Didymosphenia geminata (Lyngbye) M. Schmidt (Bacillariophyta) in the Danube basin: New data from the Drava river (northern Italy)

Abstract

The presence of Didymosphenia geminata (Lyngbye) M. Schmidt (Bacillariophyta) was revealed in the Drava river and in its affluent Rio Sesto, both flowing in the Alto Adige/Südtirol region of Italy and belonging to the Danube basin. New data are given on the distribution of the species in the Danube basin.     

Influence of queen weight and colony origin on worker response in Solenopsis geminata

Abstract. The influence of weight and colony origin of the queen of Solenopsis geminata (F.) (Hymenoptera: Formicidae) on worker attraction is studied under laboratory conditions. In the first experiment, worker response to individual queens of different weight from the same colony is evaluated. Heavier queens are more attractive than smaller queens to their own workers. In subsequent experiments, the colony origin effect is investigated and worker response to a pair of queens of the same weight from the same or different colonies is compared. When queens are from the same colony, workers do not show a significant preference between queens. However, when queens are from a different colony, workers are significantly more attracted to their own queen than to the foreign queen. Finally, the response of workers to queens of different weight from the same or different colonies is investigated. In both cases, workers are significantly more attracted to a heavier queen than a lighter queen, even if the lighter queen is their own queen. A putative pheromonal component (E)‐6‐(1‐pentenyl)‐2H‐2‐pyranone, is not positively correlated with queen weight.     

Didymosphenia geminata growth rates and bloom formation in relation to ambient dissolved phosphorus concentration

1. The bloom‐forming freshwater stalked diatom Didymosphenia geminata is unusual among algae in that nuisance growths occur almost exclusively in oligotrophic waters. Current hypotheses to explain this phenomenon have assumed supplemental acquisition of phosphorus from novel sources within the stalk/mat matrix. 2. We carried out a synoptic survey of river sites in the South Island, New Zealand, to determine whether D. geminata cell division and stalk development (measured as mat coverage or standing crop) were related to ambient phosphorus concentrations in the overlying river water. 3. High coverage (>50%) by D. geminata was largely concentrated at sites with mean dissolved reactive phosphorus (DRP) <2 mg m^?3 in the overlying water. Didymosphenia geminata was present at only one site with DRP >4 mg m^?3, with very low coverage. Cell division rate (measured as the frequency of dividing cells, FDC) was positively correlated with mean DRP suggesting that division rates were controlled by the available phosphorus concentration in ambient river water. At the same time, FDC was negatively correlated with D. geminata standing crop (measured as an index incorporating percentage cover and mat thickness). 4. In a single river reach with a stable cross‐channel gradient of total dissolved phosphorus (TDP) caused by inflows from a high‐nutrient tributary, again we observed a negative correlation between percentage cover by D. geminata and concentrations of TDP. 5. Finally, we made a series of observations on D. geminata‐dominated communities that had been exposed to water enriched with ‐N and ‐P for 4 weeks, followed by exposure to unenriched water. After 2 weeks of nutrient deprivation, D. geminata cell division rates declined by 60%, mean stalk length increased by 250%, and total carbohydrate quadrupled relative to initial values. The appearance of the community changed from a dark brown mat to a thick pale mat typical of D. geminata blooms. 6. All these results indicate that D. geminata cell division rates are actively controlled by concentrations of available phosphorus in the overlying water and that stalk production (represented by mat thickness and extent, stalk length and total carbohydrate) is inversely related to D. geminata cell division rates. They thus support an explanation for D. geminata blooms in oligotrophic rivers tied to enhanced stalk production in nutrient‐poor waters, rather than through acquisition of additional phosphorus through recycling processes within the mat.     

Are dams hotspots for Didymosphenia geminata blooms?

1. The diatom Didymosphenia geminata has emerged in recent years as a globally invasive species. Although considered native to North America, reports of nuisance blooms have increased over the last decade.
2. Previously, we determined that D. geminata was ubiquitous in two major headwaters of the South Saskatchewan River Basin (SSRB), Alberta, Canada, but found it only bloomed at certain sites, including those immediately downstream from dam outfalls. To evaluate the role of dams in the abundance and blooming of D. geminata , we compared sites just below dams to unregulated upstream reference sites in six dammed rivers of the SSRB.
3. There was a high degree of seasonal variability in D. geminata abundance among sites, but statistical analyses showed a significant propensity for the diatom to have higher cell densities and an increased frequency of blooms at dam sites.
4. Important predictor variables of D. geminata abundance included dam presence, water clarity and total phosphorus concentration. When data from dam sites were analysed, a multiple regression model using mean discharge and pH as independent predictors explained 73% of the variation in D. geminata cell density.
5. Analysis of 3 years of data from one study river (Red Deer River) revealed consistently higher D. geminata cell densities at the dam site compared to the upstream reference. This analysis also showed that average cell density fluctuated by orders of magnitude from year-to-year.
6. Due to the ecological and aesthetic concerns regarding the global spread and blooming of D. geminata , we recommend that dams be viewed as key candidates for mitigating blooms in flow regulated systems.     

