Maize weevil
Sitophilus zeamais (Motsch.)

Order: Coleoptera
Family: Curculionidae
Acronym: SZE

Ecology

The maize weevil is distributed in tropical environments. However, it is becoming established in temperate environments. In Canada, it is reported in Ontario and Quebec. The maize weevil is commonly associated with feeding on corn, rice and on other raw or processed cereals. It infests standing crops before the harvest. It is the dominant Sitophilus species in tropical subsistence agricultural systems. The maize weevil is closely related to the rice weevil.

Damage

Damage is distinctive. The maize weevil causes damage similar to that of the rice weevil and granary weevil. The larva feeds within the kernel and consumes the endosperm. The adult leaves a large, ragged exit hole in the kernel and feeds on damaged kernels.

The adult maize weevil gathers and reproduces in stored grains. This produces heat and moisture which can lead to mould development and invasion by other insect species.

Life history

The adult is small; it is 2.5 to 4 mm long. It is dark brown. The adult has a distinctive long snout and elbowed antennae. It has 4 distinct reddish patches on the elytra. It can fly.

Breeding conditions are temperatures between 15 and 34°C and 40% relative humidity.

The female lays most eggs within the first 4 weeks after it emerges. It lays one egg in each grain. The female chews a small hole in the grain to lay the egg and covers it with a waxy secretion. It lays approximately 150 eggs in its lifetime.

The larva is white, grub-like and legless. It develops and pupates in the kernel. Under optimal temperature conditions between 27 and 31°C, the maize weevil’s life cycle takes 5 to 8 weeks to complete. Development stops if the temperature falls below 17°C.

Once the adult emerges from the kernel, it mates and lays eggs immediately. Adults live from 4 to 12 months.

Control

An infestation of maize weevils can be difficult to detect because the insects behave in an aggregative fashion and the immature stage occurs only in the kernel.

To prevent an infestation, you should routinely monitor for signs of an infestation; clean bins regularly; treat bins with a registered insecticide; and properly dispose of any grain debris found outside of the storage area.

To control an established infestation fumigate; apply insecticide; and lower the temperature of the commodity to at least -5°C for a minimum of 12 weeks.

Images

Adult Maize weevil