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Larvae of A. acerata feed on leaves of the sweet potato. The young caterpillars feed on the upper leaf surface whereas the older larvae eat the whole leaf lamina except the primary midribs. Heavy attack can result in complete defoliation of the vines, over a wide area, often several times in succession (Ingram, 1970; Hill, 1983; Skoglund and Smit, 1994; Lugojja, 1996; Smit et al., 1997).
As a result of infestation young plants may die or yield few or no storage roots; storage root yield is delayed and reduced on older plants (Lefèvre, 1948; Ingram, 1970; Hill, 1983).
Control of the sweet potato butterfly in Eastern Africa largely depends on manual and chemical control measures; although cultural control strategies are also encouraged (Skoglund and Smit, 1994). Lefèvre (1948) evaluated biological control but his results were not encouraging.
The traditional method of controlling sweet potato butterfly outbreaks is to hand pick and destroy nests of young caterpillars. It is very effective when started early, before the caterpillars have dispersed. Once the caterpillars have dispersed, more drastic measures are needed (NARO, 1994; Skoglund and Smit, 1994). For effective control, hand picking should cover large areas, including neighbouring fields, to avoid rapid re-infestations (Lenné, 1991).
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
A. acerata is an important pest of sweet potato in Central Eastern Africa and has been reported from Kenya, Tanzania, Uganda, Burundi, Rwanda, Zaire, northern Zambia, and southern Ethiopia.
The larvae can produce complete defoliation of the crop during heavy infestations especially in the dry season (Smit et al., 1997). Lefèvre (1948) reported that in Kivu district, Zaire, serious attack results in delayed and/or reduced production or complete crop failure, although quantitative data on storage root yield losses due to defoliation were not presented. In the major sweet potato growing districts of Uganda, the sweet potato butterfly is considered by farmers as a moderate to serious constraint in sweet potato production (Bashaasha et al., 1995), whereas in western Kenya, farmers consider the sweet potato butterfly as a constraint only in relatively dry agro-ecological zones (Smit and Matengo, 1995).
Assuming that the photosynthetic area damaged reduces plant growth, extensive defoliation of the crop would lead to a great reduction in yield (Hill, 1983). However, storage root yield losses due to defoliation have not been adequately quantified for a long time (Lenné, 1991). Experimental single defoliation at two levels (50 and 100%) had no significant effect on sweet potato shoot survival and yield, but yields decreased as defoliation frequency increased. Highest yield loss (71%) occurred when plants were defoliated three times at 1, 2 and 3 months after planting. Defoliation occurring once or twice did not significantly affect yields (Lugojja, 1996).
After serious defoliation, farmers are also concerned about the lack of vines for planting material. Severe outbreaks often affect whole communities (Smit et al. 1997).