Temperature dependence of food intake,ammonia excretion and respiration in Ceriodaphnia reticulata (Jurine) (Lake Kinneret,Israel)*

The abundance of Ceriodaphnia reticulata (Jurine) in Lake Kinneret is restricted every year to the period March to June with a peak in May. The most constant parameter accompanying the peak is temperature with a range of 20–22° C. An attempt was made to clarify whether the estival high average temperatures observed in the epilimnion of this lake (27–28° C) could explain the decrease of the Ceriodaphnia population. Three physiological parameters: food intake, ammonia excretion and respiration rates, were measured experimentally at three temperatures (15, 22 and 27° C). The dry weight of individuals of the winter and summer populations were measured, and the percentages of egg-bearing females in the populations were calculated. It was found that temperature increase accelerates the rates of ammonia excretion and food ingestion. The acceleration was greater in the lower temperature range (15–22° C) than in the higher one (22–27° C). Conversely, the enhancing of respiration rate is higher in the upper temperature range. The resulting deficit of energy at high temperatures causes a reduction in body size and a significant diminution of egg production, which leads to a progressive decline of the population.     

Host choice by Aphidius colemani: effects of plants, plant–aphid combinations and the presence of intra-guild predators

Abstract.  1. This study first measured the effect of plant (radish, pepper, and wheat), aphid–plant combination (the green peach aphid Myzus persicae on pepper and radish, and the bird cherry-oat aphid Rhopalosiphum padi on wheat) and the host on which Aphidius colemani was reared (the cotton aphid Aphis gossypii on cucumber, M. persicae on radish and pepper, and R. padi on wheat) on host choice behaviour of the parasitoid and the performance of its offspring. Then, the effect of predator presence ( Coccinella undecimpunctata larvae) on host preference of the wasps was tested.
2. When reared on M. persicae on either radish or pepper , wasps preferred the aphid–plant combination from which they had emerged. Wasps reared on A. gossypii (naïve to all hosts offered) and R. padi preferred to parasitise M. persicae on radish and M. persicae on either radish or pepper, respectively. Rhopalosiphum padi on wheat was the least preferred and also the least suitable host, as determined by offspring body size.
3. Contrary to expectations, the presence of predators did not influence the host choice of A. colemani , even when predator-free plants were offered nearby. Results indicate that wasps are more likely to remain in some host systems but not in others, even when facing risk of predation.
4. Results are discussed in respect to field data and the relative importance of risk of predation and host preference to wasp fitness.     

Gall aphids do not select optimal galling sites (Smynthurodes betae; Pemphigidae)

Abstract. 1. In studies of insect-host plant interaction it is often suggested that insects preferentially colonize host plants (or sites within plants) on which their fitness is maximized (a positive covariance of preference and performance). This suggestion stems from the assumption that natural selection has driven the system toward optimal use of resources.
2. Our study of the galling aphid Smynthurodes betae Westw. demonstrates that the distribution of galls on leaves is not due to preference, and can be altered by manipulating the aphid arrival time or the shoot growth rate.
3. We found no correlation between gall density and performance (aphid clone size) at different positions along the shoot.
4. Because leaves on the growing shoot are not equally responsive to aphid stimulation, the colonizers have no choice but to settle on leaves that are at the right stage when they arrive.
5. S.betae colonizers did not discriminate between shoots of their host and a congeneric non-host, on which their fitness is invariably zero.
6. Synchronization between galler and host plant phenologies seems to be the key to the observed distribution of galls on the tree. The data give no support to the preference-performance hypothesis.     

Effect of the Thiol-oxidizing Agent,Diamide, on Acetylcholine Release at the Frog Endplate

REDUCED glutathione (GHS) is maintained in substantial concentration (3 × 10^?3 M) within neurones¹. The availability of new thiol-oxidizing agents like diamide^2,3, which freely enter cells and the principal action of which is to reduce the GSH concentration by conversion to GSSG (equation 1), promoted an investigation of the effects of these agents on release of transmitter at frog myoneural junctions. illustration

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Migration patterns and functional groups of spiders in a desert agroecosystem

Abstract 1. Arthropods living in annual crops suffer mortality caused by agricultural practices. Therefore, migration from surrounding habitats is crucial to maintain populations of natural enemies of insect pests in crops. In desert agroecosystems there is a pronounced contrast between managed and unmanaged habitats, where irrigated and fertilised crops are islands of productivity in an arid matrix. This contrast could either enhance or inhibit movement of natural enemies between the landscape components. 2. The importance of the surrounding arid habitats as a source for spiders in crops was examined in the Negev desert of Israel. Spiders were sampled in both arid natural habitat and adjacent wheat fields using pitfall traps and visual searching. In addition, spiders in wheat fields were sampled throughout the winter cropping season using emergence traps at increasing distances from the field edge. Stationary and movable emergence traps were used to distinguish between residents and migrant species. 3. The spider assemblage in the wheat was dominated by three families: Linyphiidae, Theridiidae, and Gnaphosidae. Spider sampling in both natural arid habitat and adjacent wheat fields enabled four functional groups to be recognised that differed in habitat preference, movement patterns, and population dynamics. Thirty‐three per cent of collected individuals were classified as crop residents whereas more than 50% were classified as migrants from the surrounding habitats. These findings suggest that the surrounding habitats influence spider assemblage composition in the fields, in spite of the marked contrast in habitat structure and productivity. 4. Spider assemblages in the wheat fields were dominated by migrant species arriving from the surrounding arid habitats. Migrant spiders inhabited the crop throughout the cropping season. The combined contribution of resident and migrant functional groups may act to prevent insect pest outbreaks in this desert agroecosystem.     

