Biology and host preference of the planthopper Taosa longula (Hemiptera: Dictyopharidae), a candidate for biocontrol of water hyacinth

Taosa longula Remes Lenicov (Hemiptera: Dictyopharidae) is a planthopper from the South American tropics that feeds on water hyacinth, Eichhornia crassipes (Mart.) Solms-Laubach (Pontederiaceae). The biology of T. longula was studied in the laboratory and field to evaluate it as a potential biological control agent for this widespread aquatic weed. The developmental time of nymphs was recorded at different temperatures (15, 19, 23, 25, 27 and 30 °C), and developmental threshold temperatures were obtained for the different instars. The host range was evaluated in terms of development and feeding preference. Development from instar I to adult was recorded in two no-choice trials, one with cut leaves of Pontederiaceae, and a second with growing whole plants. In the cut-leaf tests, adults were obtained from Pontederia cordata var. cordata, P. rotundifolia and water hyacinth. In the whole plant test, T. longula adults were obtained only from water hyacinth. Feeding preference was evaluated by means of a paired-choice test with 10 T. longula first instars on whole plants of P. c. cordata, P. rotundifolia and water hyacinth. The number of insects that fed on water hyacinth was significantly higher than on P. c. cordata and P. rotundifolia. Taosa longula showed a clear preference for water hyacinth and exhibited warm climate requirements, making it an attractive candidate for water hyacinth biological control in tropical and subtropical areas.     

Feeding behavior and spatial distribution of two planthoppers,Megamelus scutellaris (Delphacidae) and Taosa longula (Dictyopharidae), on water hyacinth

Megamelus scutellaris Berg (Delphacidae) and Taosa (Cuernavaca) longula Remes Lenicov (Dictyopharidae) are specialist planthoppers that feed and reproduce on the invasive aquatic weed, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae). They overlap geographically in several regions of South America and may, therefore, interact and compete for food and microhabitat. Preliminary observations indicated that both species do not feed on the same part of the plant. We hypothesized that they partition the resource; hence, we studied (1) the feeding mechanism at the tissue level and (2) the spatial distribution of both species on the water hyacinth plant. Salivary sheaths were detected through histological sections of plant tissues using light microscopy. The location of either planthopper species on the plant was recorded when in the presence or absence of the other species. Both species produced true salivary sheaths, mostly branched (M. scutellaris: 82%; T. longula: 84%), ending in phloem (M. scutellaris: 56%; T. longula: 52%), and xylem tissues (M. scutellaris: 24%; T. longula: 28%). They resided on different parts of the water hyacinth plant even when they did not coexist; nymphs of T. longula occurred primarily on the back side of the leaf laminas, while nymphs of M. scutellaris occupied the basal zone of the petioles. This study shows that these planthoppers complement each other and could be used in combination as control agents for water hyacinth. Further experimental studies and field observations are necessary to quantify interactions.     

Phytoremediation of mercury- and methyl mercury-contaminated sediments by water hyacinth (Eichhornia crassipes)

Phytoremediation has the potential for implementation at mercury- (Hg) and methylHg (MeHg)-contaminated sites. Water hyacinths (Eichhornia crassipes) were investigated for their ability to assimilate Hg and MeHg into plant biomass, in both aquatic and sediment-associated forms, over a 68-day hydroponic study. The suitability of E. crassipes to assimilate both Hg and MeHg was evaluated under differing phosphate (PO4) concentrations, light intensities, and sediment:aqueous phase contamination ratios. Because aquatic rhizospheres have the ability to enhance MeHg formation, the level of MeHg in water, sediment, and water hyacinth was also measured. Hg and MeHg were found to concentrate preferentially in the roots of E. crassipes with little translocation to the shoots or leaves of the plant, a result consistent with studies from similar macrophytes. Sediments were found to be the major sink for Hg as they were able to sequester Hg, making it non-bioavailable for water hyacinth uptake. An optimum PO4 concentration was observed for Hg and MeHg uptake. Increasing light intensity served to enhance the translocation of both Hg and MeHg from roots to shoots. Assimilation of Hg and MeHg into the biomass of water hyacinths represents a potential means for sustainable remediation of contaminated waters and sediments under the appropriate conditions.     

