摘要:

The reproductive output ofLepeophtheirus salmonisandCaligus elongatuswas examined for one coastal area in Ireland. Size ranges of adultL. salmoniswere examined in relation to reproductive output. The relative success ofC. elongatusandL. salmonisas parasites of farmed salmonids is discussed.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672260

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The intensity and timing of infestation events of caligid copepods in wild or cultured fish populations may be predicted from previous local production of nauplius I of the parasite. However, this relationship is not well established, the spatial scales over which it operates are unclear, and the role of host reactions to the invading copepodid is unknown. Rate of development (and population structure), generation time and rate and actual reproductive output are temperature-dependent. In Ireland between five and seven generations ofLepeophtheirus salmonis(Krøyer) can develop annually and generation time varies from over 120 days in winter to 23 days in summer. Host reactions may affect the rate of development of the parasite but are less important than temperature. Host reactions may also cause parasite mortality, but this effect is specific for individual host parasite associations. The distribution ofL. salmonisin cultured host populations is typically normal but is very over-dispersed in wild populations with heavy infestations. Parasiteinduced morphological damage to the host is correlated with physiological impacts. Physiological effects are present even when morphological damage is slight and so intermittent chemotherapeutic control of infestations cannot prevent some parasite impact from occurring.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672261

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The New World screwworm (NWS,Cochliomyia hominivorax) is an obligate parasite of warm-blooded animals. The female lays up to 300 eggs in any break in the skin, and the resulting larvae (screwworms) burrow into the surrounding living flesh. Infested animals frequently die, while the annual cost of controlling the pest in domestic animals is about US $10 per head.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672262

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Two major pests cause damage of economic importance to maize crops in France: the European corn borer (Ostrinia nubilalis), which has a worldwide distribution, and the pink maize stalk borer (Sesamia nonagrioides), which is present all around the Mediterranean. During winter, last instar larvae of these species exhibit a facultative diapause. Early forecasting of the field emergence period and a good knowledge of the overwintering survival (both strongly dependent on conditions controlling diapause maintenance and termination) are key features for effective management of these pests. In this connection physiological studies of diapause provide us with useful information. Special emphasis is given to variations of carbohydrate metabolism, particularly glycogen, trehalose and glycerol in both species. In the European corn borer the presence of glycerol and trehalose makes it possible to forecast diapause termination 2–3 months before the first field pupal molts. These data are used for the construction of a model of the population dynamics, developed by the National Institute of Agronomic Research. In the pink maize stalk borer we demonstrate the great sensibility of this pest to low temperatures, and we propose a novel cultural pest-suppressing method which is now being tested in collaboration with the General Association of Maize Producers.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672263

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Parasites are invariably characterized by a prodigious egg output and channel much of their metabolic activity towards reproduction. While certain aspects of reproduction, such as gametogenesis and egg formation, have received attention, surprisingly little is known about the mechanisms regulating reproductive physiology and behaviour. It is likely that these mechanisms will involve neuropeptides because, in the absence of endocrine glands and a circulatory system, it is the secretory (peptidergic) component of the nervous system that will serve as an endocrine system. The last few years have witnessed a growing awareness of the range of peptidergic molecules produced by parasites, a diversity that overshadows the number of transmitters produced by the conventional nervous system. Neuropeptides are distributed throughout the CNS; in addition, peptidergic elements occur in those components of the PNS that innervate the gonads and muscularised ducts of the male and female reproductive systems. Peptidergic cells are also associated with the eggforming chamber, or ootype, and the implications of this for the control of egg formation and as a possible target for chemotherapy are discussed.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672264

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The hypothesis that schistosome parasites influence physiological processes in their snail host by interfering with the (neuro-) endocrine systems regulating these processes has been verified by data obtained on the effects of parasitosis on reproduction and growth. Reproduction and growth, which show an inverse relationship, are clearly disturbed in parasitized snails. Schistosomin, a pepide of 79 amino acids, has appeared to play a crucial role in establishing these effects.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672265

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The normal sequence of spermatogenesis inFasciola hepaticahas been established. The single-celled primary spermatogonium—after three mitotic divisons and one meiotic division, accompanied by incomplete cytokinesis—gives rise to a rosette of 32 spermatid cells from which the spermatozoa differentiate. Rosette formation begins to develop at the tertiary spermatogonial stage and leads to individual cells being joined together via a central “cytophore”. As revealed by transmission electron microscopy (TEM), spermatogenesis is readily disrupted by the active sulphoxide metabolite of triclabendazole (TCBZSX), a relatively new benzimidazole anthelmintic. Following short incubation times in this drug (3 h onwards), the spermatogonial stages become mitotically inactive and detached from their normal position close to the wall of the tubule. The rosette stages become increasingly disrupted, with fragmentation of the cytoplasmic cytophore. After longer time periods (12–24 h) the testis tubules were almost completely empty with few spermatogenic stages or mature spermatozoa present. The ultrastructural effects of TCBZ-SX bear some resemblance to those observed after treatment with tubulozole, a potent microtubule inhibitor. The results with the two drugs are discussed in relation to the mode of action of triclabendazole, which at present is unknown.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672266

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In order to complete growth and development, the endoparasitoid wasp,Cotesia (=Apanteles) kariyai, inhibits pupation of its armyworm host,Pseudaletia (=Leucania) separata.In host larvae retardation of testis and spermatocyst development caused by the parasitoid was also observed. The agents causing the retardation were found in the ovaries and venom of the female adult parasitoid. When an unparasitized male host larva was artificially injected with calyx fluid obtained from ovaries together with venom, it showed the same degree of developmental retardation of testes and spermatocysts as in natural parasitization. Testes implanted in isolated abdomens of healthy larvae did not increase in size by ecdysteroid stimulation after exposure to calyx fluid plus venom. It is suggested that both symbiotic polydnavirus existing in calyx fluid and venom in the parasitoid,C. kariyai, are responsible for the parasitic retardation of the male reproductive organs in the host,P. separata.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672267

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Aphids are small plant sucking bugs that have prodigious rates of increase with an individual potentially capable of producing in the order of 1011descendants in the course of a season, which is considerably greater than the reproductive potential of other similar sized insects. It is of interest to ask: how have aphids achieved such high rates of population increase? A partial answer is that when conditions are favourable populations consist entirely of females that reproduce without males, i.e., they are parthenogenetic, and all individuals are capable of founding colonies, which rapidly increase in abundance. Thus one would expect aphids consistently to be serious pests of agriculture and forestry. However, not all years are outbreak years and it is therefore of practical importance to ask: what factors prevent aphids achieving pest status each year? This paper attempts to address these questions by taking a closer look at the reproductive biology and host plant relationships of aphids.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672268

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Seasonal reproduction is a dominant characteristic of the reproduction of major groups of marine invertebrates. The seasonality may be extreme culminating in very synchronised mass spawning events. Hypotheses to explain strongly seasonal reproduction are appraised in relation to demographic theory of life history which supposes that a limited resource (e.g., energy) may be allocated to (a) maintenance and defense against the environment (respiration, excretion, ionic regulation, etc.); (b) growth; or (c) propagule production and present reproduction. Allocation to each contributes to fitness through demographic components that can be defined by the Euler-Lotka equation. Hypotheses to account for strongly seasonal reproduction must explain the mechanism that confers selective advantage to highly seasonal non-random deployment of limited resources to reproduction.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672269

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor