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.     

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.     

Life History and Laboratory Host Range ofEccritotarsus catarinensis(Carvalho) (Heteroptera: Miridae), a New Natural Enemy Released on Water Hyacinth (Eichhornia crassipes(Mart.) Solms-Laub.) (Pontederiaceae) in South Africa

A mirid,Eccritotarsus catarinensis(Carvalho), was studied as a potentially damaging natural enemy for water hyacinth, (Eichhornia crassipes(Mart.) Solms-Laub.), in South Africa. In the laboratory, eggs were inserted into the leaf tissue parallel to the leaf surface. The four nymphal instars fed gregariously with the adults mainly on the undersurface of the leaves, causing severe chlorosis at high population levels. The duration of immature stages (egg and nymphs) was approximately 23 days, while the adults survived for approximately 50 days. Favorable biological characteristics ofE. catarinensisincluded a high rate of increase, gregarious habits, long-lived and mobile adults, and several generations per year. Laboratory host range of the mirid was determined by adult choice trials on 67 plant species in 36 families and adult no-choice trials on five species in the Pontederiaceae. Feeding was recorded on all Pontederiaceae tested and oviposition on four of the five species. However, these plant species proved to be inferior hosts forE. catarinensisin comparison to water hyacinth, suggesting thatE. catarinensiswould be an acceptable natural enemy for water hyacinth in South Africa.     

Mating preferences of two species of Eccritotarsus (Hemiptera: Miridae)

ABSTRACT

Eccritotarsus spp. are biological control agents that have been sourced from Brazil and Peru to control water hyacinth in South Africa. These agents have been released in over 30 sites and were thought to be the same species. The sequencing of mitochondrial DNA and interbreeding experiments have since confirmed the cryptic species to be separate species. The Brazilian population remains E. catarinensis while the Peruvian population is now E. eichhorniae. This paper assessed the mating behaviour of both species, to investigate behavioural traits that have resulted in reproductive isolation, which could have led to speciation. Mating choices in a form of no-choice, bi-choice and multi-choice tests were conducted within and between species in a 3:1, 2:1 and 1:1 sex ratio. The E. eichhorniae pair had more single and multiple copula incidences, higher average total copula duration and higher copula latency while the E.catarinensis♀×E.eichhorniae♂ pair had less single and multiple copula incidences, lower average total copula duration and lower copula latency. When the E.eichhorniae♀ and E.catarinensis♂ were given their respective choices, they only mated with conspecifics. However, when E.eichhorniae♀ are crossed with E.catarinensis♂ they do not produce offspring. These results suggest that interbreeding will be limited in South Africa.     

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.     

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.     

The host specificity of Anomalococcus indicus Ayyar (Hemiptera: Lecanodiaspididae), a potential biological control agent for prickly acacia (Vachellia nilotica ssp. indica) in Australia

ABSTRACT

Prickly acacia, Vachellia nilotica ssp. indica (Benth.) Kyal. & Boatwr, is a significant weed of northern Australia and has been a target of weed biological control in Australia since the 1980s. Following native range surveys in India, the scale insect Anomalococcus indicus Ayyar was identified as the most promising agent and was imported into Australia for further research. A. indicus is a major pest of prickly acacia on the Indian subcontinent, where it causes shoot tip dieback and plant death. Despite field observations suggesting the species was specific to V. nilotica, A. indicus completed development on 17 of the 84 non-target plant species tested during no-choice host specificity trials under quarantine conditions. Of these, Acacia falcata, V. bidwillii, V. sutherlandii and Neptunia major supported high numbers of mature females in all replicates. All of these species were utilised in choice trials. Combined risk scores indicate that V. sutherlandii, N. major and A. falcata may be attacked in the field. Due to the limited ability of scale insects to disperse, only those non-target species that occur on the Mitchell grass downs (i.e. V. sutherlandii) are considered to be at risk. Nevertheless, in view of the disparity between quarantine test results and the observed field host specificity of A. indicus in India, field trials are currently being conducted in India using Australian native species on which complete development has occurred. The future of A. indicus as a biological control agent for prickly acacia in Australia will be determined once results from these field trials are known.     

