Department of Conservation Ecology and Entomology

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Browsing Department of Conservation Ecology and Entomology by browse.metadata.advisor "Addison, Matthew F."

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    Initial investigation of Trichogrammatoidea lutea (Hymenoptera: Trichogrammatidae) as biological control agent of codling moth, Cydia pomonella (Lepidoptera: Tortricidae), in apple and pear orchards, under sterile insect technique (SIT)
    (Stellenbosch : Stellenbosch University, 2008-12) Wahner, Nadine; Addison, Pia; Addison, Matthew F.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    Codling moth (CM), Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae), is the major pest of apples and pears in the South Western Cape, South Africa. Apart from conventional insecticide sprays, area-wide biologically intensive control methods, such as Sterile Insect Technique (SIT) and pheromone mediated mating disruption (MD) are currently in use on two farms in the Elgin valley. The indigenous parasitoid Trichogrammatoidea lutea Girault (Hymentoptera: Trichogrammatidae) attacks eggs of false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), as well as CM and has been found to have considerable parasitism potential on both. Elevated host egg numbers, as achieved by SIT are thought to support establishment of populations of these natural enemies in the orchards. For rapid and secure Trichogrammatoidea species identification, the ITS2 sequences of Trichogrammatoidea lutea and T. cryptophlebiae Nagaraja (an indigenous FCM parasitoid on citrus) were determined and species specific primers were developed. Lifetable studies of T. lutea indicated an optimal temperature for reproduction at around 20 °C. Food was provided by the application of honey-solution soaked cotton wool, behind fine netting. The effect of food provision by this method was found to be dependent on temperature. The acceptance of CM eggs from sterilized vs. fertile parents and of radiation-sterilized eggs vs. fertile ones was assessed in choice trials. While no difference was observed between radiated and fertile eggs, sterile eggs from irradiated parents were significantly less attractive than eggs from fertile parents. In several field studies the dispersal capacity and population sustainability of released T. lutea were investigated. Trials took place in apple and pear orchards in the Elgin valley that formed part of an area-wide sterile CM SIT program. Most of the wasp releases were carried out within blocks of up to 1 ha. A square grid of up to 36 monitoring trees per block allowed spatial distribution analysis. Following single central point releases, parasitism of sentinel eggs was recorded until the end of all experiments, the longest of which lasted 37 weeks. T. lutea females were found to disperse up to 73 m, within one week. Studies concerning toxicity of four commonly used insecticides and one fungicide to immature and adult T. lutea indicated no to low susceptibility of wasps at egg- to first-instar-stage within host eggs. Contact toxicity of the tested materials to adults differed significantly, depending on the compound. All five pesticides caused significantly higher mortality among adults relative to the control. The overall aim of above studies was to determine the potential of T. lutea for broad-scale releases against CM, within a broader integrated pest management program in apple and pear orchards in the Western Cape.
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    Orchard and bin treatment with entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) for the control of the codling moth (Cydia pomonella)
    (Stellenbosch : Stellenbosch University, 2015-12) Odendaal, Deidre; Malan, Antoinette P.; Addison, Matthew F.; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: The codling moth, Cydia pomonella (Lepidoptera: Tortricidae), is the key pest of apples and pears worldwide. The withdrawal of certain fundamental chemicals from codling moth management spray programmes, due to concerns about human, environmental and ecosystem health, has resulted in the search for softer, more environmentally friendly, and safer control measures. Entomopathogenic nematodes (EPNs), naturally occur in the soil, and actively search for hosts. The interest in using EPNs from the families Heterorhabditidae and Steinernematidae as a control measure was sparked in 1953, when an EPN was discovered in an insect. The aim is to incorporate EPNs in an integrated pest management (IPM) programme, to ensure minimal residue and eventually residue-free pome fruit production in South Africa. In order to ensure EPN success, both the environmental and technical factors influencing their efficacy, were investigated in this study. The biocontrol potential of three imported EPN isolates, being Steinernema feltiae and two isolates of Heterorhabditis bacteriophora (Hb1, Hb2), as well as a local isolate, Steinernema yirgalemense, were evaluated for the control of the codling moth under local conditions. All concentrations of S. yirgalemense, applied by immersion in a suspension of nematodes, gave > 98% control. The two formulated isolates of H. bacteriophora, Hb1-f and