Intra-tree foraging behavior of Ceratitis capitata flies in relation to host fruit density and quality

We examined the intra-tree foraging behavior of individually-released, wild-population Mediterranean fruit flies (medflies), Ceratitis capitata (Wiedemann), on field-caged host trees bearing each of three different densities (0, 3, or 12 per tree) of non-infested host fruit (kumquat) or each of two levels of fruit quality (12 non-infested fruit or 12 fruit infested with eggs and covered with host marking pheromone). With increasing density of non-infested fruit, medflies tended to remain longer in trees, visit more fruit before leaving, oviposit more often, accept a proportionately smaller number of fruit visited, and emigrate sooner after the last egg was laid (i.e. have a shorter Giving-Up-Time). Medflies spent much less time, oviposited much less often, and exhibited a longer Giving-Up-Time on trees harboring pheromone-marked fruit than non-infested fruit. Variation in temperature within the range at which experiments were conducted (25–36°C) had little detectable influence on foraging behavior. We compare our findings with published findings on the intra-tree foraging behavior of another tephritid fly, Rhagoletis pomonella (Walsh), and with current foraging behavior theory. We discuss implications of our findings with respect to medfly management strategies, particularly fruit stripping in eradication programs and use of synthetic marking pheromone for control.

---

Résumé Nous avons étudié le comportement de prospection dans un arbre, de femelles d'une population sauvage de C. capitata, libérées individuellement à l'intérieur de cages contenant des Eriobotrya japonica (kumquat), portant chacun 3 densités différentes de fruits no contaminés (0, 3, 12 par arbre) et chacun 2 niveaux de qualité de fruits: 12 fruits non infestés ou 12 fruits contaminés par des oeufs et recouverts de phéromone de marquage de l'hôte. C. capitata avait terndance à rester plus longtemps dans les arbres, à visiter plus de fruits avant le quitter, à pondre plus souvent, à accepter proportionnellement un nombre plus réduit de fruits déjà visités, à émigrer plus tôt après la ponte du dernier oeuf (c'est-à-dire à présenter un temps d'abandon plus bref), quand la densité des fruits non contaminés augmentait. C. capitata a dépensé beaucoup moins de temps, pondu beaucoup moins souvent, et présenté un temps d'abandon plus long sur les arbres portant des fruits marqués par la phéromone que sur ceux ayant des fruits non contaminés. Les variations de température dans la gamme de cells où les observations ont eu lieu (23–36°C) n'ont eu qu'une faible influence décelable sur le comportement de prospection. Nous avons comparé nos résultats avec ceux publiés sur la prospection à l'intérieur de l'arbre par une autre téphritide (Rhagoletis pomonella) et avec la théorie dominante sur le comportement de prospection. Nous discutons les conséquences de nos résultats sur les stratégies de lutte contre C. capitata, en particulier l'élimination des fruits dans les plans d'erradication et l'utilisation de phéromone synthétique de marquage.

     

Tissue-specific expression of porphobilinogen deaminase. Two isoenzymes from a single gene

Porphobilinogen deaminase (hydroxymethylbilane synthase; EC 4.3.1.8), the third enzyme of the heme biosynthetic pathway, catalyzes the stepwise condensation of four porphobilinogen units to yield hydroxymethylbilane, which is in turn converted to uroporphyrinogen III by cosynthetase. We compared the apparent molecular mass of porphobilinogen deaminase from erythropoietic and from non-erythropoietic cells by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and immune-blotting. The results indicate that two isoforms of porphobilinogen deaminase can be distinguished and differ by 2000 Da. Analysis of cell-free translation products directed by mRNAs from human erythropoietic spleen and from human liver demonstrates that the two isoforms of porphobilinogen deaminase are encoded by distinct messenger RNAs. We cloned and sequenced cDNAs complementary to the non-erythropoietic form of porphobilinogen deaminase encoding RNA. Comparison of these sequences to that of human erythropoietic mRNA [Raich et al. (1986) Nucleic Acids Res. 14, 5955-5968] revealed that the two mRNA species differ by their 5' extremity. From the mRNA sequences we could deduce that an additional peptide of 17 amino acid residues at the NH2 terminus of the non-erythropoietic isoform of porphobilinogen deaminase accounts for its higher molecular mass. RNase mapping experiments demonstrate that the two porphobilinogen deaminase mRNAs are distributed according to a strict tissue-specificity, the erythropoietic form being restricted to erythropoietic cells. We propose that a single porphobilinogen deaminase gene is transcribed from two different promoters, yielding the two forms of porphobilinogen deaminase mRNAs. Our present finding may have some relevance for further understanding the porphobilinogen deaminase deficiency in certain cases of acute intermittent porphyria with an enzymatic defect restricted in non-erythropoietic cells.     

Estimating the number of genetic elements that defer senescence inDrosophila

Summary Although many different physiological and biochemical changes characterize the process of senescence, little is understood of the genetic elements that determine its age of onset. We provide here the first estimates of the number of genetic factors that extend longevity inDrosophila melanogaster. Life span was measured in F₁, F₂ and backcrosses of true-breeding long and short-lived stocks ofD. melanogaster, established by selection. Estimates of the number of effective factors delaying senescence range from about 0.3 to 1.5, indicating control by a single factor. The distribution of longevity shows this to arise as selection acts on the short-lived parental stock. Life span is extended at the cost of early fecundity.     

