Life Cycle of the Maize Weevil Sitophilus zeamais

Sitophilus zeamais, or the maize weevil, is a species of weevil that is commonly found in maize crops. The larvae damage maize crops by developing within an individual grain, eating it away from the inside out until mature, and then reproducing, releasing more crop-damaging larvae. The maize weevil is a danger to both growing crops and stored maize.

Distribution

The maize weevil is slightly larger than the rice weevil and is more prominently marked. It is also a considerably more proficient flier, allowing it to distribute itself more easily. Its main endemic areas are areas that are tropical and temperate, where maize is grown.

Reproduction

The adult female Maize weevil lays her eggs within the actual grain kernels of the maize at a rate of 25 per day spread over 100 days. The maize weevil bores into the grain with her long snout, deposits her ovipositor and lays a single egg. The eggs hatch in approximately 3 days, depending on the humidity and moisture content of the grain.

Development

The larvae, which are approximately 4 mm, white and legless, begin to eat the internal contents of the maize while developing, which takes approximately 18 to 23 days. At this point, the larvae become pupae, and they begin the transformation into the adult weevil form, much like a butterfly. This process takes approximately 6 days. During these 6 days, the pupae do not eat or move.

Maturation

The weevil then emerges, by cutting a small circular hole in the grain, as an adult and begins the process over again. The entire process takes about 30 to 45 days to complete. The adult maize weevil will also feed on the maize during its lifespan, which is approximately 5 to 8 months long, before dying.

Control

Although the weevil is not a parasite, the damage it can inflict upon a crop can be devastating. The relatively short life cycle of the maize weevil allows it to reproduce at such a rate that grain stores and crops can be decimated in one season. Because the weevils infest foodstuffs, it is impractical to kill them with pesticides. The safest method for the eradication of the pest is removal. Any maize that has been deemed contaminated should be sealed in heavy plastic and disposed of. Grain storage facilities should be inspected regularly for signs of infestation. Another method is to freeze or super heat gain stores, although this method may be impractical for larger facilities and may damage the germ layer required for seeds to be utilized for planting. For these situations, good ventilation is required to reduce the amount of available moisture in the grain to reduce the ability of the weevils to reproduce.

References

• Maize Weevil
• Ohio State University Extension Fact Sheet: Granary and Rice Weevils
• Rice Weevil & Maize Weevil (Sitophilus oryzae & Sitophilus zeamais)