Maize Weevil

This is a pest that destroyed stored maize, dried cassava, yams, sorghum and wheat. The adults and larvae feed internally on stored maize grains or in the field.

Image courtesy lucid key server

Appearance

  • The adult maize weevils are 3 -3.5mm long, dark brown or black in color and shiny and pitted with numerous punctures.
  • The punctures on the wing cases are in lines while on the thorax are in an irregular pattern.
  • The maize weevil has a snout/beak and elbowed antennae.
  • The antennae have eight segments and are often carried in an extended position when the insect is walking.
  • The larvae of the maize weevils tend to be white flesh and legless. The wing cases normally have red brown or orange brown oval markings.

Distinct features

  • Females normally chew into maize grains when they lay their eggs throughout most of their adult life up to one year.
  • Each female may lay up to 150 eggs in her lifetime. Development time ranges from about 35days under optimal conditions to over 110 days in unfavorable conditions.
  • Eggs, larval and pupal stages are all found within tunnels and chambers bored in the grain. It is difficult to detect infestations early as the larval stages feed on the internal parts and adults emerge from the grain leaving large irregular edges.
  • The sex pheromone released by the females tends to attract males.
  • The pest causes hollowing of whole previously undamaged grains .During heavy infestation, only the grain hull is left along with the powdery white frass. Grains that float in water often indicate larval damage.

image courtesy pest net

How to differentiate a maize weevil from other pests

  • Presence of wings beneath the elytra and circular rather than oval, punctures on the prothirax. (difference with granary weevil)
  • The end of the body of the maize weevil is more rounded than from the large grain borer. In addition, its mouthparts are beak like and antennae elbowed.

Image courtesy research gate

Cultural Control Methods

  • Good store hygiene
  • Cleaning the store before harvest
  • Removing and burning infested residues
  • Fumigating the store to eliminate residual infestation
  • Harvesting maize as soon as it matures
  • Use of resistant cultivars.
  • Removal of adult insects from the grain by sieving
  • Addition of inert dust such as ash and clay can help reduce insect number through desiccation

 

Biological control measures: These include some parasitoids, fungus and bacterium.

 

How to control infestation during storage

Before storage

  • The maize should be harvested as soon as its mature, dry the grain and re-dry during storage . The moisture levels should be about 12%.
  • The storage rooms need to be clean
  • Collect and dispose spilled grain in or around the storage area.
  • When using bin for storage ensure to remove all grains before re-using and for sacks don’t reuse those used for previous harvest.
  • Small amount grains should be stored in plastic containers.

 

After storage

  • Infestation can be located using sticky traps around the storage room or warehouse. The source should be located and destroyed by wrapping the foods in heavy plastic bags or in sealed containers and buried deeply in the soil.
  • For small infestations, freezing for several days, then heating for 24hours is effective
  • Sieving can also be done to remove adult weevils though it is labor intensive.

During storage it is important to store the produce in low oxygen and carbon dioxide enriched atmospheres.

Fumigation with phosphine or methyl bromide is effective in large scale stores. Pesticides are poisonous so it’s important to follow the instructions on the labels.