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PubMed1999

Differential effects of plant species on a mite pest (Tetranychus utricae) and its predator (Phytoseiulus persimilis): implications for biological control.

The influence of plant species on the population dynamics of the spider mite pest, Tetranychus urticae, and its predator, Phytoseiulus persimilis, was examined as a prerequisite to effective biological control on ornamental nursery stock. Experiments have been done to investigate how the development, fecundity and movement of T. urticae, and the movement of P. persimilis were affected by plant species. A novel experimental method, which incorporates plant structure, was used to investigate the functional response of P. persimilis. Development times for T. urticae were consistent with published data and did not differ with plant species in a biologically meaningful way. Plant species was shown to have a major influence on fecundity (P < 0.001) and movement of the pest mite (P < 0.01), but no influence on the movement of the predator. The movement of both pest and predator was shown to be related to the density of the adult pest mites on the plant (P < 0.001). Plant structure affected the functional response, particularly in relation to the ability of the predator to locate prey at low densities. The impact of these findings on the effective use of biological control on ornamental nursery stock is discussed.

Animals↗
PubMedDate not supplied

Probability of conception on different days of the menstrual cycle: an ongoing exercise.

The design of the European Multicenter Study on the probabilities of conception in different days of the menstrual cycle is reviewed. Some results, based on part of the data, are presented. These can be summarized as follows: a) Estimates of the probabilities of conception are lower than the ones previously reported in the literature; b) A strong effect of the man's age on fecundability was found. No evidence of a similar impact of the woman's age was demonstrated; c) The number of days with 'most fertile' mucus and parity affect fecundability.

Aging↗
PubMed2001

Biology, life table and host specificity of the mushroom pest, Brennandania lambi (Acari: Pygmephoroidea).

Biology and life table parameters of Brennandania lambi (Krczal) were studied at different temperatures while feeding on white mushroom (Agaricus bisporus) mycelium cultured on mushroom compost. The duration of egg and larva development, preoviposition and oviposition period, female longevity, and the time to 50% mortality declined as temperature increased from 16 to 28 degrees C. The threshold temperature of development (female) was 9 degrees C and the thermal constant for completion of development (female) was 195 day-degrees. At 16, 20. 24 and 28 degrees C, the total fecundity (eggs/female) was 71, 67, 66 and 57, respectively and the daily fecundity rate (eggs/female/day) was 5.6, 8.7, 8.7 and 9.1, respectively. The sex ratio (female/male) ranged from 1.9 to 2.1 at 16-28 degrees C. At 16, 20, 24 and 28 degrees C, the intrinsic rate of natural increase (rm) was 0.11, 0.18, 0.22 and 0.27, respectively, and the population doubling time was 6.1. 3.9. 3.2 and 2.5 days, respectively. All life stages of the mite died when exposed to 35 degrees C constant temperature for 24h. or to 32 degrees C constant temperature for 12 days or to 31-35 degrees C (average 32.9 degrees C) ambient temperature for 4 days. Brennandania lambi completed development only when fed on Ag. bisporus mycelium growing on mushroom compost. It could not survive on mushroom mycelia of Auricularia auricula. Au. polytricha, Ganoderma lucidum, Hericium erinaceus, Lentinus edodes, Pleurotus ostreatus, P. sajor-caju and Tremella juciformis.

Agaricales↗
PubMed2002

Solar UV radiation enhances the toxicity of arsenic in Ceriodaphnia dubia.

Extensive research exists regarding the toxicity of metals (including arsenic) to aquatic invertebrates. However, there has been little consideration of potential synergies between metals and ultraviolet (UV) radiation--despite considerable debate on this topic in human health research. Ultraviolet radiation is nearly ubiquitous in the natural environment, but it is generally overlooked as a confounding variable in toxicological assessments. We evaluate synergies between arsenic and solar UV radiation using the crustacean, Ceriodaphnia dubia. Both laboratory (with simulated solar radiation) and outdoor (with natural solar radiation) factorial experiments were performed with two intensities of UV (low and high) and four arsenic concentrations (0, 1, 1.25 and 1.5 mg/l). The laboratory experiment was multigenerational, examining survival and fecundity effects. The combination of high UV + 1.5 mg/l As adversely impacted survival; whereas, High UV + 0 mg/l As and Low UV + 1.5 mg/l As treatments did not. These results suggest synergism. This pattern was consistent for all three generations. Fecundity effects were not consistent across generations, and arsenic was demonstrated to have a greater impact than UV. Outdoor experiments were limited to assessing survival. Exposures in September 1999 resulted in a pattern similar to that in the laboratory exposure. High UV + 1.5 mg/l As treatment elicited diminished survival as compared to high UV + 0 mg/l As and low UV + 1.5 mg/l As. These results indicate that a synergistic effect between arsenic and UV exposure is possible under ambient conditions and within a relatively narrow dose range. The mechanism of this effect is unknown but could include synergistic genotoxic or oxidative stress. These findings point to the importance of using realistic UV exposures when determining criteria for protection of aquatic life.

