Click on images to enlarge
The maize weevil, Sitophilus zeamais. ©Gary Alpert, Harvard University, Bugwood.org
Maize damaged by Sitophilus zeamais. Photo: Frank Peairs, Colorado State University, Bugwood.org (CC-BY)
The maize weevil, Sitophilus zeamais adult. ©Georg Goergen (source CABI CPC)
The maize weevil, Sitophilus zeamais adult. Photo: USDA, ARS (Public Domain)
The maize weevil is found in all warm and tropical parts of the world. It is a pest of stored maize, dried cassava, yam, common sorghum and wheat. Both adults and larvae feed on internally on maize grains and an infestation can start in the field (when the cob is still on the plant) but most damage occurs in storage.
English: maize weevil, greater grain weevil, northern corn weevil, greater rice weevil.
Local name: Tanzania: Mdudu Tembo
Calandra chilensis Philippi and Philippi, 1864;Calandra platensis Zacher, 1922;Cossonus quadrimacula Walker, 1859
Phylum: Arthropoda; Class: Hexapoda (Insecta); Order: Coleoptera; Family: Curculionidae
The origin of the maize weevil is not known but now it is found in all warm and tropical parts of the world.
Adult maize weevils are 3 – 3.5 mm long, dark brown – black in colour and shiny and pitted with numerous punctures. The punctures on the thorax are in an irregular pattern while those on the elytra (wing cases) are in lines. The elytra also usually have four pale reddish-brown or orange-brown oval markings. The maize weevil has the characteristic rostrum (snout or beak) and elbowed antennae of the family Curculionidae (weevil family). The antennae have eight segments and are often carried in an extended position when the insect is walking. The larvae of maize weevils are white, fleshy and legless.
The maize weevil (Sitophilus zeamais) can be separated from the granary weevil (S. granarius) by the presence of wings beneath the elytra (absent in S. granarius) and by having circular, rather than oval, punctures on the prothorax. The larvae of the two species are not easy to separate.
It is possible to confuse the maize weevil with other storage insect pests such as the larger grain borer – LGB (Prostephanus truncatus). The end of the body of the maize weevil is more rounded than that of the LGB, and its mouthparts are 'beak-like' and antennae elbowed.
Females chew into maize grains where they lay their eggs throughout most of their adult life of up to one year, although 50% of their eggs may be laid in the first 4-5 weeks. Each female may lay up to 150 eggs in her lifetime. Development time ranges from about 35 days under optimal conditions to over 110 days in unfavourable conditions. Eggs, larval and pupal stages are all found within tunnels and chambers bored in the grain and are thus not normally seen. Because larval stages feed on the internal parts of the grain, it is difficult to detect infestations early. Adults emerge from the grain and can be seen walking over the grain surfaces. Adult emergence holes are large with irregular edges. Females release a sex pheromone which attracts males.
Both adult and larva damage the grain by chewing. The infestation can start in the field but most damage occurs in storage.
The maize weevil can develop on a range of cereal crops. It is a serious pest of stored maize, dried cassava roots, yam, common sorghum and wheat in the East African Region.
Post-harvest and storage
Seeds and grains
The pest causes hollowing of whole previously undamaged grains. In severe infestations only the grain hull is left along with powdery white frass (insect waste). The large emergence holes with irregular edges are characteristic. Grains which float in water often indicate larval damage.
CABI. (2010). Sitophilus zeamais (maize weevil) datasheet. Crop Protection Compendium, 2010 Edition. CAB International Publishing. Wallingford, UK. www.cabi.org/cpc. Accessed on 28 Jan 2010.
Coombs CW, Billings CJ, Porter JE, (1977). The effect of yellow split-peas (Pisum sativum L.) and other pulses on the productivity of certain strains of Sitophilus oryzae (L.) (Col. Curculionidae) and the ability of other strains to breed thereon. Journal of Stored Products Research, 13(2):53-58.
Dent D. (2000). Insect pest management.CAB International Wallingford, UK
Infonet-biovision. http://www.infonet-biovision.org/default/ct/91/pests. Accessed on 28 Jan 2010
Gaby S. (1988). Natural crop protection in the tropics. Margraf Publishers Scientific books, Germany.
Ganesalingam VK, (1977). Insects in paddy and rice in storage in the Kandy District. Ceylon. Journal of Science, Biological Sciences, 12(2):169-176.
Krischik V.A., Cuperus G and Galliart D (eds.).1995. Stored Products Management, 2nd Ed. Oklahoma State Univ. 204 pp. http://www.grainscanada.gc.ca/storage-entrepose/pip-irp/lgb-ppg-eng.htm#d accessed on 15/5/2010.
Youdeowei A. (1993) Pest and vector management in the tropics, Longman group Ltd. England, 399pp.
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]