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Du Preez G.,North West University South Africa | Swart A.,Agricultural Research Council Plant Protection Research Institute ARC PPRI | Fourie H.,North West University South Africa
Nematology | Year: 2015

Although the importance of nematodes, especially in soil ecosystems, is well appreciated, very little is known about the occurrence of and ecosystem services provided by cavernicolous nematodes. This study was undertaken to determine the nematode occurrence, density and distribution in the Wonderfontein Cave (South Africa), which is subjected to the influx of water from the Wonderfontein Spruit. Of the 53 nematode genera collected from the Wonderfontein Cave during the first (April 2013) and second (September 2013) sampling intervals, 22 have never been reported from a cave environment. Results indicated that many of the nematodes found may only be temporary residents introduced from the surface environment. This study reveals the necessity of further efforts to investigate the nematode communities associated with subterranean environments, which will provide a better understanding of the functioning of the associated ecosystems. © Koninklijke Brill NV, Leiden, 2015.


Bownes A.,Agricultural Research Council Plant Protection Research Institute ARC PPRI | Bownes A.,Rhodes University | Hill M.P.,Rhodes University | Byrne M.J.,University of Witwatersrand
Biological Control | Year: 2010

The water hyacinth grasshopper, Cornops aquaticum is being considered for release in South Africa as a biocontrol agent for water hyacinth, Eichhornia crassipes. The release decision was to be based on C. aquaticum's potential efficacy, in addition to its host specificity. An additive series analysis of competition between E. crassipes and a similar free-floating macrophyte, water lettuce (Pistia stratiotes), was used to assess the impact of C. aquaticum on E. crassipes competitive ability and potential for biomass accumulation. The data was analyzed using an inverse linear model where the competitive performance of both plant species was estimated using multiple linear regressions of the inverse of biomass yield. Eichhornia crassipes was 24 times more competitive than P. stratiotes without C. aquaticum herbivory but this was reduced to 12 in the presence of herbivory which equated to a 50% reduction in its competitive performance. Pistia stratiotes competitive ability increased from 3.8 to 4.8 (i.e. 21%) when E. crassipes was damaged by C. aquaticum. The interspecific competition coefficients from E. crassipes on P. stratiotes were also no longer statistically significant in the presence of C. aquaticum herbivory. Biomass accumulation of E. crassipes was significantly reduced by C. aquaticum herbivory at both planting densities tested. By comparison with similar studies on two of the most abundant, widespread and damaging biocontrol agents already released in South Africa, C. aquaticum has a greater impact on E. crassipes, suggesting it will be a valuable addition to the South African biological control program. © 2010 Elsevier Inc. All rights reserved.


Bownes A.,Agricultural Research Council Plant Protection Research Institute ARC PPRI | Bownes A.,Rhodes University | Hill M.P.,Rhodes University | Byrne M.J.,University of Witwatersrand
Entomologia Experimentalis et Applicata | Year: 2010

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. © 2010 The Authors. Entomologia Experimentalis et Applicata © 2010 The Netherlands Entomological Society.


Bownes A.,Agricultural Research Council Plant Protection Research Institute ARC PPRI | Bownes A.,Rhodes University | Hill M.P.,Rhodes University | Byrne M.J.,University of Witwatersrand
Biological Control | Year: 2013

Environmental nutrient availability can drive and modify both plant responses to herbivory by phytophagous insects and insect feeding patterns which, in insect-weed systems, may ultimately determine whether biological control succeeds or fails. The impacts of insect biological control agents on the invasive aquatic weed, water hyacinth ( Eichhornia crassipes) vary with nutrient levels in the environment. It was therefore considered important to evaluate nutrient-specific responses of E. crassipes to a grasshopper herbivore, Cornops aquaticum, prior to its release in South Africa. Both plant productivity and the response of E. crassipes to herbivory by C. aquaticum were nutrient dependent. Increases in plant biomass and leaf and ramet production were correlated with increases in nutrients in the water and plant biomass accumulation was reduced by herbivory at all three nutrient levels tested (high. = 67%; medium. = 100%; low. = 400%). C. aquaticum nymphs fed E. crassipes leaves with the lowest nitrogen levels produced the highest biomass of frass during their development, indicating compensatory consumption. The results suggest that environmental nutrient availability will influence efficacy of C. aquaticum. They also provide further evidence that E. crassipes problems are exacerbated by an over-abundance of nutrients in aquatic environments, and that biological control would be a highly effective management tool if aquatic systems in South Africa were less polluted. Additionally, the results also show how an understanding of the fundamental responses of E. crassipes and its insect biocontrol agents to their environment can assist in determining specific management strategies or interventions according to prevailing site-specific conditions. © 2013 Elsevier Inc.