Distribution of cytokinin-like activity in different plant parts of the water hyacinth, Eichhornia crassipes

Cytokinin-like activity in extracts of leaf laminae, petioles, shoots, roots and flowers of young plants of the water hyacinth, Eichhornia crassipes S. was analyzed following Sephadex LH-20 column chromatography using the soybean callus bioassay. In all plant parts analyzed, two prominent peaks of cytokinin activity having elution volumes similar to zeatin and zeatin riboside were detected. Putative cytokinin gluco-side-like activity was detected only in leaves and flowers. The cytokinin complements of the leaves and the roots were qualitatively different. It would appear that cytokinins supplied by the roots are metabolized in the leaves or certain cytokinins are synthesized in the leaves themselves. The possible significance and distribution of cytokinins in different plant parts in relation to roots is discussed.     

Production of biogas from water hyacinth (Eichhornia crassipes) (Mart) (Solms) in a two-stage bioreactor

A two-stage rumen-derived anaerobic digestion process was tested for the conversion of water hyacinth shoots and a mixture of the shoots with cowdung (7:3) into biogas. Under conditions similar to those of the rumen and loading rates (LR) in the range of 11.6–19.3g volatile solids (VS) l–1d–1 in the rumen reactor, the degradation efficiencies were 38% for the shoots and 43% for the mixture. The major fermentation products were volatile fatty acids (VFA) with a maximum yield of 7.92mmolg–1 VS digested, and biogas with a yield of 0.2lg–1 VS digested. The effect of varying LR, solid retention time (SRT) and dilution rates on the extent of degradation of the water hyacinth–cowdung mixture was examined. Overall conversion of the substrate was highest at the loading rate of 15.4gVS.l–1d–1. Varying the retention times between 60 and 120h had no effect on the degradation efficiency, but a decrease was observed at retention times below 60h. The overall performance of the reactor was depressed by changing the dilution rate from 0.5 to 0.34h–1. By applying a LR of 15.4VS. l–1d–1, a SRT of 90h and a dilution rate of 0.5h–1 in the rumen reactor, and connecting it to a methanogenic reactor of the upflow anaerobic sludge blanket type, 100% conversion efficiency of the VFA into biogas with a methane content of 80% was achieved. The average methane gas yield was 0.44lg–1 VS digested.     

Ecological and socio‐economic impacts of invasive water hyacinth (Eichhornia crassipes): a review

1. Water hyacinth (Eichhornia crassipes) is one of the world’s most invasive aquatic plants and is known to cause significant ecological and socio‐economic effects. 2. Water hyacinth can alter water clarity and decrease phytoplankton production, dissolved oxygen, nitrogen, phosphorous, heavy metals and concentrations of other contaminants. 3. The effects of water hyacinth on ecological communities appear to be largely nonlinear. Abundance and diversity of aquatic invertebrates generally increase in response to increased habitat heterogeneity and structural complexity provided by water hyacinth but decrease due to decreased phytoplankton (food) availability. 4. Effects of water hyacinth on fish are largely dependent on original community composition and food‐web structure. A more diverse and abundant epiphytic invertebrate community may increase fish abundance and diversity, but a decrease in phytoplankton may decrease dissolved oxygen concentrations and planktivorous fish abundance, subsequently affecting higher trophic levels. 5. Little is known about the effects of water hyacinth on waterbird communities; however, increases in macroinvertebrate and fish abundance and diversity suggest a potentially positive interaction with waterbirds when water hyacinth is at moderate density. 6. The socio‐economic effects of water hyacinth are dependent on the extent of the invasion, the uses of the impacted waterbody, control methods and the response to control efforts. Ecosystem‐level research programmes that simultaneously monitor the effects of water hyacinth on multiple trophic‐levels are needed to further our understanding of invasive species.     

Effect of physical pretreatment on dilute acid hydrolysis of water hyacinth (Eichhornia crassipes)

Effects of different physical pretreatments on water hyacinth for dilute acid hydrolysis process (121 ± 3 °C, 5% H₂SO₄, 60 min) were comparatively investigated. Untreated sample had produced 24.69 mg sugar/g dry matter. Steaming (121 ± 3 °C) and boiling (100 ± 3 °C) for 30 min had provided 35.9% and 52.4% higher sugar yield than untreated sample, respectively. The highest sugar yield (132.96 mg sugar/g dry matter) in ultrasonication was obtained at 20 min irradiation using 100% power. The highest sugar production (155.13 mg sugar/g dry matter) was obtained from pulverized samples. Hydrolysis time was reduced when using samples pretreated by drying, mechanical comminution and ultrasonication. In most methods, prolonging the pretreatment period was ineffective and led to sugar degradations. Morphology inspection and thermal analysis had provided evidences of structure disruption that led to higher sugar recovery in hydrolysis process.     

