Busseola fusca (Fuller, 1901) - African Maize Stalkborer

Summary

The African maize stalkborer is indigenous to and occurs throughout mainland sub-SaharanAfrica. Maize and sorghum are its main crop hosts. The larval stage (caterpillars) cause damage to maize by feeding on young leaves from where they can enter the stems. This may kill the plant. In older plants their feeding can damage can reduce grain production.

Common Names

African maize stalkborer

Synonyms

Busseola sorghicida Thurau, 1904;Sesamia fusca Fuller, 1901

Taxonomic Position

Phylum: Arthropoda; Class: Hexapoda (Insecta);Order: Lepidoptera; Family: Noctuidae

Origin and Distribution

The African maize stalkborer is indigenous to and occurs throughout mainland sub-Saharan Africa. It is not known to occur outside this area.This species occurs from sea level to altitudes above 2000 m and has adapted to different local conditions.

Description

Eggs

Eggs are creamy-white when laid but darken just before emergence. They are about 0.8-1mm in diameter, hemispherical, and slightly flattened with radial ridges (crenulations ) on the upper surface of each egg shell. They are usually laid in batches of 30-100 under leaf sheaths.

 

Larvae

The larvae (caterpillars) lack conspicuous hairs or markings. They are usually creamy-white, in colour, often with a distinctive grey tinge but sometimes with a pink suffusion, which may cause them to be confused with the larvae of Sesamia Calamistis (the pink maize borer). The head capsule is dark brown and the prothorax is yellowish-brown. Its spiracles (breathing holes found along the side of the body) are elongate-oval with black edges. The caterpillars have prolegs along the abdomen .

Adults

The adult wing-span is 25-35 mm. Its forewings are light to dark brown with darker markings. The hind wings are white to grey-brown.

Similar Species

The larvae of African maize stalkborer (Busseola fusca) and the pink stemborer (Sesamia calamistis) are very similar in biology and morphology but can usually be distinguished in the adult stages. Adults of the African maize stalkborer and the pink stemborer look similar in appearance but the forewings of the African maize stalkborer have dark patterns and are a darker brown than those of the pink stemborer. The larva of the African maize stalkborer has no obvious hairs or markings and the hooks (crochets) on its prolegs are arranged in a linear pattern – characteristics that distinguish it from the larva of the spotted stemborer (Chilo partellus) and the sugarcane borer (Eldana saccharina ).

Life Cycle

Adult African maize stalkborer moths lay eggs in a row between the stem and leafsheath. Each female lays on average about 200 eggs over its short lifetime which lasts several days – its exact duration depends on temperature and other factors. Egg laying on maize is usually concentrated on plants that are less than 2 months old with the leaf sheath of the youngest unfolded leaf being the most attractive part of the leaves for females. The eggs hatch in 3-5 days and larvae move into the leaf whorls to feed. When older (third instar), they tunnel into the stems where they feed for 3-5 weeks before pupating within the tunnels that they have produced in the stems. The adult moth will emerge after a pupal period of 7-14 days from a hole that they produced before pupation. Adults mate soon after emergence. Under favourable conditions the life cycle can be completed in 7-8 weeks but during dry and/or cold weather the larvae can enter a period of suspended development (diapause ) of 6 months or more in stems and other plant residues.

Pest Destructive Stage

Larva (caterpillar )

Host Range

Primary hosts are crops particularly maize, and sorghum. Secondary crop hosts are pearl millet, finger millet and sugarcane.

Wild hosts include many species of wild grasses such as: wild Sudan grass (Sorghum verticilliflorum), elephant grass (Pennisetum purpureum), Guinea grass (Panicum maximum), Johnson grass (Sorghum halepense), Hyparrhenia rufa and Rottboellia exaltata .

Host Lifestage Affected

Flowering stage and vegetative growing stage

Host Plant Part Affected

Stems, leaves and seeds. Also the inflorescence in sorghum, millet, wild grasses

Damage Symptoms

First-instar larvae feed in the young terminal leaf whorls producing characteristic patterns of small holes and 'window-panes' (patches of transparent leaf epidermis) where tissues have been eaten away. Later they eat into the growing points, which may be killed so that the dead central leaves form characteristic dry, withered 'dead-hearts'. Older larvae tunnel extensively in stems, eating out long frass-filled galleries which may weaken stems and cause breakages. Larvae also tunnel into maize cobs and into the peduncles of sorghum and millet inflorescences and may seriously affect grain production.

Symptoms by affected plant part:

  • Growing points: internal feeding; boring; external feeding; dead heart (central leaves become dry and withered); frass visible.
  • Inflorescence: abnormal colour; internal feeding; Frass visible.
  • Leaves: external feeding; young terminal leaf whorls have patterns of small holes and ‘window panes’ where tissue has been eaten away. Frass visible.
  • Roots: internal feeding.
  • Seeds: frass visible; empty grains.
  • Stems: abnormal growth; internal feeding shown by long frass-filled galleries; dead heart ; visible frass.
  • Whole plant: dead heart ; plant dead; dieback; internal feeding; frass visible.
  • Maize plants are less able to tolerate stem borer attack than sorghum and pearl millet plants and yield losses of 12% or more occur.

Pest Management

Detection methods
African maize 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 maize stalkborers may be detected in older crops and in crop residues by taking random samples of stems to dissect to find caterpillars and pupae.

Cultural practices
Intercropping maize with non-hosts crops like cassava or legumes like cowpea can reduce African maize stalkborer 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 control
Many natural enemies of the African maize stalkborer have been reported but their impact is variable across regions, seasons and crops. Two of the most abundant natural enemies of the African maize stalkborer are the larval parasitoids Cotesia sesamiae and Bracon sesamiae. They locate the stemborers while the stemborers are feeding inside the plant stems lay eggs into them. Upon hatching the larvae of the parasitic wasp feed internally in the stemborer, kill it and then exit to spin cocoons. The ability of indigenous natural enemies to control this species is too low to prevent significant damage to maize. However, they can help control to reduce densities of the African maize stalkborer as part of an integrated pest management (IPM) approach that includes habitat management practices that conserve parasitoids and predators like ants and earwigs.

Chemical control
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. 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.

Sources of Information and Links

CAB International (2006). Crop Protection Compendium. Wallingford, UK: CAB International. Accessed February 10th 2011

Le Ru B.P., Ong’amo G.O., Moyal P.,  Ngala L., Musyoka B., Abdullah Z.,  Cugala D., Defabachew B., Haile T.A., Kauma Matama T., Lada V.Y., Negassi, B., Pallangyo K., Ravolonandrianina J., Sidumo A., Omwega C.O., Schulthess F., Calatayud P.A. and Silvain J.F. (2006). Diversity of lepidopteran stem borers on monocotyledonous plants in eastern Africa and the islands of Madagascar and Zanzibar revisited. Bulletin of Entomological Research 96, 555–563.

Niyibigira E.I. (2003). Genetic variability in Cotesia flavipes and its importance in biological control of lepidopteran stemborers. PhD Thesis, Wageningen University, 162pp

Editors

Anne M. Akol, Makerere University; Maneno Y. Chidege, Tropical Pesticides Research Institute; Herbert A.L. Talwana, Makerere University; John R. Mauremootoo, BioNET-INTERNATIONAL Secretariat.

Acknowledgments

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).

Contact

BioNET-EAFRINET Regional Coordinator: eafrinet@africaonline.co.ke