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Evaluation of Pathogenic Fungi Beauveria bassiana and Metarhizium anisopliae for the Control of Tobacco Spider Mite, Tetranychus evansi Baker & Pritchard (Acarina: Tetranychidae) infesting tomatoes.

Nineteen strains of pathogenic fungi were tested in the laboratory to determine their pathogenecity to adult Tetranychus evansi. All the fungal strains were pathogenic to the mite and Beauveria bassiana strains caused mortality ranging between 55.6 to 74.3% while Metarhizium anisopliae strains caused mortality ranging between 18.1 to 73.1%. The LT50 for the most active B. bassiana and M. anisopliae strains was 4.6 and 3.9 days respectively. The LC50 for the most active B. bassiana strain was 1.1 × 107 conidia ml-1 while the LC50 for the most active strain of M. anisopliae was 0.7 ×107 conidia ml-1. The effect of pathogenic fungal infection on developmental stages of T. evansi was studied in the laboratory using one strain of B. bassiana and M. anisopliae. Mortality was low in larvae, protonymph and deutonymph at all concentrations tested between each treatment. Mortality in all stages was dose-dependent with the highest mortality occurring at 1 x 108 conidia ml-1. Egg hatchability was also tested under various concentrations of 0, 3 ×106, 1 × 107and 1 × 108 conidia ml-1 and was found to be dose-dependent with lowest hatchability occurring at 1 × 108 conidia ml-1. M. anisopliae strain ICIPE 78 and B. bassiana strain GPK significantly reduced the fecundity of female T. evansi in comparison to the control treatment. Semi-field experiments were conducted on potted tomato plants to evaluate the potential of the pathogenic fungi M. anisopliae, ICIPE 78 and B. bassiana strain GPK for biological control of T. evansi. An oil emulsion formulation and simple conidia suspension in water were applied at a concentration (1 × 108 conidia ml-1) that produced the highest mortality in the laboratory. Compared with the controls, both formulations significantly reduced mite populations. However, oil formulation caused higher mortality compared to the conidial suspension in water. The results of this study suggest that M. anisopliae and B. bassiana are potential candidates for the management of T. evansi on tomato.

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1.0 CHAPTER ONE 1.1 General introduction The tomato, Lycopersicon esculentum Mill, belongs to the vast family of Solanaceae, which also includes potatoes, capsicums, brinjals and black nightshade. It is among the most widely cultivated vegetable crops and is of great economic importance in the world. Tomato has an annual world production of about 54 million metric tons, with more than 10% being produced in Africa (FAO, 1993). The crop is also the top ranking vegetable in Eastern and Southern Africa surpassed only by brassica in some countries (GTZ IPM Horticulture, 1994). Tomato is part of everyday diet for millions of people worldwide and has dietary value in respect to carotene, thiamin, niacin, and vitamin C. It is eaten raw in salads, but the bulk is used as flavoring in sauce, stew and soup. Tomato fruits and leaves are used as medicine for treatment of earache and urinary tract diseases (FAO, 1993). Tomato which is considered as the second most important vegetable in Kenya surpassed only by brassicas is a major cash crop and a source of livelihood for many farmers in the high rainfall districts of Central Province, Western, Eastern, Rift Valley and Nyanza. In the semi-arid and arid areas of Kenya, tomatoes are grown mainly under irrigation using water supplied by permanent or seasonal rivers. The main forms of irrigation practiced by commercial farmers are furrow and sprinkler irrigation. Short-term rotation with other horticultural or food crops is sometimes practiced but is limited by land availability (Varela et al., 2001). The crop is grown for home consumption in backyard gardens of almost every homestead across the country for fresh domestic market, processing and export. Therefore, it provides employment, income and contributes to food security for large numbers of rural populations. The cultivated area under tomato has been increased since 1989 from 12,678 to 16,338 hectares in 1999 (Ministry of Agriculture & JICA, Kenya, 2001). The expansion of the cultivated area, the monoculture and irrational use of pesticides has generated an increase of arthropod pests in tomato growing areas (FPEAK, 2000). Prior to the widespread use of synthetic pesticides, spider mites were insignificant as crop pests (Penman & Chapman, 1988). The concept of secondary pest outbreaks was introduced with the spider mite as examples, whereby differential mortality caused by

International thesis/dissertation

Autore: Vitalis Wafula Wekesa Contatta »

Composta da 69 pagine.

 

Questa tesi ha raggiunto 486 click dal 11/07/2006.

 

Consultata integralmente una volta.

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