Vermicomposting of different forms of water hyacinth by the earthworm Eudrilus eugeniae,Kinberg

Six-month long trials were conducted on different vermireactors fed with one of the following forms of water hyacinth: (a) fresh whole plants, (b) dried whole plants, (c) chopped pieces of fresh plants, (d) 'spent' weed taken from reactors after extracting volatile fatty acids (VFAs), (e) precomposted fresh weed and (f) precomposted spent weed. The first four forms were studied with and without cowdung. The experiments revealed three clear trends (i) of the various forms of the weed assessed, the precomposted forms were the most favoured as feed by Eudrilus eugeniae, Kinberg, while the fresh whole form was the least favoured, (ii) the different forms of spent weed were favoured over the corresponding forms of fresh weed, and (iii) blending of cowdung (approximately 14% of the feed mass) with different forms of water hyacinth had a significant positive impact on vermicast output, growth in worm zoomass, and production of offspring relative to the corresponding unblended feed. In all reactors, the 'parent' earthworms steadily grew in size over the six-month span, and produced offspring. There was no mortality. The experiments thus confirm that water hyacinth can be sustainably vermicomposted in any of the forms with E. eugeniae.     

Composting-vermicomposting of leaf litter ensuing from the trees of mango (Mangifera indica)

Litter of the mango (Mangifera indica) tree leaves was composted and then converted into vermicast by the action of the earthworm Eudrilus eugeniae Kinberg. After over nine months of continuous operation the vermireactors with 62.5 animals l(-1) generated approximately 13.6g vermicast per litre of reactor volume (l) per day (d) whereas the reactors with 75 animals l(-1) produced approximately 14.9 g vermicast l(-1) d(-1). This difference in performance of the reactors operating in duplicate at the two different earthworm densities was statistically significant (> or = 90% confidence level) for most of the nine-month span. The animals grew well in all reactors, increasing their zoomass by approximately 103% and producing approximately 157 offspring. Not a single of the 1100 animals died during the first four months. In the subsequent five months a total of 122 worms died, representing a loss of approximately 2% per month. We attribute this to the normal process of ageing. The ability of the earthworms to survive, grow and breed in the vermireactors fed with composted mango tree leaves, and a rising trend in vermicast output inspite of the death of a few worms after four months of reactor operation, indicate the sustainability of this type of vermireactors. The studies also indicate that even better vermireactor efficiency may be possible by modifying the reactor geometry. Studies on changes in C:N ratio during composting and vermicomposting revealed that whereas composting helped in lowering the ratio due to loss of carbon in bacterial metabolism, vermicomposting had no such effect on the ratio.     

Towards maximising output from vermireactors fed with cowdung spiked paper waste

Paper waste, spiked with varying proportions of cowdung, was vermicomposted in 'low-rate' and 'high-rate' reactors. The former type of reactors had earthworm populations and feed loading rates similar to ones recommended by previous workers. The 'high-rate' reactors were operated with 12.5 times higher earthworm densities and feed loading rates. All the reactors were studied for six months to assess the vermicast output, survivability, growth and reproduction of the earthworms hence the sustainability of the reactors--for long-term, continuous operation. The studies revealed the viability of the high-rate vermireactor concept. The high-rate reactors consistently produced over 6.5 times more castings per unit digester volume with no adverse effect on the earthworm population, as reflected by (a) absence of mortality, (b) consistent growth in worm zoomass, and (c) normal rate of reproduction. The studies also revealed that an increase in the cowdung fraction in the feed from 14.3% to 20% (4:1 paper:cowdung blends to 6:1 blends) had little positive impact on the vermicast output or earthworm health. This indicated that spiking of paper feed with approximately 14% cowdung, or perhaps an even smaller fraction, might be adequate to support earthworms in the paper-fed vermireactors.     

Vermicomposting of the leaf litter of acacia (Acacia auriculiformis): Possible roles of reactor geometry,polyphenols, and lignin

Vermicomposting of the pre-composted leaf litter of acacia (Acacia auriculiformis) was studied in reactors of identical volume but with surface area: height ratios varying from 4 to 250. In separate sets of experiments with these reactors, epigeic earthworm species Eudrilus eugeniae and anecic earthworm species Lampito mauritii were employed at densities of 75 and 150 adult animals per litre of reactor volume.The results reveal that greater the surface area: volume ratio of the reactor, higher is the vermicast output in terms of vermicast output per animal; the more densely populated reactors were comparatively under-productive.Even as the vermicast production remained consistently high in all the reactors, there was significant earthworm mortality throughout the course of the experiments and the worms who survived, steadily lost weight with time. A detailed investigation of the possible causes revealed that, whereas the C:N ratio of acacia compost was comparable with that of other substrates; the polyphenols and lignin content were much higher. Studies by other authors on leaf litter consumption by earthworms in natural or man-made forests have indicated that leaf litter rich in polyphenols and lignin are not preferred by most species of earthworm. This may perhaps be the reason for the high rate of mortality and weight loss in earthworms forced to feed upon acacia in the experiments conducted by the authors.     

