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PubMed2002

Modelling population dynamics of Orius laevigatus and O. albidipennis (Hemiptera: Anthocoridae) to optimize their use as biological control agents of Frankliniella occidentalis (Thysanoptera: Thripidae).

ORIUS LAEVIGATUS: (Fieber) and O. albidipennis (Reuter) play an important role in the control of Frankliniella occidentalis (Pergande) in crops and natural vegetation in the Mediterranean area. The biological parameters of the two anthocorids were studied and modelled in relation to temperature to optimize their use in thrips control programmes. Development times and reproductive parameters of O. laevigatus and O. albidipennis were determined at 20, 25, 30 and 35 degrees C. Pre-imaginal development times ranged from 34.6 and 37.2 days at 20 degrees C to 12.3 and 10.2 days at 35 degrees C in O. laevigatus and O. albidipennis, respectively. The lower thermal development threshold was significantly higher for O. albidipennis (14.2 +/- 0.9 degrees C) than for O. laevigatus (11.3 +/- 0.7 degrees C). No significant differences in fecundities between the two anthocorids were observed at 20, 25 and 30 degrees C. At 35 degrees C, O. albidipennis had a significantly higher fecundity than O. laevigatus. Non-linear models were used to explain reproduction and female survivorship in relation to temperature. The upper reproductive thresholds were estimated at 40.9 +/- 0.3 and 35.5 +/- 0.1 degrees C for O. albidipennis and O. laevigatus, respectively. The different optimum temperatures may explain, at least in part, the different distributions of the two species in the Palaeartic region and their population dynamics in greenhouses and natural vegetation in the south of Spain. The estimation of rm as a function of temperature showed high variability between years. Three release rates of 0.75-0.25 Orius per plant are recommended from early March to mid May to deal with thrips outbreaks in pepper crops.

Animals↗
PubMed2001

Evaluation of diets for the development and reproduction of Franklinothrips orizabensis (Thysanoptera: Aeolothripidae).

The suitability of ten diets for the development and reproduction of Franklinothrips orizabensis Johansen, the key natural enemy of Scirtothrips perseae Nakahara, a pest of California grown avocados, was determined in the laboratory. The experimental diets evaluated were: (i) irradiated Ephestia kuehniella Zeller eggs; (ii) irradiated E. kuehniella eggs and avocado pollen; (iii) Tetranychus pacificus McGregor eggs; (iv) T. pacificus eggs and avocado pollen; (v) irradiated E. kuehniella eggs and T. pacificus eggs; (vi) irradiated E. kuehniella eggs, T. pacificus eggs and avocado pollen; (vii) Scirtothrips perseae; (viii) Heliothrips haemorrhoidalis (Bouchè); (ix) avocado pollen; and (x) a young avocado leaf. Franklinothrips orizabensis larvae were unable to develop to adulthood on diets 9 and 10. The remaining eight diets supported complete development of F. orizabensis, but only diets 1, 2, 5, 6, 7 and 8 produced fecund females. On diet 5, F. orizabensis exhibited high larval to adult survivorship (90%), mated females exhibited highest daily and lifetime fecundity, and the progeny of mated females were female biased (53%). Analysis of jackknife estimates of net reproduction (Ro), intrinsic rate of increase (rm), and finite rate of increase (lambda) were all significantly greater for F. orizabensis reared on irradiated E. kuehniella eggs and T. pacificus eggs (i.e. diet 5) than corresponding values for other diets on which female F. orizabensis were able to complete development and reproduce. Incorporation of avocado pollen into diets had an adverse effect on demographic statistics for F. orizabensis, and low quality diets resulted in male biased sex ratios for this predator.

Animal Feed↗
PubMed2003

The causes and processes of the mid-summer population crash of the potato aphids Macrosiphum euphorbiae and Myzus persicae (Hemiptera: Aphididae).