Risk assessment of Episimus unguiculus (Lepidoptera: Tortricidae), a biological control agent of Schinus terebinthifolia (Sapindales: Anacardiaceae) in Hawaii,USA

Schinus terebinthifolia Raddi (Anacardiaceae) is an introduced ornamental tree from South America that has become one of the most invasive weeds in Hawaii and Florida, USA. Exploratory surveys in the plant’s native range from 1950 to 2014 identified several potential biological control agents. One of these is the leaflet rolling moth Episimus unguiculus Clarke (Lepidoptera: Tortricidae), previously known as Episimus utilis Zimmerman. This biological control agent was released in Hawaii in the 1950s where high densities were occasionally observed, leading to partial control of S. terebinthifolia by the 1960s. Larvae are leaf tiers capable of completely defoliating small plants. In order to investigate the release of E. unguiculus in the continental USA, a series of laboratory no- choice, and multiple-choice tests were conducted in Florida, and a preliminary open field test with a native plant in Hawaii. Under the confined laboratory conditions imposed during the no-choice tests, E. unguiculus accepted the economically important Pistacia spp. and several other non-target plants for oviposition and development. However, in the multiple-choice tests E. unguiculus exhibited a clear preference for S. terebinthifolia relative to non-target plants accepted in the no-choice tests. Overall, the results of field observations during surveys in South America and Hawaii and host range studies completed in Hawaii and Florida showed that E. unguiculus is a narrow specialist on S. terebinthifolia, its natural host plant.     

Preference and Performance of the Polymorphic Flea-beetle, Alagoasa extrema, on Selected, Weedy Lantana camara Varieties

The possible preference that the leaf-feeding flea-beetle, Alagoasa extrema Jacoby (Coleoptera: Chrysomelidae: Alticinae), might have for different South African naturalized varieties of its host plant, Lantana camara L. (Verbenaceae), was studied under quarantine laboratory conditions. Studies included adult choice trials, larval no-choice trials and multi-generation no-choice trials using five L. camara varieties. Results indicated that A. extrema exhibited a degree of varietal preference under laboratory conditions. Variety 029 White Pink proved to be the most suitable host, although the other four tested varieties were able to support viable populations of A. extrema for three consecutive generations. Should A. extrema be released as biocontrol agent for L. camara in South Africa, all five of the tested varieties should be able to support viable populations of A. extrema in the field.     

Observations on the effect of the weevils Neochetina eichhorniae Warner and Neochetina bruchi Hustache on the growth of water hyacinth

Water hyacinth Eichhornia crassipes (Mart.) Solms. is an aquatic weed that infests most of the White Nile system in the Sudan. Serious economical and ecological problems are caused by this weed. The two weevils Neochetina eichhorniae and Neochetina bruchi were imported and released in an attempted biological control against the weed. The adults of these weevils attack the plant and feed by removing tissues from the leaf pseudolamina and petioles. The larvae tunnel inside the petioles and the crown. The optimum temperature for feeding and development of both species is 25° C. Results obtained from stocking hyacinth plants with adults and larvae of both species separately revealed that N. bruchi is more efficient in checking the growth of the plant. The progeny of a pair of N. bruchi and N. eichhorniae reared separately on 41 hyacinth plants for a period of 61 days (one generation period) reduced their population growth by 25.4% and 12.7% respectively. The progeny of both species in a mixed culture reduced the growth of the plants by 22.5% in the same period, while in the control the population of the plants increased 136.6%.     

Development and feeding of <Emphasis Type="Italic">Tetraphleps galchanoides</Emphasis>, a predator of the hemlock woolly adelgid

Tetraphleps galchanoides Ghauri (Hemiptera: Anthocoridae) nymphs were collected from hemlock woolly adelgid (HWA) Adelges tsugae Annand (Hemiptera: Adelgidae) infested Tsuga sp. in Baoxing, Sichuan, China. First and second stage nymphs collected from foliage shipped from China; were reared to adults and tested for feeding rates and host preferences. They were reared at 5, 8, 12, and 15 ± 1 °C from November to December, January to March, April, and May to June, respectively, in the quarantine laboratory at Virginia Polytechnic Institute and State University. At 8 °C, development time was 15, 20, and 40 days for the N-III, IV, and V nymphal stages, respectively. Adult males lived 83 days with a range of 21–147 days. A single adult female lived for 21 days. At 5 °C, second stage T. galchanoides nymphs consumed 0.8 HWA nymphs per day, and 2.0 HWA nymphs per day at the N-V stage. At 8 °C, consumption of HWA nymphs ranged from 1.3 to 3.4 nymphs per day for the N-III to N-V stages, respectively. Adult T. galchanoides consumed more HWA eggs than HWA adults, pine bark adelgid (PBA) Pineus strobi (Hartig) (Hemiptera: Adelgidae) adults, and eggs in no-choice tests. In choice tests with HWA eggs and PBA eggs, more HWA eggs were eaten. Adult and nymph body measurements are presented for determination of nymphal instars.     