Feeding impact of the planthopper Taosa longula (Hemiptera: Dictyopharidae) on water hyacinth,Eichhornia crassipes (Pontederiaceae)

Taosa longula Remes Lenicov (Hemiptera: Dictyopharidae), a planthopper native to South America, is a candidate for the biological control of water hyacinth, Eichhornia crassipes (Mart.) Solms-Laubach (Pontederiaceae), a serious weed worldwide. Biological control requires agents that are not only specific but also effective. Damage caused by sap-sucking insects is difficult to assess. In this work we designed an experimental and analytical procedure to evaluate the potential damage of T. longula on water hyacinth. The damage that T. longula causes to the clonal reproduction, biomass production, and growth of water hyacinth was studied through a paired greenhouse trial with floating cages. The performance of the plant, starting from two plants per treatment, was evaluated at different insect densities (5, 10, 15 and 20 nymphs per cage) until all the nymphs moulted to adults. The tests showed that individual growth and biomass production of water hyacinth was reduced due to the effect of the insect feeding above five nymphs per cage. The number of new plants produced by clonal reproduction was only significantly different above 15 nymphs per cage. These results suggest that this planthopper could be an effective agent for the biological control of water hyacinth.     

Effect of the application of water hyacinth compost/vermicompost on the growth and flowering of Crossandra undulaefolia,and on several vegetables

The impact of the application of compost/vermicompost obtained from water hyacinth (Eichhornia crassipes, Mart. Solms) on plants was assessed in terms of growth and flowering of the angiosperm crossandra (Crossandra undulaefolia). Overall nine morphological, size, and yield attributes were studied in crossandra saplings raised on water hyacinth compost or vermicompost as compared to the untreated saplings. Application of vermicompost led to statistically significant improvement in the growth and flowering of crossandra compared to the untreated plants. The impact of compost was also beneficial but a little less distinct than the positive impact of vermicompost. Qualitative studies were simultaneously conducted in five kitchen gardens owned by farmers near Pondicherry. In three of these locations water hyacinth vermicompost was applied-and no other fertilizer-for months to different species of vegetables. Water hyacinth compost was similarly applied in another two locations. In all the locations no adverse effect on any of the plant species was observed. We believe these studies would help in dispelling the apprehension of farmers that compost/vermicompost obtained form a pernicious weed like water hyacinth may have deleterious effect on other plants.     

Toxic effect of herbicides used for water hyacinth control on two insects released for its biological control in South Africa

The integrated control of water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae) has become necessary in South Africa, as biological control alone is perceived to be too slow in controlling the weed. In total, seven insect biological control agents have been released on water hyacinth in South Africa. At the same time, herbicides are applied by the water authorities in areas where the weed continues to be troublesome. This study investigated the assumption that the two control methods are compatible by testing the direct toxicity of a range of herbicide formulations and surfactants on two of the biological control agents released against water hyacinth, the weevil, Neochetina eichhorniae Warner (Coleoptera: Curculionidae) and the water hyacinth mirid, Eccritotarsus catarinensis (Carvalho) (Hemiptera: Miridae). A number of the formulations used resulted in significant mortality of the mirid and the weevil. Products containing 2,4-D amine and diquat as active ingredients caused higher mortality of both agents (up to 80% for the mirid) than formulations containing glyphosate. Furthermore, when surfactants were added to enhance herbicide efficiency, it resulted in increased toxicity to the insects. We recommend that glyphosate formulations should be used in integrated control programmes, and that surfactants be avoided in order to reduce the toxic nature of spray formulations to the insect biological control agents released against water hyacinth.     