Populations of many phloem-feeding aphid species in temperate regions increase exponentially in early summer and then 'disappear', usually over a time-scale of a few days, in July. To understand these dynamics, empirical investigation of the causes and modelling of the processes underlying population change are required. Numbers of the aphids Myzus persicae(Sulzer) and Macrosiphum euphorbiae (Thomas), monitored over three years in commercial potato fields in the UK, increased to a maximum of 2-2.5 per leaflet on 16 July in 1999 and 2001, and then declined to < 0.25 per leaflet by 26 July. In 2000, aphid numbers remained very low (< 0.25 per leaflet) throughout the season. The onset of the crash in aphid numbers (16-19 July in 1999 and 2001) was consistently associated with changes in the phloem amino acid composition of potato leaflets. Natural enemies, including syrphids, parasitoids, coccinellids, chrysopids and entomopathogenic fungi, increased in abundance throughout the sampling period. The incidence of winged emigrant aphids prior to the crash was low (< 10%). Experimental manipulation during 2001 demonstrated that, during the crash period, the fecundity of aphids (caged on leaves to exclude natural enemies) was depressed by 25-45% relative to earlier in the season, and that presence of natural enemies reduced aphid numbers by up to 68%. Using these data, an excitable medium model was constructed, which provided a robust description of aphid population dynamics in terms of plant development-induced changes in aphid fecundity and temporal change in natural enemy pressure.

Amino Acids↗
PubMed2003

Food-plant effects on larval performance do not translate into differences in fitness between populations of Panolis flammea (Lepidoptera: Noctuidae).

In the UK, Panolis flammea (Denis & Schiffermüller) is a pest of monocultures of non-native lodgepole pine Pinus contorta Douglas, but not of the indigenous host Scots pine P. sylvestrisL. This difference in population dynamics may be due to the adaptation of P. flammea populations to the phenology, chemical composition and natural enemy complement of lodgepole pine. To ascertain if there was local adaptation of P. flammea populations to lodgepole pine, this study tested for improved performance of both larvae and adults on the host plant species from which they were sourced, compared with their performance on the alternative host plant species. No difference was found in the relative mean performance of populations sourced from Scots pine or lodgepole pine plantations, when fed on Scots or lodgepole pine foliage. Larvae grew faster on Scots pine but this difference did not translate into differences in pupal weight, female body weight or fecundity. Indeed, those insects that had fed on lodgepole pine had a longer lifespan than those that had fed on Scots pine, which, if translated into greater probability of mating or higher fecundity, could contribute to the observed outbreak dynamics in the field. The prediction that the observed outbreak dynamics of P. flammea can be explained by the existence of populations locally adapted to lodgepole pine was not supported. These results cast doubt on the use of larval growth parameters as surrogates of fitness in Lepidoptera.

Adaptation, Physiological↗
PubMed2004

Influence of temperature on the development, reproduction and longevity of Ceratothripoides claratris (Thysanoptera: Thripidae) on tomatoes.

Ceratothripoides claratris (Shumsher) is a serious pest attacking tomatoes in Thailand. Temperature-dependent development of C. claratris was studied at seven constant temperatures, i.e. 22, 25, 27, 30, 34, 35 and 40 degrees C. Pre-adult survivorship was greatest (95%) at 25 and 30 degrees C and shortest at 22 degrees C. Egg-to-adult time decreased within the range of 20 to 30 degrees C and at 34 degrees C it started to increase. The lower thermal threshold for egg-to-adult development was estimated at 16 and 18 degrees C by linear regression and the modified Logan model, respectively. The optimum temperature for egg-to-adult development was estimated at 32-33 degrees C by the modified Logan model. The influence of temperature on reproduction and longevity of C. claratris was determined at 25, 30 and 35 and 40 degrees C. Both inseminated and virgin females failed to reproduce at 40 degrees C. Virgin females produced only male offspring, confirming arrhenotoky. The sex ratio of the offspring of fertilized females was strongly female-biased, except at 25 degrees C. Mean total fecundity per female and mean daily total fecundity per female were highest for both virgin and inseminated females at 30 degrees C. Female longevity was longest at 25 degrees C and shortest at 40 degrees C. Male longevity was longest at 30 degrees C and shortest at 40 degrees C. The net reproductive rate (R0) and intrinsic rate of natural increase (rm) was greatest at 30 degrees C while, mean generation time (G) and the doubling time (t) were highest at 25 degrees C. The finite rate of increase (lambda) was fairly constant (1.1-1.5 days) over the three temperatures tested. The pest potential of C. claratris for tropical Asia is discussed.

