Control Agent Of Water Hyacinth Research Articles

Performance and field host range of the life stages of Cornops aquaticum, a biological control agent of water hyacinth

AbstractHost specificity determination of weed biocontrol agents has historically relied on evidence generated through quarantine trials in the region of introduction. These trials could give ‘false positive’ results due to a maximum type I error probability, and where possible, more research under field conditions should be conducted in the region of origin. The oligophagous, semiaquatic grasshopper, Cornops aquaticum Bruner (Orthoptera: Acrididae, Tetrataeniini), was released in South Africa for the biological control of Pontederia crassipes Pellegrini and Horn (Pontederiaceae). The aim of this study was to assess how the performance and field host range of C. aquaticum varies according to its stages of development, and how this contributes to the understanding of the relationship between the fundamental (laboratory‐based) and the ecological (field‐based) host range of this grasshopper, and its implications for water hyacinth biocontrol. We conducted post‐release laboratory no‐choice trials, confining early instars (instars 1 and 2), later instars (instars 3–6), and adult females and males in mesh cages, to determine insect performance on wetland plants growing in sympatry with P. crassipes. Also, gut analysis from field‐collected C. aquaticum was done to determine the ecological host range of this insect, identifying epidermal tissue of consumed plants. In no‐choice trials, survival rates of the later instars and adult C. aquaticum were similar on Pistia stratiotes L. (Araceae), Oxycaryum cubense (Poepp. & Kunth) Lye (Cyperaceae), and P. crassipes. However, under field conditions, P. crassipes and the congeneric Pontederia azurea Sw. were the only plant contents in the guts of early instars and the most abundant species in later instars and adults. The results support the hypothesis that C. aquaticum is an oligophagous insect on the genus Pontederia, and that different life stages should be considered when conducting host‐specificity trials in externally feeding mobile herbivore species. Diet composition of field‐collected insects thus could help detect false positives in laboratory trials, being an additional and realistic approach in understanding and predicting the selection processes of the insect in the new environment. Retrospective analysis of potential agents that were rejected due to lack of host‐specificity, using the methods from this study, could add a suite of additional agents to programs where invasive weeds remain unmanaged.

Spatial population structure: patterns of adaptation in populations of the water hyacinth grasshopper Cornops aquaticum (Bruner 1906)

AbstractThe water hyacinth grasshopper Cornops aquaticum (Bruner 1906) constitutes an appropriate model to assess phenotypic and karyotypic variability in the context of differentiation and adaptation of insect populations because it occurs over a wide latitudinal range. This study represents a general analysis of phenotype, karyotype and molecular variation in native populations of C. aquaticum in South America. This is also relevant because this insect is considered a promising biological control agent of water hyacinth, a native South American aquatic plant but a pest in South Africa. Along Paraná and Uruguay River Basins, body size correlated negatively with latitude, and positively so with temperature and rainfall in both sexes. To test whether the chromosomal and phenotypic patterns were adaptive, we compared them with neutral microsatellite loci variation in populations from the medium and lower course of the Paraná River. Firstly, the lack of pairwise association between karyotype and phenotype distance matrixes with that of neutral loci suggested non-neutrality. Secondly, phenotypic differentiation for all morphometric traits (PST) was significantly larger than molecular differentiation (FST), indicating a prevailing divergence selection effect on the observed phenotypic patterns. Finally, the phenotypic and genotypic spatial structures – inferred from Bayesian approaches – were discordant: neutral genetic structure clustered together most populations except for the two southernmost, downstream ones, whereas phenotypic spatial structure groups together all the deltaic populations and singles out the two northernmost ones. The results suggest directional selection leading to higher centric fusion frequencies in the downstream populations and favouring morphometric optimal differences in relation to the environment.

Mind the gap: the delayed recovery of a population of the biological control agent Megamelus scutellaris Berg. (Hemiptera: Delphacidae) on water hyacinth after winter.

Cold winter temperatures significantly affect the biological control effort against water hyacinth, Pontederia ( = Eichhornia) crassipes Mart. (Pontederiaceae), in more temperate regions around the world. The population dynamics of the planthopper Megamelus scutellaris Berg. (Hemiptera: Delphacidae), a newly released biological control agent of water hyacinth, were recorded on the Kubusi River in the Eastern Cape Province (South Africa) over 15 months to determine the population recovery post-winter. Megamelus scutellaris incurred a severe population decline at the onset of winter when the water hyacinth plants became frost damaged. The combined effect of a population bottleneck and low minimum winter temperatures (6.12°C) below the agent's lower developmental threshold (11.46°C) caused a post-winter lag in agent density increase. Subsequently, the maximum agent population density was only reached at the end of the following summer growing season which allowed the water hyacinth population to recover in the absence of any significant biological control immediately post-winter. Supplementary releases of agents from mass-reared cultures at the beginning of the growing season (spring) is suggested as a potential method of reducing the lag-period in field populations in colder areas where natural population recovery of agents is slower.

