Effect of Silt Coverage of Water Hyacinth Roots on Pupation of Neochetina eichhorniae Warner and N. bruchi Hustache (Coleoptera: Curculionidae)

Observations under field conditions in Bangalore showed that release of Neochetina eichhorniae and N. bruchi (Coleoptera: Curculionidae) brought about successful control of the water hyacinth in water bodies where the plants were free-floating. However, in situations where the plants were partly anchored, suppression of the weed was achieved only 8 years after insect release. Studies carried out under glasshouse conditions, in which plants with free-floating and silt-covered roots were exposed to Neochetina spp., showed that fully grown larvae were incapable of pupating on silted roots of the water hyacinth. This resulted in reduced adult emergence of N. eichhorniae and N. bruchi, indicating that delayed suppression of water hyacinth in silted tanks may be due to the low population build-up of the weevils.     

Threat of water hyacinth resurgence after a successful biological control program

The aquatic weed, water hyacinth, Eichhornia crassipes, has caused serious socio-economic, industrial and domestic problems in Uganda and indeed the entire East Africa region. Control measures included the use of herbicides (in trials only), mechanical removal and biological control. Five years after the introduction of the weevils, Neochetina bruchi and Neochetina eichhorniae, the weed biomass was reduced to an insignificant level. There have been recent reports of a resurgence in the growth of the weed on Lakes Victoria, Albert and Kyoga. The significance of the successful control and apparent resurgence is discussed.     

Field efficacy and predicted host range of the pickerelweed borer, Bellura densa, a potential biological control agent of water hyacinth

The North American noctuidmoth Bellura densa offers promise as abiological control agent for use in Africa andother countries invaded by water hyacinth. Anaugmentative release at a pond in Florida, USA,eliminated water hyacinth within a few months. Laboratory studies, though, indicated thatoviposition was indiscriminate and thatdevelopment was completed on taro (Colocasia esculenta [Araceae]) as well as onseveral Pontederiaceae. Acceptability of taroas a larval food plant was confirmed in thefield when larvae were found in isolated standsof taro in Florida. Evidence of use of Peltandra virginica (Linnaeus) (Araceae) wasnoted at another site. The distribution oflarval damage was compared at a site containinga mixture of 97% taro and 3% pickerelweed(Pontederia cordata). Larvae damaged87% of the pickerelweed compared to only about5% of the taro, suggesting spillover ontotaro. In another study, 416 larvae wereliberated into a concrete tank containing waterhyacinth (818 plants) surrounded by taro (96plants). Three months later, taro accountedfor only 4% of the damaged plants, less thanthe 11% expected if host selection had beenrandom. In a similar study, larvae wereliberated onto water hyacinth in a large tankdivided into thirds, with pickerelweed or taroat either end and water hyacinth in the middle. The distributions of F₁ egg masses andincidence of damage 3 months later indicatedthat pickerelweed was preferred over taro, but26% of the taro plants were damaged. Weconclude that while B. densa prefersplants in the Pontederiaceae, it is notrestricted to this plant family. Plants in theAraceae would be at risk if this insect werereleased outside of North America, particularlyin cropping situations near water hyacinthinfestations. Bellura densa could beuseful for water hyacinth management in theU.S. if effective augmentation strategies weredeveloped.     

Impact of nutrients and herbivory by Eccritotarsus catarinensis on the biological control of water hyacinth,Eichhornia crassipes

