Mechanical limitations on feeding by meadow spittlebugs Philaenus spumarius (Homoptera: Cercopidae) on wild and cultivated host plants

Abstract. 1. Field observations on the distribution of Philaenus spumarius (L.) on pearly everlasting (Anaphalis margaritacea) and alfalfa (Medicago sativa) showed that the range of feeding sites exploited increased with instar. Development of trichomes, depth of xylem elements, and tissue hardness were measured as possible factors determining the suitability of sites on food plants.
2. Spittlebugs caged outside their normal feeding sites experienced difficulty feeding. Experimental removal of trichomes showed that trichomes prevented younger instars from feeding on the stem. The depth of the xylem elements and tissue hardness were not significant barriers to feeding near the stem apex.
3. By caging fourth and fifth instar nymphs at increasing distances below the terminal bud on A.margaritacea stems, we showed feeding ability declined with distance below the apex, and feeding was more restricted in fourth compared to fifth instars. A similar decline was demonstrated in experiments with fifth instars on M.sativa.
4. On A.margaritacea, this restriction was associated with increasing tissue hardness of the stem with distance from the apex and the presence of trichomes in regions with hard tissues. On M.sativa the associated barriers were a combination of tissue hardness and reduction in the availability of xylem vessels in the penetrable region of the stem. Although the tissues impeding stylet penetration differed in the two hosts, the critical factor in both species was the increase in the amount of lignification of those tissues at increasing distances from the terminal bud.     

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.     

Ventral pigmentation variation in the meadow spittlebug Philaenus spumarius (L.) (Hemiptera,Cicadomorpha: Cercopidae)

The meadow spittlebug Philaenus spumarius (L.) (Hemiptera, Cicadomorpha: Cercopidae) exhibits heritable colour/pattern variation on the dorsal and ventral sides of the adults. Eleven principal dorsal morphs are grouped as melanics and non-melanics according to the pigmentation of the dorsal surface. An investigation of ventral pigmentation variation in Philaenus spumarius was carried out with laboratory breeding stock obtained from Llysdinam, Wales. Analyses of the 1552 individuals, 753 females and 799 males, indicated that the pigmentation on the ventral surface of the adult individuals which vary significantly is associated with dorsal morph. Ventral parts of the dorsal melanics are usually darker than in non-melanics in both females (Kruskal-Wallis one-way ANOVA: H = 372.70, d.f. = 7, P < 0.001) and males (H = 407.36, d.f. = 7, P < 0.001). The combined “C” group morphs (flavicollis + gibbus + leuco- cephalus) are always darker than all other morphs in both sexes.     

Physiological tolerance, climate change, and a northward range shift in the spittlebug, Philaenus spumarius

Abstract.  1. Considerable evidence indicates that the Earth's climate has warmed over the past 20 years and most models predict that this process will continue or accelerate. Previous studies involving butterflies and other species have shown that ranges have shifted towards the poles although the mechanisms responsible for these range shifts have not been demonstrated conclusively.
2. Here it is reported that the range of the meadow spittlebug has moved northward along the California coast since 1988.
3. Survival and reproduction of this species in previous laboratory experiments were very sensitive to humidity and temperature. Small deviations from optimal conditions resulted in high mortality.
4. These laboratory results were corroborated by annual field censuses from one location since 1983 in which population densities of spittlebug nymphs were positively correlated with summer humidity and negatively correlated with temperature deviations from the published optimum. Thus it is shown that there are strong links between physiological tolerance and a geographic range shift associated with climatic change.     

Insect mitochondrial genomics: the complete mitochondrial genome sequence of the meadow spittlebug Philaenus spumarius (Hemiptera: Auchenorrhyncha: Cercopoidae).

We present the complete mitochondrial genome sequence of the meadow spittlebug Philaenus spumarius (Auchenorrhyncha: Cercopoidae). This contribution represents the second mitochondrial genome from the Hemiptera and the second of the three hemipteran suborders sampled. The genome is a circular molecule of 16 324 bp with a total A+T content of 77.0% and 76.7% for coding regions only. The gene content, order, and structure are consistent with the Drosophila yakuba genome structure (Clary and Wolstenholme 1985) and the hypothesized ancestral arthropod genome arrangement (Crease 1999). Nucleotide composition and codon usage are near the means observed in other insect mitochondria sequenced to date but have a higher A+T richness compared with the other hemipteran example, the kissing bug Triatoma dimidiata (Dotson and Beard. 2001. Insect Mol. Biol. 10: 205-215). The major noncoding region (the A+T rich region or putative control region) between the small ribosomal subunit and the tRNAIle gene includes two extensive repeat regions. The first repeat region includes 19 tandem repeats of a 46-bp sequence, whereas the second contains a longer sequence (146 bp) tandemly repeated four times.     