Assessing the risk of Eccritotarsus eichhorniae to pickerelweed, Pontederia cordata in North America

ABSTRACTThe mirid Eccritotarsus eichhorniae is a newly described species with potential as a biological control agent for water hyacinth, Eichhornia crassipes, in North America. A series of quarantine-based studies quantified E. eichhorniae usage of Pontederia cordata with no-choice, adult choice, nymph choice, multi-generation, and impact tests. Although greater numbers of E. eichhorniae adults developed on E. crassipes in two separate no-choice trials, some E. eichhorniae were able to complete development on P. cordata in both trials. Adults showed a clear oviposition preference for E. crassipes and F1 progeny reduced the mean relative growth rate of E. crassipes but not P. cordata. Naïve nymphs were more likely to leave P. cordata for E. crassipes but not all nymphs left P. cordata when given a choice. Both multi-generation trials showed a rapid increase in the density of adults and nymphs on E. crassipes over four to five generations while population densities on P. cordata did not change, indicating that this insect can maintain populations on this plant. The modest damage inflicted by a sibling species on E. crassipes, coupled with the ability of E. eichhorniae to persist on P. cordata, may pose an interpretation challenge to U.S. regulatory agencies concerned with non-target impacts by biological control agents. Another option for the continuing efforts to increase the biological control of E. crassipes is to prioritise the evaluation of other potential agents like Taosa longula Remes Lenicov (Homoptera: Dictopharidae) or Thrypticus truncatus Bickel and Hernández (Diptera: Dolichopodidae) over E. eichhorniae.

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

ABSTRACTWater 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.

Interaction between temperature and water nutrient levels on the fitness of Eccritotarsus catarinensis (Hemiptera: Miridae), a biological control agent of water hyacinth

Fitness traits of insect herbivores of aquatic weeds may change with environmental conditions including temperature and water nutrient levels. Both of these factors are likely to increase due to changes in global weather patterns and human activity. We tested the interaction of temperature and nutrient status on the fitness of Eccritotarsus catarinensis, a biocontrol agent against the invasive aquatic weed, water hyacinth Eichhornia crassipes. Several life history traits were evaluated on plants grown at three constant temperatures (20, 25 and 30°C) combined with three nutrient levels: oligotrophic (low), mesotrophic (medium), and eutrophic (high). When the two factors are separated, all fitness traits decreased with increasing temperature and decreasing water nutrient levels. The combination of high temperature and low water nutrient status had a greater and significant negative effect on some fitness traits: lifetime fecundity, realized fecundity and nymphal survival. The relationship between insect fitness traits and water nutrient status followed different patterns depending on temperature: a monotonic, but non-linear response at 20°C, where fitness was highest at medium water nutrient status and reduced at low and high water nutrient status; and a linear monotonic response at 25°C, where fitness increased with increasing water nutrient status. At 30°C fitness traits were equal on plants grown in water with high and medium nutrient status and lower on those grown in water with low nutrient status. We demonstrated that a combination of low nutrient waters with higher temperatures would hamper the efficacy of this agent. Our results suggested that the negative impact of the herbivorous insects on the aquatic weed would be most successful on vigorous plants, applicable for both mesotrophic and eutrophic nutrient levels, particularly in temperate areas.

Establishment of the moth: Niphograpta albiguttalis (Warner) (Lepidoptera: Pyralidae), a biological control agent of water hyacinth (Eichhornia crassipes) in waterways of Lagos and Ogun states, southwestern Nigeria

The moth Niphograpta albiguttalis was found infesting water hyacinth on waterways in Nigeria in 2009 in the areas of Badagry, Ejirin and Epe in Lagos State and Iwopin in Ogun State. This moth has not been released in Nigeria but it was released as a biological control agent for water hyacinth in Ghana in 1996 and in Benin in 1993. It is not reported to have established in those countries, but it would appear that as a result of those releases N. albiguttalis is now present in Nigeria. The larval instars found were damaging only water hyacinth with bulbous petioles. The larval developmental periods ranged between 10 and 15 days (n = 3).

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.

Establishment of the Presence of Moth: Niphograpta albiguttalis (Warner) (Lepidoptera: Pyralidae), Biological Control Agent of Water Hyacinth (Eichhornia crassipes) in Waterways of Lagos and Ogun States, Southwestern Nigeria

Establishment of the Presence of Moth: Niphograpta albiguttalis (Warner) (Lepidoptera: Pyralidae), Biological Control Agent of Water Hyacinth (Eichhornia crassipes) in Waterways of Lagos and Ogun States, Southwestern Nigeria

Morphometric differences in the grasshopper Cornops aquaticum (Bruner, 1906) from South America and South Africa