Mineral nutrient demands of the water hyacinth (Eichhornia crassipes (Mart.) Solms) in the White Nile

The possibility that the stunted growth of the water hyacinth in Bahr el Ghazal river in Sudan is influenced by nutrient elements is considered. Greenhouse experiments were carried out to determine the effects of deficiency and mineral nutrient additions on the growth of this plant. The water hyacinth was found to grow at a wide range of nutrient levels. Maximum growth was recorded at 21 mg l^–1 N, 62 mg l^–1 P, and 0.60 mg l^–1 Fe.     

Growth of water hyacinth (Eichhornia crassipes (Mart.) Solms) in the middle Paraná River (Argentina)

The productivity of water hyacinth in the middle Paraná River was measured at three initial biomass levels by means of periodic harvesting of plants contained in 2 m² floating baskets. The measuring period extended between August 1981 and July 1982. Initial biomass densities were 2, 5 and 10 kg (fw) m^–2.Compared with inner island ponds, flowing waters connected to the main river showed better conditions for water hyacinth growth. The duration of the growth period was some 30% longer than in island ponds, probably due to the relatively warmer river waters. Productivity ranged between 108 and 164 g (fw) m ^–2 d^–1 (annual average) for the lower and higher initial biomass values, respectively.     

Host specificity assessment and potential impact of Megamelus scutellaris (Hemiptera: Delphacidae) on waterhyacinth Eichhornia crassipes (Pontederiales: Pontederiaceae)

The delphacid Megamelus scutellaris Berg was evaluated for host specificity and potential impact as part of a biological control program targeting Eichhornia. crassipes. Survival and development of adults and nymphs were used as metrics with no-choice, two-choice, nymph transfer, and sustainability tests conducted under quarantine conditions. A total of 69 plant species were tested including 12 from the Pontederiaceae (including E. crassipes). Additionally, 27 native and 5 exotic associated wetland species and 11 economic species were tested. Megamelus scutellaris exhibited a high level of oviposition and developmental fidelity to E. crassipes by failing to sustain populations on any non-target test plant past the F₁ generation. Nymph transfer tests which simulated potential spill-over events found that survival was virtually non-existent on associated wetland plants, regardless of taxonomic relatedness, including on Pontederia cordata, an important and widespread native species. Eichhornia crassipes plants exposed to two consecutive generations of feeding produced 66.9% less biomass and 73.4% fewer leaves than those in the controls. We conclude that Megamelus scutellaris is safe to release on E. crassipes in the United States.     

Effects of 2,4-D on mature and juvenile plants of water hyacinth (Eichornia crassipes (Mart.) Solms)

The effects of various concentrations of the herbicide 2,4-D were investigated on two vegetative forms of water hyacinth including juvenile and mature forms. The results obtained suggest that efficient chemical control of water hyacinth may be best applied at the early stages of vegetative development of the water hyacinth, i.e. at the juvenile phase. This would require the use of 2,4-D at a concentration of 60 000 ppm (2.2 kg/ ha) which equals to half the rate of 2,4-D normally used for control of water hyacinth in the Sudan. The lower rate of 2,4-D not only means a considerable reduction in quantity and cost of the consumed herbicide but also a substantial minimisation in the level at which pollution may build up in the White Nile of the Sudan.     

Effect of temperature and water activity on spore germination and mycelial growth of three fungal biocontrol agents against water hyacinth (Eichhornia crassipes)

Aims: To determine the effect of water activity (a_w = 0·880–0·960) and temperature (15–35°C) on the percentage of viable conidia and mycelial growth of three biocontrol agents effective against water hyacinth in Mali: Alternaria sp. isolate Mlb684, Fusarium sacchari isolate Mln799 and Cadophora malorum isolate Mln715. Methods and Results: The fungi were grown in vitro on plates containing potato dextrose agar medium at different a_w values (glycerol being added to adjust the a_w). The percentage of viable conidia and radial growth rate decreased with decreasing water activity. Statistical analysis showed a significant effect of a_w, temperature and the a_w × temperature interaction on mycelial growth (P < 0·0001). Water activity emerged as the factor exerting the greatest influence. Differences were observed between the fungi tested, the C. malorum appearing more tolerant to low a_w and the F. sacchari more tolerant to high temperature (35°C). Growth models predicting the combined effect of a_w and temperature were developed and response surfaces generated, showing fairly good agreement with the experimental values. Conclusions: Our results confirm the previous finding that a_w has a greater influence than temperature on fungal growth. Under most conditions, variation of environmental factors has a detrimental influence on the percentage of viable conidia and mycelial growth rate of fungal isolates. Significance and Impact of the Study: The developed models may contribute to predicting the best environmental conditions for use of these fungi as effective biocontrol agents against water hyacinth.     

