Diversity and efficacy of tuta absoluta (meyrick) associated entomopathogenic fungi under different tomato agro- ecological zones of Tanzania

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Sokoine University of Agriculture


Tomato crop is one of the important horticultural vegetables which is used both in consumption and commercially worldwide. Insect pests are the most destructive biotic factors facing tomato production almost in the whole world. Tuta absoluta is a one of the most destructive insect which decrease tomato production and increases production cost in Tanzania and in the whole world and its economic effects globally. The management of T. absoluta by synthetic chemicals is not working properly due to resistance which is developed by of the pest .Many findings by plant researchers from different countries including Africa have been proved that the use of entomopathogenic fungi such as Beauveria bassiana, Metarhizium anisopliae, as biocontrols agent against Tuta absoluta is more efficient compare to the use of synthetic pesticides. In this study a total of twenty four soil samples were collected from tomato farms infested by Tuta absoluta, the soil samples were from different agro ecological zones of Tanzania. Culturing, Morphological, Sequencing data and results obtained showed that ten fungi were entomopathogenic fungi and fourteen were non entomopathogenic fungi among ten entomopathogenic fungi only two spp were related to Tuta absoluta management in tomato production. The entomopathogenic fungi related to Tuta absoluta control were Metarhizium spp and Aspergillus spp. Aspergillus spp is not recommended for Tuta absoluta management in tomato plants because it contains afflatoxin which is toxic to human being but it has high pathogenicity against Tuta absoluta. The pathogenicity of entomopathogenic fungi against Tuta absoluta were tested, against T. absoluta larvae, pupa, and adult stages under conditions of 19.5°C and 50%RH, 30.4°C and 70% RH, respectively, at different conidial concentrations (1.0 × 106, 1.0 × 107 , 1.0 × 108 conidial/ml) in the laboratory for twenty nine days. The factorial experiment design was used where by tomato leaflets from screen house (6 × 7 cm area) were used as experimental units that were dipped into (1.0 × 106 , 1.0 × 107 and 1.0 × 108 conidia/ml) of isolates and control (water containing 0.1% Triton X-100). Treated leaflets were dried at room temperature for elimination of excess water then was placed in Petri dishes (21 cm diameter) lined with wet paper towel and cotton covering the petiole to prevent leaf dehydration. Then, ten (10) T. absoluta larvae were inoculated separately into each of three treated leaflets and control. Each concentration was replicated three times with10 larvae. Treated leaflets were used only once at the beginning of the experiment. After 24 h, when treated leaflets are depleted, treated larvae were fed on fresh untreated leaves. Dead larvae were placed on another Petri dish lined with moist paper towel for re- isolation of fungus. Data of the larvae survival duration, number of dead larvae, number of larvae active (larvae treated but persisted), and number of adults emerged from total treated pupae, number of adult emerged was recorded at interval of 24 h and trials were monitored up to the completion of T. absoluta life cycle and lifespan. Results showed that Metarhizium anisopliae, at all concentration caused high larvae mortality rate (98.2%) followed by Aspergillus spp (71%), larvae mortality rate increased with incubation time and concentration and consequently inhibited pupation and adult emergence within a short time before the completion of the life cycle of Tuta absoluta which is 29 days. Metarhizium anisopliae reduced the life span T. absoluta adult within 5 days of post inoculation at all conidia/ml, other entomopathogenic spp (Penicillium spp, and Cladosporium spp,) were also tested against Tuta absoluta larvae, pupa and adult stages the results recoded lower pathogenicity. Penicillium spp recorded 80% of adult survival at all conidial concentration within the whole incubation time. Geotrichum candidum recorded 100% of adult survived at all conidial concentration after the incubation time. Whereas in control T. absoluta adult survived recorded 100%. This study found that Metarhizium anisopliae has the potential to be used as effective biological control against Tuta absoluta in tomato production especially at larvae stage which is the most destructive stage.


MSc.-Dissertation in Crop Science


Tuta absoluta, Meyrick, Fungi, Tomato production