A Daphnia Parasite (Caullerya mesnili) Constitutes a New Member of the Ichthyosporea,a Group of Protists near the Animal–Fungi Divergence

ABSTRACT. Caullerya mesnili is a protozoan endoparasite in the gut epithelium of Daphnia, which causes regular epidemics in lakes throughout Europe. Its classification has remained unchanged for over a century, leaving it placed with the Haplosporidia, despite speculation that this position is incorrect. The difficulty in classifying C. mesnili stems from its few known morphological and ecological characteristics, as well as a lack of genetic markers. Here we sequenced the nuclear small subunit (SSU) and internal transcribed spacer rDNA regions of C. mesnili samples from 10 locations. Based on sequence similarities, we suggest the re‐classification of C. mesnili to the Ichthyosporea, a class of protists near the animal–fungi divergence. We report average intragenomic variation of 0.75% and 2.27% in the SSU and internal transcribed spacer regions, respectively. From electron micrographs and light microscopy of histological sections we determined that C. mesnili spores grow within the intestinal epithelium where they establish themselves intercellularly. In addition, we confirmed previous accounts regarding the high virulence of this parasite. Caullerya mesnili reduces host lifespan, the number of clutches, and the total number of offspring. This high selection pressure placed on hosts supports the importance of C. mesnili as a model parasite for the study of host–parasite biology in permanent lakes.     

Cultural and insecticidal control of Thrips tabaci on onions in the Sudan

Onion thrips (Thrips tabaci) is the major pest of onions in the Sudan. In the Gezira Scheme onions are normally transplanted between October and January when the thrips population is very low. Later, thrips commence to breed. Early transplanted onions were well established before infestations became severe and, without the need for insecticidal control, produced significantly higher yields. Onions transplanted later, when thrips began to multiply, produced lower yields. Depending on the duration and intensity of infestation three to five sprays applied at fortnightly intervals were required to control thrips on the late transplanted crop. The effect of spray frequency on the development and yield of onions was investigated and the response found to be solely due to the extent of thrips control achieved. The toxicant itself had no effect on growth. Although the leaves were unaffected by the various treatments, spraying when most thrips were present increased fresh and dry leaf weights, bulb weight and, in the Hudeiba cultivar, the proportion of flowering plants. With the late-transplanted crop, light infestations led to yield losses of at least 39% whilst severe thrips attacks reduced the crop by 57%.     

Molecular Weight Determination of Nucleic Acids by Gel Electrophoresis in Non-aqueous Solution

IN most areas of research concerned with the structure, function and synthesis of nucleic acids the measurement of molecular weights plays an inescapable part. There are many instances of problems hinging on a rather precise knowledge of the molecular weight of a nucleic acid; examples of particular current interest concern both animal and viral messengers, which are larger than can be accounted for by the total protein message that they encode and ribosomal-RNA, the molecular weight of which bears on the question of the stoichiometry of ribosomal components. Unfortunately the classical methods of molecular weight determination present great difficulties. The quantities of material required are frequently outside the range of feasibility. Moreover, the non-ideality in these highly charged molecules and polydispersity^1,2 resulting from contamination with minor cellular components, or commonly products of nuclease degradation (as well as the need to determine the partial specific volume), combine to make molecular weight measurement a major research undertaking. The remarkable spread of published values for widely studied RNA species reflects these problems.     

Dissolved Oxygen Utilization as an Indicator of Total Microbial Activity on Non-metallic Materials in Contact with Potable Water

The technique for the assessment of growth of micro-organisms on non-metallic materials in contact with potable water employs standard microbiological counting techniques and a subjective visual assessment to measure the microbial activity that occurs in the test procedure. An alternative method of assessing microbial activity based on utilization of dissolved oxygen is described and compared with the existing method. The dissolved oxygen method was found to be a suitable alternative, the main advantages being reproducibility of results and a reduction in the cost of the test.     

The influence of powdery mildew (Erysiphe graminis) infection on the development of four spring wheats

Infection with Erysiphe graminis reduced the weight of the roots and aerial parts of four wheat cultivars of contrasting susceptibility at the three-leaf stage. It had little effect on the more resistant varieties at the five-leaf and flag-leaf stages. When ¹⁴C was supplied to the youngest fully expanded leaves at successive stages of growth, the proportion recovered from the roots, and that translocated to other tillers when present, was reduced, especially in the more susceptible cultivars.     

The Cure and Feeding of Windigos: A Critique

This paper suggests that, contrary to a view recently expressed, the usual treatment of windigo psychosis is not nutritional in nature. When ingestion is involved (which is rare), its sequel (vomiting to expell the windigo heart of ice) is given more curative importance, challenging the view that the northern Algonquians somehow "grasped" the idea of a nutritive cure for windigos. Nor is evidence, at this point, clear on nutritional causes of windigo.