The use of biopesticides to control insect pests of papaya (Carica papaya)

Laboratory and field experiments were carried out between June 1997 and January 1999 at Paradise farm near Nsawam in the Eastern Region of Ghana to evaluate the effectiveness of neem seed extract and Bacillus thuringiensis (Kurtaski) for controlling insect pests of papaya Carica papaya. Methanol and aqueous neem seed extracts were tested at the following concentrations 0, 50, 75 and 100 g/L. Bacillus thuringiensis was applied at the rate of 0, 0.2, 0.4, 0.6, 0.8 and 1.0 g/L. Percentage mortality and leaf damage caused by insect pests were determined in the laboratory and in the field. The population of the major insect pests, which visited the plants, was also determined. The nature of the damage caused by the insect pests found on the various developmental stages of the plants was assessed by critical visual observation. The major insect pests recorded on papaya at Paradise farm were the variegated grasshopper, Zonocerus variegates (L), mealybugs, Planococcus sp and Mexican bean beetle, Epilachna sp. It was observed in the field that the populations of these insect pests were significantly reduced by the higher doses of methanol and aqueous neem extracts as well as the Bacillus thuringiensis treatments. The neem seed extracts and Bacillus thuringiensis preparations had significant effect on the mortality of adult and nymphs of Z. variegatus in the laboratory and in the field compared to the control. The rate of mortality increased as the dose increases. Hundred grams per litre of methanol and aqueous neem seed extract and 1 g of B. thuringiensis per litre of water were the most effective and induced the highest mortality of adults and nymphs of Z. variegatus compared to the other treatments. The least percentage leaf damage was recorded on papaya plants treated with the highest dosage of neem extract and B. thuringiensis.