Predation of Clitostethus arcuatus (Col.: Coccinellidae) on Trialeurodes vaporariorum (Hem.: Aleyrodidae)

Greenhouse whitefly, Trialeurodes vaporariorum, is a serious pest of glasshouse crops. It shows resistance to different insecticides and growers are interested in finding other useful control methods. This research was carried out to study the predation potential and biology of Clitostethus arcuatus (Rossi) as one of the most important predators of this pest. Adult C. arcuatus were reared on tobacco leaves bearing colonies of greenhouse whitefly eggs under controlled conditions (25±2°C, 65±5% RH and 16 h L:8 h D). Results showed that the average developmental time of the egg, first through fourth instar larva and pupa were 2.82±0.12, 4.47±0.14, 4.54±0.1, 6.3±0.2, 7±0.22 and 3.8±0.13 days, respectively; and longevity of female and male were 66.4±2.6 and 54.9±2.5 days, respectively. The average feeding rates of female, male and larvae (first through fourth) were 61.4±0.7, 27.6±0.9 eggs/day and 12±1.03, 30.3±2.4, 41.3±2, 68.04±2 eggs/day, respectively. The larvae consumed an average of 992.2±36 eggs during the total larval developmental period with a daily mean of 45.8±0.5. A significant difference was shown between the feeding rate of fourth instar larval stages and between sexes. Females, males and one pair of C. arcuatus (♀,♂) consumed an average of 17.2±0.4, 10.6±0.8, 23.1±0.5 nymph/day; 28.5±0.9, 20.3±0.6, 47.2±0.6 pupa/day and 8±0.3, 6.5±0.54, 13.6±0.4 adult/day, respectively. The feeding rate was significantly different among whitefly life stages. Females laid an average of 3±0.23 eggs/day.     

The non-indigenous diatom Didymosphenia geminata alters benthic communities in New Zealand rivers

1. Blooms of the benthic, stalked diatom Didymosphenia geminata were first observed in New Zealand in 2004. Since then, D. geminata has spread to numerous catchments in the South Island and is also spreading in its native range. The species is a rare example of an invasive alga in lotic systems.
2. Ecosystem effects may be expected as D. geminata attains unusually high biomass in rivers. We examined data from three independent studies in three South Island, New Zealand, rivers for evidence of effects on periphyton biomass and benthic invertebrate communities.
3. The combined results confirmed that the presence of D. geminata was associated with greatly increased periphyton biomass and, in most cases, increased invertebrate densities. We also recorded shifts in community composition, dominated by increased densities of Oligochaeta. Chironomidae, Cladocera and Nematoda also generally increased in density with D. geminata . Significant increases or declines in other invertebrate taxa were inconsistent among rivers.
4. In all three studies, increased spatial invertebrate community homogeneity was associated with high D. geminata biomass at the within-river scale. However, no declines in taxon richness or diversity were detected.
5. Although ecosystem effects of D. geminata on existing periphyton biomass and invertebrate communities are measurable, no inferences can be made from the present data about effects on higher trophic levels (fish).     

Parasitic infection of the hyperiid amphipod Themisto libellula in the Canadian Beaufort Sea (Arctic Ocean), with a description of Ganymedes themistos sp. n. (Apicomplexa, Eugregarinorida)

Two parasites were found in the hyperiid amphipod Themisto libellula sampled with nets and collected by sediment traps over the annual cycle in the Canadian Beaufort Sea. The trophozoites of the newly described gregarine Ganymedes themistos sp. n. infected the digestive tract of 60.2% of the T. libellula analyzed from net collections. An unidentified ciliate infected the body cavity of 4.4% of amphipods. G. themistos possessed the ball-like structure at the anterior end and the cup-like invagination at the posterior end that are typical of the genus Ganymedes. The frequency and severity (number of parasites host⁻¹) of infection by G. themistos increased with the length of T. libellula in the range 8–20 mm, and leveled off at ca. 94% and 186 trophozoites host⁻¹ on average in the range 20–34 mm. Spatially, gregarine infection was less severe (63 ± 100 G. themistos host⁻¹) on the Slope than on the Mackenzie Shelf (110 ± 160) and in the Amundsen Gulf (132 ± 157). No evidence of an impact of trophozoite infection on the feeding and sexual maturation of the host was found. For a given size of T. libellula, infection by both parasites was more frequent in the traps than in the nets (G. themistos: 91.0% vs. 82.7%; ciliates: 16.3% vs. 6%). The 2.7 times higher infection frequency in the traps suggested that the ciliate parasite may kill its host.     