Bownes A.,Agricultural Research Council Plant Protection Research Institute ARC PPRI | Bownes A.,Rhodes University | Hill M.P.,Rhodes University | Byrne M.J.,University of Witwatersrand
Biological Control | Year: 2013

Host plant quality for phytophagous insects, of which nitrogen is one of the most crucial components, is highly variable and can be a major determinant of their performance. This has implications in insect-weed biological control systems where host plant quality can affect establishment, survival and population growth rates of the biocontrol agents. However, an understanding of bottom-up effects on these systems, particularly in aquatic environments which are prone to seasonal fluctuations in nutrient availability, can assist in directing management strategies to achieve the best results. We evaluated nutrient-mediated effects on the performance of a leaf-feeding biocontrol agent, the grasshopper Cornops aquaticum for the invasive aquatic weed, water hyacinth Eichhornia crassipes. Female C. aquaticum and their offspring had higher body weights when fed a high quality diet compared to a diet low in foliar nitrogen. Nymphal survival (high. = 82%, medium. = 71%, low. = 64%) and female fecundity increased with an increase in dietary nitrogen. High and low levels of nutrients caused a shift in the sex ratios, being female-biased on the high quality diet and male-biased on the low quality diet. These results indicate that C. aquaticum is highly sensitive to foliar nitrogen, suggesting significant potential for bottom-up regulation of this species. Changes in the abundance and distribution of C. aquaticum according to nutrient availability may therefore mediate its impact on the weed. This subsequently highlights the importance of understanding the influence of nutrients on aquatic insect-weed systems and how it can drive decision-making in strategic management programmes. © 2013 Elsevier Inc.


Mcconnachie A.J.,Agricultural Research Council Plant Protection Research Institute ARC PPRI | Strathie L.W.,Agricultural Research Council Plant Protection Research Institute ARC PPRI | Mersie W.,Virginia State University | Gebrehiwot L.,Addis Ababa Institute of Technology | And 10 more authors.
Weed Research | Year: 2011

Parthenium hysterophorus (Asteraceae), of South American origin, is considered to be one of the world's most serious invasive plants, invading Australia, Asia and Africa. As part of an international collaborative project, this study attempted to improve the understanding of the geographical distribution of P. hysterophorus in eastern and southern Africa. The climate modelling program CLIMEX was used to assist in the selection of survey localities. Roadside surveys of the distribution of the weed were conducted in Botswana, Ethiopia, South Africa, Swaziland and Uganda. Prior to these surveys, only limited P. hysterophorus locality records existed; substantially more records were obtained from surveys. Most infestations were high density (>3 plants m-2). Distribution records were used to validate the CLIMEX model, which proved a useful tool. This study increased current understanding of the distribution of P. hysterophorus and developed a baseline from which to monitor future spread and abundance of P. hysterophorus. Additional surveys are required in other countries in Africa which are predicted by CLIMEX to be at risk. This will enhance integrated management decisions for the control of a weed which has implications for food security and human health. © 2010 The Authors. Weed Research © 2010 European Weed Research Society.


Onkendi E.M.,University of Pretoria | Kariuki G.M.,Kenyatta University | Marais M.,Agricultural Research Council Plant Protection Research Institute ARC PPRI | Moleleki L.N.,University of Pretoria
Plant Pathology | Year: 2014

Meloidogyne species pose a significant threat to crop production in Africa due to the losses they cause in a wide range of agricultural crops. The direct and indirect damage caused by various Meloidogyne species results in delayed maturity, toppling, reduced yields and quality of crop produce, high costs of production and therefore loss of income. In addition, emergence of resistance-breaking Meloidogyne species has partly rendered various pest management programmes already in place ineffective, therefore putting food security of the continent at risk. It is likely that more losses may be experienced in the future due to the on-going withdrawal of nematicides. To adequately address the threat of Meloidogyne species in Africa, an accurate assessment and understanding of the species present, genetic diversity, population structure, parasitism mechanisms and how each of these factors contribute to the overall threat posed by Meloidogyne species is important. Thus, the ability to accurately characterize and identify Meloidogyne species is crucial if the threat of Meloidogyne species to crop production in Africa is to be effectively tackled. This review discusses the use of traditional versus molecular-based identification methods of Meloidogyne species and how accurate identification using a polyphasic approach can negate the eminent threat of root knot nematodes in crop production. The potential threat to Africa posed by highly damaging and resistance-breaking populations of 'emerging' Meloidogyne species is also examined. © 2014 British Society for Plant Pathology.


