Rice weevil


The rice weevil is a stored product pest which attacks seeds of several crops, including wheat, rice, and maize.

Description

The adults are usually between 3 and 4.6 mm long, with a long snout. The body color appears to be brown/black, but on close examination, four orange/red spots are arranged in a cross on the wing covers. It is easily confused with the similar looking maize weevil. The maize weevil is typically somewhat larger than the rice weevil, but rice weevils as large as the largest maize weevils and maize weevils nearly as small as the smallest rice weevils have been found. Some external features can be used to differentiate the vast majority of adults, but the only reliable features are on the genitalia. Both species can hybridize. The genitalic structure of hybrids is unknown.
Rice weevil Maize weevil
Longitudinally elliptical punctures on pronotal dorsumPunctures on pronotal dorsum typically nearly circular, rarely elliptical
Pronotal punctures are separated by a flat, median, longitudinal puncture-free zonePronotal punctures are nearly equally spaced apart, and pronotum typically has no median puncture-free area
Less than 20 pronotal punctures along the approximate midline, running from neck to scutellumMore than 20 pronotal punctures along the approximate midline, running from neck to scutellum
Scutellar elevations typically closer together compare to their longitudinal lengthScutellar elevations typically farther apart compared to their longitudinal length
Scutellar elevations typically extend longitudinally approximately more than halfway down the scutellumScutellar elevations typically extend longitudinally approximately halfway down the scutellum
Proepimera meets behind the fore coxae and along the posterior edge, has a distinct notch along the posterior edge at the site of the meeting pointProepimera meets behind the fore coxae and has a barely discernible notch along the posterior edge at the site of the meeting point
Male aedeagus is smooth and shiny on the dorsal surfaceMale aedeagus has two dorsal, longitudinal grooves
Epipharyngeal rods of larvae have virtually the same width throughoutEpipharyngeal rods of larvae tapering apically
Lateral lobes of Y-shaped sclerite of female genitalia not tapering and rounded at apexLateral lobes of Y-shaped sclerite of female genitalia tapering and pointed at apex
Less than 5 sensory organs at the tip of the labial palps of larvaeMore than 5 sensory organs at the tip of the labial palps of larvae

Biology

Adult rice weevils are able to fly, and can live for up to two years. Females lay 2-6 eggs per day and up to 300 over their lifetime. The female uses strong mandibles to chew a hole into a grain kernel after which she deposits a single egg within the hole, sealing it with secretions from her ovipositor. The larva develops within the grain, hollowing it out while feeding. It then pupates within the grain kernel and emerges 2–4 days after eclosion.
Male S. orzyae produce an aggregation pheromone called sitophilure to which males and females are drawn. A synthetic version is available which attracts rice weevils, maize weevils and grain weevils. Females produce a pheromone which attracts only males.

Control

Control of weevils involves locating and removing all potentially infested food sources. Rice weevils in all stages of development can be killed by freezing infested food below 0 °F for a period of three days, or heating to 60 °C for a period of 15 minutes.