Microstructure and nanomechanical properties of single stalks from diatom Didymosphenia geminata and their change due to adsorption of selected metal ions

We present topographical and nanomechanical characterization of single Didymosphenia geminata stalk. We compared the samples before and after adsorption of metal ions from freshwater samples. Transmission electron microscopy studies of single stalk cross‐sections have shown three distinct layers and an additional thin extra coat on the external layer (called “EL”). Using scanning electron microscopy and atomic force microscopy (AFM), we found that topography of single stalks after ionic adsorption differed significantly from topography of pristine stalks. AFM nanoindentation studies in ambient conditions yielded elastic moduli of 214 ± 170 MPa for pristine stalks and 294 ± 108 MPa for stalks after ionic adsorption. Statistical tests showed that those results were significantly different. We conducted only preliminary comparisons between ionic adsorption of several stalks in air and in water. While the stalks with ions were on average stiffer than the pristine stalks in air, they became more compliant than the pristine stalks in water. We also heated the stalks and detected EL softening at 50°C ± 15°C. AFM nanoindentation in air on the softened samples yielded elastic moduli of 26 ± 9 MPa for pristine samples and 43 ± 22 MPa for stalks with absorbed metal ions. Substantial decrease of the EL elastic moduli after heating was expected. Significantly different elastic moduli for the samples after ionic adsorption in both cases (i.e., for heated and nonheated samples), as well as behavior of the stalks immersed in water, point to permanent structural EL changes due to ions.     

Tick infestation risk and <Emphasis Type="Italic">Borrelia burgdorferi</Emphasis> s.l. infection-induced increase in host-finding efficacy of female <Emphasis Type="Italic">Ixodes ricinus</Emphasis> under natural conditions

An investigation of the risk of human tick infestation, together with the prevalence of Borrelia burgdorferi s.l. infection, was conducted in a sylvatic habitat in western Germany to provide data needed for future risk-benefit evaluations of acaricides used for clothing impregnation. Additionally, data were collected on behavioural changes in Borrelia burgdorferi s.l.-infected adult female I. ricinus ticks and the possible impact of such changes on host-finding efficacy. The risk of I. ricinus-infestation was determined by collecting from the protective clothing of volunteers and by dragging in known tick-infested sites in the Kühkopf Mountain area, Koblenz, Germany, from June through October 2006. The overall tick infestation rate per person per hour was 7.4 ± 5.5, with the following sex- and stage-specific differences: males 0.32 ± 0.37, females 1.1 ± 1.2, nymphs 3.6 ± 4.4, larvae 2.4 ± 3.5. Concurrent dragging revealed an average 19.4 ± 16.2 times higher infestation rate as well as a markedly lower infection rate with borreliae in adult I. ricinus ticks when compared to ticks collected from exposed human volunteers. Although the difference in infection rates was statistically significant (P < 0.023) only in adult female ticks, our data indicate that B. burgdorferi s.l. infection may increase host-finding efficacy in adult I. ricinus. The overall exposure risk was 1.0 B. burgdorferi s.l.-infected ticks per person per hour of exposure, or 0.25 ticks per 100 m walking distance in the study area.     

Temperature effect on the predation rate of Anthocoris nemorum (Het.: Anthocoridae) on cabbage aphids (Hom.: Aphididae)

The temperature‐dependent predation by Anthocoris nemorum L. (Het.: Anthocoridae) on second instar Brevicoryne brassicae L. (Hom.: Aphididae) at constant temperatures of 12, 15 and 20°C increased linearly with temperature with a mean (±SE) consumption of 6.9 (±0.8), 9.28 (±1) and 15.9 (±0.8) respectively. The estimated lower temperature threshold for predation (T₀) was 6.4°C.     

Eimeria tahamensis N. Sp. (Apicomplexa: Eimeriidae) from the Arabian Quail (Coturnix delegorguei arabica)1

Eimeria tahamensis n. sp. is described from the harlequin quail (Coturnix delegorguei arabica) from Tahama, Saudi Arabia. The sporulated oocysts of E. tahamensis n. sp. are ellipsoid, 36.5–42 × 25.5–29 (41.2 ± 1.34 × 28.4 ± 0.81) μm, with a thick two-layered wall and one polar granule but without a micropyle or an oocyst residuum. The sporocysts are ovoid, 14–16 × 9–11.5 (15.3 ± 0.7 × 10.8 ± 0.64) μm, with a knob-like Stieda body and sporocyst residuum, but without a substiedal body. The sporozoites are often located transversely at the two ends of the sporocysts. The host bird belongs to the order Galliformes.     

