Survival and development of Pieris brassicae larvae upon application of sublethal doses of chlordimeform

Larvae of the large cabbage white butterfly, Pieris brassicae L. are important pests of cruciferous crops. Third and fifth instars were treated topically with sublethal doses of the formamidine pesticide chlordimeform. A number of excitable actions were induced but they did not persist beyond 24 hours. Following the initial period, however, subsequent development was delayed and mortality increased, particularly when third instars were treated. Dosing fifth-instar larvae caused few further deaths. A link is suggested between these results and the nutritional status of the insects, and they are discussed in terms of how they might contribute towards control.

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Résumé Les chenilles de troisième et cinquième stades de P. brassicae L. ont reçu une application superficielle de chlordiméforme, insecticide à la formamidine. Les doses inférieures à 335 g/g ont été sublétales, provoquant plusieurs formes d'excitation. Bien que leur comportement soit redevenu normal en 24 heures, les troisièmes stades traités ont eu leur développement retardé et une mortalité accrue. Le traitement des chenilles plus âgées a eu moins d'effets. Une relation est suggérée entre ces observations et le régime alimentaire de cet insecte; une réduction de l'alimentation, plus importante chez les chenilles de troisième que de cinquième stade de P. brassicae, accompagne le début des altérations du comportement provoquées par le chlordiméforme. La discussion porte sur le mécanisme de contrôle sublétal du chlordiméforme, impliquant des effects immédiats et retardés.

     

Effects of gravel size and peat material concentrations on embryo survival and alevin emergence of brown trout,Salmo trutta L.

Embryo survival and alevin emergence pattern of brown trout were studied in simulated redds with different homogeneous gravel sizes and different concentrations of peat material. Optimal survival (95%) occurred in 18 mm gravel and survival decreased with decreasing gravel size. High concentrations (40%) of peat material resulted in low survival (65%). The proportion of premature emerging alevins increased in finer gravels and at high peat concentrations. Premature alevins had a large yolk sac and are probably very vulnerable to predators.     

Factors affecting the survival of E. coli in a river

The relationships between physical, chemical and microbial characteristics of an aquatic ecosystem and the survival of E. coli have been studied. Two conditions of the ecosystem (warm and cold) are considered. T₉₀ (time necessary for 90% of a bacterial population to die) in the warm situation shows an inverse exponential relationship with water temperature. Besides the direct relationship temperature-T₉₀, there is an indirect effect of temperature upon T₉₀ through the natural microflora of the water. The relationships between temperature and the heterotrophic population, and between the heterotrophic population and the bacterial consumers (P.F.U.), are exponential and linear, respectively.     

Influence of Meloidogyne hapla on Alfalfa Yield and Host Population Dynamics

Self-thinning in alfalfa, a dynamic process involving the progressive elimination of the weakest plants, was enhanced by Meloidogyne hapla. Alfalfa stand densities decreased exponentially with time and were reduced 62% (P = 0.05) in the presence of M. hapla. As stand densities decreased over time, mean plant weights increased at a rate 2.59 times faster in the absence of M. hapla. In a stepwise multiple regression analysis, 65% of the total variation in yield could be explained by changes in stand density and 85% by average weight of individual stems. Alfalfa yields were suppressed (P = 0.05) by M. hapla, with suppression generally increasing with time and as the nematode population density increased. Yield suppression was attributable primarily to the decline in plant numbers and to suppression in individual plant weights.     

Factors to consider in performing survival studies with insect cells

Summary Insect cell lines are not well-suited to colony formation in liquid medium following low-density cell plating. The present studies demonstrate that the time of addition of fetal bovine serum to the culture medium and the number of γ-irradiated feeder cells added to each plate are important factors in developing a useful colony formation assay. TN-368 lepidopteran and WR69-DM-1 dipteran cell lines were used for these experiments. Both cell types display increased plating efficiencies if serum is added to the medium one or more days prior to plating as compared to adding serum immediately before plating. Growth curves obtained by seeding cells at higher densities also indicate that cell growth is slightly better if serum is added one or more days before seeding. These findings are especially important for survival and toxicity studies because the results demonstrate that even seemingly minor factors involved in cell survival assays may benefit treated cells to a greater degree than untreated control cells, thus providing an erroneous assessment of cell survival. This work was supported by USPHS grant R01-CA34158, awarded by the National Cancer Institute, DHHS, Bethesda, MD.     

