Rice is a common food staple around the world, with an estimated 500 million tonnes grown every year. Rice is mainly self-pollinating, but also benefits from additional pollination by bees and other insects.
But other living things can also be important to rice growing. For example, in Asia ducks are often added to rice fields, as they eat all the weeds, which would otherwise flourish in the rice paddies. Ducks don’t like the taste of the rice plants so they leave them alone, and they are light enough to walk about in a rice paddy without damaging the crop.
However in the later stages of the rice season, the bitterness of the rice flowers starts to reduce, and the ducks begin to eat the rice plants. But this is easily solved as the farmers then eat the ducks. Circle of life and all that.
Spiders are also a potentially important ally to rice flowers. Rice fields are often attacked by pests, such as the yellow stem borer, which can infest a rice field and reduce the yield by up to 50%. But a bit further up the food chain are wolf-spiders, who see the yellow stem borer as lunch. So farmers often try to attract more spiders, by surrounding their fields with areas of natural habitat for the spiders, in order to encourage them to help protect their crops.
As the number of yellow stem borer pests increases, so does the number of spiders. But how do the spiders know where to go to find the fields with the most pests?
It turns out this is due to something called herbivore-induced-plant-volatiles. Which is a terrible name for something which is actually very cool.
When a rice plant is attacked by a herbivore, which in this case is the yellow stem borer, it emits a chemical, known as a volatile. And this chemical compound is detected by nearby plants, who then prepare themselves for the attack. Tests have shown that rice plants exposed to HIPVs are naturally more resilient to pests. So rice plants are actually able to warn each other of incoming threats.
And if the idea of plants talking to each other isn’t mind blowing enough, it looks like wolf spiders have evolved to also pick up the chemical alerts. So when the rice plants emit the chemical signal to warn each other, spiders also pick up the signal and head to the rescue.
Unfortunately, this delicate natural balance is often disrupted by chemical pesticides, which are very effective against pests such as the yellow stem borer, and are also very cheap and convenient. But the pesticide approach isn’t exactly a precision weapon, as they also kill or damage all other living creatures in the area. For example, many pesticides are banned in the EU because they have been shown to cause irreparable damage to the nervous systems of bees.
It is tempting to blame the farmers for their use of pesticides, and on large commercial farms this criticism is probably fair, but on small family farms in developing countries, it is a harsh economic reality that pesticides are sometimes the only way to keep rice farming viable. And with over 80% of the world’s farms under 2 hectares, this is a big problem.
So unless governments step in, it looks like the only solution is to come up with viable alternatives. Could fields be ‘vaccinated’ with HIPVs to provide a barrier to pests? Or is this just the sort of meddling with nature that caused the pesticide problem in the first place?
The research continues…