Animals↗
PubMed2002

Effects of triflumuron on the two-spotted spider mite, Tetranychus urticae (Acari: Tetranichydae).

The effects of triflumuron on the mortality, fecundity, and fertility of the two-spotted spider mite, Tetranychus urticae, were evaluated in the laboratory. No differences in toxicity for larvae, protonymphs and deutonymphs were observed, but immature stages were 3.8-times more susceptible than adults at the LC50. The compound exhibited a direct contact ovicidal activity influenced by eggs age. 48-72 h old eggs were significantly more sensitive than eggs of the other age classes. No hatch inhibition was observed in eggs laid by treated adult females using a sublethal dose at two physiological times (<12 and 48-72 h old). However. fecundity decreased in younger treated females, but it increased in the older-ones. The toxicity for immatures and eggs, and the sublethal effects described suggest that triflumuron could be an interesting incorporation in integrated pest programs of T. urticae.

Animals↗
PubMed1998

A chromosomal analysis of the phenotypic plasticity of some life history traits in relation to developmental temperature.

The capacity to delay egg deposition in D. melanogaster females in the absence of a sexual partner is genetically determined and opposite types can be artificially selected. In natural populations, the relative frequency of these genotypes varies geographically and seasonally, with temperature as a selective factor. However, the retention duration of these genotypes can be modified by developmental temperature change. To study the genetic control of this response, chromosome substitution between opposite types of line was carried out in order to produce every possible homozygous chromosomal combination of the three major chromosomes (X,2,3). Eggs of these eight constructed lines were developed at two different temperatures (25 degrees C and 14 degrees C). Low temperature development directly affected the number of ovarioles but also modified the subsequent expression of adult characteristics such as retention duration and fecundity. The comparison of the eight lines revealed that, although the 3 chromosomes were involved in the genetic determinism of each trait, only one or two of them were sensitive to temperature change, and these differed according to the trait. For retention duration and fecundity, the effect of chromosome 3 from the long retention strain was particularly affected by low temperature, showing antagonism between the selective effect detected in natural populations and the effect on phenotypic plasticity studied here.

Animals↗
PubMed2003

Tritrophic interactions between transgenic potato expressing snowdrop lectin (GNA), an aphid pest (peach-potato aphid; Myzus persicae (Sulz.) and a beneficial predator (2-spot ladybird; Adalia bipunctata L.).

Tritrophic interactions between transgenic potato expressing the insecticidal lectin from snowdrop (Galanthus nivalis agglutinin; GNA), an aphid pest, Myzus persicae (Sulz.), and a beneficial predator, the 2-spot ladybird (Adalia bipunctata L.) were investigated. Clonal plants expressing GNA at 0.1-0.2% total soluble protein in leaves were used. No significant effects on development and survival of ladybird larvae fed on aphids from these transgenic plants were observed, with larval survival in the experimental group being 90% compared to 89% for controls. There were also no effects on subsequent female or male longevity. Female fecundity was also investigated. Although no significant differences (p > 0.05) were observed in egg production between control and experimental groups, a 10%, reduction (p < 0.01) in egg viability (determined by % hatch) occurred in ladybirds fed aphids reared on transgenic plants. Additional studies were carried out using aphids fed on artificial diet containing GNA, to deliver quantified levels of the protein to ladybird adults. GNA had no deleterious effects upon adult longevity, but resulted in a consistent trend for improved fecundity. Egg production was increased by up to 70% and egg viability also increased significantly. The results suggest that GNA is not deleterious to ladybirds. Results from these studies highlight the need to discriminate between direct and indirect effects when studying tritrophic interactions between plants/pests/natural enemies. Furthermore, it emphasises the importance of demonstrating 'cause and effect'.

