The rice is never sterile. It gets contaminated during growth, harvesting, processing and packaging. Then, favourable conditions will allow all kinds of organisms to grow and flourish. It is certainly not " generatio spontanea" !

see also this link 

https://en.wikipedia.org/wiki/Spontaneous_generation  

Sir

I' m extremely happy to see the answer to my quarry. I' m 

thankful to you for your prompt reply. I' m looking forward 

for more replies.

From 

Shaista Jabeen

During harvesting the rice kernel is already "contaminated". What I do know is that weevils bore into the core of the kernel and they lay eggs in the kernel. Depending on temperature and humidity, these eggs will grow and hatch into weevils. Typical in humid environment in south east asia it takes about 8weeks. The warmer the faster it grows. The modus operandi of weevils is it bores into the rice kernel and prevents detection. 

Larvae are a slightly different category. The attraction point is the silos or any storage areas. During the storage (say in rice silo at the rice processor) the moths fly into the silos and lay their eggs. This eventually get carried into the rice and eventually growing. The larvae may not be efficiently removed during processing, especially in silos after rice sorting operations. Seriously speaking, its an indication of 1) silo cleanliness 2) rice that has not been properly clean/sorted as such the larva gets in. It hibernates and after a long time, it grows to a moth. 

Sir

Is there any solution to drive these moths and larvae from the rice.How 

to protect our products from such weevils.

1) Silos, conveyor belts, whatever production equipment must be cleaned regularly. the areas to watch out for are the "dead" ends like silo walls, edges, conveyor belt tunnel walls, production floor walls. Typically one does not pay much attention to such areas. Problem is that the insects fly onto such areas and lay their eggs there. SO have a regular inspection mechanism to inspect walls, dead ends, silos. I use to do this on a regular basis weekly. Recommend to clean the said stuff monthly basis. Workers climb into silos to clean walls of silos where many of such insects harbours. This is probably the area that has most impact. 

2) inspection - one should regularly walk around in the warehouse and production floors. If you encounter flying moths etc, means its already contaminated. The more you see the more contaminated. Its my way of knowing how bad the rice are contaminated

3) air control in production floor or rice production facility should be controlled in such a manner that at any time there is no direct expose to outside air. Deploy air locks. If really necessary for direct expose due to heat and humidity, use proper screens. 

4) If you rice is polished, sorted (color sorter) would have remove such matters. So after production the rice should be stored in a more controlled environment, recommend that you do not store next to unprocessed rice. Pests are known to "fly". Practice FIFO. 

5) Install insect pest killer/electrocutor etc. Talk to your pest controller they can recommend you the areas to look at. I often put extra sticky pads near electrocutor, thereby you can monitor your moth count. Often leave the electrocutors on at night when the whole warehouse and production is stopped. The light in the dark attracts them to the electrocutors. Talk to a good pest controller. I come across good ones that are passionate to help and some just up to rip you off.

6) Fumigation - the rice/pulse are typically fumigated in enclosed rooms (similar to gas rooms) or using tarpaulins. Fumigants are injected in a stored for a certain time. This is common for raw rice or finished rice. I recommend that you also do that to production equipment, esp silos, conveying tunnels/belts/buckets ... the gas can seep thru crevices and assist. The safety is important as methyl bromide is lethal.

The above mostly tackles moth issues. There is nothing you can do once its in the rice. For weevils, the same applies.But for weevils it is very well know that rice that has been microwaved or frozen can "kill" the weevils making them sterile. 

hope it gives you lead to work on and research