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.