Animals↗
PubMed2003

Host nutritive quality and host plant choice in two grass miners: primary roles for primary compounds?

The relationship between host plant choice and plant nutritional quality was investigated in two oligophagous grass miners Chromatomyia milii and C. nigra (Diptera, Agromyzidae). We tested whether host choice is determined by chemically mediated host suitability for offspring performance and/or adult performance. A second goal was to relate the observed variation among the different fitness parameters to quantitative and qualitative variation in foliar food quality. Choice experiments illustrated that both miners discriminated among grass species, and that C. milii has a smaller host range than C. nigra, as observed under natural conditions. Oviposition preference was correlated with adult feeding preference and related adult performance (longevity and fecundity) for both miners. Offspring performance measures (survival and pupal size) of at least C. nigra were more weakly related to host preference. Nearly all variation in adult performance of both miners was explained by foliar protein content, which had a positive effect on adult longevity and fecundity. Pupal size of both miners was positively related to foliar water and amino acid content and negatively related to lignin content. No clear relationship between host chemistry and offspring survival was observed. These observations show that fitness parameters are differentially related to host chemistry. Secondly, they suggest that chemically mediated host suitability for adult performance is an important determinant of host choice in this species. Finally, the results suggest a primary role for foliar protein content in host choice of the study species in general and in shaping the host range of C. milii in particular.

Animals↗
PubMed2001

IVF births and pregnancies: an exploration of two methods of assessment using life-table analysis.

PURPOSE: Our purpose was to explore two methods of expressing the performance of IVF programs. METHODS: Using life-table methods, hazard and cure rates and a "monthly fecundability rate" were calculated for an Ontario IVF clinic. The rates were evaluated for their meaningfulness as indicators of the clinic's performance. RESULTS AND CONCLUSIONS: While the hazard rate describes monthly fertility among those who will eventually become pregnant, the fecundability rate describes fertility for all patients who enter the program, making it the more appropriate index for program comparisons. However, from a prospective patient's perspective, both methods are valid indices for summarizing a program's performance.

Birth Rate↗
PubMed2003

Side-effects of three pesticides on the predatory mite, Phytoseiulus persimilis (Acari: Phytoseiidae).

Side-effects of three commonly used pesticides in Iran were evaluated on an introduced strain of the predatory mite. Phytoseiulus persimilis Athias-Henriot, reared for about 10 years without exposure to any pesticides. Application of pesticides was carried out either to detached bean leaves using a Potter tower at 1 mg wet deposit per cm2 or by a hand sprayer on bean plants until run off. According to an EPPO decision making scheme, pirimiphos-methyl was found to be harmful (E=90.8%) and heptenophos harmless (E=-3.7%) to the predatory mite in the residual initial toxicity tests. For determination of the hazard class of malathion a field test was found to be necessary (E=59.8%). Categories of 1, 2, 3 were determined for heptenophos, malathion and primiphos-methyl, respectively, using IOBC classification. Despite being harmful, it is possible to use pirimiphos-methyl 10 days before release of P. persimilis. Investigation of the contribution of both lethal and sub-lethal effects to total impact indicated the dominance of lethality in the case of pirimiphos-methyl, while malathion acted by both mechanisms. Heptenophos did not have negative effects on fecundity of P. persimilis but rather caused a higher rate of fecundity in comparison with the control. The mortality found in the heptenophos test was not significantly different from the control.

Analysis of Variance↗
PubMed2003

Enhanced invertase activities in the galls of Hormaphis hamamelidis.

Invertases are sucrose hydrolyzing enzymes often associated with plant tissues acting as physiological sinks, and plant galls are physiological sinks. We investigated several types of invertase and their potential benefits in galls of the aphid Hormaphis hamamelidis. Invertase activities in galls differed from those in leaves throughout the growing season. Vacuolar invertase activities (per g FW) were always greater in galls than leaves. In contrast, cell wall invertase activities per g FW started low in galls, but increased with time and were greater than those in leaves after 1 month. Gall growth was most closely related to vacuolar invertase activity, whereas leaf growth was correlated with both vacuolar and cell wall invertase activities. In separate correlational studies of aphid fecundity and invertase activities, cell wall invertase activity per gall accounted for 15-21% of the variation in offspring per gall. Gall dry weight explained more of the variation in offspring per gall (34.2%) than did gall volume (17.8%), a likely indication of the importance of sink strength over the life of the gall. Increased invertase activity probably underlies the enhanced sink strength commonly observed in galls. Hormaphis hamamelidis fundatrices appear to maximize reproductive output by eliciting multiple beneficial responses from their hosts. Initial gall growth correlated positively with high vacuolar invertase activity, while later in the season aphid fecundity correlated positively with cell wall invertase activity.

