| dc.description.abstract | Fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) emerged as one of the most important global pests of maize in recent years. The crops that are most infested in Africa are maize and sorghum. In its native area of the Neotropics in Central and South America, S. frugiperda is largely controlled by means of Bt maize and the application of chemical insecticides. The arrival of this invasive pest species threatens food security in Africa. Unfamiliarity with this pest resulted in large scale use of insecticides in many countries, especially by small holder farmers, which, in the past did not often apply insecticides for control of maize pests. The use of insecticides is in most cases not affordable to small holder farmers. Alternative control methods, for example, biopesticides are also used for S. frugiperda control. These methods are more appropriate for smallholder farmers in developing countries because they are readily accessible and not expensive. Soap solutions, ash, sand and soil, applied into whorls of maize plants to control S. frugiperda larvae are other alternative methods used by smallholder farmers. The efficacy of many of these natural local innovations have not been determined under controlled conditions, and variable results have been reported from farmers’ fields. The aim of this study was therefore, to determine the effect of the application of soil and wood ash into the whorls of maize plants on the mortality and movement behaviour (ballooning/escape) of fall armyworm (FAW) larvae. Bioassays were also conducted in which the preferences of 1st- and 3rd-instar larvae for whorl leaf tissue treated with ash and soil were determined. Pilot experiments, followed by 11 laboratory and field trials were conducted. In these experiments, ash was applied as either a preventative treatment (before larvae were inoculated onto plants) for 1st-instar larvae, or a curative treatment (after larvae were inoculated onto plants) for 1st-, 3rd- and 5th-instar larvae. The efficacy of application of wet ash was also compared to that of a dry ash application. The incidence of ballooning of 1st-, 3rd- and 5th-instar larvae was low (ranged from 5 to 21.17%) and did not differ significantly between treatments. Curative application of dry ash against 1st-instar larvae resulted in significantly lower rates of ballooning compared to other treatments. Significantly higher levels of mortality of 1st-instar larvae were recorded inside plant whorls that were curatively treated with wet (65.6%) and dry ash (67.5%), compared to the control treatment (22.0%). This was however not the case with 3rd-instar larvae under laboratory conditions. In preference tests, significantly higher numbers of 1st- and 3rd-instar larvae preferred to settle on untreated leaf tissue compared to the wet ash, dry ash and soil treatments, indicating that the presence of these compounds had a repellent effect. Variable results were recorded in the field trials. The application of ash and soil into plant whorls as curative treatments, resulted in significant reductions in the survival of 3rd-instar larvae in field trials. Significantly lower levels of survival of 3rd-instar larvae were recorded with the dry ash (21.4%), soil (25%) and wet ash (33.9%) treatments, compared to the control (69.6%). However, neither preventative nor curative applications against 1st- instar larvae resulted in significant mortality in field experiments. Leaf damage scores (1-9 rating scale) made 5 days after inoculation of plants with neonate larvae, differed significantly between treatments (range: 3.2 – 4.1). It can be concluded that the use of ash and soil treatments by small holder farmers in Africa and beyond has a potential to contribute to integrated pest management (IPM) against S. frugiperda larvae. However, these local innovations are not always effective in controlling S. frugiperda larvae and the level of efficacy of control varies a lot as observed in this study. Adoption of local innovations to manage this pest is fundamental to the implementation of IPM. Long-term management of S. frugiperda should be based on IPM principles which include the use of local innovations, host plant resistance, cultural control practices and minimizing the application of chemical pesticides to protect natural enemies. | en_US |
