Sawflies (Athalia spp)
Sawflies are sporadic but serious pests of brassicas. The cabbage sawfly (Athalia sjostedti) has been reported as a major pest in Tanzania. Sawfly adults are wasps with dark head and thorax, bright yellow abdomen, and two pairs of membranous wings. They are about 1 cm long. Eggs are laid singly inside the leaf. Larvae are oily, black or greenish in colour with a swollen part just behind the head, which makes them appear humped. They look very similar to caterpillars, but they have 6 to 9 pairs of prolegs (abdominal legs), whilst caterpillars have 5 pairs or less. Larvae measure up to 2 cm when fully grown. Larvae eat the blades of leaves leaving just the main veins. They drop from the plant to pupate in the soil.
- Destruction of wild plants of the family of cabbages in the vicinity of the crop.
- Ploughing in of volunteer plants at the end of the season helps reduce sawfly populations.
- Manual collection and destruction of larvae is feasible when there are few sawflies on the crop.