Industrial melanism in the spittlebug Philaenus spumarius (L) (Homoptera: Aphrophoridae)*

The visible polymorphism of the spittlebug, Philaenus spumarius, has been investigated in the vicinity of a smokeless fuel factory in the Cynon Valley of south Wales. The factory is a significant source of local particulate air pollution. A striking relationship exists between the combined frequencies of the eight dark (melanic) morphs and proximity to the factory. Maximum melanic phenotype frequencies of over 95“, occur in both sexes immediately adjacent to it and decline to levels normal for south Wales 1.5–6 km away, depending on direction. This relationship is largely confined to sites within the valley; samples from adjacent localities outside it have melanic frequencies within normal limits for the south Wales area. Maximum melanic phenotype frequencies in the Cynon Valley are far higher than any known from elsewhere in the species range in Europe, Asia and North America. No consistent difference is apparent in total melanic frequency between males and females at any of the sites in this study. However, marked differences exist between the sexes in the relative contributions of the eight melanic phenotypes to the overall association with the factory. For females the industrial melanism is entirely attributable to the group flanicollis + gibbus + leucocephalus (mainly leucocephalus) whereas in males both this group and the group quadnmaculatus + albomaculatus + leucopthalmus contribute to the relationship. It is suggested that this relationship is due to the selective effects of the local air pollution from the factory. The exact nature of the selection involved is as yet uncertain; it would appear to be strong since the local adaptation involved has developed in a maximum of 40 generations since the factory was opened. Finally, comparison is made with two other insects, a ladybird and a moth, in which high frequencies of melanic forms are also associated with this pollution source.     

Xylem feeding by spittlebug nymphs: some observations by optical and cryo-scanning electron microscopy

The feeding of spittlebug nymphs (Philaenus spumarius) from mature xylem vessels was studied by optical and cryo-analytical scanning electron microscopy. Feeding did not produce xylem embolisms and vessels remained liquid-filled during the day. Saliva secreted by the insect forms a hardened lining (salivary sheath) between the stylet bundle and the plant tissues. This sheath is continuous through the hole made by the stylets as they enter a vessel, and it extends into the vessel and along its periphery beyond the breach. The sheath is heterogeneous, with a thin outer layer adjoining the plant tissues and a thicker layer that contacts the stylet bundle. Both layers give positive histochemical reactions for proteins and, in fresh tissues, contain a red, strongly autofluorescent pigment, possibly condensed tannin derived from the plant (which is lost during tissue preparation), and other phenyl propanoid compounds, which are retained and which may produce the intense reaction of the periodic-acid-Schiff's-positive inner layer. It is concluded that the salivary sheath allows the insects to feed from functioning vessels without embolizing them or losing xylem fluid to the surrounding tissues. These findings and others in the entomological literature indicate low daytime tensions in the xylem conduits of the host plants.     

Artificial diet delivery system for Philaenus spumarius,the European vector of Xylella fastidiosa

Artificial diets represent an essential tool for investigations on the intimate relationship between plant pathogens and their vectors. Previous research failed in devising an artificial diet delivery system for the meadow spittlebug Philaenus spumarius, to date considered the most important vector of the bacterium Xylella fastidiosa in Europe. Here, we describe a new delivery “tube system” by which we succeeded in artificial feeding of P. spumarius with holidic diets (one sucrose diet and two amino acids diets). Spittlebug probing and feeding behaviour on either the tube system or a traditional “flat system” realized out of a small Petri dish filled with diet and covered with stretched Parafilm^® were observed in real time by video‐EPG (Electrical Penetration Graph), in order to assess the occurrence of ingestion and excretion. Moreover, we evaluated P. spumarius survival on either the tube system filled with the two holidic diets that gave the best EPG results or an empty tube system serving as control. Contrary to the flat system, where just brief stylet insertions through the Parafilm^® were recorded, the spittlebug ingested the artificial diets when delivered with the tube system. Survival on the diets provided with the tube system was significantly greater than the control, with no differences between the diets tested. Furthermore, the tube system was suitable also for another spittlebug species shown to be a competent vector of X. fastidiosa, that is Neophilaenus campestris. The tool we devised opens new perspectives for investigations on X. fastidiosa/spittlebugs interactions, as well as for the functional analysis of mutant X. fastidiosa strains in respect to insect colonization and transmission.     

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.     

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.     

