Summary

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.

Common Names

English: maize weevil, greater grain weevil, northern corn weevil, greater rice weevil.

Local name: Tanzania: Mdudu Tembo

Synonyms

Calandra chilensis Philippi and Philippi, 1864;Calandra platensis Zacher, 1922;Cossonus quadrimacula Walker, 1859

Taxonomic Position

Phylum: Arthropoda; Class: Hexapoda (Insecta); Order: Coleoptera; Family: Curculionidae

Origin and Distribution

The origin of the maize weevil is not known but now it is found in all warm and tropical parts of the world.

Description

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.

Similar Species

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.

Life Cycle

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.

Pest Destructive Stage

Both adult and larva damage the grain by chewing. The infestation can start in the field but most damage occurs in storage.

Host Range

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.

Host Lifestage Affected

Post-harvest and storage

Host Plant Part Affected

Seeds and grains

Damage Symptoms

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.

Pest Management

Sources of Information and Links

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: [email protected]