Browsing by Author "Okeyo-Owuor, J. Barack"

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    Population ecology of the Legume pod borer, Maruca Testulalis geyer (Lepidoptera: Pyralidae) in relation to its natural enemies on cowpea in Western Kenya.
    (University of Dar es Salaam, 1988) Okeyo-Owuor, J. Barack
    Studies were conducted at the International Centre of Insect Physiology and Ecology, Mbita Point Field Station (MPFS) farm and the Lambwe Valley farmer's field during 1983 - 1985, to determine the natural population changes of Maruca testulalis Geyer (Lepidoptera; Pyralidae). The role of natural enemies, host plants and climatic factors on natural population, development and survival of M. testulalis was investigated. Further investigations on the biology of Tetrastichus sesamiae (Chalcididae, Eulophidae} a gregarious pupal endo-parasitoid as well as bioassays on Nosema sp., a protozoan pathogen of the pest were conducted in the MPFS laboratory. It was found that M. testulalis colonised the crop at least 15 days after plant emergence when the first adult moths were recorded in the pheromone traps. The egg and larval populations started increasing steadily at the flower initiation stage reaching a peak between 42 and 54 DAPE at both sites. Only one generation of M. testulalis occurred on each crop of cowgea. From the partial ecological life tables it was found that total real mortality for the generations at MPFS and Lambwe ranged between 51.7 - 98.9% and 96.4 - 97.7% respectively indicating very low survival in this species. Several natural enemies were found associated with M. testulalis, including 7 parasitoids, five of which attacked pupae and 2 on larvae. No egg parasitoid was found. The major pathogenic microorganisms found on dead M. testulalis larvae and pupae were Nosema sp. and Bacillus sp. Observable parasitism played negligible role in causing mortality on M. testulalis being only 0.02 - 0.09 and 0.04 - 0.06% at MPFS and Lambwe respectively. Pathogens especially Nosema sp. and Bacillus sp. contributed significantly to mortality of M. testulalis at both sites. Disappearance designated as other losses not due to either parasitoids or pathogens also accounted for a large proportion of mortality. Analysis using key factor and correlation methods revealed that disappearance at the egg stage (ko) was the key-factor causing population change at MPFS, while in Lambwe, although, more observations are necessary for this analysis, the factor k3, representing disease at 3rd instar larval stage, was identified as the key factor. Temperature and rainfall also affected seasonal abundance of M. testulalis under field conditions. Under laboratory conditions, temperature was found to be an important factor affecting development and survival of the pest. Biological studies on T. sesamiae showed that the development period range from I4 - 18 days. Major factors identified to influence the biology and efficiency of the parasitoid includes quality of food, age of host pupae and different host species. Results from bioassay for pathogens showed that Nosema sp. was the most virulent naturally occurring pathogen on M. testulalis.