Mehelis C.N.,U.S. Department of Agriculture | Balciunas J.K.,U.S. Department of Agriculture | Reddy A.M.,U.S. Department of Agriculture | Westhuizen L.V.D.,Agricultural Research Council Plant Protection Research Institute ARC PPRI | And 2 more authors.
Environmental Entomology | Year: 2015

Cape-ivy (Delairea odorata Lemaire) is an ornamental vine native to South Africa that has escaped into natural areas in coastal California and Oregon, displacing native vegetation. Surveys in South Africa led to the discovery of the leaf- and stem-mining moth Digitivalva delaireae Gaedike and Kruger (Lepidoptera: Glyphipterigidae: Acrolepiinae) as one of several common and damaging native herbivores on Cape-ivy. In greenhouse studies, adult female life span averaged 16 d (46 d maximum). Most (72%) mated females began laying eggs within 72 h of emergence. Females had an average lifetime fecundity of 52 eggs, with >70% laid on leaf laminae, and 89% of eggs were laid by the 15th day postemergence. Lifetime fertility (adult production) averaged three to four offspring per female. At 25°C, egg hatch required 10 d, pupal formation 26 d, and adult emergence 41 d, while under variable greenhouse and laboratory conditions development to adult required 54-60 d. In four-way choice tests, involving 100 plant species other than Cape-ivy, including 11 genera and 37 species in the Asteraceae, subtribe Senecioninae from both native and invaded ranges, D. delaireae inflicted damage and produced pupae only on Cape-ivy. Leaf mining damage occurred on 30% of leaves of native Senecio hydrophilus in no-choice tests and on 2% of leaves in dual-choice tests, but no pupation occurred. If approved for field release in the continental United States, the moth D. delaireae is expected to produce multiple generations per year on Cape-ivy, and to pose little risk of damage to native plants. © Published by Oxford University Press on behalf of Entomological Society of America 2015. This work is written by US Government employees and is in the public domain in the US.


PubMed | Agricultural Research Council Plant Protection Research Institute ARC PPRI and U.S. Department of Agriculture
Type: Journal Article | Journal: Environmental entomology | Year: 2015

Cape-ivy (Delairea odorata Lemaire) is an ornamental vine native to South Africa that has escaped into natural areas in coastal California and Oregon, displacing native vegetation. Surveys in South Africa led to the discovery of the leaf- and stem-mining moth Digitivalva delaireae Gaedike and Kruger (Lepidoptera: Glyphipterigidae: Acrolepiinae) as one of several common and damaging native herbivores on Cape-ivy. In greenhouse studies, adult female life span averaged 16 d (46 d maximum). Most (72%) mated females began laying eggs within 72 h of emergence. Females had an average lifetime fecundity of 52 eggs, with >70% laid on leaf laminae, and 89% of eggs were laid by the 15th day postemergence. Lifetime fertility (adult production) averaged three to four offspring per female. At 25 C, egg hatch required 10 d, pupal formation 26 d, and adult emergence 41 d, while under variable greenhouse and laboratory conditions development to adult required 54-60 d. In four-way choice tests, involving 100 plant species other than Cape-ivy, including 11 genera and 37 species in the Asteraceae, subtribe Senecioninae from both native and invaded ranges, D. delaireae inflicted damage and produced pupae only on Cape-ivy. Leaf mining damage occurred on 30% of leaves of native Senecio hydrophilus in no-choice tests and on 2% of leaves in dual-choice tests, but no pupation occurred. If approved for field release in the continental United States, the moth D. delaireae is expected to produce multiple generations per year on Cape-ivy, and to pose little risk of damage to native plants.


A monoecious Malaysian/Indonesian biotype of the invasive aquatic weed, Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae) recently invaded South Africa and has been targeted for biological control. Two ephydrid leaf-mining flies, originating on genetically distinct H. verticillata biotypes were considered as prospective agents. Hydrellia pakistanae Deonier (Diptera: Ephydridae) is a widely established biological control agent of a dioecious Indian/Pakistani H. verticillata biotype in North America, and an unnamed Hydrellia fly, Hydrellia sp. was collected in Singapore on a similar host plant biotype to the one invading South Africa. The suitability of the two fly species as biocontrol agents for H. verticillata in South Africa was assessed by comparing their fundamental host ranges as well as their performance and leaf-mining on the South African biotype of H. verticillata. Additionally, fitness parameters of H. pakistanae reared on South African H. verticillata were compared to the same parameters measured on the U.S. dioecious biotype. The two fly species showed minor differences in non-target host use in no-choice larval development trials. Hydrellia sp. had higher survival, longevity and fecundity and shorter egg to adult development times on South African H. verticillata compared to H. pakistanae. Further, leaf-mining by the two fly species was similar and H. pakistanae's performance on South African H. verticillata was inferior in comparison to its performance on the U.S. dioecious H. verticillata biotype. These findings guided a decision to reject H. pakistanae as a biocontrol agent for H. verticillata in South Africa in favor of its congener, Hydrellia sp. © 2015 Elsevier Inc.

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