THE TOXICITY OF SOME INSECTICIDES TO FIFTH-INSTAR NYMPHS OF THE DESERT LOCUST

The toxicities of the insecticides γ-BHC, diazinon, dieldrin, DNC, heptachlor and parathion to fifth-instar hoppers of the desert locust were determined. Parathion and dieldrin were the most toxic, followed in descending order by heptachlor, γ-BHC, diazinon and DNC. The resistance of the hoppers to γ-BHC and DNC changed appreciably with age within the instar.
The effects of some factors which might influence the resistance of the insects were examined and are discussed.     

THE INFLUENCE OF ACIDITY ON THE MULTIPLICATION OF LACTIC STREPTOCOCCAL BACTERIOPHAGE IN LIQUID MEDIA

SUMMARY: Mass lysis of lactic streptococci infected with baeteriophage at 30° was prevented at pH 5·10. At lower pH values no multiplication of phage followed infection, and prolonged incubation at 30° resulted in loss of phage particles from unlysed samples. Adsorption of phage particles on host cells was unaffected by acidity, but no phage penetration of host cells took place. Host cell properties were apparently unchanged by adsorption of phage particles in acid whey.     

啮齿动物的巢区面积估算法

巢区(Home range)是动物在其巢附近进行取食、生殖、育幼等日常活动的区域(Burt 1940)。标志流放法是应用最广的调查啮齿动物巢区的方法,尤其是按方格式布笼。但对同一野外调查结果,由于估算方法不同,巢区估算值相差很大,并且至今尚无学者提出一致公认的估算法。1980年5-10月,我们在青海省门源县的高寒草甸生态系统定位站调查根田鼠的巢区,按多种估算法对同一批实际调查结果估计了巢区面积,并对结果进行了分析比较,检查其特点和优缺点,并提出修正平均值法,作为我们今后讨论根田鼠巢区动态的基础。 对方格式布笼的调查结果进行巢区的估算方法,基本上分二大类,图形法和概率性模型法。图形法是按照捕点分布划出巢区,并直接求出巢区面积,如最小面积法,包括或不包括周边地带法,最大距离法和复合散布图法。     

STUDIES IN THE MODE OF ACTION OF INSECTICIDES

Homogenates of the thoracic nervous system of Locusta migratoria migratoriodes are able to hydrolyse acetylcholine (ACh) and o -nitrophenylacetate (NPA), and this hydrolysis can be inhibited by tetraethylpyrophosphate (TEPP) at approximately the same molar concentration for both substrates. It is possible that one acetyl-esterase is responsible for the breakdown of the two substances, and there is no reason to assume the existence of a specific acetylcholinesterase. In normal horse serum, on the other hand, the pseudocholinesterase is quite distinct from the enzyme responsible for the breakdown of NPA.
In an attempt to correlate the inhibition of the locust nerve cord acetylesterase with toxic activity to insects and mice, four chlorinated diethyl-phenylphosphates were tested as contact poisons against a number of insects and by injection against locusts and mice, and also as in vitro inhibitors of locust nerve cord acetylesterase and horse-serum pseudocholinesterase. The chemicals were the 2-chloro-, 4-chloro, 2:4-dichloro- and 2:4:5-trichloro- analogues of diethyl-phenylphosphate.
Good correlation exists between their in vitro activity against the nerve-cord acetylesterase and their contact activity to aphids, but not between the former and injection toxicity to locusts. No correlation could be established between the inhibition of horse-serum cholinesterase and injection toxicity to mice. It is thought likely that the inhibition of nerve-cord acetylesterase is of greater importance in aphids than in other insects, where the toxic action of the phosphoric esters is at least partly concerned with other vital processes, and that a detoxication mechanism in the mammal breaks down some of the phosphoric esters, but not others.     

STUDIES IN THE MODE OF ACTION OF INSECTICIDES

Acetylcholine, choline chloride, acetyl-β-methylcholine, benzoylcholine, carbamyl choline, adrenaline and d -tubocurarine are non-toxic when injected into the locust. Prostigmine is also non-toxic, and eserine considerably less toxic to the locust than to man.
The toxic effect of tetraethyl pyrophosphate (TEPP) cannot be antagonized by injection of atropine or enhanced by d -tubocurarine.
The injection of acetylcholine chloride following injection of TEPP does not affect subsequent mortality.
These findings are discussed, and it is suggested that the physiology of the nervous system of the insect is unlike that of the mammal, neither cholinesters nor adrenaline being concerned in it. Phosphorus insecticides are thought to inhibit a general esterase not specifically connected with cholinesters.     

A FIBER APPARATUS IN THE NUCLEUS OF THE YEAST CELL

The structure and mode of division of the nucleus of budding yeast cells have been studied by phase-contrast microscopy during life and by ordinary microscopy after Helly fixation. The components of the nucleus were differentially stained by the Feulgen procedure, with Giemsa solution after hydrolysis, and with iron alum haematoxylin. New information was obtained in cells fixed in Helly's by directly staining them with 0.005% acid fuchsin in 1% acetic acid in water. Electron micrographs have been made of sections of cells that were first fixed with 3% glutaraldehyde, then divested of their walls with snail juice, and postfixed with osmium tetroxide. Light and electron microscopy have given concordant information about the organization of the yeast nucleus. A peripheral segment of the nucleus is occupied by relatively dense matter (the "peripheral cluster" of Mundkur) which is Feulgen negative. The greater part of the nucleus is filled with fine-grained Feulgen-positive matter of low density in which chromosomes could not be identified. Chromosomes become visible in this region under the light microscope at meiosis. In the chromatin lies a short fiber with strong affinity for acid fuchsin. The nucleus divides by elongation and constriction, and during this process the fiber becomes long and thin. Electron microscopy has resolved it into a bundle of dark-edged 150 to 180 A filaments which extends between "centriolar plaques" that are attached to the nuclear envelope.