The spittlebug Philaenus spumarius feeds from mature xylem at the full hydraulic tension of the transpiration stream

Feeding dynamics in the spittlebug Philaenus spumarius were analysed to determine the food source. Evidence from previous reports indicates that this species and similar insects feed from the xylem. However, it is not clear whether they extract sap from the main transpiration stream, or from some subsidiary compartment of xylem, such as immature or cavitated vessels. In feeding from such subsidiary compartments, the insects could avoid the large hydraulic tensions thought to prevail in xylem on the main transpiration stream. Philaenus , for example, is shown here to initiate feeding, and to feed rapidly, from plants in which the full xylem tension is estimated at −10 bar. From measurements of feeding rates and feeding patterns in stressed and unstressed plants, it is shown that Philaenus cannot feed from subsidiary xylem compartments. It is concluded that this insect feeds directly from the main transpiration stream, and at the full hydraulic tension which prevails there. The anatomy of the feeding pump in Philaenus appears consistent with this conclusion. Spittlebugs therefore offer an experimental tool for quasi- non-invasive sampling of the transpiration stream.     

Localized industrial melanism in the spittlebug Philaenus spumarius (L.) (Homoptera: Aphrophoridae) in Cardiff docks, south Wales

Twenty-four large adult samples of the meadow spittlebug, Philaenus spumarius , were collected from within a 4 times 3 km area containing Cardiff docks, south Wales. All samples are highly polymorphic for colour and pattern and show marked geographic variation in the combined frequency of the eight melanic morphs (from <15% to > 75%). Maximum melanic phenotype frequencies in both sexes coincide with dock wharfs currently containing large accumulations of pulverized coal and these samples are heavily contaminated with small coal particles. However, interpretation of this association is complicated by the existence, until 1976, of a smokeless fuel factory causing local air pollution immediately adjacent to the area of highest melanic frequency. It is suggested that the association of high levels of melanism in P. spumarius with areas heavily contaminated with particulate pollutants is due to direct selective effects of small particles favouring melanies.     

Lagged effects of North Atlantic Oscillation on spittlebug Philaenus spumarius (Homoptera) abundance and survival

The North Atlantic Oscillation (NAO) is a large‐scale pattern of climate variability that has been shown to have important ecological effects on a wide spectrum of taxa. Studies on terrestrial invertebrates are, however, lacking. We studied climate‐connected causes of changes in population sizes in island populations of the spittlebug Philaenus spumarius (L.) (Homoptera). Three populations living in meadows on small Baltic Sea islands were investigated during the years 1970–2005 in Tvärminne archipelago, southern Finland. A separate analysis was done on the effects of NAO and local climate variables on spittlebug survival in 1969–1978, for which survival data existed for two islands. We studied survival at two stages of the life cycle: growth rate from females to next year's instars (probably mostly related to overwintering egg survival), and survival from third instar stage to adult. The latter is connected to mortality caused by desiccation of plants and spittle masses. Higher winter NAO values were consistently associated with smaller population sizes on all three islands. Local climate variables entering the most parsimonious autoregressive models of population abundance were April and May mean temperature, May precipitation, an index of May humidity, and mean temperature of the coldest month of the previous winter. High winter NAO values had a clear negative effect on late instar survival in 1969–1978. Even May–June humidity and mean temperature of the coldest month were associated with late instar survival. The climate variables studied (including NAO) had no effect on the growth rate from females to next year's instars. NAO probably affected the populations primarily in late spring. Cold and snowy winters contribute to later snow melt and greater spring humidity in the meadows. We show that winter NAO has a considerable lagged effect on April and May temperature; even this second lagged effect contributes to differences in humidity. The lagged effect of the winter NAO to spring temperatures covers a large area in northern Europe and has been relatively stationary for 100 years at least in the Baltic area.     