Many water hyacinth infestations in South Africa are the symptom of eutrophication, and as a result, biological control of this weed is variable. This study examined the effects of herbivory by the mirid, Eccritotarsus catarinensis, on water hyacinth grown at high, medium and low nitrogen (N) and phosphorus (P) nutrient concentrations. Water nutrient concentration appears to be the overriding factor affecting plant growth parameters of water hyacinth plants—at high nutrient concentrations, leaf and daughter plant production were more than double than at low nutrient concentrations, while stem length was twice as great at high nutrient concentrations compared to low concentrations. Chlorophyll content was also twice as high at high nutrient concentrations than low concentrations. Conversely, flower production at high nutrient concentrations was less than half that at low concentrations. Herbivory by E. catarinensis did not have as great an effect on water hyacinth vigour as nutrient concentration did, although it significantly reduced the production of daughter plants by 23 ± 9%, the length of the second petiole by 13 ± 5%, and chlorophyll content of water hyacinth leaves by 15 ± 6%. In terms of insect numbers, mirids performed better on plants grown under medium nutrient conditions (99 ± 28 S.E.), compared to high nutrient concentrations (52 ± 27 S.E.), and low nutrient concentrations (25 ± 30 S.E.). Thus, these results suggest that the fastest and most significant reduction in water hyacinth proliferation would be reached by lowering the water nutrient concentrations, and herbivory by E. catarinensis alone is not sufficient to reduce all aspects of water hyacinth vigour, especially at very high nutrient concentrations.     

Chlorophyll fluorometry as a method of determining the effectiveness of a biological control agent in post-release evaluations

ABSTRACT

The impact of the planthopper Megamelus scutellaris, a biocontrol agent of water hyacinth in South Africa, was assessed using chlorophyll fluorometry in a greenhouse study under two different eutrophic nutrient treatments and agent densities (high and low). The results indicated that plants grown in low nutrients with high densities of M. scutellaris showed the greatest reduction in the fluorescence parameters Fv/Fm and PI_abs. The successful use of chlorophyll fluorometry for the detection of subtle insect damage to water hyacinth leaves could have future application in post-release studies to measure the impact of M. scutellaris in the field.     

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.     

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.     

Impacts of a sub-lethal dose of glyphosate on water hyacinth nutrients and its indirect effects on Neochetina weevils

A sub-lethal dose of a herbicide under field conditions was applied to determine if it stimulates an increase in water hyacinth nutrients, thereby increasing feeding intensity by Neochetina spp. weevils used as biocontrol agents of the weed. Nitrogen (N) and carbon (C) were measured and compared between sprayed plants and control plants. At one site (Delta Park), N levels were lower in the sprayed plants compared to the control plants both in the leaves and the crown. At the second site (Farm Dam), leaf N was also lower in the sprayed plants than in the control plants, while no difference was found in crown N. Mean number of feeding scars per cm² at Delta Park was significantly higher on the sprayed plants compared to the control plants, while no significant difference was found at Farm Dam. At Delta Park, there was no correlation, however, between the number of weevil feeding scars and leaf N or C:N ratio in sprayed plants. In conclusion, the sub-lethal dose of glyphosate did not directly result in an increase in weevil feeding intensity but it can be recommended in an integrated control system to retard water hyacinth growth while conserving the weevil population.     

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.     

Cryptic species of a water hyacinth biological control agent revealed in South Africa: host specificity,impact, and thermal tolerance

The discovery that cryptic species are more abundant than previously thought has implications for weed biological control, as there is a risk that cryptic species may be inadvertently released with consequences for the safety of the practice. A cryptic species of a biological control agent released for the control of the invasive alien macrophyte, water hyacinth, Eichhornia crassipes (C. Mart.) Solms. (Pontederiaceae), was recently discovered in South Africa. The two species were considered a single species prior to genetic analysis and interbreeding experiments. The original biological control agent retains the name Eccritotarsus catarinensis (Carvalho) (Heteroptera: Miridae) whereas the new species has been described as Eccritotarsus eichhorniae Henry. In this study, we compared the host specificity, efficacy, and thermal physiologies of the two species. The host specificity of the two species within the Pontederiaceae was very similar and both are safe for release in South Africa. Comparison of the per capita impact of the two species indicated that E. eichhorniae was the more damaging species but this is likely to be influenced by temperature, with E. catarinensis being more effective under lower temperatures and E. eichhorniae being more effective under higher temperatures. Releasing the correct species for the thermal environment of each release site will improve the level of control of water hyacinth in South Africa. This example highlights the need to keep populations of biological control agents from different native range collection localities separate, and to screen for host specificity and efficacy.     

