Sesamia calamistis (Pink Stalk Borer)
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The Pink Stalk Borer is indigenous to Africa, occurring in
savanna areas with a distinct dry season. Host plants include a wide variety of
native grass species but also include cultivated grasses such as sugarcane,
wheat and maize.
The life cycle is usually completed in 6-8 weeks during
the summer months, but takes longer if part of it takes place in the winter
months. There are no distinct generations: eggs, larvae, pupae and adults can
all be present in a population at any one time.
Adults. The adults emerge from their pupae and mate
in the usual moth fashion where the female releases a sex pheromone that
attracts a male from downwind.
Eggs. The female moth, once mated, lays her eggs at
night under the leaf sheaths of plants, in batches of up to 100 or more. Eggs
hatch about a week after being laid.
Larvae. Soon after emergence, the larvae bite into
the stem of the grass or, on maize, through the sheathing leaves into the maize
cobs. Caterpillars move on to new plants once the one they have been feeding on
has died from their feeding activities. Larval development takes 3-6 weeks in
summer during which time they normally pass through 6-7 instars.
Pupae. Final instar larvae spin a cocoon round
themselves, inside the hollowed-out stem of the plant or in the sheathing leaves or, in the case
of maize, in the tunnels they have made in the cob. Inside the cocoon they moult
into pupae and after 2-3 weeks the adult emerges.
out more about pests of maize in southern Africa
& Moran, V.C. 1982. Insects and mites of cultivated plants in South
Africa. Butterworths, Durban.
Chinwada, P. & Overholt, W.A. 2001.
Natural enemies of maize stemborers on the highveld of Zimbabwe. African
Entomology 9: 67-75.