Intracellular recording in the medullary pacemaker nucleus of the weakly electric fish,Apteronotus, during modulatory behaviors

1. The weakly electric gymnotiform fish, Apteronotus leptorhynchus, can be induced to perform a variety of modulations of its quasi-sinusoidal, electric organ discharge (EOD) in acute physiological preparations. These modulations, many of which are communicatory in function, include the jamming avoidance response (JAR). We have recorded intracellularly from neurons of the medullary pacemaker nucleus which is responsible for maintaining the ongoing EOD frequency during these modulatory behaviors. 2. We have used dye-filled microelectrodes to characterize single cell morphology of the two types of cells in the pacemaker nucleus (relay and pacemaker cells) and to localize anatomically the site of the differing responses we see during frequency modulations. We have also recorded with KCl-filled electrodes and attributed these data to cell type and location on the basis of characteristic behavior during these modulations. 3. Much of our data deals with chirps, brief accelerations of the EOD frequency lasting 10 to 14 ms. We see distinct patterns of activity in the pacemaker nucleus corresponding to different anatomical locations: the relay cell soma and axon, and the pacemaker cell soma and axon. Most of these loci show a marked rise in baseline voltage during the acceleration in spike frequency. The most unusual of these is the pacemaker cell axon which displays an often extreme decline in spike amplitude concurrent with the chirp (Fig. 7A). 4. 'Yodeling' (Dye 1987) appears to involve similar, characteristic changes in the pattern of firing as those seen during chirping. Similar quantitative analyses suggest that the JAR involves a different mechanism, however.     

Complete maps of IS1, IS2, IS3, IS4, IS5, IS30 and IS150 locations in Escherichia coli K12

Summary In this paper complete distribution maps are presented of the seven IS elements 1, 2, 3, 4, 5, 30 and 150. These maps were obtained during the construction of an almost complete restriction map of the Escherichia coli genome of K12 strain BHB2600. The positions of IS elements were correlated to this map. The distribution of integration sites of all IS types is nonrandom. Besides a large gap from 79 min to 96 min, there is a pronounced IS cluster at 6 min and another at 97 min, map locations that have low gene incidences on the classical map. One cluster coincides with a region of IS induced rearrangements. The IS distribution pattern was compared to patterns of strains W3110 and HB101.     

The effect of water and nitrogen amendments on photosynthesis,leaf demography,and resource-use efficiency in Larrea tridentata,a desert evergreen shrub

Summary In the Chihuahuan Desert of southern New Mexico, both water and nitrogen limit the primary productivity of Larrea tridentata, a xerophytic evergreen shrub. Net photosynthesis was positively correlated to leaf N, but only in plants that received supplemental water. Nutrient-use efficiency, defined as photosynthetic carbon gain per unit N invested in leaf tissue, declined with increasing leaf N. However, water-use efficiency, defined as the ratio of photosynthesis to transpiration, increased with increasing leaf N, and thus these two measures of resource-use efficiency were inversely correlated. Resorption efficiency was not significantly altered over the nutrient gradient, nor was it affected by irrigation treatments. Leaf longevity decreased significantly with fertilization although the absolute magnitude of this decrease was fairly small, in part due to a large background of insect-induced mortality. Age-specific gas exchange measurements support the hypothesis that leaf aging represents a redistribution of resources, rather than actual deterioration or declining resource-use efficiency.     

Seasonal variation in leaf chemistry of the coast live oak Quercus agrifolia and implications for the California oak moth Phryganidia californica

Summary The perennial foliage of the California coast live oak (Quercus agrifolia Nee) permits herbivores to feed on this oak species throughout the year. Patterns of herbivory for a two-year period on Q. agrifolia were observed in relation to seasonal and age-related changes in the nutritional and defensive characteristics of leaves. Nitrogen and phosphorus contents were higher in new leaves compared to mature foliage. Structural compounds (e.g., cellulose) in leaves rapidly increased with age. Concentrations of tatal phenolics (Folin-Denis) and astringency were higher in new foliage, and concentrations of condensed tannins gradually increased as the leaves matured. Peaks of herbivore damage were observed in June and in September–October, and were caused by outbreaks of the California oak moth (Phryganidia californica). P. californica, a bivoltine oak specialist, exhibited feeding preferences in June for old leaves over emerging leaves, and showed no preferences for leaf classes in September. These results suggest that P. californica is adapted to survive on nutritionally poor foliage and to circumvent quantitative defenses such as condensed tannins.     

Nuclear-magnetic-resonance imaging of leaves ofMesembryanthemum crystallinum L. plants grown at high salinity

Differences in water binding were measured in the leaf cells ofMesembryanthemum crystallinum L. plants grown under high-salinity conditions by using nuclear-magnetic-resonance (NMR) imaging. The 7-Tesla proton NMR imaging system yielded a spatial resolution of 20·20·100 m³. Images recorded with different spin-echo times (4.4 ms to 18 ms) showed that the water concentrations in the bladder cells (located on the upper and lower leaf surface), in the mesophyll cells and in the water-conducting vessels were nearly identical. All of the water in the bladder cells and in the water-conducting vessels was found to be mobile, whilst part of the water in the mesophyll cells was bound. Patches of mesophyll cells could be identified which bound water more strongly than the surrounding mesophyll cells. Optical investigations of leaf cross-sections revealed two types of mesophyll cells of different sizes and chloroplast contents. It is therefore likely that in the small-sized mesophyll cells water is strongly bound. A long-term asymmetric water exchange between the mesophyll cells and the bladder cells during Crassulacean acid metabolism has been described in the literature. The high density of these mesophyll cells in the lower epidermis is a possible cause of this asymmetry.Abbreviations CAM Crassulacean acid metabolism - NMR nuclear magnetic resonance - T_E spin-echo time