Animals↗
PubMed2006

Reproductive traits of Monochamus galloprovincialis (Coleoptera: Cerambycidae) under laboratory conditions.

The pine sawyer Monochamus galloprovincialis (Olivier) is the vector of the introduced pine wood nematode Bursaphelenchus xylophilus (Steiner & Bührer) Nickle in Portugal, and until recently was considered a secondary forest insect. Under laboratory conditions, a study of biological and reproductive traits of 37 insect pairs was conducted. The longevity of both sexes was similar, being 61.2+/-6.5 days for males and 64.0+/-6.3 days for females (mean+/-SE). Sixteen small-sized insects (22% of the population) died within 20 days and before starting to reproduce. The sexual maturation period (without egg laying) was 20.4+/-0.7 days (mean+/-SE), while the oviposition period lasted 54.0+/-4.2 days (mean+/-SE). The oviposition rate increased very quickly during the first weeks of life, peaking to almost two eggs per day during days 30-44, and gradually dropping in the following weeks. The females laid an average of 67.0+/-5.96 (mean+/-SE) eggs through their lives. The hatch rate was 92.6+/-1.0% (mean+/-SE). There were large individual variations in longevity and fecundity parameters, and principal component analysis based on 16 morphological and biological parameters separated the breeding insects into four distinct groups. Almost half of the reproducing beetles were large-sized insects, with high longevity and fecundity traits. Overall, the reproductive potential of the Portuguese population of M. galloprovincialis seems to be smaller than that described for other Monochamus vectors of the pine wood nematode both in North America and Japan.

Animals↗
PubMed2001

Evaluation of avermectins as sandfly control agents.

The potential of avermectins as environmentally safe agents for the control of the sandfly vectors of Leishmania spp. was investigated in the laboratory. Female Phlebotomus papatasi and P. langeroni were fed either bloodmeals containing laboratory-grade ivermectin or sugarmeals containing a commercial-product based on abamectin. Low concentrations of either avermectin killed the sandflies, with median lethal concentrations (LC(50)) of just 13 ng ivermectin or 0.5 ng abamectin/ml for P. papatasi and 44 ng ivermectin or 35 ng abamectin/ml for P. langeroni. The feeding of female sandflies of both species with generally sublethal doses (LC(30)) of ivermectin in blood led to markedly reduced survival and fecundity (i.e. number of eggs laid/ovipositing female). However, addition of ivermectin to the bloodmeal (or of abamectin to the sugarmeal) of the females had no statistically significant effect on the proportion of their eggs that hatched. The results indicate that very small amounts of avermectin in their blood- or sugar-meals could control P. papatasi and P. langeroni, by killing many flies and, in the case of ivermectin, by reducing the fecundity of the survivors.

Animals↗
PubMed1985

Observations on the growth and population dynamics of Bulinus rohlfsi in an outdoor laboratory at Volta Lake, Ghana.

Two cohorts of Bulinus rohlfsi were reared separately in an outdoor laboratory at Volta Lake, Ghana. One group was kept in lake water with a mud substratum, the other in lake water without mud. Both cohorts were able to tolerate water temperatures ranging from 22.0 to 35.5 degrees C, but growth and survival were significantly greater for the cohort with mud. The overall intrinsic rate of natural increase, r, per fortnight was 1.096 for the snails having the mud substratum and 1.642 for the cohort not having it. The 'r' values were strongly influenced by high early fecundity of the snails in lake water only and low early fecundity of the snails with mud. Oviposition among the latter cohort was suppressed at times of high turbidity in the water above the mud substratum, caused primarily by suspended clay.

Animals↗
PubMedDate not supplied

Infecundity and consumption of polychlorinated biphenyl-contaminated fish.

