The role of parasitoids in regulation of beanfly ophiomyia spp. Complex, at Kakamega, Kenya.
Abstract
Investigations were carried out on the phenology of
beanflies (Ophiomyia spp.) and their parasi toids under
different cultural practices (cropping system and different
fertilizer levels) ln the field in Kakamega, Western Kenya.
Three species of beanflies Ophiomyia spencerella
(Greathead) , Ophiomyia phaseoli (Tryon) and Ophiomyia
centrosemantis (de Meij) were recorded. Of these, O.
spencerella was the dominant species constituting over 94%
of the beanfly complex in Kakamega while O. phaseoli and O.
centrosemantis constituted 4% and 2% respectively.
Beanflies appeared in the field 1-2 weeks after crop
emergence and their population rose si qn i f i cant.Ly to a peak
3-4 weeks after crop emergence only to stabilize
thereafter. This trend was observed on the April, June and
September 1996 crops. Three species of parasitoids emerged
from samples of the beanfly pupae collected from the field.
These comprised of a braconid Opius phaseoli which emerged
from Ophiomyia phaseoli and O. spencerella; a cynipid
Eucoilidea sp. and a Pteromalid Mesopolobus sp which
emerged from O. spencerella. Of these, Opius phaseoli was
the most dominant species parasitizing Ophiomyia phaseoli,
while Eucoilidea sp. was the most dominant species
parasitizing o. spencerella. Mesopolobus sp. appeared in
very small numbers. The percentage parasitism of the
beanfly increased progressively to a peak during the 7-8
week after emergence suggesting a lack of synchrony in the
phenology of these parasitoids with that of their beanfly
host. Apparently, the parasite populations build up too
late well after the beans had been attacked suggesting that
parasites alone cannot keep the pest population under
check. Intercropping and fertilizer application appeared
not to have an effect on the abundance of beanflies and
parasitoids and may not therefore be useful control options
against the stem maggot as previously thought.
Citation
Master of Science in AgriculturePublisher
University of Nairobi Faculty of Agriculture, University of Nairobi