Population genetics of the spittlebug genus Philaenus (Homoptera: Gercopidae) in Greece

The electrophoretically detectable variability of 18 enzyme loci was studied in three species of the genus Philaenus: P. loukasi, P. spumarius and P. signatus . Four natural populations of P. loukasi , three of P. spumarius and two of P. signatus were analysed. Two loci, aldehyde oxidase-1 and aldehyde oxidase-2 were found to be in strong linkage disequilibrium in both populations of P. signatus . The enzyme loci acid phosphatase, peptidase-2, mannose-phosphate isomerase and aldehyde oxidase-2 proved to be powerful tools for the identification of the species in question. The colour polymorphism is discussed as well as the low average heterozygosities maintained by the three species (0.099 for P. loukasi , 0.027 for P. spumarius and 0.066 for P. signatus) . On the basis of electrophoretic data a phylogenetic tree is constructed.     

Elytral polymorphism in spittlebugs: Philaenus spumarius (L.) from the Inner Hebrides

The frequencies of colour and pattern morphs of the elytra of Philaenus spumarius are similar on three of the Small Isles of the Inner Hebrides (Eigg, Canna and Muck); the population on the fourth island (Rhum: is somewhat distinct but is like that at sea level on the nearby mountainous mainland. These similarities and differences suggest that these morph frequencies are regulated by natural selection.     

Transpiration inhibition by stored xylem sap from well-watered maize plants

There is increasing evidence that a chemical signal exists in xylem sap of plants subjected to water deficits which influences physiological responses in plant shoots. An important method of studying this signal is the transpiration response of excised leaves exposed to xylem sap collected from plants. However, Munns et al [Plant, Cell & Environment 16, 867–877] cautioned that transpiration inhibition is observed when xylem sap collected from wheat and barley is stored before determining physiological activity. The objective of the study reported here was to determine if transpiration inhibition develops in maize sap collected from well-watered plants when the sap is stored under various conditions. It was found that storage of maize sap collected from well-watered plants for only 1 d at -20°C resulted in the development of substantial transpiration inhibition in bioassay leaves. Storage of sap at 4°C resulted in the development of the effect after 2 weeks, while storage at ?86°C showed only small transpiration inhibition after 3 weeks. The major source of the transpiration inhibition was the development of a substance in the stored sap that resulted in physical blockage of the transpiration stream in bioassay leaves. However, a small signal component may also have developed in the stored sap. Because of the possibility of ionic activity under freezing conditions at ?20°C, calcium was studied for its potential involvement in the transpiration inhibition. However, the calcium concentrations found to inhibit transpiration were nearly an order of magnitude larger than the calcium concentrations observed in xylem sap.     

Genetic control of colour /pattern polymorphism in British populations of the spittlebug Philaenus sputnarius (L.) (Homoptera: Aphrophoridae)

The results of breeding experiments designed to determine the genetic control of the colour/pattern polymorphism in Philaenus spumarius in certain British populations are described and contrasted to previously published results for material taken from populations in southern Finland. The 11 principal phenotypes are controlled by seven alleles at a single autosomal locus, with complex patterns of dominance and co-dominance. In Finland, and most of the rest of the species' extensive range, the eight melanic morphs are wholly or substantially limited to the females, in which they are dominant to the typical form. Previously, this sex limitation has been explained in terms of reduced penetrance of melanic alleles in males and/or dominance reversal between the sexes, such that the eight melanic phenotypes (controlled by five alleles which are adjacent in the dominance heirarchy) are dominant to typical in the females but recessive in the males. Published data on morph frequencies in S Finland and on breeding experiments using material collected from these populations are re-examined and it is shown that neither theory accounts adequately for all the evidence. By contrast, in most British populations there is greatly increased penetrance in males of the melanic morphs which are strictly female-limited elsewhere. Breeding experiments, using P. spumarius taken from selected British populations, provide clear evidence that melanics are dominant to typical in both sexes. This difference in genetic control is entirely consistent with the balance of morph frequencies between the sexes in the populations from which the breeding material for the two separate studies was taken. Experimental material for this study was taken from populations in the Cynon Valley in south Wales, which have the highest melanic frequencies in the species' range and show particularly clear expression of melanic phenotypes in males. Both of these features are strongly correlated with severe aerial pollution from a local smokeless fuel factory. Selection for melanism in these populations is clearly strong, which probably accounts for the high level of penetrance and the dominance of melanics to typical in both sexes. Although further experiments are needed, it is suggested that regulatory loci, controlling the penetrance and expression of melanic alleles in males, could account for the observed differences in genetic control between populations in Britain and Finland.     

