STUDIES OF FLUCTUATIONS IN INSECT POPULATIONS XIII. AN IMPROVED METHOD OF ASCERTAINING THE CORRECT DATE TO SAMPLE WHEN ASSESSING LARVAL INFESTATIONS OF THE WHEAT-BLOSSOM MIDGES

Fully fed larvae of the wheat-blossom midges need moist conditions in order to descend from the ears to the soil. A dry spell coinciding with the fully fed stage therefore causes an accumulation of larvae, which subsequently leave the ears in a body when rain comes. Conversely, in wet weather each larva leaves the wheat as soon as it finishes feeding, and, since all the eggs are not laid on the same day, the descent will then be a gradual process.
A method is described of taking small samples of wheat ears at frequent intervals, thus facilitating the determination of the correct date on which to take the main sample for the assessment of infestation by the two wheat-blossom midges.     

昆虫不育性药剂的研究——Ⅳ.昆虫不育剂的筛选

本文继续报告了另一批化合物(102种)作为家蝇成虫不育性药剂的筛选结果,仍用Mitlin(1958)或Labrecque(1960)的方法。结果指出:1)在取代嘌呤和嘧啶类中,5-氟乳清酸(5-Fo)(北昆-137)和5-氟尿嘧啶(5-Fu)(北昆 134)的效果为最好,不育性效果的级别是第一级(用 0.5%的剂量,处理24小时,不产卵,或卵不孵化或产卵量及孵化率抑制达90%以上);2)低剂量(0.01%)秋水仙素(北昆 139)长期处理效果极好,高剂量(1%)短期处理(24小时)造成全部死亡,用0.5%饲喂24小时,不能达到全部不育的效果,因此不育级别在1-2级之间;3)乙胺嘧啶类抗叶酸剂都有—定的效果,能减少家蝇的产卵数量,但对于孵化率没有影响;4)氨基甲酸酯类有几种(北昆56、45、57、59)具有较高或极高的毒性及击倒性,但是没有不育性作用,北昆58为北昆57、59的同分异构体,它的毒性极低,而有—定的不育性效果(三级);5)又试验了一批新的氮芥类化合物,作用也不显著,其中之一带有二个乙烯亚胺基(北昆73)效果较高,但由于该化合物已有些变质,尚待进一步试验证实;6)N-甲基羟基脲素(北昆74)的效果不高,但用1%浓度,处理96小时,产卵数为对照的40%,估计在长期饲喂时可能有效;7)结构类似 DDT的对二氯苯三氟甲基甲醇(北昆136),与文献上的报导相反,没有不育作用,但具有极高的毒性;8)喹啉类及其他类型化合物一般均无效。     

小麦吸浆虫研究Ⅱ.幼虫在麦穗上的生活

小麦红吸浆虫的生活圈是大家都知道的,它分为地上和地下两个部分。其中在地上部分所经历的时间很短促,主要是它的幼虫在麦穗上成长的一段时间。正是由于幼虫在麦粒上成长,因而造成小麦生产上的损失。 研究这种害虫,除了解它的发生时期以外,必然要注意到这样几个问题:一是成虫发生的数量,二是幼虫在麦穗上的数量,三是幼虫对麦粒的为害。其中有关于成虫发生数     

SYNCHRONOUS FLUCTUATIONS IN POPULATIONS OF SOME RAPTORS AND THEIR PREY

Raptorial birds which depend on a small number of prey species, especially those living in open habitats in the tundra, semi-desert and desert belts of the Palaearctic, undergo local fluctuations in numbers which are synchronous with the fluctuations in numbers of their main prey species. In this they contrast with the asynchronous or lagging type of predator-prey oscillation which has received wider attention in the literature.
Evidence from ringing recoveries shows that the species which fluctuate locally in synchrony with their prey tend to move greater distances from their birth-place or previous breeding place than those with more stable populations. The former species also tend to be split into fewer sub-specifically distinct forms than the latter. It is argued that the species which are subject to a fluctuating food supply have evolved, as an important adaptation, the ability to undertake more or less extensive 'searching migrations', which enable them to find and settle in areas of adequate food supply, often far removed from the previous breeding area. In the longer evolutionary aspect, this ability may be a factor promoting food specialization.
The synchronous population fluctuations of raptorial birds with their prey are compared with the asynchronous or lagging oscillations of carnivorous mammals.     

