The Use of Biopesticides to Control Insect Pests of Pawpaw ( Carica Papaya)

Abstract

Laboratory and field experiments were carried out between June 1997 and Januaiy 1999 at Paradise farm near Nsawam in the Eastern Region of Ghana to determine the major insect pests of papaya, Carica papaya and to evaluate the effectiveness of Bacillus thuringiensis and neem seed extract for controlling the insect pests of papaya. Methanolic and aqueous neem seed extracts were tested at the following concentrations 0 , 50, 75 and 100 g/1. Bacillus thuringiensis was applied at the rate of 0, 0.2, 0.4, 0.6, 0.8 and 1.0 g/1. Percentage mortality and leaf damage caused by insect pests were determined in the laboratory and in the field. The nature of the damage caused by the insect pests on the various growth stages of the plants was assessed by visual observation. The major insect pests recorded on papaya at Paradise farm were the variegated grasshopper, Zonocerus variegatus, mealy bugs, Planococcus sp and the Mexican bean beetle, Epilachna sp. It was observed in the field that the population of these insect pests were significantly ( p<0.05) reduced by the higher doses of methanolic and aqueous neem extracts as well as the Bacillus thuringiensis treatments. The neem seed extracts and Bacillus thuringiensis preparations had significant ( p<0.05) effect on the mortality of adult and nymphs of Z. variegatus in the laboratory and in the field compared to the control. Mortality increased with increasing dosage. Hundred grams per litre of methanolic and aqueous neem seed extract and 1 g of B. thuringiensis per litre of water were equally effective and induced the highest mortality of adults and nymphs of Z variegatus compared to the other treatments. The least leaf damage was recorded on papaya plants treated with the highest dosage of neem extract and B. thuringiensis tested in the laboratory. Growth and yield parameters including plant girth, height, spread of leaf,

number of leaves, number of flowers, fruit weight and the final yield per hectare were also determined in the field... Methanolic and aqueous neem seed extracts promoted vegetative growth of papaya plants by significantly ( p<0.05) increasing plant height, girth, number of leaves, flowers and yield compared to the untreated plants. The results of the experiment indicate that 100 g/1 of aqueous and methanolic seed extracts could be used to control pests of papaya in the field. However, aqueous extraction may be recommended because it is cheaper and the extraction is also easier.