Recovery of methane-rich gas from solid-feed anaerobic digestion of ipomoea (Ipomoea carnea)

Studies are presented on new types of anaerobic digesters in which chopped or dry crushed Ipomoea carnea was fed without any other pretreatment, in an attempt to develop commercially viable means of utilizing the otherwise very harmful plant. Two types of solid-feed anaerobic digesters (SFADs) were studied. The first type had a single vessel in which the bottom 35% portion was separated from the top portion by a perforated PVC disk. The weed was charged from the top and inoculated with anaerobically digested cowdung-water slurry. The fermentation of the weed in the reactor led to the formation of volatile fatty acids (VFAs) plus some biogas. The leachate, rich in the VFAs, was passed through the perforated PVC sheet and collected in the lower portion of the vessel. The other type of reactors had two vessels, the first one was fully charged with the weed and the second received the VFA leachate. With both types were attached upflow anaerobic filters (UAFs) which converted the leachate into combustible biogas consisting of approximately 70% methane. All SFADs developed very consistent performance in terms of biogas yield within 17 weeks of start. The two-compartment reactors yielded significantly more biogas than the single-compartment reactors of corresponding total volume, and the reactors with which anaerobic filters (AF) were attached yielded more biogas than the ones without AF. The best performing units generated 2.41m(3) of biogas per m(3) of digester volume, as compared to 0.1-0.2m(3) of biogas, m(-3)d(-1), obtainable with conventional digesters. This indicates the viability of this technology. The spent weed can be vermicomposted directly to obtain good soil-conditioner cum fertilizer; earthworm Eudrilus eugeniae produced 540mg vermicast per animal every day, achieving near total conversion of feed to vermicast in 20 days. The proposed systems, thus, makes it possible to accomplish total utilization of ipomoea.     

Assessing density–damage relationships between water hyacinth and its grasshopper herbivore

Plants are variable in their responses to insect herbivory. Experimental increases in densities of phytophagous insects can reveal the type of plant response to herbivory in terms of impact and compensatory ability. The relationship between insect density and plant damage of a grasshopper, Cornops aquaticum Brüner (Orthoptera: Acrididae: Tetrataeniini), a candidate biological control agent, and an invasive aquatic plant, water hyacinth, Eichhornia crassipes Mart. Solms‐Laubach (Pontederiaceae), was investigated to assess potential damage to the weed. The impact of different densities of male and female grasshoppers on E. crassipes growth parameters was determined in a quarantine glasshouse experiment. Damage curves indicated that the relationship between plant biomass reduction and insect density was curvilinear whereas leaf production was linear. Female C. aquaticum were more damaging than males, causing high rates of plant mortality before the end of the trial at densities of three and four per plant. Feeding by C. aquaticum significantly reduced the total plant biomass and the number of leaves produced, and female grasshoppers caused a greater reduction in the number of leaves produced by water hyacinth plants than males. Grasshopper herbivory suppressed vegetative reproduction in E. crassipes, suggesting C. aquaticum could contribute to a reduction in the density and spread of E. crassipes infestations. The results showed that E. crassipes vigour and productivity decreases with an increase in feeding intensity by the grasshopper. Cornops aquaticum should therefore be considered for release in South Africa based on its host specificity and potential impact on E. crassipes.     

Biological control of water hyacinth in California’s Sacramento–San Joaquin River Delta: observations on establishment and spread

Water hyacinth (Eichhornia crassipes (Martius) Solms-Laubach) is a serious invasive weed in the Sacramento–San Joaquin River Delta of California. Three insects: Neochetina eichhorniae Warner and Neochetina bruchi Hustache (Coleoptera: Curculionidae) and Niphograpta (=Sameodes) albiguttalis (Warren) (Lepidoptera: Crambidae) were released during 1982–1987 at four locations for the biological control of water hyacinth. Observations in 1985 suggested that all three species had established. By 2002, water hyacinth populations in the Delta still required an aggressive chemical control campaign and the status of the biological control agents was in question. In late 2002, a field survey to determine the distribution and abundance of the released insects was performed. Water hyacinth plants were collected by boat in the main water channels and from land at smaller sloughs and examined for insects. In total, 27 sites with water hyacinth distributed across the Delta were examined of which 21 had weevils. Weevil abundance ranged from 0 to 10.9 weevils per plant, with an average of 0.93 (±0.47 SEM) adult weevils per plant. All weevils (n?=?518) were identified as N. bruchi. No N. eichhorniae were recovered and no larvae or evidence of larval feeding by N. albiguttalis were observed. A total of 322 weevils were examined for microsporidia and none was found infected, indicating an infection rate of less than 1%. These results suggest that N. bruchi may be the only established biological control agent of water hyacinth in the Delta and that infection by microsporidia does not appear to be limiting its population abundance.     