Animals↗
PubMed1985

The effects of gene-environment interaction on the expression of longevity.

Several previous attempts at selecting for increased life span with Drosophila have failed to obtain a response to selection, and postulate that life span is controlled by non-genetic maternal effects instead of genes. In other experiments, however, populations have responded. This study uses a set of true-breeding long- and short-lived stocks developed by in vitro selection to examine the effect on life span of developmental environment and outcrossing. The expression of genes for life span is shown here to vary as a result of a gene-environment interaction and is strongly affected by the environment during development. The longevity of F1 crosses between long- and short-lived parental lines is additive when the density of larvae is high and unfixed, showing that life span is controlled by genes and not nongenetic maternal effects. But, when numbers of larvae are held low and constant, as in studies where selection fails, life span of crosses and parental lines is greatly restricted. The failure of some previous attempts at selection, therefore, appears to have resulted from the introduction, through experimental design, of strong artifactual environmental effects that limit the phenotypic expression of genes for life span and the effectiveness of selection. Comparison of fecundity in parental and F1 lines shows that selection for increased life span antagonistically reduces early-life fecundity. Short-lived, parental lines, reproduced at an early age in life, lay 22-24 per cent more eggs in the same period than do long-lived lines selected for reproduction at a late age.

Animals↗
PubMed2005

Parasites and climate synchronize red grouse populations.

There is circumstantial evidence that correlated climatic conditions can drive animal populations into synchronous fluctuations in abundance. However, it is unclear whether climate directly affects the survival and fecundity of individuals, or indirectly, by influencing food and natural enemies. Here we propose that climate affects trophic interactions and could be an important mechanism for synchronizing spatially distributed populations. We show that in specific years the size of red grouse populations in northern England either increases or decreases in synchrony. In these years, widespread and correlated climatic conditions during May and July affect populations regionally and influence the density-dependent transmission of the gastrointestinal nematode Trichostrongylus tenuis, a parasite that reduces grouse fecundity. This in turn forces grouse populations into synchrony. We conclude that specific climatic events may lead to outbreaks of infectious diseases or pests that may cause dramatic, synchronized changes in the abundance of their hosts.

Animals↗
PubMed2002

Genome sequence of the endocellular obligate symbiont of tsetse flies, Wigglesworthia glossinidia.

Many insects that rely on a single food source throughout their developmental cycle harbor beneficial microbes that provide nutrients absent from their restricted diet. Tsetse flies, the vectors of African trypanosomes, feed exclusively on blood and rely on one such intracellular microbe for nutritional provisioning and fecundity. As a result of co-evolution with hosts over millions of years, these mutualists have lost the ability to survive outside the sheltered environment of their host insect cells. We present the complete annotated genome of Wigglesworthia glossinidia brevipalpis, which is composed of one chromosome of 697,724 base pairs (bp) and one small plasmid, called pWig1, of 5,200 bp. Genes involved in the biosynthesis of vitamin metabolites, apparently essential for host nutrition and fecundity, have been retained. Unexpectedly, this obligate's genome bears hallmarks of both parasitic and free-living microbes, and the gene encoding the important regulatory protein DnaA is absent.

Animals↗
PubMed2004

Effect of captivity on genetic variance for five traits in the large milkweed bug (Oncopeltus fasciatus).

