The Effect of Grain Number per Ear (Sink Size) on Source Activity and its Water-Relations in Wheat

Blum, A., Mayer, J. and Golan, G. 1988. The effect of grainnumber per ear (sink size) on source activity and its water-relationsin wheat.–J. exp. Bot. 39: 106–114. Work was done to evaluate the nature of sink-source relationshipsin wheat (Triticum aestivum L.), when the strength of the sinkwas modified by the removal of half of the grain from the earat about anthesis. The main hypothesis was that sink-sourcerelationship would be modified by water stress and that a weakersink would improve the drought resistance of the source. Two experiments were performed. The first experiment evaluatedthe effect of de-graining in two wheat varieties grown in thefield. The second experiment (in the greenhouse) evaluated theeffect of de-graining in plants subjected to water stress afteranthesis by immersing the root system in a solution of polyethyleneglycol (6000), as compared with non-stressed controls. In bothexperiments measurements were performed after de-graining toprovide data on leaf gas exchange, leaf water potential, osmoticadjustment of leaves and ears (greenhouse), the percent of stemweight loss as an index of stem reserve mobilization, finalroot weight (greenhouse) and ear weight components. De-graining caused a decrease in flag leaf stomatal conductance,carbon exchange rate (CER) and transpiration and an increasein flag leaf water potential. These effects were stronger withwater stress. De-graining did not affect osmotic adjustmentin the flag leaf but induced better adjustment in glumes andawns. De-graining decreased the percent of stem weight lossand increased final root weight, especially under drought stress. A weaker sink was, therefore, considered to improve plant droughtresistance in terms of the maintenance of higher leaf waterpotential, a larger root, a better osmotic adjustment in theear and, possibly, increased flag leaf longevity. The ‘cost’of this improved drought resistance was in reduced flag leafCER and reduced stem (and root?) reserve mobilization. Key words: Drought resistance, carbon exchange rate, stomata, transpiration, osmotic adjustment, leaf water potential, root, awns, yield     

Effects of diet and activity on lipid levels of adult Mediterranean fruit flies

Abstract. The objectives of this study were to determine whether adult Mediterranean fruit flies, Ceratitis capitata Wiedeman (Diptera: Tephritidae), are capable of synthesizing lipids, and whether adult diet affects this ability.Lipid levels in females fed protein and carbohydrate or carbohydrate alone declined significantly from emergence to the fourth day of life and then rose back to teneral levels on the fifth day, before oviposition took place on the sixth day.In males fed protein and carbohydrate, lipid levels initially declined as males aged and then stabilized.In carbohydrate-fed males lipid levels declined following emergence and recovered somewhat by the sixth day.Lipid levels declined significantly when flies underwent post-emergence starvation, but after substantial feeding on the above-mentioned diets they eventually (within 6–7 days) reached teneral levels in all experimental groups.Multivariate analysis of variance revealed that differences in lipid contents are primarily related to the flies' age, which corresponds to the various sex-specific activities these flies exhibit.Average lipid investment in eggs was found to equal teneral lipid levels in females.Without lipogenic abilities, oviposition would completely deplete female lipid reserves.We conclude that adult medflies are capaple of lipid synthesis, and that this capability is modulated by individual and sex-specific activity patterns.     

Nutritional reserves regulate male participation in Mediterranean fruit fly leks

1. The mating system of Mediterranean fruit flies ( Ceratitis capitata , Diptera: Tephritidae), is based on male leks that form on the foliage of trees. Following observations that not all males participate in leks, the hypotheses that (a) small males are absent from leks and (b) males with inadequate nutrient reserves are unable to participate in leks were examined.
2. The size and weight of lekking males ( n = 183) and resting males captured at the same time in the vicinity of leks ( n = 148) were established. In addition, using biochemical techniques, the amounts of sugar, glycogen, lipid and protein in each individual were established quantitatively.
3. There was no significant size difference between lekking and resting males. However, lekking males were significantly heavier and contained significantly more sugars and protein than resting males.
4. In conclusion, leks are exclusive, and only males with adequate nutritional reserves may join. Thus, in this species, reproductive success is closely linked to foraging success.     

Encystation of Entamoeba invadens IP-1 Is Induced by Lowering the Osmotic Pressure and Depletion of Nutrients from the Medium1

ABSTRACT. Trophozoites of Entamoeba invadens IP-1 can be induced to encyst in simple solutions composed of semipermeable constituents (buffer, salts, or sugars) provided that their osmotic pressure is in the range of 60–160 mosmol/kg. Optimal yield of mature cysts was obtained when the osmotic pressure of the medium was 110 mosmol/kg. Encystation could be obtained in the absence of serum although higher yields were obtained in its presence. No difference in the yield of mature cysts was found when either dialyzed or full serum was used. High yields of encystation were obtained (>70%) in the presence of 5% serum in solutions of NaCl, KCl, or MgSO₄, suggesting that the mechanism of encystation is not induced via sodium or potassium channels. Cysts were obtained in the presence of 72 mM glucose, indicating that depletion of a carbon source is not the only requirement for encystation. A rapid change in the density of the Entamoeba cells was observed upon transfer of trophozoites (density 1.061–1.073 g/ml) from growth medium to the low osmotic pressure encystation solutions. Within the first 2 min their density decreased (to 1.050 g/ml), but it soon increased, reaching within 30 min a density higher than 1.120 g/ml. As the encystation process continued to completion, the density of the cells gradually decreased, the mature cysts reaching a density of 1.049–1.061 g/ml.     