Economic evaluation of water loss saving due to the biological control of water hyacinth at New Year’s Dam,Eastern Cape province,South Africa

Water hyacinth Eichhornia crassipes is considered the most damaging aquatic weed in the world. However, few studies have quantified the impact of this weed economically and ecologically, and even fewer studies have quantified the benefits of its control. This paper focuses on water loss saving as the benefit derived from biological control of this plant between 1990 and 2013 at New Year’s Dam, Alicedale, Eastern Cape, South Africa. Estimates of water loss due to evapotranspiration from water hyacinth vary significantly; therefore, the study used three different rates, high, medium and low. A conservative raw agriculture value of R 0.26 per m³ was used to calculate the benefits derived by the water saved. The present benefit and cost values were determined using 10% and 5% discount rates. The benefit/cost ratio at the low evapotranspiration rate was less than one, implying that biological control was not economically viable but, at the higher evapotranspiration rates, the return justified the costs of biological control. However, at the marginal value product of water, the inclusion of the costs of damage to infrastructure, or the adverse effects of water hyacinth on biodiversity, would justify the use of biological control, even at the low transpiration rate.     

Assessing the true status of the fish species Labeo cylindricus (Peters 1868) (Teleostei: Cyprinidae) in Lake Baringo,Kenya

Eutrophication contributes to the proliferation of alien invasive weed species such as water hyacinth Eichhornia crassipes. Although the South American moth Niphograpta albiguttalis was released in South Africa in 1990 as a biological control agent against water hyacinth, no post-release evaluations have yet been conducted here. The impact of N. albiguttalis on water hyacinth growth was quantified under low-, medium- and high-nutrient concentrations in a greenhouse experiment. Niphograpta albiguttalis was damaging to water hyacinth in all three nutrient treatments, but significant damage in most plant parameters was found only under high-nutrient treatments. However, E. crassipes plants grown in high-nutrient water were healthier, and presumably had higher fitness, than plants not exposed to herbivory at lower-nutrient levels. Niphograpta albiguttalis is likely to be most damaging to water hyacinth in eutrophic water systems, but the damage will not result in acceptable levels of control because of the plant's high productivity under these conditions. Niphograpta albiguttalis is a suitable agent for controlling water hyacinth infestations in eutrophic water systems, but should be used in combination with other biological control agents and included in an integrated management plan also involving herbicidal control and water quality management.     

The role of eutrophication in the biological control of water hyacinth, <Emphasis Type="Italic">Eichhornia crassipes</Emphasis>, in South Africa

South Africa has some of the most eutrophic aquatic systems in the world, as a result of the adoption of an unnecessarily high 1 mg l⁻¹ phosphorus (P) standard for all water treatment works in the 1970 s. The floating aquatic macrophyte, water hyacinth (Eichhornia crassipes (Mart.) Solms (Pontederiaceae)), has taken advantage of these nutrient rich systems, becoming highly invasive and damaging. Despite the implementation of a biological control programme in South Africa, water hyacinth remains the worst aquatic weed. A meta-analysis of published and unpublished laboratory studies that investigated the combined effect of P and nitrogen (N) water nutrient concentration and control agent herbivory showed that water nutrient status was more important than herbivory in water hyacinth growth. Analysis of long-term field data collected monthly from 14 sites around South Africa between 2004 and 2005 supported these findings. Therefore the first step in any water hyacinth control programme should be to reduce the nutrient status of the water body.     

不同耕作与施肥方式对有机玉米田杂草群落和作物产量的影响

农田杂草是农业生态系统的重要组成部分。有机农田杂草控制是农业生产的一大难题,通过施肥方式改变杂草的竞争格局有望成为杂草控制的新途径。以暖温带有机玉米田为研究对象,设置了5种不同处理,即不施肥对照处理（CK）、施用牛粪处理（CM）、施用蚯蚓处理过的牛粪处理（EM）、免耕秸秆不覆盖处理（NT）和免耕秸秆覆盖处理（NS）,研究不同耕作和施肥方式对田间杂草密度、生物量、生物多样性及作物产量的影响。结果表明,在有机玉米农田内共发现杂草17种,CK杂草总密度最高,但杂草总生物量和生物多样性指数较低。EM杂草总生物量和牛筋草（Eleusine indica）生物量最高,分别比CK增加了192.6%和224.8%（P〈0.01）,物种丰富度和生物多样性指数较低,优势集中度指数较高。NS杂草总密度、总生物量和生物多样性与NT相比显著降低。此外,EM玉米（Zea mays）产量比CK高40.2%（P〈0.01）,比CM高19.6%（P〈0.01）。施用蚯蚓处理过的牛粪不仅提高了玉米产量,而且可以促进优势种杂草的生长,提高杂草群落的优势集中度。     

A potential native natural enemy of invasive aquatic weed – water hyacinth

A potential native natural enemy of invasive aquatic weed water hyacinth was found in Shanghai of China: Chironomus larva. The larva can dig into the bulbiform petiole of water hyacinth, the petiole will be broken and decomposed soon, and also, the canker of water hyacinth will fall off. So this larva will be a native natural enemy of water hyacinth for controlling its invasion. From other side, water hyacinth will be gradually naturalized to a component of native ecosystem, although it maybe needs a long time.     

