Storage Pests
A multitude of insects is adapted to the relatively dry environment of stored rice. Rice grain infesting insects can develop at grain moistures as low as 8%. They not only consume large quantities of grain but they reduce the value by altering the perception of quality. Insect activity also changes the environment in the bin to make it more conducive to fungal growth. Principle insects infesting stored rice include the rice weevil (Sitophilus oryzae), the lesser grain borer (Rhyzopertha dominica), and the confused flour beetle (Tribolium confusum). Milled rice products may also become infested with indianmeal moth (Plodia interpunctella).
Rice weevils have long snouts with chewing mouthparts at the end. They are dark brown and about an eighth of an inch in length. Egg, larval, and pupil stages are spent inside the rice kernel. Generally there is only one larva per seed. To the naked eye there is little evidence of damage until the adult emerges from the hollow seed. The rice weevil is capable of flight but can also be transported in infested lots of grain.
The lesser grain borer can be one of the most damaging insects found in stored rice. Its body is cylindrical, about 1/8 inch long, with a distinctive helmet-like hood over the head. Larvae develop inside the rice kernel and are therefore invisible during most of their life cycle. Grain dust and a sweet must odor characterize the presence of the lesser grain borer. Accumulated and compacted dust can lead to poor aeration in the bin and a greater potential for grain spoilage.
Adult confused flour beetles are 1/6 inch long, shiny and reddish-brown. Larvae are light tan with darkened heads. The presence of broken kernels provides a suitable environment for larval development. When agitated the confused flour beetles secrete chemicals called quinones, which have a pungent odor, and cause infested grains to turn pink.
Indianmeal moths eat cereal grains, grain products and several other food products. The outer portion of the wings is reddish-brown with irregular dark bands. The hind wings have a fringe of hair. The young feeding larvae leave silken threads that tend to pull the rice kernels together. As the infestation grows the layers of threads cover the grain.
Control of storage insects depends on cleaning of storage facilities between harvests, carefully controlling the temperature and humidity, and the use of recommended control measures.
Other pests associated with rice production
Crayfish are crustaceans that burrow into levees and around irrigation structures. Crayfish occasionally eat rice seeds and seedlings. Crayfish damage to rice seeds can be distinguished from other pest damage because the seed is crushed or macerated. Their economic damage to rice, however, is principally through the disruption of irrigation systems, especially by burrowing around rice boxes. After the field is drained crayfish burrow into the soil, producing soil chimneys around the edge of the burrow. Currently no pesticides are registered for the control of crayfish. One control strategy that is available is to drain the field and drive the crayfish into their burrows in order to allow the seedlings to establish.
Mosquitoes can breed in rice fields, but their larvae do not feed on rice. Complete surface drainage, elimination of seep areas, use of the mosquitofish (Gambusia affinis), application of the bacterial product Bti (Bacillus thuringiensis var. israelensis), and synthetic chemical applications (by mosquito abatement districts) help reduce mosquito populations. Rice growers are required to make an effort to control mosquito populations in their fields.
ˆ top of page ˆ
