BIOASSAY SYSTEMS FOR THE PYRETHRINS

The special properties of pyrethrum assays with crawling insects by the film technique lend themselves to the twin cross-over design, hitherto restricted to assays with graded responses. The conditions under which this design is appropriate, and the treatment of control responses, are discussed. The design is particularly efficient with laboratory cultures of insects with fairly stable tolerance levels, and is also useful with heterogeneous populations collected in the field. Examples of the increased precision afforded are considered. The reversibility of the primary responses of grain weevils to the pyrethrins is also demonstrated.     

A METHOD FOR MEASURING THE NARCOTIC ACTION OF CHEMICALS USING THE GRAIN WEEVIL, CALANDRA GRANARIA

A method of measuring narcotic potency is described. Grain weevils ( Calandra granaria ) are exposed to the narcotic vapour in 2l. round-bottomed flasks illuminated from the bottom, and narcotic potency measured as number of grain weevils so affected as to be unable to climb the glass walls. Some common anaesthetics have been examined as an illustration of this method. Results are fitted by the probit plane
Y= A + b ₁ log α+ b ₂ log t ,
where Y = a function of the number of insects affected (probit); α= the thermodynamic concentration of the narcotic vapour; t = time of exposure of insects to the narcotic vapour. The values of the coefficients b ₁ and b₂ are discussed in relation to the biological action of the narcotic vapours.     

THE BIOLOGY OF THE RICE WEEVIL, CALANDRA ORYZAE (L.)

The length of the developmental instars of Calandra oryzae has been estimated at relative humidities of 50, 60, 70 and 80% at 21° C., at 70% at 18, 25 and 30° C., and at 80% at 18° C., by the dissection daily of samples of infested wheat-grains. The results are expressed as a median obtained by the method of probit analysis. Comparison of this method, with estimates of median and mean obtained by orthodox arithmetical methods from similar work on Rhizopertha , show that the probit method gives good estimates.
About 90% of the eggs laid are fertile. Normally only one adult will develop in a grain, all other individuals being destroyed by cannibalism. The sex ratio is unity. It was not possible to cross C. oryzae and C. granaria.
The daily oviposition rate of C. oryzae at 17, 21 and 25° C. increases with relative humidity. There is a critical point at about 60% r.h . below which egg laying declines rapidly, and mortality is high. At 100% r.h . the oviposition rates per female per day are approximately 1.3, 2.5 and 3.4 at 17, 21 and 25° C. respectively.
In experimental conditions most eggs per grain are obtained by giving isolated females one grain each, but more eggs are laid by females given more than one grain. Daily egg output is reduced by grouping females or including males. In culture, depths of grain up to 7 cm. do not discourage egg laying.     

具有抛物线解的Kolmogorov三次系统的极限环的存在性问题

本文证明了具有既不与两坐标轴相切,又不通过原点的抛物线解的Kolmogorov三次系统可以存在极限环．     

EXPERIMENTS WITH THE METHYLENE BLUE REDUCTION TEST FOR MILK

SUMMARY: The effects of shaking milk samples before the addition of methylene blue, delaying the time of addition of the dye, adding a second quantity of dye with a hypodermic syringe after the initial charge had been decolourized and of increasing the storage time or varying the testing time have been studied in five separate experiments. Vigorous shaking at the time of dye addition lengthened the reduction time. This effect was more pronounced when the milk was stored in a tube than in a bottle. Delayed addition of the dye resulted in a shorter reduction time than expected for inverted samples and longer than expected for samples which were not inverted between the time they were put into the 37° bath and the addition of the dye. Second additons of dye did not usually have reduction times exceeding 1 hr. Methylene blue reduction times did not necessarily decrease with successive tests carried out over a period of time on one sample: a time of 30 min. might persist over a series of tests for 4 hr. or more and small increase and decrease in reduction time with successive tests were also noted.     

CONSTRUCTION AND GROWTH KINETICS OF A BIOLUMINESCENT METHIONINE AUXOTROPH ESCHERICHIA COLI STRAIN FOR POTENTIAL USE IN A METHIONINE BIOASSAY

Methionine is one of the essential and first limiting amino acids in animal nutrition. In this study, an Escherichia coli methionine auxotroph bacterial strain that exhibits a linear growth response to methionine concentrations was transformed with a plasmid containing genes encoding ampicillin resistance and bioluminescence in order to develop a microbiological technique for methionine quantitation. Transformants were selected based on antibiotic resistance and plasmid containing candidates were confirmed by restriction enzyme digestion and gel electrophoresis. To confirm the bioluminescent phenotype, video imaging of the strain using long exposure photography yielded colonies exhibiting bioluminescence. The strain was also tested in the presence of ampicillin supplemented media with increasing methionine concentrations and growth response (measured as optical density, OD), growth rates and methionine affinities were compared before and after transformation. Although the transformed E. coli methionine auxotroph exhibited somewhat different growth kinetic responses than the nontransformed strain, the standard curves used for estimating methionine concentrations were not different. Based on the results in this study the transformed bioluminescent strain could be used as an OD-based assay if bioluminescence equipment and materials are not available.     

