Department of Plant Science

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Browsing Department of Plant Science by Author "Arunga, Esther"

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    Combining Host Plant Resistance, Selective Insecticides, and Biological Control Agents for Integrated Management of Tuta absoluta
    (2020-07-07) Nderitu, Peris Wangari; Jonsson, Mattias; Arunga, Esther; Otieno, Mark; Muturi, John Jamleck; Wafula, Geoffrey O.; ; ;
    Combination of pest management strategies that minimize pesticide use and conserve natural enemies is important for a sustainable environment. Overreliance on synthetic insecticides in the management of Tuta absoluta has led to pesticide resistance leading to difficulties in managing the pest. In this regard, alternative measures need to be put in place to reduce the effects of this pest. The objective of this study was, therefore, to assess the effectiveness of host plant resistance, biological control, and selective insecticides when used in combination, in the management of T. absoluta in tomato production. The study was set up in a greenhouse in a completely randomized design involving two tomato varieties, an insecticide (chlorantraniliprole), and a biological control agent(Macrolophus pygmaeus), applied singly or in combination. Data were collected on T. absoluta damage from the lower, intermediate, and upper leaves. The results from this study show that a combination of insecticide with a moderately resistant variety had a significantly lower T. absoluta damage as compared with a susceptible variety combined with an insecticide. However, the moderately resistant variety when combined with insecticide showed no effect when the biological control agent was added. The susceptible variety significantly reduced T. absoluta damage when combined with the biological control agent. These results indicate that treatment combinations in insect pest management can be utilized. The present study results indicate that using a moderately resistant variety (Riogrande VF) in combination with the insecticide chlorantraniliprole (Coragen®) and a susceptible variety (Pesa F1) in combination with the biological control agent (M. pygmaeus) can improve T. absoluta management. Under good habitat management, the susceptible variety will perform equally as the moderately resistant variety due to suppression of the T. absoluta populations by natural enemies. These findings show the importance of environmental conservation both by enhancing natural enemy abundance and use of selective insecticide in the management of T. absoluta in tomato production. Combinations in this present study are likely to reduce insecticide doses, thereby reducing the cost of production and enhancing environmental compatibility with natural enemies.
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    EVALUATION OF TOMATO VARIETIES FOR RESISTANCE TO TOMATO LEAFMINER (TUTA ABSOLUTA) IN KIRINYAGA COUNTY, KENYA
    (African Journal of Horticultural Science, 2020-07) Nderitu, Wangari Peris; Arunga, Esther; Mattias, Jonsson; Otieno, Mark; Muturi, John Jamleck; ; ;
    The tomato leafminer (Tuta absoluta) (Meyrick) (Lepidoptera: Gelechiidae) is an invasive insect pest of tomato crops in many parts of Africa. It causes substantial economic losses to tomato crops in Kenya. Majority of farmers have resulted to intensive insecticide application that has led to development of insecticide resistance. It is therefore critical to develop sustainable management strategies that can be used in Integrated Pest Management (IPM) programmes against the tomato leaf miner. Genetic breeding against the tomato leaf miner can be promising since effective cultural control is difficult. The objective of this study was to evaluate level of resistance of popular tomato varieties to tomato leaf miner in Kirinyaga County, Kenya. The four tomato varieties Rambo F1, Pesa F1, RiograndeVF and Cal J were evaluated for resistance against T. absoluta under field conditions. Mwea East Sub-County is characterised by intensive tomato production, diverse cultural practises and high usage of synthetic pesticides against the tomato leaf miner. The experiment was laid out in a randomized complete block design in two locations (Kariithi and Kimbimbi), which have irrigation schemes that allows tomato production throughout the year. Presence of mines was assessed on leaves obtained from the lower, intermediate and upper canopy of tomato plants at days 20, 40, 60 and 80 after planting. Fruit damage was estimated at the end of the cropping cycle. Data was subjected to arcsin square root transformation and analysis of the level of pest damage on different tomato varieties, was done using general linear mixed effects models, performed using the lme function in the nlme package in R 3.4.2.The results of this study show that larvae mining damage on the leaves was observed in all the evaluated tomato varieties, but it was significantly higher on Pesa F1 hybrid variety (p > 0.001) than Riogrande VF and Cal J. Fruit damage was also significantly higher on Pesa F1 variety (p > 0.01) than Riogrande VF and Cal J. These results suggest that most of the commercially grown tomato varieties are susceptible to T.absoluta infestation. However, Riogrande VF and Cal J can be incorporated in IPM programs. Further studies need to be done for introgression of resistance genes from wild varieties into cultivated tomato varieties.