Ecological studies on cowpea borers. I. evaluation of yield loss of cowpea due to the pod borers.
1989
Ohno K. | Alam M.Z.
Cowpea pods are infested by a lot of insect pests. It is said that among them pod borer causes serious damage on the yield. The study was conducted to clear the attacking pattern and then evaluate the yield loss due to the pod borers. In the field at IPSA the number of bores and borers were counted every week from 17 June to 23 March, 1989. Harvested pods were measured and then dissected under binocular microscope to learn the damage of infestation on cowpea seeds. At least two species, Maruca sp. and a butterfly (Lycaenidae) attacked the cowpea. Overall infestation rate was 54.4% at the first harvesting time, while it varied from 12.4 to 41.4% during survey period. The number of seeds fed on by borers in one pod was lower than that expected from amount consumed by one borer at high density. It is suggested that there is the interference between larvae when they use one pod. To estimate the yield loss due to the borers, mean weight of healthy (Wh) and infested (Wi) seeds, mean no. of seeds in healthy (Bh) and infested (Bi) pods and also infestation rate (I) were taken into consideration. A total yield loss due to borer infestation was estimated to be less than 20% and much lower than the infestation rate itself. Frequency distribution of the number of bores per pod fitted poison distribution with the same mean density. Therefore, a total yield loss is simulated with the above parameters and the Poission distribution to express the infestation rate (I) as the function of mean density of bores. The results are discussed in terms of reliable methods to estimate yield loss.
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