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What Are Maize Weevils?

By Caitlin Shih
Updated Jun 04, 2024
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Maize weevils, or referred to in the United States as greater rice weevils, are a species of beetle bearing its name from its status as a larger relation of the rice weevil. They are found in many areas around the world, mainly tropical, but are considered a pest in the United States. Maize weevils are generally anywhere from .09 to .15 inches (2.5 to 4 millimeters) and their four red or yellowish spots are usually visible on the back. They are known for attacking most crops and food items pertaining to grain, and while they usually breed within the grain, they can breed within other types of crops as well. Preventing and controlling infestations can be difficult and typically requires scrupulous monitoring in order to eliminate infestations at their root before they get out of hand.

The maize weevil is, for the most part, distributed in tropical areas around the world, but has since become established in more temperate climates such as areas in North America. Maize weevils are especially common in countries where maize is a prominent crop, such as Brazil, Argentina and Morocco. It has become a fairly established pest in the United States, and it has been reported in eastern Canada, specifically Ontario and Quebec.

Young maize weevils are white and legless with fleshy larva when they hatch out of their eggs. Adult maize weevils can be colored in the range of brown to black and are most identifiable by the four spots on their wing covers, which tend to be more distinctive than the rice weevil's spots. The maize weevil's snout is thin and long and its antennae are elbowed in structure, facing forward. They bear much similarity to rice weevils, but are essentially larger, stronger versions with sturdier, more efficient wings.

Maize weevils are capable of consuming and living in any type of grain or seed apart from maize and rice, including wheat, chestnuts, peas, and rye. The maize weevil can also consume processed versions of grain, not just live crops, including cereals, macaroni, and noodles that have been left out in humidity. In terms of breeding, maize weevils are also capable of laying their eggs in fruits that have been stored in a humid environment, as their tolerance for moisture is wider than their relations' are.

The breeding process of maize weevils often causes significant damage for the owner's grain. Typically, the female maize weevil will chew open a hole in the grain kernel and deposit her egg there, one egg per kernel. She also secretes a waxy substance that plugs the hole, and when the larva hatches, it immediately feeds and eventually emerges outside to begin again. An adult maize weevil can live for five to eight months, and females can lay several hundred eggs in their lifetimes.

The nature of the breeding process makes it difficult to detect signs of infestation with the naked eye. Preventative strategies usually work the best. Humidity is a large part of the maize weevil's habitat, so keeping grain-related items dry and clean works well in combination with monitoring and quickly disposing of any infected grain.

One can usually test to see if some grain has been attacked by seeing whether it floats in water. If it is lightweight and floats, it could be indicative of the hole the female has bore in it. For large infestations, one may need to apply more serious measures, such as a thorough and scrupulous cleaning of all cracks, corners and areas near the infected grain in addition to regular insecticidal tactics.

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Discussion Comments
By Markerrag — On Apr 01, 2014

Are those at all related to the dreaded boll weevil? If so, those things are no joke. Nothing can cause a cotton farmer to cuss more than a field full of boll weevils. They are hard to get rid of and multiply faster than a field full of rabbits with calculators.

How on earth did the maize weevil make it's way to the good old U.S. of A and do they thwart typical control methods as easily as cotton-chomping weevils?

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