Biologic capacity for reproduction, or fecundity, may be threatened by environmental contaminants, especially compounds capable of disrupting endocrine pathways. Telephone interviews that focused on reproductive events were conducted with female members of the New York State Angler Cohort Study who became pregnant between 1991 and 1993 and who reported known time to pregnancy (N = 895; 73%). Consumption of polychlorinated biphenyl-contaminated Lake Ontario sportfish and other factors were ascertained in 1991. The authors classified the women as follows: (a) fecund (time to pregnancy < or =12 cycles; n = 723); (b) having resolved infecundity (time to pregnancy > 12 cycles; n = 81); or (c) having unresolved infecundity (time to pregnancy > 12 cycles without pregnancy; n = 94). Adjusted odds ratios for duration of fish consumption for both resolved and unresolved infecundity were elevated (1.46 and 1.19, respectively), although confidence intervals included unity. Frequency of recent fish consumption was associated with an increased risk for select categories, although confidence intervals included one.

Adolescent↗
PubMed2002

Continuity of women's work, breastfeeding, and fertility in Ghana in the 1980s.

Much of the inconsistency that has appeared in studies of the effect of women's work on fertility in less developed countries has been attributed to the varying accessibility of employment in the modern sector. The analysis presented in this paper shows that continuity of work matters more than sector of work. It also confirms that, even in a setting of low contraceptive prevalence, increased fecundity associated with the less intense breastfeeding practices of working women do not result in shorter birth intervals. The influence of women's work on fertility control is likely to be underestimated if the effects of sporadic versus continuous work are conflated, or if fecundity differentials by work status are unmeasured.

Breast Feeding↗
PubMedDate not supplied

Inbreeding and fertility in a South Indian population.

Among 1913 women in Karnataka State, South India, 37.74% had married a relative (a consanguineous union), 60.79% were non-consanguineously married, and 1.46% did not know whether they had married a relative. Mean number of living offspring for consanguineously married women who had completed their reproduction was 3.89, and for the non-consanguineous 4.07. There is no significant difference in the mean level of fertility for the two groups measured in this way. Pre-natal mortality is lower (but not significantly) among consanguineously married women who have completed their reproduction than among the non-consanguineous group, but post-natal mortality is significantly higher among the conceptuses of the consanguineously married women. Although consanguineously married women conceive more frequently, that is, are more fecund than the non-consanguineous women (mean number of conceptions being 6.61 and 6.28, respectively), the difference is not significant. The differential survival of the offspring results in the consanguineous group having slightly lower net fertility, although the difference is not statistically significant. The lower sterility rates of the consanguineously married women (3.21% of all consanguineously married women show primary sterility compared to 3.47% of the non-consanguineous) may be due to greater compatibility of uniting gametes in the consanguineous marriages. The data reveal that women married to a relative and having completed their reproduction show higher fecundity, lower pre-natal mortality, higher post-natal mortality, lower sterility rates, and thus no significant difference in net fertility to those who had not married a relative.

Adolescent↗
PubMed1993

[The effect of commercial preparations of benlate, dithane M-45, copper sulfate and dichlofluanid on the fertility of Drosophila melanogaster meigen].

Four day old Drosophila pairs were maintained on nutritive media surface treated with fungicide doses according to the standard level recommended by the manufacturers. The flies were treated for 1 to 6 weeks and the eggs laid in 3 hours were counted each week during and after treatment. The capacity of treated flies egg laying was determined on treated media and then on untreated one. For the benomyl preparation (Benlate) and the mancozebe preparation (Dithane M45), there was an overall reduction of the egg mass on treated media but not on untreated media. There appears to be an essential repulsive effect which perturbs egg laying and causes a retention of eggs. However, after 3 to 4 weeks the quantity of egg mass also diminished on untreated media. Once the treatment was terminated the capacity to lay eggs partially returned. The copper sulfate preparation (Bouillie bordelaise) also exhibited a repulsive effect as exhibited by a retention of a certain number of eggs, but there was a more direct and fast effect on fecundity. Effect was more brutal with the dichlofluanide preparation (Euparène), and rapidly irreversible: the egg masses were very reduced after only one week of treatment on both treated and untreated media, and after termination of treatment there was an incomplete and temporary recuperation of the capacity to lay eggs. The results presented here are in agreement with those obtained previously concerning longevity. At the doses recommended for agricultural treatments, Benlate and Dithane M45 showed low toxicity for Drosophila adults in comparison with Bouillie bordelaise and Euparène which revealed a high toxicity in agreement with the fecundity and longevity data.