Understanding the changes in genetic variance which may occur as populations move from nature into captivity has been considered important when populations in captivity are used as models of wild ones. However, the inherent significance of these changes has not previously been appreciated in a conservation context: are the methods aimed at founding captive populations with gene diversity representative of natural populations likely also to capture representative quantitative genetic variation? Here, I investigate changes in heritability and a less traditional measure, evolvability, between nature and captivity for the large milkweed bug, Oncopeltus fasciatus, to address this question. Founders were collected from a 100-km transect across the north-eastern US, and five traits (wing colour, pronotum colour, wing length, early fecundity and later fecundity) were recorded for founders and for their offspring during two generations in captivity. Analyses reveal significant heritable variation for some life history and morphological traits in both environments, with comparable absolute levels of evolvability across all traits (0-30%). Randomization tests show that while changes in heritability and total phenotypic variance were highly variable, additive genetic variance and evolvability remained stable across the environmental transition in the three morphological traits (changing 1-2% or less), while they declined significantly in the two life-history traits (5-8%). Although it is unclear whether the declines were due to selection or gene-by-environment interactions (or both), such declines do not appear inevitable: captive populations with small numbers of founders may contain substantial amounts of the evolvability found in nature, at least for some traits.

Animal Husbandry↗
PubMed2005

Mating system, sex ratio, and persistence of females in the gynodioecious shrub Daphne laureola L. (Thymelaeaceae).

Although in gynodioecious populations male steriles require a fecundity advantage to compensate for their gametic disadvantage, southern Spanish populations of the long-lived shrub Daphne laureola do not show any fecundity advantage over hermaphrodites in terms of seed production and early seedling establishment. By using allozyme markers, we assess the mating system of this species in five populations differing in sex ratio, and infer levels of inbreeding depression over the whole life cycle by comparing the inbreeding coefficients at the seed and adult plant stages. Extremely low outcrossing rates (0.001<t<0.125) were consistently found for hermaphrodites in all populations, whereas, as expected, female progeny were entirely outcrossed. In most populations, offspring were much more inbred than their parents, and heterozygosity of adults was greater than expected from outcrossing rate estimates, with very few selfed progeny appearing to reproduce in the field. The combination of extensive selfing in hermaphrodites and a strong inbreeding depression expressed late in the life cycle (and thus, only estimable by indirect measures based on genetic markers) may explain the persistence and high frequency of D. laureola females in southern Spanish populations.

Biological Evolution↗
PubMed1999

A genetic analysis of the relationship between life-history variation and heat-shock tolerance in Drosophila buzzatii.

Although exposure to environmental stress is common in most populations, and the physiological effects of stress on individuals are well studied, the evolutionary importance of stress to populations is not well understood. To address multitrait responses to environmental change and potential constraints on character evolution, we analysed, in 100 isofemale lines of Drosophila buzzatii, the genetic relationships between resistance to a short heat shock and several life-history traits: survival in benign conditions, larval developmental time, fecundity and longevity. Estimates of heritability of larval thermotolerance were low, but significant, and all life-history traits varied significantly among isofemale lines. Several of these traits covaried significantly. Most correlations indicated positive life-history relationships, but males and females from lines where female fecundity was higher developed more slowly in the absence of stress, which is a negative life-history relationship. The stress reduced or negated many trait associations, and showed one additional relationship; more larvae from lines that developed fast at 25 degrees C survived to adult after stress than did larvae from slow developing lines. These shifts in fitness relationships, when a single stress bout is applied, suggest that even small increases in environmental stress can have profound effects on evolutionary relationships among life-history traits.

Animals↗
PubMed2002

Interleukin-4 influences the production of microfilariae in a mouse model of Brugia infection.

Sub-cutaneous infection of interleukin (IL)-4-/- mice on the BALB/c background with third stage larva (L3) of Brugia pahangi revealed an altered cytokine profile consistent with the absence of the Th2 promoting cytokine IL-4. Splenocytes from IL-4-/- mice secreted significantly more antigen (Ag)-specific IL-2 and interferon-gamma and significantly less Ag-specific IL-5, compared to those from L3-infected wild-type mice. However, levels of Ag-specific IL-13 were similar between groups. Despite the alteration in immune responses, there was no significant difference in recovery of developing worms from the peritoneal cavity of the two strains of mice at any time postinfection. However, at later time points of infection, the IL-4-/- mice contained large numbers of microfilariae (Mf) in the peritoneal cavity while the wild-type mice contained comparatively few Mf. The differences in Mf levels appear to relate to differences in worm fecundity in the two strains of mice, with adult female worms from the wild-type mice containing few developing Mf. Moreover, implantation of sexually mature adult female worms into the peritoneal cavity of both strains of mice resulted in equal levels of Mf, confirming that the primary role of IL-4 is to limit fecundity during the maturation phase of infection.

Animals↗