Nutrient limitation to the decomposition of water hyacinth ( Eichhornia crassipes)

The responses of decomposition to N and P supply were investigated in three leaf types of water hyacinth (Eichhornia crassipes (Mart.) Solms): dead green leaves collected from Donghu Lake; green, and brown leaves collected from outdoor tanks. The ratios of C:N, C:P, lignin:N and lignin:P were lowest in the green leaves collected from Donghu Lake, and highest in the brown leaves collected from outdoor tanks. Decomposition constant (k) of water hyacinth varied greatly, ranged from 0.006 to 0.099 d^–1. Leaf litters decayed most quickly within the initial two weeks during the experimental period, but decomposition rate decreased significantly in the following days. Decomposition and nutrient (N and P) release were fastest in the green leaves collected from Donghu Lake, intermediate in the green leaves collected from outdoor tanks, slowest in the brown leaves collected from outdoor tanks. Statistical analyses revealed that the effects of P-availability on decomposition rate and N, P release rate of the three litter types were significant, whereas the impacts of N-availability was insignificant (p > 0.05) except for the brown leaves collected from outdoor tanks. These results suggest that decomposition rate and nutrient content dynamics of water hyacinth differ with their growth habitats, and could partly be regulated by nutrient availability, especially by P-availability, in the environments.     

High-rate composting-vermicomposting of water hyacinth (Eichhornia crassipes,Mart. Solms)

In an attempt to develop a system with which the aquatic weed water hyacinth (Eichhornia crassipes, Mart. Solms) can be economically processed to generate vermicompost in large quantities, the weed was first composted by a 'high-rate' method and then subjected to vermicomposting in reactors operating at much larger densities of earthworm than recommended hitherto: 50, 62.5, 75, 87.5, 100, 112.5, 125, 137.5, and 150 adults of Eudrilus eugeniae Kinberg per litre of digester volume. The composting step was accomplished in 20 days and the composted weed was found to be vermicomposted three times as rapidly as uncomposted water hyacinth [Bioresource Technology 76 (2001) 177]. The studies substantiated the feasibility of high-rate composting-vermicomposting systems, as all reactors yielded consistent vermicast output during seven months of operation. There was no earthworm mortality during the first four months in spite of the high animal densities in the reactors. In the subsequent three months a total of 79 worms died out of 1650, representing less than 1.6% mortality per month. The results also indicated that an increase in the surface-to-volume ratio of the reactors might further improve their efficiency.     

Partitioning of Soluble Calcium in the Water Hyacinth (Eichhornia crassipes (Martius) Solms) in Lake Victoria,Uganda

Abstract: An investigation of soluble calcium partitioning in organs of the water hyacinth growing along the shores of L. Victoria, bordering Jinja town was carried out. The levels of Na⁺, K⁺, Mg²⁺ and Ca²⁺ in the lake water were also estimated. The pH and electrical conductivity of lake water were determined. There was a differential accumulation of Ca and oxalate between component organs of the water hyacinth. The concentration of oxalate in the various organs was more than twice that of Ca. Soluble Ca decreased with age in all organs except the leaf, while oxalate increased with age in all organs except the rhizome. There were site variations in the partitioning of both Ca and oxalate in the water hyacinth.     

Occurrence and effectiveness of an indigenous strain of Myrothecium roridum Tode: Fries as a bioherbicide for water hyacinth (Eichhornia crassipes) in Nigeria

In a study to isolate fungal pathogens with potential for the biocontrol of water hyacinth (Eichhornia crassipes), some lakes in the Lagos State and its environs, Nigeria, were surveyed for diseased water hyacinth (E. crassipes). The fungi present in the diseased tissue were isolated and identified as: Aspergillus niger, Aspergillus flavus, Penicillium sp., Curvularia pallescens, Fusarium solani and Myrothecium roridum. The pathogenicity of isolates of these fungi on fresh, non-diseased water hyacinth plants was investigated. Myrothecium was the only species capable of inducing disease symptoms. Necrosis was observed on water hyacinth leaves three days post inoculation (DPI) with M. roridum (1 × 10⁶ spores/ml). The leaves and the petioles were withered at the end of day 24, and the disease incidence and disease severity were 100% and 8.67%, respectively. Molecular analysis of the internal transcribed spacer rDNA of the M. roridum isolate from water hyacinth showed >98% homology to authenticated sequences of M. roridum. The isolate, deposited at the International Mycological Institute, UK, as M. roridum Tode: Fries (IMI 394934), possesses the level of virulence needed in a potential mycoherbicide for use in the management of water hyacinth.     