Aniline Compounds↗
PubMed1994

Effects of interleukin 12 on immune responses and host protection in mice infected with intestinal nematode parasites.

The cytokine interleukin (IL) 12 stimulates T cell and natural killer cell production of interferon (IFN) gamma and inhibits T cell production of IL-4. We investigated the effects of IL-12 on cytokine gene expression, immunoglobulin (Ig)E, mucosal mast cell, and eosinophil responses, and the course of infection in mice inoculated with the nematode parasite Nippostrongylus brasiliensis, as well as the IFN-gamma dependence of these effects. IL-12 stimulated IFN-gamma and IL-10 gene expression during primary and secondary N. brasiliensis infections and inhibited IL-3, IL-4, IL-5, and IL-9 gene expression during primary infections but had little inhibitory effect during secondary infections. IL-12 inhibited IgE, mucosal mast cell, and blood and tissue eosinophil responses during primary infections, but only eosinophil responses during secondary infections. IL-12 enhanced adult worm survival and egg production during primary, but not secondary infections. IL-12 needed to be administered by day 4 of a primary infection to inhibit IgE and mucosal mast cell responses, and by day 6 to strongly inhibit eosinophil responses and to enhance worm survival and fecundity. Anti-IFN-gamma mAb inhibited the effects of IL-12 on IgE secretion, intestinal mucosal mastocytosis, and parasite survival and fecundity, but did not affect IL-12 inhibition of eosinophilia. These observations indicate that IL-12, if administered during the initiation of eosinophilia. These observations indicate that IL-12, if administered during the initiation of an immune response, can change the response from one that is characterized by the production of T helper (Th)2-associated cytokines to one characterized by the production of Th-1 associated cytokines. However, IL-12 treatment has less of an effect once the production of Th2-associated cytokines has become established. In addition, our results provide evidence that Th2-associated responses protect against, and/or Th1-associated responses exacerbate, nematode infections.

Animals↗
PubMed1999

Density-dependent variation in lifetime breeding success and natural and sexual selection in Soay rams.

Variation in male lifetime breeding success (LBS) is central to understanding selection, yet it has rarely been measured in natural populations of large mammals. Here, we first describe variation in the opportunity for selection in cohorts of Soay rams (Ovis aries) on the archipelago of St. Kilda, Scotland, that were born during years of varying population density. Variation in LBS is closely coupled with demography, as rams born in years of low density following population crashes enjoy greater LBS than do those born in high-density years. Paradoxically, the opportunity for selection was greatest in the largest cohorts, those born in years of high population density, owing to low juvenile breeding success and overwinter survival. Variation in longevity and the contribution of nonbreeders were the most important components of the total variance in LBS in cohorts born in years of high density, while variation in fecundity was more important in cohorts born in low-density years. The opportunity for sexual selection is thus stronger in cohorts born in low-density years, as many rams in these cohorts survive to compete for mates as adults in subsequent ruts. Variation in population density in the year of birth also influenced the intensity of selection. Individuals born in years of high population density underwent strong natural selection in favor of longer hindlimbs over their first winter. In contrast, in cohorts born in low-density years, there was no natural selection on hindlimb in the first year of life. Longer hindlimbs were associated with increased fecundity over the entire lifetime of individuals born in low-density years. Natural and sexual selection thus act on the same trait in the same direction at different life-history stages in Soay rams, depending on the population density experienced in the year of birth.

Journal Article↗
PubMed2000

High and Dry: Drought Stress, Sex-Allocation Trade-offs, and Selection on Flower Size in the Alpine Wildflower Polemonium viscosum (Polemoniaceae).