不同营养水平对外来物种凤眼莲生长特征及其竞争力的影响

入侵种凤眼莲(Eichhorniacrassipes)在中国的泛滥不仅与其强大的适应力和繁殖能力有关,还与水体的富营养化有很大的关系。作者通过盆栽实验比较了三个营养水平的模拟富营养条件下凤眼莲的生长特征和对当地种黄花水龙(Ludwigiapeploidesssp.stipulacea)和黑藻(Hydrillaverticillata)两个不同生长型的影响。结果表明:富营养条件增强了凤眼莲的生长繁殖能力,使其平均每母株克隆分株数、平均株高以及总生物量极大的增加。凤眼莲的生长优势导致了其竞争优势,对黄花水龙和黑藻都发生了明显的竞争效应。迅速繁殖的凤眼莲覆盖大量水面,通过排挤作用抑制了黄花水龙的生长(低营养水平除外);黑藻因光照缺乏,导致正常光合作用受阻,生物量急剧下降。凤眼莲对黑藻的竞争效应较黄花水龙更强。富营养化的水体为凤眼莲的成功入侵提供了优越条件,因此解决当前水体的富营养化状况能有效控制凤眼莲入侵,同时也有利于本地生物多样性的保护。     

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.     

Population regulation of a classical biological control agent: larval density dependence in Neochetina eichhorniae (Coleoptera: Curculionidae), a biological control agent of water hyacinth Eichhornia crassipes

The release of classical biological control agents has reduced the economic, environmental and social problems caused by water hyacinth, Eichhornia crassipes; however, additional control measures are needed in some locations. Water hyacinth plants were treated with different densities of eggs of the weevil Neochetina eichhorniae Warner, one of the main control agents, under different nutrient regimes in a controlled experiment. Plants were destructively sampled and the development of N. eichhorniae was assessed. The survival of first and second instars declined as larval density increased. Plant nutrient status did not directly affect the mortality rate of larvae, but at higher nutrient concentrations larvae developed faster and were larger at a given developmental stage. It is argued that the density dependence operating in N. eichhorniae occurs through an interaction between young larvae and leaf longevity. Consequently, events which disrupt water hyacinth leaf dynamics, e.g. frost or foliar herbicides, will have a disproportionately large effect on the control agents and may reduce the level of control of the host.     

The attitudes of riparian communities to the presence of water hyacinth in the Wouri River Basin,Douala, Cameroon

Since publication of the first record of Eichhornia crassipes in Cameroon in 1997, the weed has become highly invasive in the Wouri River Basin. Between June and September 2014, a socio-economic survey using participatory and qualitative methods was undertaken in the riparian villages of the Wouri River Basin to assess the perception of respondents to the presence of water hyacinth. The survey revealed that water hyacinth was a significant threat to activities along the river, which included fishing, sand extraction and river transportation. The presence of water hyacinth mats reduced catch rates of several common fish species, river transportation by 75%, and significantly reduced the income for sand extraction. Cameroon employs manual clearing of water hyacinth; however, respondents indicated they would consider other control methods, provided they do not have any negative impacts.     

马缨丹叶提取液对水葫芦叶片中超氧物歧化酶活性和过氧化氢积累的影响

水葫芦[Eichhornia crassipes（Mart）Solms]是世界上繁殖最快、危害最严重的多年生水生杂草之一。为了避免化学除草剂对水体的污染,生物防治已成为当前水葫芦治理的重要方向。马缨丹（Lantana camara）是马鞭草科的一种植物,其叶片提取物对水葫芦有很强的毒性。研究结果表明：经马缨丹叶提取液处理的水葫芦叶片中,超氧物歧化酶（SOD）活性与H2O2浓度均显著升高,但过氧化氢酶的活性受到抑制,膜脂过氧化程度明显增加。H2O2的组织化学染色结果表明H2O2在气孔细胞中有异常高的积累,H2O2过量产生同时导致水葫芦叶片失绿与细胞死亡。因此,氧胁迫可能是马缨丹提取液对水葫芦毒害的主要原因之一。