The effects of insect–insect interactions on the performance of three biological control agents released against water hyacinth

Insect–insect interactions can have implications for biological control programmes when multiple agent species are released. In many cases there is an increase in the efficacy when more than one species is used; however, there is a possibility that releasing an additional species into a programme could have a negative effect. The interactions between three arthropod agents of water hyacinth Eichhornia crassipes (Martius) Solms-Laubach, Eccritotarsus catarinensis (Carvalho), Neochetina bruchi Hustache and Neochetina eichhorniae Warner were investigated in an experiment to measure the impact that pairwise combinations of the insects may have on their performance. There was a significant interaction between the mirid E. catarinensis and the weevil N. eichhorniae, with significantly fewer weevil feeding scars when in combination with the mirid (approximately 0.2 scars per cm²) than when alone (approximately 0.4 scars per cm²). There were also slightly fewer petioles mined by N. eichhorniae when in combination with the mirid. Interestingly there was a negative interaction between the two weevil species when in combination, with the number of feeding scars being significantly lower per individual when the two species were in combination. None of the insects performed significantly better when in combination with another insect, however, the mirid was never negatively affected by the presence of either weevil species. The interactions observed between the insects tested were identifiable but subtle and are unlikely to have implications on establishment or performance of the insects in the introduced range, South Africa.     

A microcosm investigation of fe (iron) removal using macrophytes of ramsar lake: A phytoremediation approach

The present study deals with the microcosm study of Fe (Iron) phytoremediation using Eichhornia crassipes, Lemna minor, Pistia stratiotes and Salvinia cucullata species collected from the Loktak Lake, a Ramsar Site which exists in north-eastern India (an Indo-Burma hotspot region). Efficiency of these four macrophytes was compared using different Fe concentrations of 1 mg L^?1, 3 mg L^?1 and 5 mg L^?1 for 4 days, 8 days and 12 days, respectively. E. crassipes was the most efficient macrophyte whereas L. minor was the least efficient. E. crassipes removed the highest percentage of Fe, i.e. 89% from 1 mg L^?1, 81.3% from 3 mg L^?1 and 73.2% from 5 mg L^?1 in 12-day experiment.     

Pre-release evaluation of absolute spillover impact risk of Physonota maculiventris (Chrysomelidae: Cassidinae) on non-target plant species Helianthus annuus (Asteraceae) and Zea mays (Poaceae) in South Africa

The tortoise beetle, Physonota maculiventris (Coleoptera: Chrysomelidae), a candidate biological control agent of Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae) was screened for spillover risks on non-target plant species in South Africa. Studies were conducted to measure the absolute feeding damage and reproductive performance of P. maculiventris on non-target plant species, Helianthus annuus L. (Asteraceae) and Zea mays L. (Poaceae). The influence of spillover on generational build-up performance on the non-target plant species was also investigated. Adult female beetles were switched from T. diversifolia at 14 (actively feeding colony) or 24 (gravid colony) days to the non-target species. Likewise, as a backup or control, female beetles were exposed to H. annuus in a no-choice situation and switched to T. diversifolia and Z. mays. Feeding damage, adult longevity and egg production of P. maculiventris were significantly lower on H. annuus, compared to those metrics on T. diversifolia. Gravid P. maculiventris adults switched from T. diversifolia on the 14th day after emergence laid a few egg batches on the leaf surfaces of Z. mays, but no signs of feeding were observed. Furthermore, the population of P. maculiventris significantly increased by 11.7 fold (26.8–312.5 adults) between the first (F1) and second (F2) generations on T. diversifolia, while on the non-target, H. annuus, it decreased from 6.3 to zero (0). The study concludes that P. maculiventris will sustain its populations entirely on the target, T. diversifolia population stands associated with or without H. annuus and Z. mays cultivations at different scales in South Africa.     

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.     

Effect of mating combinations on the host parasitisation and sex allocation in solitary endoparasitoid,Aenasius arizonensis (Hymenoptera: Encyrtidae)

Aenasius arizonensis (Girault) is an important solitary endoparasitoid of Phenacoccus solenopsis Tinsley. To optimise the mass production of high-quality females, it is important to assess the influence of mating regimes on the progeny fitness and sex allocation. We, therefore, hypothesise that mating combinations in A. arizonensis adults emerged from different host instars may influence parasitism and sex allocation in the subsequent generation. Therefore, we compared three nymphal instars (1st, 2nd and 3rd) and adults host stages of P. solenopsis for parasitism and sex allocation by A. arizonensis. Further, F₁ female progeny of the parasitoid emerged from different host instars was henceforth evaluated for its fitness in six mating combinations. A. arizonensis females parasitised all the host stages except the 1st instar nymphs. The parasitised 2nd instar nymphs yielded only males, while the sex ratio in the later host instars was strongly female-biased. The parasitoid females preferred 3rd instar nymphs with respect to higher parasitism (74.0–84.0%) and produced more females in the F₁ progeny as compared to other host stages. F₁ females that emerged from 3rd instar nymphs produced significantly higher parasitism (74.0–79.0%). These mating combinations also yielded more female progeny in the F₂ generation. However, parasitism by F₁ females was significantly lower (9.0–12.0%) when mated with males that emerged from 2nd instar P. solenopsis nymphs. Moreover, latter combinations yielded only male progeny in F₂ generation. These findings can be used in laboratory mass rearing of this parasitoid vis-à-vis biological control of P. solenopsis.     

