Persistent populations of males of the African armyworm, Spodoptera exempta (Walker) (Lepidoptera: Noctuidae), in Malawi

Abstract

Regular catches of males of Spodoptera exempta (Walker) were made in 41 pheromone disc traps scattered throughout Malawi in 1978-82. Each trap had a vial, replaced monthly, containing 2 mg of a 13-3:1 mixture of two sex-pheromone components of the female. Over the five-year period, males were caught every month at a majority of sites throughout the country, suggesting that they came from populations resident in Malawi. Sites at which moths were regularly caught had areas with green grass throughout the year which could have sustained larvae within their vicinity. A few sites at which moths were caught only occasionally had very dry immediate surroundings in the dry season, and it is suggested that moths caught at these sites are primarily migrants from either within or outside Malawi. There was no obvious relationship between site elevation, monthly rainfall and monthly moth catches or whether moths were caught persistently or irregularly. The results strongly suggest that some of the moths captured throughout the year in Malawi developed locally while some originate in other countries such as Mozambique.

The effect of larval phase on flight performance of African armyworm moths, Spodoptera exempta (Walker) (Lepidoptera: Noctuidae)

“…exempta shows a density-dependent phase polyphenism (Faure, 1943). The gregaria phase is characteristic of outbreak populations which occur typically during the rains (Haggis, 1986), while low density populations of the solitaria form are believed to persist in favourable habitats over much of the range of the species throughout the year (Rose, 1979;Gatehouse, 1986;Nyirenda, 1985). The high and low density forms will be referred to here as the phases gregaria and solitaria, although the terms active and passive were proposed by Whellan (1954).…”

The relationship between outbreaks, rainfall and low density populations of the African armyworm, Spodoptera exempta, in Kenya

“…), southern Ethiopia (T. Megenasa, unpubl. report 1988) and in Malawi where there is some rainfall throughout much of the year (Nyirenda, 1985). The present studies are particularly valuable as they show that the very low numbers of moths caught in the armyworm off-season in Kenya are a part of a decline in numbers from peaks reached during the long rains each year, and that the peaks are related to the number of recorded outbreaks in Kenya.…”

“…Dunstan, L. D. C. Fishpool, G. A. Mallya andW. report 1988) and in Malawi where there is some rainfall throughout much of the year (Nyirenda, 1985). reports 1982-1986), Uganda (J. Bowden, pers.…”

The bionomics of the African armyworm Spodoptera exempta in relation to its status as a migrant pest

“…All studies on the bionomics, seasonal distribution and migration of populations have largely depended on information on the time and place of outbreaks, collected by agricultural officers through their national organizations and also on moth-trap data provided by the armyworm forecast and warning services now established in member countries of DLCO-EA and in other countries including Burundi (A. Autrique personal communication), Malawi (Nyirenda 1985), South Africa (Roome 1974), Zimbabwe (B.W. Blair unpublished data) and the Yemen (Moharram and Nasseh 1989).…”

“…Burnt or grazed grasslands, where there is new growth after rain, may often become infested (Brown 1962;Rose and Law 1976). (Nyirenda 1985) and Uganda (J. Bowden unpublished data).…”