Relationships between feeding of Philaenus spumarius (L.) and the amino acid concentration in the xylem sap

Summary. 1. P.spwnarius nymphs selected young, upper leaves of Xanthium strumarium plants, which have a relatively high amino acid concentration in the xylem sap.
2. Nymphs selected or rejected a host leaf as a feeding site after a test ingestion of plant sap.
3. Nymphs fed on detached leaves kept with their petioles in a solution of amino acids, in preference to leaves with petioles in a solution containing no amino acids.
4. Nymphs caged on leaves with relatively high amino acid concentrations in the xylem sap suffered a lower mortality after 7 days than nymphs caged on leaves with low amino acid concentrations in the xylem sap.
5. Mean excretory rate increased with the increase in the amino acid concentration in the xylem sap for third and fourth instar nymphs, and adults, but not in fifth instars.     

Biosystematic studies on the spittlebug genus Philaenus with the description of a new species

Populations of the genus Philaenus were collected during the last 12 years at several places in Greece ranging in altitude from sea level to 2000 m. Within some of these populations the species P. spumarius (Linnaeus, 1758), which is widely distributed in Greece, and the Mediterranean species P. signatus (Melichar, 1896) occurred together. These two species can be easily distinguished by the size of the adults, and more precisely by internal genital structures. Surprisingly, some mountainous populations of P. spumarius also contained a new species. Externally the new species closely resembled P. spumarius , but careful examination of the male genitalia provided clear identification characteristics. The new species comprised one bisexual common colour morph similar to populi of P. spumarius and P. signatus and two rare unisexual morphs which are lacking both in P. spumarius and P. signatus. The new species occurred only at altitudes above 1200 m on Eryngium spp. (Umbelliferae) between June and August.     

Accumulation of weathered pp'-DDE in xylem sap of grafted watermelon

Movement of weathered p,p'-dichlorodiphenyldichloroethane (p,p'-DDE) from contaminated soil to the rhizosphere pore water to the xylem sap of grafted watermelon was studied under green house conditions. p,p'-DDE concentrations in pore water and xylem sap was compared in intact plants, homografted, and compatible heterografts of Cucurbita pepo spp. pepo and Citrullus lanatus plants. An average p,p'-DDE concentrations in pore water of contaminated soil ranged from 0.36 microg/L to 0.55 microg/L and there were no statistically significant among the cultivars. Conversely, the xylem sap p,p'-DDE concentration of heterografted watermelon having a zucchini rootstock and watermelon scion was 71 microg/L and it was greater than intact watermelon plants (0.49 microg/L) but less than that of intact plants of zucchini (141 microg/L). Homografting showed no effect on xylem sap p,p'-DDE concentrations of the identical cultivars. The bio-concentration factors (BCFs) which is an average p,p'-DDE concentration in xylem sap over average p,p'-DDE in pore water were 344, 325, 197, 1.28, and 0.89 for intact plant of zucchini, homografted zucchini, heterografted watermelon, homografted watermelon, and intact plant of watermelon, respectively. Xylem sap p,p'-DDE concentrations of the heterografted watermelon plants were clearly influenced by plant phylogeny and enhanced by the zucchini rootstock compared to intact watermelon plants.     