Sex-allocation trade-offs may maintain variation in secondary sexual characteristics if such traits vary in their benefits or costs in association with different genders. In Polemonium viscosum, large flowers benefit both male and female aspects of reproduction. In this study, I explore how resource investment in flower size influences the cost of allocation to male and female function. Large flowers exact a water cost in P. viscosum under dry conditions. In an extreme drought in 1997, experimentally watered plants had higher survival and fecundity than controls. By comparing allocation patterns between plants dying from drought and survivors, I tested whether the demographic cost of large flowers increases with allocation to fecundity. Controls that died showed a positive relationship between flower size and fruit production, while survivors showed a negative relationship or trade-off. Watered plants showed no such trade-off. To test whether drought affects the relationship of corolla size to male function, I used leaf-water potential in 1998 to classify plants as stressed or unstressed. Corolla size showed positive correlations to pollen per flower regardless of drought stress. I conclude that under drought the demographic cost of producing large flowers is gender dependent, such that viability selection favors either small-flowered plants with female-biased reproduction or larger-flowered plants with male-biased reproduction.

Polemonium viscosum↗
PubMed2003

Spatial dynamics in model plant communities: what do we really know?

A variety of models have shown that spatial dynamics and small-scale endogenous heterogeneity (e.g., forest gaps or local resource depletion zones) can change the rate and outcome of competition in communities of plants or other sessile organisms. However, the theory appears complicated and hard to connect to real systems. We synthesize results from three different kinds of models: interacting particle systems, moment equations for spatial point processes, and metapopulation or patch models. Studies using all three frameworks agree that spatial dynamics need not enhance coexistence nor slow down dynamics; their effects depend on the underlying competitive interactions in the community. When similar species would coexist in a nonspatial habitat, endogenous spatial structure inhibits coexistence and slows dynamics. When a dominant species disperses poorly and the weaker species has higher fecundity or better dispersal, competition-colonization trade-offs enhance coexistence. Even when species have equal dispersal and per-generation fecundity, spatial successional niches where the weaker and faster-growing species can rapidly exploit ephemeral local resources can enhance coexistence. When interspecific competition is strong, spatial dynamics reduce founder control at large scales and short dispersal becomes advantageous. We describe a series of empirical tests to detect and distinguish among the suggested scenarios.

Ecosystem↗
PubMed2003

Determinism in a transient assemblage: the roles of dispersal and local competition.

Both dispersal and local competitive ability may determine the outcome of competition among species that cannot coexist locally. I develop a spatially implicit model of two-species competition at a small spatial scale. The model predicts the relative fitness of two competitors based on local reproductive rates and regional dispersal rates in the context of the number, size, and extinction probability of habitat patches in the landscape. I test the predictions of this model experimentally using two genotypes of the bacteriophagous soil nematode Caenorhabditis elegans in patchy microcosms. One genotype has higher fecundity while the other is a better disperser. With such a fecundity-dispersal trade-off between competitors, the model predicts that relative fitness will be affected most by local population size when patches do not go extinct and by the number of patches when there is a high probability of patch extinction. The microcosm experiments support the model predictions. Both approaches suggest that competitive dominance in a patchily distributed transient assemblage will depend upon the architecture and predictability of the environment. These mechanisms, operating at a small scale with high spatial admixture, may be embedded in a larger metacommunity process.

Animals↗
PubMed2004

Life-history consequences of investment in free-spawned eggs and their accessory coats.

The optimal trade-off between offspring size and number can depend on details of the mode of reproduction or development. In marine organisms, broadcast spawning is widespread, and external coats are a common feature of spawned eggs. Egg jelly coats are thought to influence several aspects of fertilization and early development, including the size of the target for sperm, fertilization efficiency, egg suspension time, polyspermy, embryo survival, and fecundity. These costs and benefits of investment in jelly result in trade-offs that can influence optimal reproductive allocation and the evolution of egg size. I develop an optimization model that sequentially incorporates assumptions about the function of egg coats in fertilization. The model predicts large variation in coat size and limited variation in ovum size under a broad range of conditions. Heterogeneity among spawning events further limits the range of ovum sizes predicted to evolve under sperm limitation. In contrast, variation in larval mortality predicts a broad range of optimal ovum sizes that more closely reflects natural variation among broadcast-spawning invertebrates. By decoupling physical and energetic size, egg coats can enhance fertilization, maintain high fecundity, and buffer the evolution of ovum size from variation in spawning conditions.

Animals↗