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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. Source

Mudavanhu P.,Agricultural Research Council Plant Protection Research Institute ARC PPRI | Mudavanhu P.,Stellenbosch University | Addison P.,Stellenbosch University | Conlong D.E.,Stellenbosch University | Conlong D.E.,South African Sugarcane Research Institute
Entomologia Experimentalis et Applicata | Year: 2014

Mating ability, survival, and fitness of mass-produced sterile insects when released into the wild, are critical to the success of the sterile insect technique (SIT) as a pest management strategy, but their field performance remains one of the greatest challenges. Thermal stress tolerance by irradiated insects is a determinant of sterile insect quality, hence knowledge of their physiological competitiveness is essential for developing the SIT. Here, we report the results of experiments investigating effects of laboratory rearing and increasing radiation dosage on thermal limits to activity of the adult stage of Eldana saccharina Walker (Lepidoptera: Pyralidae). The critical thermal maximum (CTmax) and critical thermal minimum (CTmin) were assayed using a dynamic method on both sexes of E. saccharina moths in laboratory vs. wild populations (to determine effect of rearing history). Furthermore, the laboratory population was exposed to 150, 200, and 250 Gy, to determine the effect of radiation dose. Laboratory-reared E. saccharina were more heat tolerant compared to wild moths for both sexes (CTmax = 44.5 vs. 44.3 °C), whereas in the case of CTmin (3.7 vs. 4.4 °C), wild moths were more cold tolerant than their laboratory-reared counterparts. Irradiation had a negative effect on both CTmax and CTmin. Moths treated at the lowest radiation dose were more cold and heat tolerant than those treated at the highest dosages (CTmin = 4.5 vs. 6.2 °C; CTmax = 43.9 vs. 43.5 °C), thereby reinforcing the importance of lower dosages rather than those that induce full sterility against E. saccharina. In general, sex had no influence on critical thermal limits in all moth treatments except for those irradiated at 150 Gy. The data presented in this article provide evidence that increasing radiation dose impacts on fitness of laboratory-produced moths relative to their wild counterparts, which in turn could affect the effectiveness of the SIT programme. © 2014 The Netherlands Entomological Society. Source

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. Source

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. Source

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. Source

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