Efficacy of selected biopesticides and botanical extracts in managing rice stem borer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) in Tanzania

Stem borers have been reported as the most injurious insect pests of rice among the insects that attack rice crop globally. Management of stem borers has been relied on the us e of synthetic insecticides but has been ineffective due to the cryptic nature of the attack, disruption of environment and unaffordability to purchase insecticides by small- scale farmers. The attempts to control insects have changed over time from chemicals to natural control methods. Among the various natural control methods, biopesticides and botanical extracts have received considerable attention as a viable alternative to chemical pesticides. This study was therefore aimed at evaluating the efficacy of fungi based biopesticides and botanical extracts in controlling rice stem borers in screen house under artificial infestation and in laboratory test condition at the Sokoine University of Agriculture, Morogoro, Tanzania between March 2017 and January 2018. The experiment was laid out in a randomised complete block design for screen house trial and a completely randomised design for laboratory trial. All the treatments in all two trials were replicated four times. The two trials involved six treatments which includes two commercial biopesticides (Beauveria bassiana and Metarhizium anisopliae), two botanical extracts (Neorautanenia mitis and Derris elliptica), and one synthetic insecticide (Amekan 344EC) which was the mixture of (Cypermethrin (144 g/L) + Imidacloprid (200 g/L)) and untreated control. The results showed a significant influence of biopesticides and botanical extract in reduction Chillo partellus damage incidences, increased mortality and increased rice grain yield (p < 0.01). Both biopesticides and botanical extracts reduced damage incidences from 45% - 64.28% dead heart, 42.01% - 76.19% whitehead and decreased yield loss from 60.01% - 19.7 % caused by C. partellus. Grain yield of treated samples (4.837 – 6.387 t/ha) with the stem borer mortality rate of 57.51% - 78.12% were higher than 0 - 2.837t/ha from untreated control plots. The control measures used has shown a great influence on grain yield due to a reduction of damage incidences and increased C. partellus mortality. The study, therefore, indicated the possibility of controlling rice stem borers using fungi based biopesticides and botanical extracts.