Sweet Potato moth
Namibian crop pests  #  49
Helcystogramma convolvuli Order: Lepidoptera Family: Gelechiidae
Helcystogramma convolvuli (Walsingham, 1908) (Gelechiidae)  Identified by Ole Karsholt, ZMUC, Dk
 
 Sweet potato leaves folded by caterpillars

Close-up of caterpillar
A Sweet Potato leaf opened to observe the caterpillar

 

Common names: 

 No vernacular names were recorded

Pest status:

 The sweet potato moth seem to be common where sweet potato is grown on a larger scale. The damage seem to be insignificant, as sweet potato can stand losing a lot of leaf area without noticable reduction in tuber yield.

Only observed at two sites in North Central Namibia so far as large sweet potato fields are not common : 
Epalela Vegetable Garden, on the west bank of Olushandja Dam in Omusati region. 16.V.1995 and later. Large sweet potato field attacked. Every single plant infested.
Tsumeb, Extension office garden, 1998. All sweet potato plants were infested.

Description:

 Eggs are laid one by one on sweet potato leaves. They are conspicously blue and easy to spot on the leaves.

The attacked leaves are conspicous as they are folded (flat) along the midrib. The caterpillars do not eat holes throughout but instead leave transparent windows in the leaf.

The caterpillar is black and cream coloured in rings across the body. The head is brown. The caterpillar may be found near the midrib of attacked leaves when these are opened very carefully. It is very lively and jumps from the leaf at the slightest touch.

Very few adult moths have been hatched from caterpillars yet. The moth is black with a few brown spots on the wings. The moth is so inconspicous that it has never been observed on the plants although there should have been plenty of them around.

Control:

 Control is not recommended at present.

Other notes:

 		 The species is easy to find and pick in large numbers from damaged leaves. It also rears easily but is the hatching is often overlooked among the dry leaves in rearing cages. The moth is tiny and fragile and it is important to pin it the same day it hatched.

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