Refixation of xylem sap CO2 in Populus deltoides

Vascular plants have respiring tissues which are perfused by the transpiration stream, allowing solubilization of respiratory CO₂ in the xylem sap. The transpiration stream could provide a conduit for the internal delivery of respiratory CO₂ to leaves. Trees have large amounts of respiring tissues in the root systems and stems, and may have elevated levels of CO₂ in the xylem sap which could be delivered to and refixed by the leaves. Xylem sap from the shoots of three Populus deltoides trees had mean dissolved inorganic carbon concentrations (CO₂+H₂CO₃+HCO^?₃) ranging from 0. 5 to 0. 9 mM. When excised leaves were allowed to transpire 1 mM[¹⁴C]NaHCO₃, 99. 6% of the label was fixed in the light. Seventy-seven percent of the label was fixed in major veins and the remainder was fixed in the minor veins. Autoradiography confirmed that label was confined to the vasculature. In the dark, approximately 80% of the transpired label escaped the leaf, the remainder was fixed in the major veins, slightly elevating dark respiration measurements. This indicates that the vascular tissue in P. deltoides leaves is supplied with a carbon source distinct from the atmospheric source fixed by interveinal lamina. However, the contribution of CO₂ delivered to the leaves in the transpiration stream and fixed in the veins was only 0. 5% of atmospheric CO₂ uptake. In the light 90% of the label was found in sugar, starch and protein, a pattern similar to that found for atmospheric uptake of[¹⁴C]CO₂. Compared with leaves labelled in the light, leaves labelled in the dark had more label in organic acid, amino acid and protein and less label in sugar and starch. After a 5-s pulse the majority of the label fed to petioles in both the light and the dark was found in malate. The majority of the label was found in malate at 120 s in the dark; only 2% of the label was found in phosphorylated compounds at 120 s. The proportion of label found in phosphorylated compounds increased from 17% at 5 s to 80% at 120 s in the light. This suggests that CO₂ delivered to leaves in the light via the transpiration stream is fixed in the veins, a small portion through dark fixation into malate, the remainder by C-3 photosynthesis.     

Extraction of tracheal sap from Citrus and analysis of its nitrogenous compounds

Tracheal sap was extracted from sections of stems (0.5 to 1.5 cm in diameter and 7.5 to 15.0 cm in length) of orange trees (Citrus sinensis (L.) Osbeck cv. Washington Navel) by using a combination of the vacuum and liquid displacement methods. The volume of sap obtained and its concentration of nitrogenous compounds were dependent on the volume of displacing liquid used for the extraction. Four ml of water-saturated 1-butanol extracted essentially all of the xylem fluid present in the stem sections without apparent production of artifacts. The time of sampling affected the nitrogen concentration of the tracheal sap, but not the content of xylem nitrogen per volume of stem material. The orientation of the stems in the tree and the diameter of the stems had an effect on their contents of xylem nitrogen, with southeastern orientation and thinner stems showing higher concentrations. We could not detect the presence of ammonium, nitrites or proteins in the tracheal sap of orange trees. Most of the nitrogen was present as amino acids and about 2% of the total in the form of nitrates. The qualitative composition of amino acids, as determined by TLC, was the same both in winter and spring tracheal sap. The main components of the sap were proline and arginine in winter, and these amino acids together with asparagine and aspartic acid in spring.     

Seasonal dynamics of nutrients in leaves and xylem sap of coffee plants as related to different soil compartments

The northwestern province of Costa Rica is a marginal coffee growing area. At the onset of the rainy season low redox potentials probably induce the mobilization of soil Mn resulting in enhanced plant uptake of Mn. To test this hypothesis we monitored from April to the end of June 1995 the mobile Mn in the soil and nutrient and Mn concentrations in leaves and xylem sap of coffee plants. Every 2 weeks we took aggregate and bulk soil samples. The aggregates were mechanically separated into interior and exterior, air-dried and all soil samples were extracted with 1 M NH₄NO₃. We also extracted the field moist soil with distilled water. In addition, the 3rd and the youngest pair of coffee leaves and xylem sap were sampled and analyzed. According to the results of leaf analyses the nutrient supply of the coffee plants in general seemed to be balanced. However, Mn concentrations of 223 mg kg^-1 in the 3rd leaf pair at 18 April were above the optimum and the youngest leaves indicated Fe deficiency, but senescent leaves accumulated Fe and overcame the deficiency. Manganese concentrations in the xylem sap showed a pronounced maximum 2 weeks prior to a similar maximum of mobile Mn in the aggregate exterior. But in general the temporal variation of nutrient concentrations (especially Ca and Mg) in the plants are well correlated with the easily extractable nutrient concentrations in bulk soil. Probably due to its specific absorption and high rates of redistribution within the plant, K in the soil extracts did not correlate with plant concentrations. Element concentrations of youngest leaves could not be correlated with soil concentrations and are not considered to be an adequate tool for monitoring current nutrient uptake. Since plant element concentrations did not correlate with the aggregate interior, plants probably cannot use that nutrient source efficiently.     