Hb2-f, gave < 30% control. When using the same nematode isolates, produced in vivo, S. yirgalemense still resulted in a higher codling moth control of > 90%, compared to 54% and 31% control of the H. bacteriophora Hb1 and Hb2 isolates, respectively. In follow up field trials, S. feltiae resulted in ≥ 80% control, and was thus more effective than both S. yirgalemense and the H. bacteriophora (Hb1) isolates, with 66% and 24%, and 24% and 9% control, for two separate trials, respectively. To validate the data obtained from the field trials, subsequent laboratory bioassays were conducted evaluating temperature regimes, following the same cycle as under natural conditions, with a constant humidity of 100%. Steinernema feltiae proved to be most effective, causing > 90% mortality, followed by S. yirgalemense, with 78% mortality. The two H. bacteriophora isolates (Hb1, Hb2) under the above-mentioned laboratory conditions, resulted in 73% and 59% control, respectively. Humidity thus seems to be the most important factor affecting EPN efficacy during above-ground applications. Steinernema feltiae proved to be a better candidate than S. yirgalemense for the control of the codling moth. The efficacy of different EPN isolates in controlling diapausing codling moth larvae at different temperatures was also evaluated, under local conditions, using spray application. Steinernema feltiae and two isolates of H. bacteriophora Hb1 and Hb2, including two local isolates, S. yirgalemense and Steinernema jeffreyense, were evaluated. The use of S. jeffreyense resulted in the most effective control, with 67% mortality, followed by H. bacteriophora (Hb1) with 42%, and then by S. yirgalemense with 41%. Laboratory bioassays simulating field conditions revealed that S. feltiae was most virulent to codling moth larvae, with 67% mortality by infection, followed by S. yirgalemense with 58%, the H. bacteriophora strain Hb1 with 48%, and the Hb2 strain with 24%. A comparison of the infection and penetration rate of two isolates of H. bacteriophora (Hb1, Hb2), S. feltiae and S. yirgalemense, which was carried out in multiwell plates at 14°C and 25°C, respectively, confirms the dramatic effect of temperature on EPN efficacy. At 14°C, all treatments with EPN species resulted in slower codling moth mortality than they did at 25°C, as after 48 h, < 15% mortality was recorded for all species, whereas at the warmer temperature, > 98% mortality was recorded for all species. After the exposure of washed, cool-treated larvae to 25°C for 24 h, the application of both S. feltiae and S. yirgalemense resulted in 100% mortality, whereas the application of the two H. bacteriophora isolates, Hb1 and Hb2, resulted in 68% and 54% control, respectively, over the same time period. At 14°C, S. feltiae had the highest average penetration rate of 20 IJs/insect, followed by S. yirgalemense with 14 IJs/insect, whereas S. yirgalemense had the highest penetration rate at 25°C, with 39 IJs/insect, followed by S. feltiae, with 9 IJs/insect. The two H. bacteriophora isolates had higher average penetration rates at the higher temperature. This study has highlighted the biocontrol potential of S. jeffreyense, as well as showing that S. feltiae is a cold-active nematode, whereas the other three EPN isolates prefer warmer temperatures. Stacked wooden fruit bins are regarded as preferred overwintering sites for codling moth diapausing larvae. Control strategies against the codling moth in South Africa have been hampered by the reinfestation of orchards by nearby stacked infested fruit bins or by the movement of bins between orchards. Worldwide, wooden fruit bins are systematically being replaced with plastic bins, which, in South Africa, will only be phased out over a few years. The objective of this study was to evaluate the potential of H. bacteriophora, S. feltiae, and S. yirgalemense, to disinfest miniature wooden fruit bins under controlled conditions in the laboratory. After dipping minibins in a suspension of 25 IJs/ml of all three EPN species, under optimum conditions of temperature and humidity, the highest percentage of control was obtained using S. feltiae (75%) followed by S. yirgalemense (57%), and then by H. bacteriophora (Hb1) (27%). The addition of adjuvants significantly increased (p < 0.001) S. feltiae infectivity to > 95%, whereas it did not result in a significant increase in H. bacteriophora or S. yirgalemense infectivity. The results indicated that H. bacteriophora would not be a suitable candidate to use for the control of the codling moth larvae in wooden fruit bins. The current preferred candidate for control would be S. feltiae, whose efficacy could be increased by means of the addition of an adjuvant. During winter, when the whole codling moth population are larvae and in diapause, no control measures are applied in orchards. This study has shown that EPNs can be sprayed in orchards to lower the codling moth cohort emerging after winter, as well as be included in an IPM programme. EPNs can act as a second line of defence, through supplementary control, and ensure effective control of the codling moth larvae which survived chemical spray applications, to safeguard against resistant codling moth populations in the next season.