Scientific Name: Sitophilus zeamais Motschulsky, 1855  

Common Names: Maize weevil, greater grain weevil, northern corn weevil, greater rice weevil 

Synonyms

Calandra chilensis, Calandra platensis, Cossonus quadrimacula

Taxonomic Position

Phylum: Arthropoda

Class: Hexapoda (Insecta)

Order: Coleoptera

Family: Curculionidae

Geographical distribution  

Asia - Afghanistan, India (Maharashtra, Sikkim and Uttar Pradesh),  Indonesia, Iran, Iraq, Israel, Japan, Kazakhstan, Malaysia, Myanmar, Nepal, Pakistan, Saudi Arabia, Singapore, Sri Lanka, Syria, Thailand, Turkey, Yemen

Africa - Algeria, Angola, Cameroon, Egypt, Morocco, South Africa, Spain,   Swaziland

North America - Mexico, USA

South America -Argentina, Chile, Peru

Europe- Austria, Belgium, Bosnia-Hercegovina, Croatia, Czech Republic, Denmark, France, Germany, Germany, Greece, Hungary, Ireland, Italy, Poland, Romania, Russian Federation, Serbia, Slovenia, Spain, Sweden, UK, Ukraine

Oceania – South and Western Australia, New South wales,

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.

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.

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.

Identification features

Adult

• 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 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.

Adult – dorsal view	Antennal View	Pygidium

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.

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.

Detection methods

• Because the maize weevil larvae develop inside the grain it is difficult to detect the pest by visual inspection unless its numbers are very high.
• Sitophilus spp. can be trapped woth a range of commercially available pitfall and probe traps placed at the surface or inserted into grain bulks.
• Efficacy of traps can be enhanced by the addition of baits such as cracked grain and grain oils and synthetic aggregation pheromones.
• Disturbance of the grain causes adult Sitophilus spp. to migrate upwards and become visible on the surface.
• Egg plug staining method can be used for early detection of weevil infestation.
• X-ray radiography technique can be used to detect hidden larvae developing within the grains.