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Eggs of Sesamia calamistis. Image source: CIMMYT
Larva, pupa and adult moth of Sesamia calamistis. Image source: IRD Laboratoire Evolution, Génomes et Spéciation
Larvae of Sesamia calamistis feeding on maize. Image source: CIMMYT
Larva (caterpillar) of Sesamia calamistis. Image source: IRD Laboratoire Evolution, Génomes et Spéciation
This species is found in sub-Saharan Africa and some of the islands in the Indian Ocean. It commonly occurs in wetter localities at all altitudes. The main crops affected are maize, sorghum, pearl millet, wheat, rice and sugarcane. The larvae (caterpillars) Larvae (caterpillars) can tunnel into the stem which can result in broken stems or drying and eventual death of the growing point of the maize.
African pink stem borer, pink stalk borer, pink stalk borer of sugarcane, African pink borer of sugarcane, Mauritius pink borer of sugarcane, southern pink borer of sugarcane
Sesamia mediastriga Bethune-Baker, 1911
Phylum: Arthropoda; Class: Hexapoda (Insecta); Order: Lepidoptera; Family: Noctuidae
This species is found in sub-Saharan Africa and some of the islands in the Indian Ocean. It commonly occurs in wetter localities at all altitudes from sea-level to 2400 m altitude. It is more common in Uganda, with its extensive swampy areas, than in Kenya and Tanzania, where it tends to be limited to the hills, lake-sides, rivers and irrigated areas.
Eggs are hemispherical, about 1 mm in diameter and slightly flattened with radial ridges (crenullations). They are creamy-white when laid but darken as they develop.
The larva of the African pink stalkborer looks smooth and shiny and lack obvious hairs or markings. Their colour is variable but they are usually creamy-white with a distinctive pink suffusion (hence the common name). The head and prothoracic shield (a plate on the dorsal surface of the thorax) are brown; the dorsal part of the last abdominal segment bearing the anus (the suranal plate) is yellow-brown. Setae (bristles) are present on small, inconspicuous pinacula (hardened - sclerotized - areas that indicate points of muscle attachment) and the spiracles (breathing holes found along the side of the body) are elongate-oval with black surrounds. The crochets (hooks) of the larval abdominal prolegs are arranged in lines as is the case for noctuid stemborers. This contrasts with pyralid borers whose crochets are arranged in circles. Mature larvae are between 30-40 mm long, pink with buff and pink dorsal markings and a brown head .
Pupae are up to about 18 mm long, brown to yellowish-brown with a wrinkled (creased) frontal region of the head and a terminal "tail" (cremaster) with four large and two small spines.
The wingspan in females of the African pink stalkborer is 20-30 mm and in males a little less. The forewings are pale-brownish, with variable but generally inconspicuous darker markings along the margin and an overall silky appearance. Hind wings are white.
The purple stemborer (Sesamia inferens) (Lepidopetera: Noctuidae) which attacks maize, sorghum, pearl millet, finger millet, wheat, rice, oats,barley, sugarcane and some wild grasses
Eggs are inserted between the lower leaf sheaths and the stem in batches of 10-40 and arranged in two to four contiguous rows. On average, each female lays around 300 eggs in a period of five days. Egg laying occurs from the time plants are two weeks old until flowering. The most serious damage, however, occurs at early plant stages.
Most larvae penetrate the stem shortly after they emerge from their eggs. Larval feeding might result in dead hearts and the tunneling and girdling activity of the larvae often results in stalk breakage. During the ear filling period, the majority of the larvae occur in the ears. Development of the larvae takes four to six weeks. Most larvae pupate within the stem or cobs.
The African pink stalkborer breeds throughout the year and has no period of suspended development (diapause ). However, it is less abundant during the dry season when it is limited to mature grasses - elephant grass (Pennisetum purpureum), Setaria species and itchgrass (Rottboellia exaltata) among others, as a food source.
Larva (caterpillar )
Primary crop hosts: maize, sorghum, pearl millet, wheat, rice, sugarcane
Wild hosts: Poaceae (grasses) e.g. Pennisetum purpureum, Setaria species and itchgrass (Rottboellia exaltata) and Sedges (Cyperaceae) such as Cyperus distans
Flowering stage and vegetative growing stage.
Growing points of stem, seeds and whole plant
Symptoms by affected plant part:
African pink stalkborer 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. African pink stalkborers may be detected in older crops and in crop residues by taking random samples of stems to dissect to find caterpillars and pupae.
Intercropping 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.
Several species of parasitic wasps attack the African pink stalkborer but those able to effect significant control are the larval parasitoids Cotesia sesamia (on larvae ), Descampsina sesamiae (on larvae and pupae), Pediobius furvus (on pupae), Sturmiopsis parasitica (on larvae and pupae) and the egg parasitoids, Telenomus busseolae and T. isis. The wasps locate and lay their eggs in the stemborer (egg, larva or pupa). Upon hatching the larvae of the parasitic wasp feed internally in the stemborer, and then exit the stemborer and spin cocoons. Habitat management practices that conserve these parasitoids and predators like ants and earwigs can help in the control of the African pink stalkborer.
Chemical 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. Spray or granular applications of carbaryl, endosulfan, trichlorfon, carbofuran, diazinon or fenitrothion have been recommended in the past. Application of a 50:50 mixture of powdered neem kernels and sawdust to the leaf whorls of young plants is also reportedly effective.Pesticides are poisons so it is essential to follow all safety precautions on labels.
Kfir R., Overholt W.A., Khan Z.R. and Polaszek A. (2002). Biology and management of economically important lepidopteran cereal stem borers in Africa. Annual Review of Entomology, 47: 701-731.
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]