Effect of high external NaCl concentrations on ion transport within the shoot of Lupinus albus. I. Ions in xylem sap

Abstract. Xylem sap was collected from individual leaves of intact transpiring lupin plants exposed to increasing concentrations of NaCl by applying pneumatic pressure to the roots. Concentrations of Na⁺ and Cl⁻ in the xylem sap increased linearly with increases in the external NaCl concentration, averaging about 10% of the external concentration. Concentrations of K⁺ and NO₃⁻, the other major inorganic ions in the sap, were constant at about 2.5 and 1.5 mol m⁻³, respectively. There was no preferential direction of Na ⁺ or Cl⁻ to either young or old leaves: leaves of all ages received xylem sap having similar concentrations of Na⁺ and Cl⁻, and transpiration rates (per unit leaf area) were also similar for all leaves. Plants exposed to 120–160 mol m⁻³ NaCl rapidly developed injury of oldest leaves; when this occurred, the Na⁺ concentration in the leaflet midrib sap had increased to about 40 mol m⁻³ and the total solute concentration to 130 osmol m⁻³. This suggests that uptake of salts from the transpiration stream had fallen behind the rate of delivery to the leaf and that salts were building up in the apoplast.     

Stomatal response to drying soil in relation to changes in the xylem sap composition of Helianthus annuus. II. Stomatal sensitivity to abscisic acid imported from the xylem sap

Sunflower plants [Helianthus annuus L.) were subjected to soil drought. Leaf conductance declined with soil water content even when the shoot was kept turgid throughout the drying period. The concentration of abscisic acid in the xylem sap increased with decreasing soil water content. No general relation could be established between abscisic acid concentration in the xylem sap and leaf conductance due to marked differences in the sensitivity of leaf conductance of individual plants to abscisic acid from the xylem sap. The combination of these results with data from Gollan, Schurr & Schulze (1992, see pp. 551–559, this issue) reveals close connection of the effectiveness of abscisic acid as a root to shoot signal to the nutritional status of the plant.     

Nitrate and reduced-N concentrations in the xylem sap of Stellaria media, Xanthium strumarium and six legume species

Abstract At an applied nitrate concentration of 1 mol m^?3, the proportion of xylem sap nitrogen as nitrate was < 15% for Cajanus cajan, Lupinus albus and Trifolium repens, 33% for Pisum sativum and within the range 57–62% for Glycine max, Phaseolus vulgar is, Stellaria media and Xanthium strumarium. At an applied nitrate concentration of 10 mol m～³ the value had increased to 66% for T. repens while at 20 mol m^?3 nitrate values had increased to 46, 51 and 49% for C. cajan, L. albus and Pisum sativum, respectively, and 89% and 85% for 5. media and X. strumarium, respectively. Glycine max and Phaseolus vulgaris differed from the other species in that the proportion of their xylem sap nitrogen as nitrate remained constant (～ 60%) as applied nitrate concentration increased from 1 to 20 mol m^?3. The proportion of total plant nitrate reductase activity in the shoot of C. cajan, S. media and X. strumarium increased as applied nitrate concentration increased from 1 to 20 mol m^?3. Values at the lower and upper concentrations were, respectively, 26 and 72% for C. cajan. 48 and 80% for X. strumarium and 68 and 87% for S. media. The partitioning of nitrate assimilation between root and shoot in these species is discussed.