Diamondback moth females oviposit more on plants infested by non‐parasitised than by parasitised conspecifics

Abstract 1. When offered a choice, female diamondback moths (Plutella xylostella) oviposited more eggs on plants with non‐parasitised conspecific larvae than on plants with parasitised larvae. 2. The leaf area consumed by parasitised larvae was significantly lower than that by non‐parasitised larvae. However, this quantitative difference in larval damage did not explain the female’s ability to discriminate between plants with parasitised and non‐parasitised larvae, as females showed an equal oviposition preference for plants infested by higher or lower densities of non‐parasitised larvae. 3. Pupal weight and duration of the larval stage of P. xylostella were independent of whether larvae were reared on plants that were previously infested by either non‐parasitised or parasitised larvae. 4. The larval parasitoid Cotesia vestalis did not distinguish between plants infested by non‐parasitised larvae and plants infested by larvae that had already been parasitised by conspecific wasps. 5. Based on these data, it can be concluded that the moth oviposition preference for plants infested by non‐parasitised conspecifics relative to plants infested by parasitised conspecifics was not explained by plant quality or by the attractiveness of plants towards wasps. It is hypothesised that one of the reasons for this preference is avoidance of plants where a relatively high risk of parasitism is expected due to the emergence of parasitoids from the parasitised host larvae.     

DEPENDENCE OF PERIODIC DNA SYNTHESIS ON PROTEIN SYNTHESIS: DELAY OF DNA SYNTHESIS IN THE EARLY CLEAVAGE STAGE OF SEA URCHIN EMBRYOS TREATED WITH CYCLOHEXIMIDE AND COLCHICINE

The effects of cycloheximide and colchicine on cleavage and syntheses of DNA and proteins in cleaving embryos of the sea urchin, Hemicentrotus pulcherrimus , were examined. Cycloheximide caused delay of cell division with prolongation of the streak stage. Both inhibitors also caused delay in initiation of DNA synthesis. The decrease in the rate and prolongation of the period of DNA synthesis caused by these inhibitors varied with their concentrations and the time of administration. Initiation of DNA synthesis was delayed when cycloheximide was added to suspensions of embryos between the time after preceding DNA synthesis terminated and a definite time before the predicted time of initiation of the next synthesis of DNA, except at the stage of pronuclear fusion. However, when the inhibitor was added after initiation of the synthesis, the latter proceeded normally. Addition of 10 m m cycloheximide immediately after fertilization or 2 m m cycloheximide 60 min before fertilization also delayed DNA synthesis at the stage of pronuclear fusion, indicating that synthesis at this stage also required prior protein synthesis. Colchicine had less inhibitory effect on protein synthesis, but greatly delayed initiation of DNA synthesis and prolonged its duration. These facts suggest that a definite amount of a particular protein must be synthesized and accumulated in each synthetic cycle before initiation of DNA synthesis.     

Change in CO2 balance under a series of forestry activities in a cool-temperate mixed forest with dense undergrowth

To evaluate the effects on CO₂ exchange of clearcutting a mixed forest and replacing it with a plantation, 4.5 years of continuous eddy covariance measurements of CO₂ fluxes and soil respiration measurements were conducted in a conifer-broadleaf mixed forest in Hokkaido, Japan. The mixed forest was a weak carbon sink (net ecosystem exchange, −44 g C m⁻² yr⁻¹), and it became a large carbon source (569 g C m⁻² yr⁻¹) after clearcutting. However, the large emission in the harvest year rapidly decreased in the following 2 years (495 and 153 g C m⁻² yr⁻¹, respectively) as the gross primary production (GPP) increased, while the total ecosystem respiration (RE) remained relatively stable. The rapid increase in GPP was attributed to an increase in biomass and photosynthetic activity of Sasa dwarf bamboo, an understory species. Soil respiration increased in the 3 years following clearcutting, in the first year mainly owing to the change in the gap ratio of the forest, and in the following years because of increased root respiration by the bamboo. The ratio of soil respiration to RE increased from 44% in the forest to nearly 100% after clearcutting, and aboveground parts of the vegetation contributed little to the RE although the respiration chamber measurements showed heterogeneous soil condition after clearcutting.     

ENHANCEMENT OF 5-FLUOROURACIL CYTOTOXICITY BY CISPLATIN IN BRAIN TUMOUR CELL LINES

Cisplatin reportedly plays an important role as a chemical modulator in enhancing the chemotherapeutic effects of 5-fluorouracil on tumour cells. The aim of the present study was to test the synergistic cytotoxicity of cisplatin and 5-fluorouracil in 5-fluorouracil-resistant (C6) and -sensitive (9L) rat brain tumour cell lines. Survival fractions, determined using colony-formation assays, were compared following 5-fluorouracil treatment, with and without cisplatin. The presence of cisplatin (1–10μm ) enhanced cytotoxicity by more than three times compared with 5-fluorouracil alone in 5-fluorouracil-resistant C6 cells, whereas no enhancement effects were noted in 9L cells. These results suggest that a cisplatin-fluorouracil-based regimen may be promising in the treatment of 5-fluorouracil-resistant brain tumours.     