The semi-aquatic grasshopper Cornops aquaticum is native to South America and inhabits lowlands from southern Mexico to Central Argentina and Uruguay. It is host-specific to aquatic plants in the genera Eichhornia and Pontederia. A quarantine population has existed in South Africa for 10 y, and it is planned to release it there as a biological control agent of water hyacinth, E. crassipes. Various studies of C. aquaticum are coordinated under HICWA (www.mpil-ploen.mpg.de). This paper compares the morphometry of the release population and 11 native populations in South America. We tested four hypotheses: 1) South African and South American populations of C. aquaticum differ in morphology; 2) the South African laboratory population is more similar to other isolated populations in South America than to nonisolated populations; 3) morphology differs across sites; 4) morphology differs with host plant. South African populations differed from continental nonisolated populations, but not from continental isolated ones. Isolated populations presented smaller individuals than nonisolated, but there was also a change in male morphology: while in nonisolated populations male wing length was similar to their body length, in isolated populations, male wings were smaller than body length. Females were larger when on Eicchornia azurea than on E. crassipes, while males presented larger wings than their body on E. azurea, and similar lengths on E. crassipes. These morphological changes may have resulted from phenotypic plasticity, selection for small size, or because of a loss of genetic diversity in quantitative traits.

Failure of Eccritotarsus catarinensis, a biological control agent of waterhyacinth, to persist on pickerelweed, a non-target host in South Africa, after forced establishment

Abstract Waterhyacinth (Eichhornia crassipes) is the most damaging aquatic weed in South Africa, where five arthropod biological control agents have been released to date. The most recent introduction, a South American mirid, Eccritotarsus catarinensis, was shown to utilize Pontederia cordata (pickerelweed) during laboratory host-specificity trials. This did not influence the decision to release the mirid in South Africa, where the exotic pickerelweed is a declared invader. However, in the United States of America where waterhyacinth is also a problem, the possibility of spillover damage on indigenous pickerelweed may preclude the release of the mirid. In this study, E. catarinensis did not establish on pickerelweed in the field in South Africa, following either confined releases, where the mirids were initially released into sleeve cages, or unconfined releases where mirid-infested pickerelweed plants were placed amongst pickerelweed stands. We thus recommend that E. catarinensis be considered as an additional control agent of waterhyacinth in North America.

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.

Potential Effects of Beauveria bassiana (Balsmo) Vuillemin on Neochetina bruchi Hustache (Coleoptera: Curculionidae), a Biological Control Agent of Water Hyacinth

Abstract The potential effects of Beauveria bassiana, an entomopathogen, on the biological control agent of water hyacinth, Neochetina bruchi, were assessed. In bioassays, B. bassiana induced mortality of the eggs, larvae, and adults when the N. bruchi stages were either sprayed or dipped in conidia concentrations of 5 × 105, 5 × 106, 5 × 107, 5 × 108, and 5 × 109 conidia/ml. The fungus caused highest mortality in larvae, whereas eggs were most resistant. Mortality increased in all insect stages as the conidia concentrations increased. The LT50 values of the pathogen on eggs at 5 × 108 and 5 × 109 conidia/ml were 10 and 7.2 days, respectively. For larvae and adults, the LT50 values at 5 × 109 conidia/ml were 3.6 and 6 days, respectively. The LC50 values were significantly different for all three stages at day 12 posttreatment, with the values of 9.5 × 107, 7.6 × 105, and 8.9 × 106 conidia/ml for eggs, larvae, and adults, respectively. The prevalence of B. bassiana in adult N. bruchi was measured at three water bodies in Zimbabwe. The prevalence of B. bassiana was highest in February–March of 2000. At Lake Chivero, the maximum reached 38%, whereas it was much lower at Lake Kariba and at Kudzwe Dam. Differences in the prevalence of B. bassiana appeared to be coupled with herbicide sprays used for the control of the water hyacinth problem. The prevalence was highest at sites where herbicides were used regularly and lowest where no herbicides were used. The temperatures at Lake Chivero were lower than those at the two other sites and this difference may have influenced the level of B. bassiana prevalence in N. bruchi.

Infectivity of Insect Pathogens against Neochetina eichhorniae, a Biological Control Agent of Waterhyacinth

Several insect pathogens were tested for infectivity against Neochetina eichhorniae Warner (Coleoptera:Curculionidae), a biological control agent for waterhyacinth, Eichhornia crassipes (Mart.) Solms. No mortality resulted from exposure to 21 strains of Bacillus thuringiensis. No significant mortality resulted from exposure to 2 strains of Metarhizium anisopliae. Although treatment of adult weevils with 6 strains of Beauvaria bassiana produced no significant mortality, 2 strains (BbAFA - 35%, Bb 5647 - 65%) did result in statistically significant mortality. Exposure to 2 strains of Steinernema carpocapsae resulted in 60-70% mortality. Our results indicate limited potential for these insect pathogens to control N. eichhorniae in resource recovery or wastewater treatment facilities.