Leishmaniasis in the Jordan Valley. V. Dispersal characteristics of the sandfly Phlebotomus papatasi

Several characteristics of dispersing and non-dispersing Phlebotomus papatasi (Scopoli) were quantified and compared. The majority of dispersing sandflies, trapped crossing fallow fields, were females (68.5% v. 51.1%); of the dispersing females, 55.4% were parous, 48.1% were inseminated and 11.6% were gravid. In the population of sandflies sampled exiting from burrows of the sand rat Psammomys obesus Cretschmar, these categories, respectively, represented 39%, 90% and 26% of the females examined. Leishmania promastigotes were found in 9% of females exiting from P. obesus burrows, and in 2.7% of the dispersing females. The anthrone test established that the reason for activity of gravid females is sugar feeding. These females do not disperse and are suitable targets for future control measures.     

The effect of sand depth,feeding regime,density, and body mass on the foraging behaviour of a pit‐building antlion

Abstract 1. Pit‐building antlions are small sit‐and‐wait arthropod predators, which dig conical pits in sandy soils. We studied how biotic (conspecific density and feeding regime) and abiotic (sand depth) factors affect pit diameter and depth, while taking into account the larval body mass. 2. Pit diameter increased with larval body mass at a decelerating rate. In addition, larger larvae tended to relocate less frequently than smaller ones. 3. Sand depth positively affected overall pit size, while increasing conspecific density had a weaker but negative effect on pit size. 4. Feeding the antlions resulted in an increase in pit diameter compared with an unfed control group. However, as prey size increased this positive effect diminished. This result suggests that the existence of prey provides information about the quality of the microhabitat, triggering pit extension. However, similarly to the reduction in the foraging effort of saturated predators, antlions provided with large prey invested only little effort in pit enlargement. 5. Antlions were previously shown to be sensitive to prey and conspecific vibrations in the sand. We thus expected the feeding regime of the neighbour to affect antlion behaviour – surrogate of discriminating between local and global shortage of prey. Nevertheless, antlions with fed neighbours (a local prey shortage) did not show different behaviour compared with a control group in which both antlions were unfed (a global prey shortage).     

Energy budget of swarming male mosquitoes

Abstract.

• 1 The objective of this study was to determine, in the field, the energetic costs of swarming for male Anopheles freeborni (Diptera: Culicidae). By comparing the caloric contents of resting males to marked males captured after swarming, we established when sugar feeding takes place, what energy source is used to fuel swarming flight, and how much energy is invested in this activity.
• 2 Sugar-feeding takes place sometime during the night after swarming is concluded. Nectar sugars are therefore not immediately available to fuel flight. Stored sugars (trehalose and glucose) and glycogen are the primary sources of energy for flight. Lipids are not used to fuel flight but may be used in resting metabolism.
• 3 Male size is not related to feeding success. For males of all sizes, swarming consumes more than 50% of available calories. Accordingly, the ability of an individual to find and exploit nectar sources will greatly affect reproductive success.

     

Effect of bacteria on nutritional status and reproductive success of the Mediterranean fruit fly Ceratitis capitata

Abstract.  Mediterranean fruit flies ( Ceratitis capitata Wiedemann, Diptera: Tephritidae) harbor a community of diazotrophic bacteria in their digestive system. The present study aims to test the hypothesis that bacteria contribute to fly fitness by enhancing copulatory success and egg production in males and females, respectively. After eclosion, flies were fed a full diet containing peptides, sugar and minerals, or a sugar diet, lacking peptides. Subgroups from each diet were fed a mixture of the antibiotics ciprofloxacin and piperacillin. The presence of bacteria, food consumption, weight gain, lipid and protein levels, oviposition in females and copulatory success of males were quantified in the four groups. The antibiotic treatment effectively cleared the gut of bacteria. The relative amounts of food consumed (with or without antibiotics) are similar in all groups. The antibiotics do not inhibit feeding, and their ingestion does not affect dry weight or the amount of protein stored, yet females feeding on the full diet without antibiotics have increased lipid levels. Females fed the full diet produce significantly more eggs than females on the sugar diet, but the presence of bacteria does not affect numbers of eggs produced. However, in the absence of bacteria, the oviposition rate of nutritionally stressed females is significantly accelerated. The presence of bacteria in sugar fed males does not provide them with a mating advantage. Conversely, in males fed a full diet, the presence of bacteria is associated significantly with a shorter latency to mate. It is concluded that, because the bacterial community is present at all stages of the fly's life cycle, at least some species are effectively transmitted from parents to offspring, and removal of bacteria affects measurable physiological and behavioural parameters related to fitness, the association between bacteria and the medfly is mutualistic.