What to Do When Summer Grains Get Buggy? Causes, Prevention and Eating Advice

Once summer arrives, the large quantities of grain crops at home start to get bugs and crawl everywhere, which makes people panic. So what should you do when grain crops get bugs? Can they still be eaten? How do you prevent it? Why are bugs so common in summer?

Common grains and cereals in supermarkets include rice, millet, glutinous rice, red rice, black rice, corn, oats, buckwheat, flour and other varieties. Among common grains, rice and millet, as raw-material grains, can generally be cooked and eaten directly; while processed grains such as wheat, corn and oats need to be ground into flour or rolled into flakes before eating.

Generally, grain products in supermarkets are mainly divided into packaged products and bulk products. Because packaged products have been pre-processed, they rarely get bugs during their shelf life; bug infestations mainly occur in bulk grains and in packaged grains after the bag has been opened.

1. Can grains and cereals still be eaten once they have bugs?

If we find that the grains stored at home already have bugs, what should we do? Whether they can be eaten depends on the specific situation.

(2) Generally speaking, the insect bodies themselves in infested grains are harmless, and as long as the infestation is not too serious, they can be eaten. For example, rice weevils feed on rice and do not bite humans, so if there are not many insects, you just need to “sift them out” or wash the grain clean, and it can be eaten with confidence. There is no need to throw away a whole bag of rice just because a few insects got into it, otherwise it would cause a great waste.

So is it harmful to eat the larvae and the invisible eggs? Rest assured, neither larvae nor eggs carry pathogens, and they do no harm to the human body. If you accidentally eat them, it does not matter.

However, in some cases, bug-infested grains do pose a threat to human health. For example, when adult red flour beetles gather together, they produce a secretion called benzoquinone, which is carcinogenic; if this kind of adult insect appears in the grain, do not eat it. Also, the pupae of the Indian meal moth spin silk, which easily makes flour clump and spoil; if this kind of adult insect appears in the flour, do not eat it either.

(2) After grains are infected by insects, their original protective outer layers are destroyed, making them susceptible to infection by certain plant pathogenic fungi. These pathogenic fungi often produce mycotoxins harmful to human health, such as the notorious aflatoxin and the vomitoxin produced by Fusarium, etc. The threat these toxins pose to human health is far greater than that of the insects. Therefore, when infested grains are also clumped and moldy, do not eat them.

2. How to prevent grains at home from getting bugs?

First, experts suggest improving storage conditions and keeping grain storage containers clean to prevent rice weevils and other storage pests from entering, thereby reducing the chance of infestation. Methods to prevent bugs include the following:

1. Grain storage tools should be clean and tightly sealed. It is best to put grains in jars, earthenware pots or buckets, and to have tight-fitting lids. If using cloth bags, put a plastic bag over the outside of the cloth bag and tie the opening tightly.

2. Soak the cloth bag in boiled Sichuan pepper water, then put the grains in the bag after it has dried, and wrap some fresh Sichuan peppercorns of the current year in gauze and place them at the top, middle and bottom of the grain, then tie the bag opening tightly. This both prevents mold and repels insects.

3. Mix kelp and rice in a weight ratio of 1:100, and take the kelp out once a week to dry off moisture. This can keep the rice dry and mold-free and can also kill rice weevils.

4. Put a few crab shells, turtle shells or large onion heads in the storage box, or sprinkle a 1-cun-thick layer of plant ash, cover it with white paper or gauze, seal the container, and place it in a dry, cool place; this can also achieve the purpose of preventing insect damage.

5. If the amount of grain stored is small, you can also protect it with insect-proof packaging or by adding long-acting odor insect repellents to the packaging bag.

6. When the stored grains already show signs of bugs but have not yet become clumped and moldy, you can remove the small insects by the following methods:

(1) Sift them out

When adult insects appear in grains, the most commonly used method is to “sift them out”. Pass the infested grain through a sieve to sift out the small insects, burn the removed insects, and clean the grain container, paying special attention to insects in the crevices so as to root out the hidden danger.

