Pest of Rice (Sitophilus Oryzae) | Zoology Optional Notes for UPSC PDF Download

Distribution of Sitophilus Oryzae (Rice Weevils)

Rice weevils, also known as Sitophilus Oryzae, are insects that have a cosmopolitan distribution. They originated in the Far East region and can be found anywhere with favorable physical conditions for their growth. They tend to infest grain storages and processing plants, targeting various grains such as wheat, oats, rye, barley, rice, and corn. They can also be found infesting beans, sunflower seeds, and dried corn. It's important to note that rice weevils do not bite or damage wood.

Identification of Rice Weevils

Rice weevils have chewing type mouthparts, and their most significant identification feature is their long snout. Adult rice weevils are reddish-brown in color and have irregularly shaped pits on their thorax. They also have four light spots on their wing covers. During their larval stage, rice weevils are legless and have a white to creamy white color with a small head. The pupa stage of rice weevils resembles the adults, with snouts and other characteristic features.

Life Cycle of Rice Weevils

• Egg: Female rice weevils lay their eggs in crevices of kernels or dust. Each female can lay about 4 eggs per day and a total of about 250-400 eggs during its 5-month lifespan. The eggs hatch in 3 days.
• Larva: The larvae feed inside the grain kernel for 18 days. This is the stage where the insect grows, consuming several times its own weight and periodically moulting to increase in size.
  
• Pupa: The pupa stage lasts for 6 days, during which the pupa undergoes significant internal and external changes. Some species of rice weevils enclose the pupa in a cocoon constructed by the larva.
• Adult: The emerged adult rice weevils are between 0.1 and 1.7 cm long. They have three pairs of legs and their bodies are divided into head, thorax, and abdomen. The adults move and penetrate deeply into the bulk of grains, becoming widely distributed.

Feeding Habit and Development of Rice Weevils

Female rice weevils drill a tiny hole in the grain kernel to deposit their eggs, which is then plugged with a gelatinous substance. Inside the grain kernel, the eggs hatch into young larvae that migrate towards the center of the grain. The larva feeds, grows, and develops into a pupa inside the grain. The pupa undergoes major internal and external changes to develop into an adult, which emerges through the hole of emergence. The emerged adults are ready to mate and continue the generation.

Damage Caused by Rice Weevils

Rice weevils are highly destructive pests of stored grain, completely destroying the grain. Their attack is evidenced by surface heating of the grain, dampness that may cause germination, and the presence of numerous adults.

Control Measures to Avoid Rice Weevils

• Remove infested food products.
• Discard heavily infested material.
• Repackage material into new infection-free containers.
• Placing the products in the freezer for several weeks may help kill adults and larvae.