Patterns of protein synthesis during the germination of pea axes,and the effects of an interrupting desiccation period

As germination of axes of Pisum sativum L. seeds progressed, profound quantitative and qualitative changes occurred in the patterns of protein synthesis. This was shown by fluorography of gels following two-dimensional polyacrylamide gel electrophoresis separation of [³⁵S]methioninelabelled proteins. The effects of desiccation during germination on these in-vivo protein-synthesis patterns were followed. Desiccation differentially affected the synthesis of proteins. Usually, however, upon rehydration following desiccation the types of proteins being synthesized were recognizable as those synthesized earlier during imbibition of control, once-imbibed axes: seeds imbibed for 8 h, and then dried, did not recommence synthesis of proteins typical of 8-h-imbibed control seeds, but rather of 4-h-imbibed control seeds. Seeds imbibed for 12 h, and then dried and rehydrated, synthesized proteins typical of 4-h-and 8-h-control seeds. Thus drying of germinating pea axes caused the proteinsynthesizing mechanism to revert to producing proteins typical of earlier stages of imbibition. Drying during germination never caused the seed to revert to the metabolic status of the initial mature dry state, however.Abbreviation DR dried and rehydrated     

Early ontogeny of Adinia xenica (Pisces,Cyprinodontiformes): 3. Comparison and evolutionary significance of some patterns in epigenesis of egg-scattering,hiding and bearing cyprinodontiforms

Synopsis Developmental patterns as seen in cyprinodontiforms fishes with different reproductive styles are compared, and discussed in relation to ecology and evolutionary significance. The discussion centres around Adinia xenica (its detailed ontogeny presented in two previous sequels to this paper), and, from the existing literature, Fundulus heteroclitus (closely related), Austrofundulus myersi (an annual) and Platypoecilus maculatus (a livebearer). The embryonic resting interval is present in various forms in the first three species, and differences in it and the overall patterns of development are shown to be consistent with ecological conditions. Termination of the resting interval leads immediately to hatching, a process in A. xenica, as in F. heteroclitus, apparently initiated by the appropriate summation of internal and external factors. These factors include any or all of: metabolic changes and increased oxygen requirements, response to light, reduced environmental oxygen, agitation, and increased hydrostatic pressure. They all can cause increased movement by the embryo which is credited with rupturing hatching gland cells and releasing the enzyme(s). Annual fishes experience 3 pronounced resting intervals, termed diapauses. These are discussed in the context of apparent steps and thresholds, and evolutionary ecology. A possible evolutionary sequence, from a simple fractional spawning pattern to diapause, is presented. Morphological differences in primary embryonic respiratory surfaces, as seen in the four species, are related to environmental conditions. The above illustrate ways in which the same basic structures and events are modified to cope with different habitats.     

The first born,their dispersal,and vole cycles

Summary On the basis of some empirical data and the existing theory of vole cycles, a new hypothesis is proposed. It explains cyclicity as an effect of obligatory dispersal of the first seasonal cohort of young (Y1) from their natal (optimal) habitats into vacant (suboptimal) habitats. This behaviour could evolve, because it increases contribution of genetic lineages with dispersing Y1, to subsequent generation. It is assumed that the dispersal of Y1 is common among vole species, it does not change during consecutive phases of the cycle, and it does not vary between cyclic and non-cyclic populations. It results in multiannual cycles only under a certain set of spatial and climatic conditions, which are discussed in a paper. Otherwise it results in annual dynamics.     

Spatial Patterns of Entomopathogenic Nematodes in Microcosms: Implications for Laboratory Experiments

Laboratory microcosms were used to: i) measure the effects of soil moisture on survival of Steinernema riobravis and ii) investigate the suitability of using microcosms to study motility and survival of these nematodes. Nematodes recovered from soil contained in petri dishes declined by more than 95% during 7 days, whereas nematodes recovered from the inner surfaces of dishes increased 35-fold. After 7 days in dishes, >20 times as many nematodes were recovered from dish surfaces than from soil. Nematodes exhibited a negative geotropism; greater numbers of nematodes were recovered from the lid surfaces than from the surfaces of dishes. Survivorship of nematodes in soil in plastic centrifuge tubes was somewhat greater than in petri dishes, and fewer nematodes ascended above the soil line in tubes than dishes. Downward migration of nematodes was inversely related to soil column diameter, possibly due to relatively unimpeded movement along container surfaces. An assay was developed by which nematodes were rinsed from the inner surfaces of centrifuge tubes into the soil. The resulting slurry was then processed on Baermann trays to recover motile nematodes. Nematode survival in soil in centrifuge tubes was higher at soil moistures between 2-4% than at lower (0.5-1.0%) and higher (4.0-12.0%) moisture levels. Survival of S. riobravis may be enhanced by quiescence induced by moisture deficits.