Residual effects of four pesticides on the predatory bug,Orius albidipennis Reut. (Hem.: Anthocoridae)

Residual effects of abamectin (0.02%), propargite (0.1%), dichlorvos (DDVP) (0.15%) and pymetrozine (0.15%) were determined on Orius albidipennis at laboratory conditions. Planted cucumbers were sprayed with the highest recommended concentrations of all insecticides and experimental treatments were monitored during 20 days based on the period of pesticides residues. On the first day after spraying, the greatest of mortality belonged to dichlorvos and pymetrozine (97 ± 1.22, 57 ± 3.1, respectively, p < 0.01), while abamectin and propargite had the highest mortality after four (44 ± 1.87 and 24 ± 2.91, respectively, p < 0.01) and eight (51 ± 2.91 and 17 ± 2.23, respectively, p < 0.01) days after spraying. At day 16th, post treatment, abamectin had the highest residual mortalities on O. albidipennis (15 ± 1.58, p < 0.01) and finally mortality results at the 20th day showed there is no significant difference between insecticides (p < 0.01).     

An energy budget for Simocephalus vetulus (O. F. Muller) (Crustacea : Cladocera)

We discuss the energetics of a cladoceran, Simocephalus vetulus at different temperatures (8.0 ± 1.0, 15.0 ± 1.0, 21.0 ± 1.0 and 28.0 ± 1.0 °C) and food (Chlamydomonas sp.) concentrations (25 × 10³, 50 × 10³, 75 × 10³ and 100 × 10³ cells ml⁻¹). Increase in temperature accelerated ingestion and, to some extent, oxygen consumption. The study revealed a high reproduction efficiency in S. vetulus. Net growth efficiency (ECI) was higher (13.17–41.18%) in pre-adults than in adults (2.71–8.40%). The assimilated energy (A) increased with increasing food concentration at all temperatures. Assimilation efficiency (AD) decreased with increasing food concentrations. The energy used for growth (P) was nearly constant at all food levels because the egested energy increased and assimilation efficiency decreased as food concentration increased.     

Survival ofVarroa jacobsoni Oud. (Acari: Varroidae) away from its living hostApis mellifera L.

Mite survival was measured on eight different substrates: cloth, wax comb, dead drones, dead workers, metal, wood, pollen and control. Trials were conducted at both 26°C and 13°C. Substrate type, temperature and their interactions significantly affected the survival ofV. jacobsoni. Longest survival (71±1.1 h) was recorded on dead worker bees (Apis mellifera L.) held at 26°C. Shortest survivals were observed on cloth (21±1.3 h), no substrate (21±1.3 h), metal (20±1.1 h) and pollen (18±1.3 h), all maintained at 13°C.     

The clonal structure of Quercus geminata revealed by conserved microsatellite loci

The scrub oak communities of the southeastern USA may have existed at their present locations for thousands of years. These oaks form suckers, and excavations of root systems suggest that clones may occupy very large areas. Resolution of the clonal nature of scrub oaks is important both to manage the tracts of this ecosystem that remain, and in conducting long-term ecological studies, where the study area must substantially exceed the area occupied by any single clone. Microsatellites were used to determine the genetic diversity of a dominant oak species within a 2-ha long-term experimental site on Merritt Island at the Kennedy Space Center. This area contains a long-term study of the effects of elevated CO2 on the ecosystem. Conservation of seven microsatellite loci, previously identified in the sessile oak, Quercus petraea, was tested in two Florida scrub oak species, Q. geminata and Q. myrtifolia. Sequence analysis revealed that all seven microsatellite loci were conserved in Q. geminata and five loci were conserved in Q. myrtifolia. Six microsatellite loci were polymorphic in Q. geminata and these were subsequently used to investigate the clonal structure of the Q. geminata population. Twenty-one unique combinations of microsatellites, or haplotypes, occurred only once, whereas the remaining 26 individuals belonged to a total of seven different haplotypes. Trees with identical haplotypes were in close proximity, supporting the interpretation that they were clones. The results showed that there is significant genetic diversity within the 2-ha experimental site. Microsatellites provided a powerful and noninvasive tool for distinguishing individual genotypes and determining an adequate area for long-term ecosystem studies.     