The effect of two biological control agents, the weevil Neochetina eichhorniae and the mirid Eccritotarsus catarinensis on water hyacinth, Eichhornia crassipes , grown in culture with water lettuce, Pistia stratiotes

We assessed the effect of two biological control agents, the mirid Eccritotarsus catarinensis (Carvalho) and the weevil Neochetina eichhorniae (Warner), singly or in combination, on the competitive ability of their host plant, water hyacinth, Eichhornia crassipes (Mart.) Solms-Laub., grown in a screen house, in competition with another aquatic plant (Pistia stratiotes L.). Water hyacinth plant growth characteristics measured included fresh weight, leaf and petiole lengths, number of inflorescences produced, and new shoots. Without herbivory, water hyacinth was 18 times more competitive than water lettuce (across all experimental combinations of initial plant densities), as estimated from fresh weights. Both insect species, singly or in combination, reduced water hyacinth plant growth characteristics. E. catarinensis alone was less damaging than the weevil and under normal conditions, i.e., floating water hyacinth, is not expected to increase control of water hyacinth beyond that of the weevil. When combined with the weevil, half the inoculum of weevils and half the inoculum of mirids produced the same growth reduction as the full inoculum of the weevil. Under conditions where the weevils are not effective because water hyacinths are seasonally rooted in mud, the mirid, which lives entirely on leaves, should become a useful additional biological control agent. Handling Editor: John Scott.     

Bostrycin and 4-deoxybostrycin: two nonspecific phytotoxins produced by Alternaria eichhorniae.

Two crystalline red pigments with phytotoxic activity were isolated from culture filtrates of Alternaria eichhorniae, a pathogen of the water hyacinth Eichhornia crassipes. The pigments were present in the ratio of 4:1 and were identified as bostrycin and 4-deoxybostrycin, respectively. This is the first isolation of 4-deoxybostrycin from a natural source. Bostrycin, 4-deoxybostrycin, and their isopropylidene derivatives induced necrosis on tested plant leaves comparable to the A. eichhorniae-induced necrosis on water hyacinth. The lowest phytotoxic concentrations of crystalline bostrycin and 4-deoxybostrycin on water hyacinth leaves were about 7 and 30 microgram/ml, respectively. Both substances were inhibitory to Bacillus subtilis but were inactive against the fungus Geotrichum candidum.     

Effect of habitat complexity on biological control by the red imported fire ant (Hymenoptera: Formicidae) in collards

A potentially important and understudied biological control agent in US agroecosystems is the red imported fire ant, Solenopsis invicta Buren. Red imported fire ants may be particularly important biological control agents because we can manipulate their abundance with changes in habitat complexity. The effect of habitat complexity on biological control by fire ants was determined using plots of collards intercropped with white clover (complex habitat) and simple collard monocrops. The most economically significant pests of collards are larvae of the diamondback moth (DBM), Plutella xylostella (L.). Predation of DBM larvae by fire ants was more rapid and efficient in the intercrop than the monocrop. Red imported fire ants were 23% less abundant in the intercrop than the monocrop, however, suggesting that fire ants had a greater per capita effect on DBM survival in the complex habitat. Red imported fire ant predation of DBM larvae was significantly affected by larval density. Red imported fire ants also reduced the survival of leaf beetles, another economically significant pest taxa, by 45%. Furthermore, collard leaf damage tended to be inversely related to fire ant density and fire ants were more effective at reducing crop damage in the complex intercrop. Our study indicates the ability of red imported fire ants to be effective biological control agents and suggests that increasing habitat complexity can enhance red imported fire ant efficacy and herbivore control.     