Contest‐type competition between age classes in scramble‐type Callosobruchus maculatus (Coleoptera: Bruchidae)

We examined the effect of age differences on competition type in individuals of a scramble‐type strain of Callosobruchus maculatus (F.). When oviposition of two individuals on a bean was manipulated to introduce time intervals using two lines with different adult body colors, the frequency of two‐adult emergence decreased with the introduction of sequential oviposition. This result indicates that an age difference between two individuals induces contest competition. The frequency of adult emergence in older individuals decreased, whereas in younger individuals it increased with the introduction of sequential oviposition. Using a dissecting microscope, we observed that bodies of older individuals that died in the bean during the 4‐day oviposition interval were crushed at the pupal stage under the pupal chambers of younger individuals. These results show that an age difference between two larvae in a bean causes contest competition due to one‐sided interference by a younger individual during pupation of an older individual. Based on these experimental results, we discuss the ecological cause of contest competition and the population‐level consequences of identified interactions in scramble‐type C. maculatus.     

Initiation of Sperm Motility Induced by Cyclic AMP in Hamster and Boar

When the plasma membrane of hamster and boar spermatozoa was extraced by treatment with Triton X-100 and the demembranated spermatozoa were transferred to a reactivating medium containing only ATP, axonemes were initially immotile, and then gradually became motile. Under these experimental conditions, the cAMP content in the reactivating medium increased soon. This suggests that cAMP is synthesized from ATP by adenylate cyclase involved in incompletely removed or solubilized residual sperm membrane and that the autosynthesized cAMP causes the delay in motility initiation. This delayed initiation of motility did not occur when phosphodiesterase was added to the reactivating medium and the phosphodiesterase-dependent quiescent sperm became motile instantaneously at any time when excess cAMP was supplemented. Furthermore, demembranated sperm which were diluted in the reactivating medium containing ATP and cAMP, immediately became motile. cAMP levels in the cell increased during the initiation of sperm motility in both species. These results suggest that cAMP is the real factor indispensable for the initiation of sperm motility at ejaculation in mammals.     

POLYSOMES OF THE SEA URCHIN EMBRYO: AN IMPROVED METHOD FOR EXTRACTION OF INTEGRATED POLYSOMES

Suitable conditions for extracting integrated polysomes from embryos of the sea urchins, Hemicentrotus pulcherrimus and Pseudocentrotus depressus were investigated.
Integrated polysomes could not be extracted under the conditions reported by other investigators. It was found, however, that use of 5 m m MgCl₂, 0.30 m KCl, 0.5 m m EDTA and 2 m m cycloheximide was effective for maintaining the integrity of polysomes. At higher concentrations of Mg²⁺, and even at higher concentrations of K⁺, monosomes and polysomes aggregated to form polysome-like particles which had sedimentation patterns with a small amount of nascent peptide. Thus, a medium consisting of 0.05 m Tris-HCl buffer, pH 7.5, 0.30 m KCl. 5 m m MgCl₂, 0.5 m m EDTA-2K, 2 m m cycloheximide, 5 m m mercaptoethanol and 0.5% (v/v) Nonidet P-40 is concluded to be the most suitable for extraction of sea urchin polysomes. Under the conditions used EDTA did not suppress polysome degradation completely and their degradation was linear with time.     

Host‐searching responses to herbivory‐associated chemical information and patch use depend on mating status of female solitary parasitoid wasps

1. In a tritrophic interaction system consisting of plants, herbivores, and their parasitoids, chemicals released from plants after herbivory are known to play important roles for many female parasitoids to find their hosts efficiently. On the plant side, chemical information associated with herbivory can act as an indirect defence by attracting the natural enemies of the host herbivores. 2. However, mated and virgin females of haplodiploid parasitoids might not necessarily respond to such chemical cues in the same way. Since virgin females can produce only sons, they might refrain from searching for hosts to invest eggs until copulation, in order to produce both sexes. 3. Here, we investigated differential host‐searching behaviours shown by mated and virgin females in the solitary parasitoid wasp, Cotesia vestalis, in response to herbivory‐associated chemical information from cruciferous plants infested by their host larvae, Plutella xylostella. 4. Mated females showed a significantly higher flight preference for host‐infested plants over intact plants, while no preference was observed with virgin females. Mated females also showed more intensive antennal searching and ovipositor probing behaviours to leaf squares with wounds caused by hosts than did virgin females. Furthermore, mated females stayed longer in host patches with higher parasitism rates than virgin females. 5. These results indicate that mating status of C. vestalis females clearly influences their host‐searching behaviour in response to herbivory‐associated chemical information and patch exploitation. Female parasitoids seem to forage for hosts depending on their own physiological condition in a tritrophic system.     

The Biology of Gregarina fernandoi n. sp. in the Cockroach Pysnoscelus surinamensis with Observations on its Development and Cytochemical Nature

SYNOPSIS. Gregarina fernandoi n. sp. is a eugregarine. Its structure, development and life history in the gut of the cockroach Pycnoscelus surinamensis are described. It is named as a new species on the basis of its size, nuclear structure, structure and form of the gametocyst and oocyst. Observations were made on the different stages of the parasite and related to the pH of the gut. In the ceca, pH 4.5–5, the parasite was in its early stages of development, in the midgut, pH 6.5–7, it was in syzygy and in the rectum, pH 7.5–8, gametocysts were found.