(2) Freeze them

Rice and flour that have been stored for a long time are most prone to getting bugs in summer, while the infestation rate is lower in winter. Based on this, put the remaining rice and flour stored after winter into clean bags respectively, and send them in batches into the freezer compartment of the refrigerator, letting them endure 24 hours of “harsh winter”. Rice and flour treated this way are unlikely to get bugs when summer comes, probably because rice weevils and flour worms cannot withstand the ruthlessness of the “harsh winter” and perish on their own in the “harsh winter”.

(3) Air them out

Put the grains, rice and flour in a cool, ventilated place, and insert chopsticks into the infested rice and flour; the insects deep inside will crawl out from the warmer rice and flour. This method is simple and convenient, but takes a long time to remove the insects.

3. Why do grains and cereals easily get bugs in summer?

Whether raw-material or processed grains, once eggs are present, when temperature and humidity reach certain conditions, the eggs will hatch into adults. There are generally three sources of eggs.

1. When the grain is still in the field, it already carries eggs. Although wheat, corn and oats go through impact steps during processing, which can crush and kill adult insects in the grain, some carried eggs (mainly present in the embryo) cannot be killed, and they enter the finished product along with it, hatching into larvae under suitable conditions.

2. Pests and eggs exist in granaries, grain-loading tools, equipment and transport vehicles. But this probability is relatively small, because cold-chain transport is now mainly used, and under low temperatures the eggs do not easily survive.

3. There may be insect sources in environments such as warehouses, supermarkets and kitchens. Some eggs hide at the bottom of rice jars, in the seams of rice bags, in wall cracks and in floor cracks; when the environment is suitable, the eggs hatch into adults. If other grain products in the supermarket get bugs, the adults may go “visiting” the neighboring grains, causing those grains to get bugs.

In summer, because the ambient temperature and humidity are relatively high, the eggs dormant in the grains begin to stir, first hatching into “plump and white” larvae, and after a longer or shorter time, molting into adults, completing their life cycle.

Common grain infestations include rice weevils and Indian meal moths, among others. Rice weevils mainly grow in granular grains such as rice and millet, while Indian meal moths are commonly found in various grains.

The rice weevil, also known as the snout beetle, belongs to the family Curculionidae in the order Coleoptera, and is a major pest of stored grain. Its adult is about the size of two sesame seeds, brown-black, with a long, pointed snout and six legs, commonly found in rice and legume grains; the larva is rice-white and about three to five millimeters long. Adults gnaw on the grains, and larvae bore inside the grains. It harms rice, paddy, wheat, corn, sorghum and so on. The life cycle of the rice weevil is about 20-50 days; larvae hatch from mid-to-late June to early-to-mid July and bore into the grains, with the larval stage lasting about 30 days; they pupate in mid-to-late July, with the pupal stage lasting 7-10 days; adults emerge in early August.

Larvae and adults of the rice weevil

The flying insects produced in flour and other grains mainly include two kinds. One is called the red flour beetle; its larva is cylindrical, and its adult is reddish-brown or brown with a relatively hard shell. The red flour beetle is an insect of the family Tenebrionidae in the order Coleoptera, distributed in most provinces and regions of China and in tropical and warmer regions of the world; its optimum development temperature is 27-30°C; at a relative humidity of 70%, it completes one generation in about 27 days at 30°C; it mainly harms flour. This insect has stink glands that secrete a foul liquid, giving the flour a musty, fishy smell, and its secretion also contains the carcinogen benzoquinone.

Adult red flour beetle

The other is called the Indian meal moth, which is distributed all over the world. In China, it has not yet been found in Tibet, but it is distributed in all other provinces, cities and autonomous regions. The larva of the Indian meal moth is cylindrical, and the adult has wings and can fly. The larva of the Indian meal moth likes to eat the embryo of grain kernels, often spinning silk to bind grain kernels and excrement together and forming a web to seal the surface, causing it to clump and spoil. Sometimes we find something like a spider web in grain stored for a long time; that is the “masterpiece” of the Indian meal moth.