Natural enemies of sesame webworm and the effect of additive intercropping on its incidence in Uganda

Objectives: This study aimed to increase the grain yield of sesame by protecting it against sesame webworm. The specific objectives were to determine the effect of additive intercropping on incidence of sesame webworm and the occurrence of natural enemies with potential to biologically control the pest. Methodology and results: Five plant population densities of sesame incorporated mid-way between finger millet rows spaced at 45 X 7.5 cm were 44444, 55556, 74074, 111111 and 222222 plants/ha. The control was sole sesame at a population density of 333333 plants/ha. The treatments were laid out in a completely randomised block design, with four replicates. Data were collected on incidence of sesame webworm and sesame grain yield. Webworm larvae recovered from this trial were reared and monitored for emergence of natural enemies. Additive intercropping had no significant effect on the incidence of sesame webworm. Sesame webworm larvae recovered from sole sesame had higher mortality (63.1%) than those from intercrops with 49.2%. Two natural enemies of the sesame webworm, Hemipimpla sp. and a nematode of the Order Mermithid, were discovered. Conclusion and application of findings: Additive intercropping of sesame with finger millet has no benefit towards controlling sesame webworm and yet intercropping results into a significant (P=0.02) reduction in sesame grain yield. Mortality of sesame webworm larvae recovered from sole sesame was higher than for those from sesame + finger millet intercrop. Therefore, sole cropping of sesame is recommended for its high yields. Two natural enemies of sesame webworm namely Hemipimpla sp. and a Mermithid nematode exist in Uganda. An evaluation of these natural enemies for efficacy in the control of sesame webworm is recommended. Sesame webworm larvae died due to unknown factors, besides the two named natural enemies. These factors need to be identified.

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