A new approach to the auchenorrhyncha (Hemiptera, Insecta) cytogenetics: chromosomes of the meadow spittlebug Philaenus spumarius (L.) examined using various chromosome banding techniques

The karyotype of the meadow spittlebug Philaenus spumarius (L.) was studied using conventional chromosome staining, C- and AgNOR- banding, and fluorescent CMA3- and DAPI- techniques. This is the first report on differential staining of the holocentric chromosomes of Auchenorrhyncha. The karyotype of Ph. spumarius includes 2n = 22 + XX/X0. The autosomal pair 1 is large and carries a gap in every homologue. After silver staining, NORs were revealed in both this chromosome pair and a middle-sized pair, most likely 6 or 7. In spermatocyte meiosis, the majority of bivalents formed one chiasma each. The bivalent 1 showed from 1 to 4 chiasmata, the value of 1 or 2 being prevalent. Two further bivalents also showed two chiasmata in some cells. After C-banding, terminal and interstitial dot-type C-heterochromatic blocks were revealed in the chromosomes. In 4 of 11 studied males, the autosomal pair 1 was polymorphic for an extra segment attached to one of the homologues. The segment consisted of both heterochromatic and euchromatic portions. No defined signals were observed in any chromosome treated with DAPI. After CMA3- staining, bright fluorescent signals were obtained in the NOR-bearing chromosomes, suggesting GC-rich DNA bound to the NORs.     

Costs and benefits of host feeding in the parasitoid wasp Trichogramma turkestanica

Females of the parasitoid wasp Trichogramma turkestanica Meyer (Hymenoptera: Trichogrammatidae) generally host feed after ovipositing on the first egg of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) they encounter. We measured the impact of host feeding on the fecundity and longevity of females, in absence of host or food, and on the fitness of their progeny. We also determined if the frequency of host feeding is influenced by the humidity level at which T. turkestanica females developed. Host feeding increased egg production by 70% but decreased female longevity. This impact of host feeding on the longevity of females is probably due to the allocation of carbohydrates to egg production at the expense of somatic maintenance. Humidity did not influence the occurrence or duration of host feeding. The size of individuals developing in eggs on which females host fed was smaller, indicating that their fitness was affected.     

The mechanism of trichome resistance in Anaphalis margaritacea to the meadow spittlebug Philaenus spumarius

This study demonstrated how simple, lanate trichomes on the stem of Anaphalis margaritacea (D.C.) inhibit feeding by young nymphs of Philaenus spumarius (L.). Nymphs were caged on stems which were subsequently sectioned and examined for feeding marks. The lack of stylet punctures at sites where nymphs were unable to feed indicated that trichomes prevented the start of stylet penetration rather than interfering with the progress of the stylets after penetration had begun. Trichome resistance declined progressively with spittlebug instar from complete resistance to first instar nymphs through complete absence of resistance to fifth instar nymphs. Discriminant analysis of the effect of number of trichomes per mm², vertical density, and height on trichome resistance to third instar nymphs revealed that trichome height was the critical factor in resistance. Variation in the percent of nymphs in each instar able to feed when caged on the stem was (1) positively correlated with degree to which the average rostrum length of the instar exceeded the trichome height, (2) independent of trichome density, which was uniformly high on all stems. Trichomes prevented stylet penetration where trichome height exceeded the length of the nymph's rostrum, probably because the necessary stimuli were not received when the sensilla on the tip of the rostrum could not touch the surface of the stem. A similar mechanism may explain resistance of simple trichomes to crop pests in the Cicadellidae.

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Résumé Ce travail montre comment des trichomes simples et laineux sur les tiges d'Anaphalis margaritacea (D.C.) inhibent la prise d'aliments par les jeunes larves de Philaenus spumarius L. Les larves ont été encagées sur des tiges qui ont été ultérieurement coupées et les piqûres alimentaires dénombrées. L'absence de piqûres par les stylets aux lieux où les larves ont été incapables de s'alimenter a montré que les trichomes ont empêché le début de la pénétration des stylets plus qu'ils n'ont entravé leur progression après le début de la pénétration. La résistance des trichomes diminue progressivement: totale pour le premier stade larvaire, elle est devenue nulle au cinquième stade. Une analyse discriminante des effets de la densité des trichome par mm², de la densité verticale, de leur hauteur sur la résistance des trichomes aux larves de 3ème stade, a révélé que la hauteur du trichome est le facteur de résistance. La variation dans le pourcentage de larves de chaque stade encagées sur la tige, capables de consommer, présentait une relation positive avec le degré par lequel la longueur du rostre dépasse la hauteur du trichome, quelle que soit la densité des trichomes qui est toujours élevée sur toutes les tiges. Les trichomes ont empêché la pénétration des stylets quand leur hauteur a dépassé la longueur du rostre, probablement parce que les stimuli nécessaires n'ont pas été reçus quant l'extrémité du rostre ne pouvait pas atteindre la surface de la tige. Un mécanisme semblable peut expliquer la résistance de trichomes simples aux Cicadellidae.

