The coastal stemborer is present throughout
Coastal stalk borer
Chilotraea argyrolepia (Hampson, 1919);Diatraea argyrolepia
Phylum: Arthropoda; Class: Hexapoda (Insecta);Order: Lepidoptera;Family: Crambidae
The coastal stemborer is present throughout
The coastal stemborer is very similar in appearance to the spotted stemborer (Chilo partellus), but is limited to the coastal areas of East Africa.
Chilo partellus (Spotted stemborer)
Eggs are laid in batches on leaf surfaces, usually close to the midrib. They hatch after 4-10 days.
Young caterpillars initially feed in the leaf whorl. Older caterpillars tunnel into stems, eating out extensive galleries, within which they feed and grow for 2-3 weeks. When larvae are fully grown, they pupate and remain inside the maize stem. After 7-14 days adults emerge from pupae and come out of the stem. They mate and lay eggs on maize plants again and continue damaging the crop. During the dry season, larvae may enter a state of suspended development (diapause ) for several months and will only pupate with the onset of rains. Adults emerge from pupae in the late afternoon or early evening. They are active at night and rest on plants and plant debris during the day. They are rarely seen, during the day unless they are disturbed.
The whole life cycle takes about 3-4 weeks, varying according to temperature and other factors. Five or more successive generations may develop in favourable conditions.
Larva (caterpillar )
Vegetative stage or before harvest. Younger plants of less than two months old are more often attacked.
Damage occurs as a series of small holes in lines (pin holes) in younger leaves and/or patches of transparent leaf epidermis (window panes) in older leaves. Holes in stems caused by larvae tunnelling into the stem which results in broken stems or drying and eventual death of the growing point of the maize (deadheart).
Detection methods Coastal stemborer infestations may be detected by walking through young crops looking for characteristic feeding marks on funnel leaves, the presence of dead hearts and holes in tunnelled stems. Samples of affected stems can then cut open to find caterpillars and pupae. It is best to rear them until they reach the adult stage to identify the species as it is very difficult to identify the species from the larvae and pupae. Coastal stemborers may be detected in older crops and in crop residues by taking random samples of stems to dissect to find caterpillars and pupae.
Cultural practicesIntercropping maize with non-hosts crops like cassava or legumes like cowpea can reduce spotted stemborer damage. Alternatively, maize can be intercropped with a repellent plant such as silver leaf desmodium (Desmodium uncinatum) and a trap plant, such as Napier grass (Pennisetum purpureum), molasses grass (Melinis minutiflora) as a border crop around this intercrop to protect maize from stemborers. The trap plant draws the adult female away from the crop. More eggs are laid on the trap plant than on the crop but the larvae develop poorly or not at all on the trap plant. This practice is known as "push-pull".
Good crop hygiene through the destruction of maize residues by burning to get rid of the larvae and pupae within the stems, and removal of volunteer crop plants and/or alternative hosts, prevents carry-over populations. This helps in limiting the initial establishment of stemborers that would infest the next crop.
Early slashing of maize stubble and laying it out on the ground where the sun's heat destroys the larvae and pupae within can also be utilised.
Biological controlA number of species of parasitic wasps have been recorded attacking the coastal stemborer. These include Cotesia flavipes, C. sesamia and Sturmiopsis parasitica. These locate and lay their eggs in the stemborers while the stemborers are feeding inside the plant stems. Upon hatching the larvae of the parasitic wasp feed internally in the stemborer, and then exit the stemborer and spin cocoons. S. parasitica also attacks the pupae. Habitat management practices that conserve these parasitoids and predators like ants and earwigs can help in the control of stemborers.
Chemical controlChemical control can be achieved by applications of granules or dusts to the leaf whorl early in crop growth to kill early larval instars. This method has limited effectiveness once the larvae bore into the stem. Neem products (powder from ground neem seeds) are reportedly effective and may be applied to the leaf whorl in a 1:1 mixture with dry clay or sawdust. Pesticides are poisons so it is essential to follow all safety precautions on labels.
CAB International 2006. Crop Protection Compendium. Wallingford, UK, CAB International. Accessed February 16th 2011.
Overholt W.A, Maes K.V.N and Goebel F.R. 2001. Field guide to the stemborer larvae of maize, sorghum and sugarcane in Eastern and Southern Africa. ICIPE Science Press, Nairobi, Kenya.
Polaszek A. (ed.) (1998). African cereal stemborers; economic importance, taxonomy, natural enemies and control. CAB International, Wallingford, Oxon, UK. 530pp.
Anne M. Akol, Makerere University; Maneno Y. Chidege, Tropical Pesticides Research Institute; Herbert A.L. Talwana, Makerere University; John R. Mauremootoo, BioNET-INTERNATIONAL Secretariat.
We recognise the support from the National Museums of Kenya, Tropical Pesticides Research Institute (TPRI) - Tanzania and Makerere University, Uganda. This activity was undertaken as part of the BioNET-EAFRINET UVIMA Project (Taxonomy for Development in East Africa).
BioNET-EAFRINET Regional Coordinator: [email protected]