Gonad maturation,morphological and physiological changes during the first reproductive cycle of the crayfish Cherax quadricarinatus female

Summary

Concurrent morphological, anatomical and physiological changes took place during the first reproductive cycle in the Australian red-claw crayfish Cherax quadricarinatus, which prepared the female for spawning and holding of the newly deposited eggs. The endopod became longer and wider than the exopod and developed a mixture of plumose and long thin simple (ovigerous) setae. Small oocytes (0.24±0.05 mm) were present in the immature ovary. The growing ovary contained two distinct oocyte populations: one consisted of small (0.55±0.07 mm), barely growing oocytes, while the other consisted of large oocytes, which increased in size continuously (0.73 to 2.55 mm) until egg laying took place. A gradual change in the relative abundance of ovarian polypeptides occurred until the late vitellogenic stage (large oocytes < 1.8 mm). Three predominant female-specific, SDS-PAGE separated, polypeptides were observed (103, 78 and 73 kDa) that may represent vitellin subunits. The most abundant carotenoid in the ovary was astaxanthin, while β-carotene was present at a lower concentration. The strong correlation between the increasing diameter of the oocyte and the concentration of astaxanthin in the ovary and in the hemolymph suggested an association of astaxanthin with vitellin and vitellogenin.     

Interaction of Daylength and Applied Gibberellins on Stem Growth and Leaf Production in Three Varieties of Celery

Pressman, E. and Negbi, M. 1987. Interaction of daylength andapplied gibberellins on stem growth and leaf production in threevarieties of celery.—J. exp. Bot. 38: 968–971. Exogenous application of gibberellins (GAs) stimulated stemlength. The extent of this stimulation was less in long photoperiods,as long days (LD) or as long nights interrupted by night breaks(NB), than it was in short days (SD). Long photoperiods increasedthe length and erectness of leaves and reduced leaf number.Similar morphological changes were stimulated by applied GAs,which were more effective on plants grown in SD than on thosein LD. It is suggested that long photoperiods cause these morphologicalchanges via the production or metabolism of endogenous GAs,but it is not clear how endogenous GAs interact with the appliedones. Key words: Daylength, gibberellins, stem growth, leaf production, celery     

The structure and function of the scutellum of the Grarnineae

NEGBI, M., 1984. The structure and function of the scutellum of the Gramineae. Four kinds of scutella, of which only the first is universally known, can be distinguished in the Gramineae. (1) The scutellum sew stricto , the kind most commonly described in textbooks. In this scutellum the only growth activity during germination is the development of every epithelial cell into a separate elongated papilla. These papillae are involved in secretion of hydrolases, gibberellins and other hormonal factors which in their turn activate the aleurone layer; and in absorption of the mobilized endosperm reserves. (2) The kind characteristic of Auma is found in several genera. In this the scutellar tip elongates during germination, reaches the distal end of the endosperm sac and develops papillae over its whole surface. (3) The kind found in Cizuniu in which the scutellar tip elongates and extends to the far end of the caryopsis during embryo development, but not during germination. In this scutellum only the abaxial surface faces the bulk of the storage endosperm and probably only this surface becomes papillate. Several bamboo genera have the kind of scutellum characterized by Melocannu . This scutellum has evolved as a storage organ and in mature caryopses the endosperm is reduced. This kind is associated with vivipary and with the presence of storage tissue in the pericarp.
The vascularization and the structure of the scutellar epithelium, as studied mainly in a limited number of species belonging to the first kind, are related to the functions of the scutellum. The scutellum has a prime role in controlling the mobilization of endosperm reserves.     

THE STRIPED COLOUR PATTERN AND STRIPED/NON-STRIPED POLYMORPHISM IN SNAKES (REPTILIA: OPHIDIA)*

The occurrence of striped colour patterns and of striped/non-striped polymorphism systems among snakes is reviewed from literature data augmented by some personal observations. Among 1367 species, 190 were striped or had striped morphs. Of 11 families, the striped pattern was common mainly among Colubridae, presumably in relation to the active escape behaviour strategy, prevalent in this family. The striped species tended to cluster in a small number of genera. The 40 striped/non-striped polymorphism systems found, fall into five categories, according to the coloration patterns of the alternative morphs: (I) blotched (cryptic); (2) barred (or ringed); (3) plain; (4) melanistic; (5) albinistic. Most polymorphisms are presumably maintained by eco-behavioural trade-offs, depending on the category and on the habitat: The striped morph is presumed more effective in active escape and sometimes also in camouflage; the alternative morph may be more effective in camouflage, in active escape or in thermoregulation. Hence morph frequency depends on the habitat. Striped-albinistic polymorphism in Elaphe climacophora presumably depends on human protection of the albino morph.