Effect of rhizobacteria on arsenic uptake by macrophyte Eichhornia crassipes (Mart.) Solms

Wastewater flowing in streams and nallahs across India carries several trace metals, including metalloid arsenic (As), which are considered serious environmental contaminants due to their toxicity, and recalcitrant nature. In this study, we determined the phytoremediation of As by Eichhornia crassipes (Mart.) Solms either alone or in association with plant growth-promoting rhizobacteria. Pseudomonas and Azotobacter inoculation to E. crassipes resulted in enhanced As removal compared to uninoculated control. Co-inoculation with a consortium of Pseudomonas, Azotobacter, Azospirillum, Actinomyces, and Bacillus resulted in a higher As (p < 0.05) phytoaccumulation efficiency. P. aeruginosa strain jogii was found particularly effective in augmenting As removal by E. crassipes. Our findings indicate that the synergistic association of E. crassipes and various rhizobacteria is an effective strategy to enhance removal of As and thus may be utilized as an efficient biological alternative for the removal of this metalloid from wastewaters.     

Leaf scarring by the weevils Neochetina eichhorniae and N. bruchi enhances infection by the fungus Cercospora piaropi on waterhyacinth, Eichhornia crassipes

Additive or synergistic effects among introduced and native insect and plant pathogen agents are necessary to achieve biological control of waterhyacinth (Eichhornia crassipes), a globally damaging aquatic weed. In field plots, plants were infested with waterhyacinth weevils (Neoechetina bruchi and N. eichhorniae) and leaves were scarred by weevil feeding. Subsequent infection by the fungal pathogen Cercospora piaropi caused necrotic lesions to form on leaves. Necrosis development was 7.5- and 10.5-fold greater in plots augmented with both weevils and C. piaropi and weevils alone, respectively, than in plots receiving only C. piaropi. Twenty-four days after weevil infestation, the percentage of laminar area covered by lesions on third-youngest and oldest live leaves was elevated 2.3–2.5-fold in plots augmented with weevils. Scar density and necrosis coverage on young leaf laminae were positively correlated, even though antipathogenic soluble peroxidases were elevated 3-fold in plots augmented with weevils alone or weevils and C. piaropi. Combined weevil and fungal augmentation decreased shoot densities and leaves per plant. In a no-choice bioassay, weevil feeding on oldest but not young leaves was reduced 44 two weeks after C. piaropi inoculation. Protein content and peroxidase activities were elevated 2–6-fold in oldest leaves three weeks after inoculation. Augmentation with both waterhyacinth weevils and C. piaropi led to the development of an additive biological control impact, mediated by one or more direct interactions between these agents, and not plant quality effects.     

Host range evaluation of the leaf-feeding beetle,Zygogramma bicolorata and the stem-boring weevil,Listronotus setosipennis demonstrates their suitability for biological control of the invasive weed,Parthenium hysterophorus in Ethiopia

The invasive weed, parthenium (Parthenium hysterophorus L.) (Asteraceae: tribe Heliantheae), damages agriculture, adversely impacts biodiversity and is hazardous to human and animal health in Ethiopia. The host range of two natural enemies, a leaf-feeding beetle, Zygogramma bicolorata (Coleoptera: Chrysomelidae) and a stem-boring weevil, Listronotus setosipennis (Coleoptera: Curculionidae) was evaluated for biological control of the weed in Ethiopia. The specificity of Z. bicolorata and L. setosipennis was assessed against 29 and 31 non-target plant species, respectively. The host range of Z. bicolorata and L. setosipennis was first assessed using no-choice tests to examine their oviposition and feeding response on non-target plants. Although oviposition by Z. bicolorata occurred on six non-target species in four Asteraceae species in no-choice tests, it was significantly lower than on parthenium and no larvae developed. Zygogramma bicolorata nibbled the leaves of one of the five niger seed (Guizotia abyssinica L. – an oil seed crop closely related to parthenium) cultivars tested, but feeding and oviposition were significantly less than on parthenium. Furthermore, choice tests indicated that Z. bicolorata did not oviposit nor feed on G. abyssinica when parthenium was present. In no-choice tests, L. setosipennis did not oviposit on any of the non-target species assessed. Mean oviposition on parthenium was 39.0?±?3.4 eggs per plant whereas no eggs were laid on any of the 31 species tested. Based on these and other host range tests, permission was obtained to field release Z. bicolorata and L. setosipennis in Ethiopia.