Eimeria ladronensis n. sp. and E. albigulae (Apicomplexa: Eimeriidae) from the Woodrat,Neotoma albigula (Rodentia: Cricetidae)1

Of 50 white-throated woodrats (Neotoma albigula) collected from Socorro Co., New Mexico, 21 (42%) had eimerian oocysts in their feces when examined. Of the 21 Neotoma found positive for Eimeria, 19 (90%) harbored a single eimerian species at time of examination. Eimeria albigulae Levine, Ivens & Kruidenier, 1957, was found in 18 (86%), and E. ladronensis n. sp. was found in five (24%) infected woodrats. Sporulated oocysts of E. ladronensis are ellipsoidal, 19–25 × 13–15 (21.4 ± 1.3 × 14.1 ± 1.1) μm, have a smooth wall and one or two polar granules, but lack a micropyle and an oocyst residuum. Sporocysts are tapered at one end, 7–10 × 6–7 (8.5 ± 0.7 × 6.5 ± 0.3) μm, and have a Stieda body and sporocyst residuum, but no substieda body. Prepatent periods for E. albigulae and E. ladronensis n. sp. are 5–6 and 8–9 days, respectively; patent periods are 7–18 and approximately 11 days, respectively.     

Survival and fecundity of Dichroplus maculipennis and Ronderosia bergi (Orthoptera: Acrididae: Melanoplinae) following infection by Beauveria bassiana (Ascomycota: Hypocreales) under laboratory conditions

This study examined the effects of strain Beauveria bassiana (LPSC 1067) on nymphal development time, fecundity and adult survival in Dichroplus maculipennis and Ronderosia bergi under laboratory conditions. It was observed that infection with 1×10³ conidia/ml altered nymphal development time, fecundity and adult survival in both species. Mortality of D. maculipennis during third through the last instar (sixth) was significantly higher among treated nymphs (66±3.8%) than in controls (15±1.7%). Similarly, mortality in R. bergi during third through the last instar (fifth) was higher in treated nymphs (71±2.8%) than in controls (19±1.5%). Nymphal development times of both infected D. maculipennis and R. bergi were longer than controls. On the other hand, among survivors of both the species, control adults lived longer than infected adults. Finally, control grasshoppers of both species were much more successful reproductively than infected grasshoppers.     

Age-stage two-sex life table analysis of Sesamia nonagrioides (Lep.: Noctuidae) reared on different host plants

The effects of maize and sugarcane were studied on the demographic parameters of Sesamia nonagrioides under controlled environmental conditions. Life table parameters were estimated using age-stage two-sex life table method. Total developmental times of immature stages were 53.51 ± 0.42 and 39.58 ± 0.14 days on maize and sugarcane, respectively. The fecundity values were found to be 93.07 ± 2.94 and 122.95 ± 6.72 eggs/female on maize and sugarcane, respectively. Based on the analysis, the intrinsic rates of increase (r) and the mean generation time (T) of S. nonagrioides were determined as 0.0909 ± 0.0027 and 0.0579 ± 0.0021 day^?1; 42.09 ± 0.21 and 56.83 ± 0.63 days on sugarcane and maize, respectively. Consequently, the sugarcane was a better host for development and population increase of S. nonagrioides than maize. These results can be used to predict population dynamics of the pest on the natural hosts and to improve mass rearing technique on natural diets in insectariums.     

Feeding efficiencies of Chironomus plumosus (L.) and C. anthracinus Zett. (Diptera: Chironomidae) in mesotrophic Lake Erken

SUMMARY.

• 1 Absorption efficiencies of nitrogen and carbon in two Chironomus species found dominating in the profundal zone of mesotrophic Lake Erken were determined gravimetrically.
• 2 Absorption efficiencies for C. plumosus showed greater seasonal variation than those of C. anthracinus, with low efficiencies coinciding with the summer dominance of flagellate phytoplankton and with high C:N ratios.
• 3 Overall mean absorption efficiencies (±SE) for carbon and nitrogen, respectively, were 26.8% (±1.9) and 29.3% (±1.9) for C. plumosus, 24.6% (±1.7) and 28.1% (±1.8) for C. anthracinus.
• 4 Significant differences were found to exist between the C: N ratios of the superficial 2 cm sediment layers and those of Chironomus anterior midgut contents.
• 5 C. anthracinus appears to be a deposit feeder ingesting particulate matter scraped from the recently deposited surface sediments. The greater seasonal variation found in the absorption efficiencies of C. plumosus, together with the lower C:N ratios, support the contention that this species is a filter feeder with the nutritional quality of ingested matter depending primarily on pelagic inputs.