In collaboration with the Natural Sciences Museum of Granollers in Spain, my research team has found that bats play a crucial role in protecting our rice crops. The rice borer moth (Chilo suppressalis) is one of the world’s most widespread and destructive rice pests. We discovered that bats, beyond consuming these moths, may further suppress damage by frightening them. Many moths listen for bat echolocation and modify their behavior where bats are heard. We quantified the economic value of bats in protecting one of the world’s most important crops.
To give some context, insectivorous bats can consume up to 80–100% of their body weight nightly1,2, and more studies are reporting the vital roles of these threatened predators of agricultural pests3,4,5.
Rice is often severely affected by meteorological events and by pests, from bacteria to fungi and insects. The rice borer moth is an especially serious pest6,7. This moth’s caterpillars can feed for up to 30 days inside rice stems, weakening the plant and preventing the proper formation of rice grains.
In 2015, a pioneering study led by Puig-Montserrat, from the Natural Sciences Museum of Granollers, documented the role of soprano pipistrelle bats (Pipistrellus pygmaeus) in controlling the rice borer moth in the Iberian Peninsula3. Bat boxes were used to attract soprano pipistrelles near the rice paddies, resulting in a significant decline in pests. In fact, since 2011, those farmers with bat colonies in their rice fields have no longer needed to use insecticides. As asked by Dr. Adrià López-Baucells, the principal investigator of that project, “Is there a more ecological, sustainable, and economical way to control a pest than this?”
Last year, our team quantified the services bats provide in rice paddies in Spain. We set two main project objectives: first, to quantify the economic value of pest suppression by bats as predators of the rice borer moth; and second, to evaluate the effect of bat ultrasounds on the egg-laying behavior of this insect pest.
During the summer of 2021, we used innovative experimental exclosures in rice plantations. An exclosure consisted of a structure covered by a mesh net that formed an exclusion cage. These prevented bats from hunting over the excluded rice area but allowed a normal insect flow in and out of the structure. To make it easier to understand, on a small piece of land we created a new agricultural world without bats. By assessing the productivity under these conditions, we were able to quantify the pest suppression potential of bats by comparing crop damage inside versus outside the exclosures.
We also assessed the effect of bat ultrasounds on the expected behavior of the rice borer moth when laying eggs. This moth is tympanic, and scientific evidence suggests that it can detect bat ultrasounds and change its behavior when bats are foraging nearby. However, in the case of the rice borer moth, this was only speculation. To test this hypothesis, we used small captivity boxes to keep moths alive and allow them to lay eggs during their adult stage. Half of the boxes were placed in a room isolated from any bat ultrasound, again simulating a world without bats. The other half were located in a different room and exposed to regular nocturnal bat ultrasounds.
And what did we discover? The preliminary results indicate that bats, such as common pipistrelles (Pipistrellus pipistrellus), significantly reduce rice borer moth damage on rice crops. Although our data are still being analyzed, and therefore are subject to possible change, our preliminary estimates indicate that the combined impact of bats (by predation and probably by ultrasound disturbance) may annually save 17–146 kg of rice per hectare. According to rice market values published by the Ministry of Agriculture, Fisheries, and Food of the Government of Spain, this translates to 93–110 €/ha/year. Extrapolating this at a national level, considering that there currently are 109,411 hectares of planted rice in Spain, bats could be protecting a total of 0.48–16 tons of rice each year in Spain alone. In economic terms, this means that healthy bat populations in agricultural lands may save 1.2–12.1 million euros per year just in Spain, even without considering the avoided pesticide costs related to a lower use of agrochemicals!
In parallel, our second study suggests that, as happens with other tympanic moths, adults of the rice borer can also detect bat ultrasounds and change their behavior. We found that, in the presence of bat ultrasounds, there was a significant effect on egg-laying. This resulted in smaller egg clutches (50% smaller on average!), meaning fewer larvae and higher yields. The consequences for farmers could be profound if bats indeed are both capturing moths and frightening others into laying fewer eggs.
Given the extent of bat decline combined with the recent onslaught of scary disease speculation, studies to better understand bat values are increasingly important. Promoting bats in agricultural areas may not only help farmers but also lead to a more eco-friendly and sustainable way of life that favors human health, food security, and biodiversity.
Carme Tuneu-Corral is a Catalan researcher who has been studying bats in Europe and Africa for six years. She is currently working on her PhD, focused on assessment of the ecosystem services provided by bats in agricultural lands. For the past two years, she has developed her research in rice fields in Spain, quantifying the effect of bats as suppressors of insect pests in this extraordinarily important crop. Her project has also led her to study the endemic bats of Madagascar, where she is currently working to identify which species provide the most pest control services to farmers. She also hopes to raise awareness of the essential roles these animals play in healthy ecosystems.
References
- Kunz, T.H., de Torrez, E.B., Bauer, D., Lobova, T., Fleming, T.H. (2011). Ecosystem services provided by bats. New York Academy of Sciences. 1223, 1–38.
- Kurta, A., Bell, G. P., Nagy, K. A., & Kunz, T. H. (1989). Energetics of pregnancy and lactation in free ranging little brown bats (Myotis lucifugus). Physiological Zoology, 62(3), 804-818.
- Puig-Montserrat, X., Torre, I., López-Baucells, A., Guerrieri, E., Monti, M. M., Ràfols-García, R., … & Flaquer, C. (2015). Pest control service provided by bats in Mediterranean rice paddies: linking agroecosystems structure to ecological functions. Mammalian Biology, 80(3), 237-245.
- Maine, J. J., & Boyles, J. G. (2015). Bats initiate vital agroecological interactions in corn. Proceedings of the National Academy of sciences, 112(40), 12438-12443.
- Boyles, J. G., Cryan, P. M., McCracken , G. F., & Kunz, T. H. (2011). Economic importance of bats in agriculture. Science, 332(6025), 41-42
CABI, current year. Invasive Species Compendium. Wallingford, UK: CAB International. www.cabi.org/isc
- Heinrichs, E. A., & Rangaswamy Muniappan, R. M. (2017). IPM for tropical crops: rice. CABI Reviews, (2017), 1-31.