Meteorological weather station data can be used in climate matching studies of biological control agents

Meteorological weather station data are often used in climate matching studies to predict potential distributions of biological control agents, yet, this does not take into account the effects of microclimates experienced by the agents. Comparisons of the number of generations that the mirid, Eccritotarsus catarinensis, a biological control agent of water hyacinth, Eichhornia crassipes (Mart.) Solms-Laub (Pontederiaceae), was predicted to complete using meteorological weather station data, on site air temperature and water hyacinth canopy microclimate temperatures recorded over two years showed that there were no significant differences between the temperature data sources. Therefore, meteorological weather station data used in degree-day models of biological control agents are useful in explaining broad establishment patterns.     

Development and Degeneration of Flight Muscles in Neochetina eichhorniae (Coleoptera; Curculionidae), Potential Biocontrol Agent of the Aquatic Weed, Eichorniae crassipes

The water hyacinth weevil, Neochetina eichhorniae, is an effective biological control agent of the aquatic weed Eichorniae crassipes. The adults under field conditions have degenerated indirect flight muscles that explains their inability to fly. A study on the factors initiating flight muscle development in adults was carried out. Among the various abiotic factors studied, density of weevils per plant and high temperature in presence of food initiated and accelerated flight muscle development. Absence of food did not influence muscle development. No inter-relationship between flight muscle development and degeneration could be observed.     

The effect of water pollution on biological control of water hyacinth

South Africa has one of the world’s biggest gold mining regions with an associated problem of acid mine drainage (AMD), which increases the bioavailability of heavy metal contaminants in water. The prevalence of water hyacinth (Eichhornia crassipes) in South African water systems, despite the release of seven biocontrol agents since 1974, is often attributed to high levels of eutrophication. Metal concentration in plant shoots is known to affect insect herbivory. Nevertheless, little is known about the effect of heavy metals or AMD on Neochetina eichhorniae and Neochetina bruchi, which are the most widely established biocontrol agents on E. crassipes in South Africa. Herein, the effect of eight different heavy metals common in AMD (arsenic (As), gold (Au), copper (Cu), iron (Fe), mercury (Hg), manganese (Mn), uranium (U) and zinc (Zn)), as well as three different simulated AMD concentration treatments (low, medium and high), on the performance of Neochetina weevils were investigated by releasing adults on plants growing in tubs and pools, three weeks after the addition of individual metal or AMD treatments. After six weeks, the number of weevil larvae per plant, the number of adult survivors per plant, the number of adult feeding scars on leaves, and the number of larval mines per plant were recorded. Two females of N. eichhorniae and N. bruchi from each tub were dissected and the number of ovariole follicles was counted. Adult feeding in Neochetina was significantly reduced on plants exposed to both Cu and As while larval feeding was significantly reduced on plants exposed to Hg, Zn, As and Cu, with Cu causing the greatest effect. Similarly, weevil feeding and reproduction were reduced in the medium and high concentration AMD treatments. Larval development was significantly impaired by both metal and AMD treatments. These negative effects disagree with published data which showed no effect of metals on Neochetina weevils. The disparity is explained by long exposure of the weevils on whole plants, rather than short exposure to excised leaves, as recorded in the literature. Finally these findings provide evidence that some heavy metals and AMD might be constraining biocontrol agents of water hyacinth in South Africa.     

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.     

Potential impacts of water hyacinth invasion and management on water quality and human health in Lake Tana watershed,Northwest Ethiopia

Incursion of water hyacinth, Eichhornia crassipes, has been a potential threat to Lake Tana and its ecosystem services. Its expansion is currently managed by abstraction (removing by hand); nonetheless, the disposal of mats and formation of pools are remaining problematic. This study aimed to assess the potential effects of water hyacinth and its management on water quality and human health. Biotic and abiotic data were collected on open water, water hyacinth covered and water hyacinth cleared out habitats. A total of 3673 invertebrates belonging to twenty-one families were collected from 45 sites. Culicidae was the most abundant family accounting (37.2%), followed by Unionoidae (19.4%) and Sphaeriidae (8.1%). Abundance of anopheline and culicine larvae were significantly higher in water hyacinth cleared out habitats (p?<?0.05). Water conductivity and total dissolved solids were significantly higher in habitats covered with water hyacinth (p?<?0.05). In conclusion, water hyacinth infestation had a negative impact on water quality and biotic communities. The physical abstraction of water hyacinth provided a very good habitat for the proliferation of mosquito larvae. Therefore, integrating water hyacinth management practices along with mosquito larvae control strategy could help to abate the potential risk of malaria outbreak in the region. In addition, developing watershed scale nutrient management systems could have a vital contribution for managing water hyacinth invasion in the study area.     