Removal of Chlorpyrifos by Water Hyacinth (Eichhornia crassipes) and the Role of a Plant-Associated Bacterium

The objective of this research was to study the efficiency of water hyacinth (Eichhornia crassipes) and the role of any plant-associated bacteria in removing chlorpyrifos from water. The relative growth rate (RGR) of E. crassipes in the presence of 0.1 mg/L chlorpyrifos was not significantly different from that in its absence and only slightly decreased at concentrations of 0.5 and 1.0 mg/L by ～1.1- and ～1.2-fold, respectively, with an observed dry weight based RGR_DW for E. crassipes of 0.036–0.041 mg/g/d. The removal rate constants of chlorpyrifos in the absence of plants were low at 3.52, 2.29 and 1.84 h^?1 for concentrations of 0.1, 0.5 and 1.0 mg/L, respectively, but were some 3.89- to 4.87-fold higher in the presence of E. crassipes. Chlorpyrifos removal was markedly facilitated by the presence of a root-associated bacterium, preliminarily identified as Acinetobacter sp. strain WHA. The interaction of E. crassipes and Acinetobacter sp. strain WHA provide an efficient and ecological alternative to accelerate the removal and degradation of chlorpyrifos pollution from aquatic systems including wastewater.     

Azotobacter chroococcum in the phyllosphere of water hyacinth (Eichhornia crassipes Mort. Solms)

Summary Water hyacinth (Eichhornia crassipes) harbours Azotobacter chroococcum in large numbers on and in its leaves. This may account for its prolific growth of the plants in water containing only traces of combined nitrogen. re]19721201     

Phytoremediation of wastewater toxicity using water hyacinth (Eichhornia crassipes) and water lettuce (Pistia stratiotes)

This paper elucidates the phytoremediation potential of water hyacinth and water lettuce on the reduction of wastewater toxicity. Acute toxicity tests were performed in an aquarium with a population of Sarotherodon melanotheron, contaminated by different concentrations of wastewaters before and after phytoremediation with Eichhornia crassipes and Pistia stratiotes. Lethal concentrations (LC₅₀) of the fish's population obtained during 24 hours of exposures were determined. COD, BOD, ammonium, TKN and PO₄^3? concentrations in wastewaters were of 1850.29, 973.33, 38.34, 61.49 and 39.23 mg L^?1, respectively, for each plant. Phytoremediation reduced 58.87% of ammonium content, 50.04% of PO₄^3?, 82.45% of COD and 84.91% of BOD. After 15 days of the experiment, metal contents in treated wastewaters decreased from 6.65 to 97.56% for water hyacinth and 3.51 to 93.51% for water lettuce tanks. Toxicity tests showed that the mortality of fish exposed increased with increase in concentration of pollutants in wastewaters and the time of exposure. Therefore, the highest value of LC₅₀ was recorded for fish subjected to 3 hours of exposure (16.37%). The lowest rate was obtained after an exposure of 20 to 24 hours (5.85%). After phytoremediation, the effluents purified by Eichhornia crassipes can maintain the fish life beyond 24 hours of exposure.     

Morphological identification of fungi associated with Eichhornia crassipes (Mart.-Solms) Laubach in the Wouri River Basin,Douala, Cameroon

In many parts of the world, excess growth of Eichhornia crassipes (Pontederiaceae) poses a serious threat to aquatic environments. In Cameroon, where manual clearing is still undertaken, little is known about fungal diversity associated with the plant, or its potential for biological control. Surveys of the Wouri River Basin in the Littoral Region of Cameroon were conducted during a rainy season (May–October 2014) and a dry season (November 2015–April 2016) at various sites, to identify fungi associated with water hyacinth. Fungi were isolated and identified from symptomatic plant parts collected. In the rainy season, 130 fungal isolates belonging to 12 genera were identified morphologically, whereas 299 isolates belonging to 23 genera were identified during the dry season. With the exception of Fusarium oxysporum and Phytophthora sp., the genera represented new records for Cameroon, and Chaetomium strumarium, Colletotrichum gloesporioides, C. acutatum, C. dematium, Curvularia pallescens and Pytomyces chartarum were considered new host records for E. crassipes in Africa. Isolates of Acremonium zonatum, Chaetomium strumarium, Alternaria eichhorniae, Phytophthora sp. and Rhizoctonia sp. showed the highest frequency of occurrence on E. crassipes in the Wouri River Basin and, given their record as plant pathogens, could be potentially useful in the development of mycoherbicides for this weed in Cameroon.