansion of the cumulus mass and secretion of mucoid material, which are characteristic responses to LH, were also observed after GnRHa administration. However, while the action of 5 micrograms ovine LH/ml on the cumulus cells was mediated by cAMP, no accumulation of the nucleotide could be detected in follicles exposed to GnRHa (10(-7) M). We conclude that even though GnRHa and LH/hCG seem to elicit similar responses in the ovarian follicle they differ in their kinetics, their efficiency and the mediator of their action.     

Disparate effects of endogenous and exogenous oestradiol on luteal phase function in women

Five normally ovulating women were induced to superovulate with pulsatile 'pure' FSH (28 i.u. every 3 h by a s.c. pump), and another 5 women were given an i.m. injection of 10 mg oestradiol benzoate in the late follicular phase. Serum oestradiol concentrations in the luteal phase were similar in both groups and significantly higher than in corresponding control cycles. The luteal phase was of shorter duration in the FSH (11.2 +/- 0.7 days) than in the control (13.4 +/- 0.2 days) and the oestrogen-treatment cycles (13.4 +/- 0.7 days) (P less than 0.05, mean +/- s.e.m.). FSH cycles had significantly lower early luteal serum LH (Day 1: 5.3 +/- 1.5 mi.u./ml) and mid-luteal serum progesterone values (35.4 +/- 3.5 nmol/l) compared with the control (27.8 +/- 5.8 mi.u./ml and 65.4 +/- 5.7 nmol/l, respectively) and oestrogen treatment cycles (25.3 +/- 8.3 mi.u./ml and 59.1 +/- 8.4 nmol/l, respectively) (P less than 0.05, mean +/- s.e.m.). These results suggest that, in hyperstimulated cycles, the luteal phase can be disrupted even without follicle aspiration, and that suppression of endogenous LH secretion may be responsible.     

Variation of Fungicide Resistance in Czech Populations of Pseudoperonospora cubensis

During the growing seasons between the years 2001 and 2004, 98 isolates of Pseudoperonospora cubensis from nine regions of Czech Republic were collected and screened for tolerance/resistance to the three frequently used fungicides (propamocarb, fosetyl‐Al, metalaxyl). Fungicides were tested in five different concentrations, using a floating disc bioassay. Fungicide effectiveness varied considerably. Propamocarb appeared most effective and all the isolates collected in the years 2001–2003 were found sensitive to all tested concentrations [607–9712 μg active ingredient (a.i.)/ml]. In 2004, some strains with increased resistance to propamocarb were detected. These strains were characterized by tolerance at the lowest concentrations (607 μg a.i./ml, eventually on 1214 μg a.i./ml); however, they were controlled by 2428 μg a.i./ml. Fosetyl‐Al was effective at the recommended concentration of 1600 μg a.i./ml against all isolates. However, the occurrence of isolates (collected in 2001) which sporulated at low concentrations (400 and 800 μg a.i./ml) indicated that the selection for tolerance occurs in the pathogen population. Nevertheless, this phenomenon was not confirmed with the P. cubensis isolates collected between the years 2002 and 2004. Metalaxyl was found ineffective, because 97% of the isolates showed the resistance to the recommended concentration (200 μg a.i./ml), and the other 3% of isolates expressed tolerant response. The majority of the isolates showed profuse and/or limited sporulation at higher concentrations (400 and 800 μg a.i./ml). A substantial shift to highly metalaxyl resistant strains was evident in the Czech P. cubensis populations during 2001–2004.