EXPERIMENTS WITH SOILS USED FOR CASING BEDS OF THE CULTIVATED MUSHROOM, PSALLIOTA CAMPESTRIS

In the present paper an account is given of observations and experiments on the influence of the casing soil on the cropping of beds of the cultivated mushroom, Psalliota campestris. It is shown from the results of a survey of cropping at thirty-nine mushroom farms that when the compost and cultural conditions are suitable for cropping, the production of mushrooms may be largely determined by the soil used for casing. Casing soils are classified into four grades depending on the numbers of sporophores formed, their rate of growth and the type of mushroom produced. A laboratory method of assessing the cropping potentialities of soils is described, and examples are given of its use for investigating field factors affecting the selection of soils for casing and the nature of the soil factors affecting cropping. It is suggested that chemical substances or specific surfaces in soils may promote cropping, but that close contact with air is necessary for them to be effective. It is concluded that direct trial is the only reliable method of assessing the value of a material for casing and that considerable fundamental research is needed on casing soils.     

A THEORY OF INJURY AND RECOVERY : II. EXPERIMENTS WITH MIXTURES.

1. The equations which serve to predict the injury of tissue in 0.52 M NaCl and in 0.278 M CaCl₂ and its subsequent recovery (when it is replaced in sea water) also enable us to predict the behavior of tissue in mixtures of these solutions, as well as its recovery in sea water after exposure to mixtures. 2. The reactions which are assumed in order to account for the behavior of the tissue proceed as if they were inhibited by a salt compound formed by the union of NaCl and CaCl₂ with some constituent of the protoplasm (certain of these reactions are accelerated by CaCl₂). 3. In this and preceding papers a quantitative theory is developed in order to explain: (a) the toxicity of NaCl and CaCl₂; (b) the antagonism between these substances; (c) the fact that recovery (in sea water) may be partial or complete, depending on the length of exposure to the toxic solution.     

肌苷产生菌抗低浓度8—氮鸟嘌呤突变株选育

以枯草芽孢杆菌SM－12－2为出发菌株,经物理、化学诱变剂连续处理,获得一株缺失AMP脱氨酶活性的突变株A－308。再对该突变株进行选育,获得一株抗低浓度8－氮鸟嘌呤突变株No．164。该突变株肌苷产量较亲株有明显提高,发酵周期缩短,菌落形态也有很大差别,摇瓶发酵肌苷产量18．75g／L。     

A BIOASSAY FOR COMPARING THE ACCEPTABILITY TO SLUGS OF PLANT EXTRACTS OR SOLUTIONS OF PURE CHEMICALS

A bioassay utilising a Y maze is described in which the responsesof slugs to aqueous plant extracts, or solutions of pure chemicalscan be evaluated. (Received 17 November 1977;     

EXPERIMENTS ON THE POSSIBLE CONTAMINATION OF HONEY WITH SCHRADAN

The reported low toxicity of schradan to honey-bees has been confirmed. This has led to the consideration of the possibility that this systemic insecticide might be present in nectar and subsequently appear in honey in an unchanged form.
Using radioactive schradan labelled with ³²P, it has been shown that spray applications of this insecticide to mustard and borage plants result in the contamination of nectar. A series of nectar samples taken over a 4-week period following spraying showed on radio assay a progressive decrease in total ³²P content and also in the amount of schradan present in proportion to the decomposition products. The highest figure recorded for the schradan content of nectar was 21 p.p.m.
Tests on the stability of schradan in contact with the honey stomach of the bee and also in contact with the enzyme invertase, in vitro , showed that no appreciable breakdown occurred. Furthermore it was shown that schradan was stable in contact with honey over a period of 2 1/2 months.
It is concluded that this systemic insecticide may appear in an unchanged form in the honey obtained from the nectar of plants which have been sprayed less than 4 weeks previously.     

生态学中一类n维反应扩散方程组解的性质

本文讨论一类不满足所谓的拟单调条件的反应扩散方程组的初边值问题．应用谱论和单调性方法证明了问题解的存在唯一性和平衡解的渐近稳定性．并进一步讨论了生态学中n种群单食物链模型的第二初值问题,得到了问题的非负平衡解的存在性和渐近性以及相应的吸引区域．     

STUDIES ON THE PERMEABILITY OF MEMBRANES : III. ELECTRIC TRANSFER EXPERIMENTS WITH THE DRIED COLLODION MEMBRANE.

The transfer numbers of the ions of electrolytes in the dried collodion membrane, as determined in a previous paper indirectly from the E.M.F. of concentration chains, can also be determined directly by electrical transfer experiments. It is shown that the difficulties involved in such experiments can be overcome. The transfer numbers obtained by the two methods are in satisfactory agreement. The experimental results obtained in the transfer experiments furnish an additional argument in favor of maintaining the theory that the electromotive effects observed in varying concentrations of different electrolytes with the dried collodion membrane may be referred to differences in the mobilities of the anions and cations within the membrane. As was shown by the method of the previous paper, the transfer number depends largely on concentration. There are some minor discrepancies between the values of the transfer numbers obtained by the two methods which, as yet, cannot be completely explained.