Seasonal population changes of five parasitoids attacking the scale insect Nipponaclerda biwakoensis on the common reed, with special reference to predation by wintering birds

Seasonal changes in the abundance of five species of hymenopterous parasitoids (four species of Encyrtidae and one species of Eulophidae) attacking the scale insect Nipponaclerda biwakoensis on the common reed were investigated for 2 years in Lake Biwa, with special reference to predation by the reed bunting, Emberiza schoeniclus, during winter. The scales settled on reed shoot stems under sheath leaves, passing through three discrete generations per year. The abundance of adult female scales increased exponentially from July (first generation) to December (third generation). Adult female scales of the third generation overwintered on reed shoots. During winter, female scale abundance dramatically declined, whereas the number of predation marks made by reed buntings using their bills on reed sheath leaves increased. The generations of all five parasitoids were synchronized with the host scale generations, and the five parasitoids overwintered as larvae inside the scale bodies. The abundance of parasitized scales and parasitoid adults emerging from the scales also increased from July to December, but greatly decreased during winter. The overall parasitism rate of the female scales remained at relatively low levels (less than 40%) throughout the year, including before and after winter. A bird exclusion experiment revealed that the dramatic winter decrease of the abundance of the scale and its five parasitoids was due to intensive and non‐selective predation by the buntings on unparasitized and parasitized scales. Additionally, the proportion of immature parasitoids removed by birds varied between the five parasitoid species. Thus, seasonal population changes of the five scale parasitoids are considerably affected by bird predation on overwintering immature parasitoids.     

MAGNESIUM ION-REQUIRING STEP IN FERTILIZATION OF SEA URCHINS*

The magnesium ion-requiring step in fertilization of sea urchins was investigated. When eggs were inseminated in Mg-free sea water, several spermatozoa were found to bind to each egg surface with their reacted acrosomes without elevation of fertilization membrane. The number of binding jelly-treated spermatozoa to an egg did not differ regardless of the presence or virtual absence of magnesium ions. Although fertilization did not occur in Ca, Mg-deficient sea water (CM-deficient SW) even when jelly-treated spermatozoa were employed, some eggs could be fertilized by the addition of magnesium to the CM-deficient SW 60 sec after insemination, when jelly-treated spermatozoa had completely lost their fertilizing capacity in the CM-deficient SW. The acrosomal process of jelly-treated spermatozoa appeared to penetrate the vitelline layer in the CM-deficient SW. DTT- or pancreatin-treated eggs could not be fertilized in the virtual absence of magnesium. Re-fertilization using the fertilized eggs deprived of fertilization membrane did not occur under conditions of magnesium deficiency. These results suggest that external magnesium ions are indispensable at least for the fertilization process following penetration of the vitelline layer by the spermatozoa, such as fusion of the plasma membrane between an egg and a reacted spermatozoon, or the subsequent step(s) such as sperm penetration into egg interior and egg activation which precedes the cortical reaction.     

Changes in Adrenergic Innervation to Chromatophores During Prolonged Background Adaptation in the Medaka,Oryzias latipes

The pattern of adrenergic innervation to scale chromatophores of the wild-type medaka, Oryzias latipes, was examined by autoradiography with ³H-norepinephrine and found for the first time to be changed reversibly during prolonged background adaptation. In scales of the medaka, which was adapted to a black background for 10-15 days, a great number of melanophores and dense networks of varicose fibers were observed: many fibers built up a radial plexus around each melanophore. However, the dense distribution of varicose fibers disappeared with a decrease in the number of melanophores during long-term adaptation to a white background. As to the changes in the innervation pattern to amelanotic melanophores of the medaka, orange-red variety, a similar result was obtained. Although the increase in the number of leucophores was observed in the medaka adapted to a white background, no exact plexuses of labeled fibers were confirmed around leucophores. From these results, it is concluded that the density of chromatic nerve fibers changes in parallel with the variation of the number of melanophores during prolonged background adaptation.     

COMPARATIVE STUDIES ON VARIOUS CALLUSES AND CROWN GALL OF JERUSALEM ARTICHOKE II. SOME BIOCHEMICAL PROPERTIES

A callus isolated from Jerusalem artichoke tuber was found tohave much more cell wall material and tyrosinase activity thanthe original tuber, and its dry weight was dependent on thesucrose concentration in the culture medium. All calluses anda crown gall tested contained no detectable inulin. Even thoughdifferent cultures were widely different in their dry weight,this was closely related to their total hexose content, andthe latter in turn was proportional to their free hexose content. (Received January 18, 1967; )     

Light-Induced Pigment Aggregation in Xanthophores of the Medaka,Oryzias latipes

The response mechanism of medaka xanthophores to light was examined at the cellular level. Innervated and denervated xanthophores of adult medakas responded to light (9,000 lux) within 30 sec by pigment aggregation, and this aggregation was not mediated through α-adrenoceptors on the cell membrane. Maximum sensitivity to light was at wavelengths of 410–420 nm, and the direct effect of light was reversible. Xanthophore responsiveness to light in summer was higher than that in winter. Ca²⁺ and calmodulin were not involved in the response, but rather, an important role for cAMP and phos-phodiesterase (PDE) was suggested. It seems likely that photoreception by visual pigment which is sensitive to light at wavelengths of 410–420 nm increases PDE activity, probably via a G-protein, such as occurs with visual cells in the retina, which causes a decrease in levels of cytosolic cAMP, in turn leading to pigment aggregation within medaka xanthophores.     

Mitosis in Beating Cardiac Muscle Cells from Newt Embryos In Vitro

Cardiac muscle cells from newt embryos were cultured at relatively low cell density. Within 10 days in culture, 2 cell types (spindle and flat type) were distinguished both among beating and non-beating cells. Mitosis in single beating cells was frequently observed both in spindle and flat cells. Some cells maintained almost constant contractile activities throughout the mitotic stages, while the others transiently stopped beating during mitosis, which accords well to the case in chick embryos (1). Ultra-thin section shows the presence of myofibril's structure in a dividing cell, as shown in newborn rats (2, 3, 4), chick embryos (1, 5, 6, 7) and adult newts (8, 9). As a consequence of mitosis, 3 types (spindle, flat and mixed type) of beating colonies developed after 34 weeks in culture. Cell proliferation was accompanied with pulsation and could be directly pursued till the 4th division, suggesting that differentiated myocardiac cells with myofibrils proliferate by their mitoses in vivo , maintaining rhythmic contraction.     

Effects of Chemical Substances on Rate of Locomotion in the Amoeba Mayorella penardi1

The relationship between the locomotive velocity of amoeba which had not been fed for 24 h and the concentration of the test solutions was examined. With solutions of L-amino acids, protein substances, and alcian blue 8GS, an increase in velocity began at very low concentrations, reaching a maximum at a higher concentration and as the concentration increased further, the velocity fell to zero. In contrast, no increase was observed with D-glutamic acid and β-alanine. Moreover, the velocity of well fed amoebae did not increase significantly even in L-amino acid solution. These results may suggest a correlation between orthokinesis and amoeboid phagocytosis.