Mass rearing the weevil Hylobius transversovittatus (Coleoptera: Curculionidae), biological control agent of Lythrum salicaria, on semiartificial diet

Lythrum salicaria L., purple loosestrife, an invasive Eurasian perennial, is degrading wetlands across temperate North America. Chemical, physical, and mechanical methods failed to provide long-term control. Therefore, four host-specific insect species (two leaf feeders, a root feeder, and a flower feeder) were introduced as biological control agents. To increase the availability of adults of the root feeding weevil Hylobius transversovittatus Goeze for field releases, we developed a semiartificial diet. Suitability of different diet formulations (varying vitamin mixes, salt mixes, antimicrobials, water content, root content) and temperatures for larval development were evaluated. We also monitored how rearing on artificial diet and the number of larvae per container affected larval development time, larval survival, adult weight, and incidences of deformities. Rearing larvae on artificial diet reduced development time from 1-2 yr to 2-3 mo. Larval development was fastest and survival rates highest under constant temperatures of 25 degrees C. Hatch rate and larval survival decreased if eggs were surface sterilized. Using FABCO antimicrobials could not prevent fungal contamination; use of methyl paraben and sorbic acid was successful in suppressing fungal and bacterial growth throughout larval development time to <10%. The moisture content of the diet did not significantly affect larval survival, development, or adult weight. Decreasing the proportion of purple loosestrife roots in the diet reduced adult weight and the proportion of larvae completing development, and increased development time; no larvae were able to complete development in root-free diet. With an increase in the number of larvae per cup, survival rates were reduced. The experiments revealed a female biased sex ratio: females consistently developed faster and were heavier than males. Incidence of adult deformities was consistently below 5%. Increased availability of adults for field release as a result of mass production using the semiartificial diet will accelerate the biocontrol program targeting purple loosestrife. We are able to produce several hundred weevils per week and have adapted the diet to rear other root-feeding weevils.     

Importation,releases, and establishment ofNeochetina spp. (Col.: Curculionidae) for the biological control of water hyacinth,Ecchhornia crassipes (Lil.: Pontederiaceae), in Benin,West Africa

Water hyacinth,Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae) was first reported in Bénin in 1977 and about 10 years later became the major floating water weed in the south east, obstructing boat traffic and fisheries. Water hyacinth multiplies in permanently fresh water in the swampy upper reaches of the Sô River and in tributaries of the Ouémé River. From there it is moved by wind and water flow to the coastal lagoons. The coastal lagoons are brackish during the dry season and water hyacinth eventually dies. In 1991,Neochetina eichhorniae (Warner) (Col.: Curculionidae) of South American origin was imported from Australia via quarantine in Britain to Bénin. A small infestation of the fungusBeauveria bassiana (Bals.) Vuill. (Hyphomycetes) was eliminated from the colony before release by sterilizing eggs and rearing a fungus-free generation. Between late 1991 and mid 1993, about 23,900N. eichhorniae were released at 11 localities along the Ouémé River and in the head waters of the Sô River. Regular monitoring revealed feeding scars by adults on leaves and tunnelling by larvae in petioles at all release sites. By October 1993,N. eichhorniae had spread up to 20 km from some release sites.Neochetina bruchi Hustache was imported in 1992. A total of about 5,700 weevils has been released in six localities since mid 1992. Recoveries of offspring were made in all but one locality. Despite the negative impact of water flow, wind, penetration of salt water, and removal of infested water hyacinth by fishermen,N. eichhorniae andN. bruchi are established in Bénin in a situation typical for coastal West Africa.