FURTHER STUDIES ON THE KINETICS OF OSMOSIS IN LIVING CELLS

Using unfertilized eggs of Arbacia punctulata as natural osmometers an attempt has been made to account for the course of swelling and shrinking of these cells in anisotonic solutions by means of the laws governing osmosis and diffusion. The method employed has been to compute permeability of the cell to water, as measured by the rate of volume change per unit of cell surface per unit of osmotic pressure outstanding between the cell and its medium. Permeability to water as here defined and as somewhat differently defined by Northrop is approximately constant during swelling and shrinking, at least for the first several minutes of these processes. Permeability is found to be independent of the osmotic pressure of the solution in which cells are swelling. Water is found to leave cells more readily than it enters, that is, permeability is greater during exosmosis than during endosmosis.     

TEMPORAL FLUCTUATIONS IN DEMOGRAPHIC PARAMETERS AND THE GENETIC VARIANCE AMONG POPULATIONS

Contrary to assumptions commonly made in the study of population genetics, the demographic properties of many populations are not always constant. Important characteristics of populations such as migration rate and population size may vary in time and space. Moreover, local populations often come and go; the rate of extinction and the properties of colonization may also vary. In this paper, the approach to equilibrium following a disturbance in the genetic variance among populations is described. The rate of migration is shown to be critical in determining the extent to which extinction and recolonization affects genetic differentiation. Perturbations and variations through time and space in demographic parameters such as population size and migration rate are shown to be important in determining the partitioning of genetic variance. Equations are given to predict the average through time of genetic differentiation among populations in the event of a single disturbance or in constant fluctuations in the pertinent demographic parameters. In general, these fluctuations increase the F_ST of a species. Spatial demographic variation affects F_STmuch more than temporal variation. These demographic properties make some species unsuitable for the empirical analysis of migration with indirect genetic measures. Demographic instability may play a large role in the evolution of genetic variation.     

五种库蠓脂肪酸的研究

本文用气相色语法分析了不显库蠓(Culicoides obsoletus)、兴安库蠓(C, sinanoensis)、怒江库蠓(C.Nujiangensis)、灰黑库蠓(C.Pulicaris)和刺整库蠓(C.Punctatus)等5种库蠓雌虫脂 肪醛的组成和含量。 结果表明,5种库蠓均含有12-14种主要脂肪酸,并以棕榈油酸(C_16：1)、棕搁酸 (C_16：0)、油酸(C_18：1)、硬脂酸(C_18：0)含量最高,共占脂肪酸总量的70%以上。对主要脂肪酸的含量进行聚类分析,发现不显库蠓种团内任意两种库蠓间的欧氏距离小于不显库蠓种团种类与灰黑库蠓种团种类间的欧氏距离,说明脂肪酸的定性、定量分析结果对库蠓分类有一定的参考价值。     

FURTHER STUDIES ON MEIOSIS IN THE MYXOMYCETES

Ross, Ian K. (Yale U., New Haven, Conn.) Further studies on meiosis in the Myxomycetes. Amer. Jour. Bot. 48(3): 244–248. Illus. 1961.—Photomicrographs of meiotic figures in 5 species of Myxomycetes are presented as further evidence of the time and location of meiosis in these organisms. Three members of the Physarales studied differed from species studied previously in that the cleavage of the protoplasm began during the second meiotic division and not after the divisions had been completed. Chromosome numbers were found to be in accord with previous observations and ranged from n = 25 to 90 depending on the species.