     

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.     

Mating success in the spittlebug Cercopis sanguinolenta (Scopoli, 1763) (Homoptera, Cercopidae): the role of body size and mobility

In insects, a sexual size dimorphism commonly occurs, with larger females. However, as a deviation from this general rule, larger males are found in some species. In these species often sexual selection for large males has been presumed. The spittlebug Cercopis sanguinolenta exhibits a distinct sexual size dimorphism with larger males. Mating behaviour was studied in a field population in respect to mating success of males and females. The aim of this study was to examine the mechanisms that lead to the observed non-random mating pattern. The results showed a mating pattern without size-assortative mating. A correlation was found between mating success and body size in males. In females no such correlation was found. The mobility of males depends on their body size and mobility is high only when females are present. However, in an analysis of covariance it was found that male mating success is not correlated with mobility, when controlled for body size. The mating system of the spittlebug was classified as scramble competition polygyny. Electronic Publication     

基于稳定同位素研究海州湾短吻红舌鳎的摄食生态

根据2018年春季和秋季在海州湾海域进行底拖网调查采集的样品,基于碳氮稳定同位素分析,对海州湾短吻红舌鳎的摄食生态进行研究.结果 表明:海州湾短吻红舌鳎的δ13C值平均值为(-17.79±1.00)‰,其范围在-20.75‰～-15.91‰;δ15N值平均值为(9.37±1.33)‰,其范围在5.98‰～ 12.02‰...     

Natural occurrence of the entomopathogenic genus Pandora on spittlebug pests of crops and pastures in Argentina

The natural occurrence of entomophathogenic fungi infecting spittlebugs (Hemiptera: Cercopidae) considered serious pests to pasture grasses and crops in Argentina was investigated during summer?autumn (December to May) from 2013 to 2016. Adults and nymphs of spittlebugs were collected from Sorghum halepense and Setaria parviflora var. parviflora in San Miguel de Tucumán, Tucumán province. The entomopathogenic fungal species were characterized on the basis of morphological keys and molecular techniques. Microscopic characters were described from material mounted in lactophenol/aceto‐orcein (1% w/v), and the amplification of the fungal SSU rDNA was carried out using the universal primers nu‐SSU‐0021‐5′ and nu‐SSU‐1780‐3′. Summarized information about occurrence of fungal infections on spittlebugs populations is provided. This study reports for the first time the occurrence of the genus Pandora infecting adults of the economically important spittlebugs Deois (Deois) mourei, D. (D.) knoblauchii, Isozulia christenseni christenseni and Notozulia entreriana from Argentina expanding the host range and geographical distribution of entomophthoralean fungi.     

Assessment of the biocontrol effects of three aromatic plants on multiple trophic levels of the arthropod community in an agroforestry ecosystem

1. Studies have shown that plant diversity plays a major role in influencing arthropod community composition. However, the effects of increasing plant species diversity on arthropod abundance at multiple trophic levels in the presence of aromatic plants have not been well documented. 2. To explore the potential of using aromatic plants to biocontrol arthropods at multiple trophic levels, three aromatic plant species – French marigold (Tagetes patula L.), Ageratum (Ageratum houstonianum Mill.) and Catnip (Nepeta cataria L.) – were introduced into an apple orchard to increase ground plant species composition. 3. The aromatic plants influenced the structure of arthropod communities at multiple trophic levels, particularly the herbivores in the tree canopy and predators in ground covers. Aromatic plants negatively influenced total arthropod community abundance. Compared with the control treatment, the total arthropod community abundance in the treated areas declined 24.99–33.84% and 14.35–24.65% in the tree canopy and ground covers, respectively. 4. Aromatic plants negatively influenced herbivore abundance, both overall and relative to the total community. By contrast, aromatic plants positively influenced predator abundance, both overall and relative to the total community, in the treatments containing both ageratum and catnip. However, aromatic plants had no effect on species richness at each trophic level or on parasitoid abundance. 5. These results suggest that increasing ground plant species diversity by introducing aromatic plants into apple orchards may considerably affect arthropod community composition, and that aromatic plants are potentially effective for the biocontrol of herbivore pests in agroforestry ecosystems.