Research on the Use of Bats in the Ecological Management of Insect Pests in Rice Paddies, Girona, Spain

Project location: SPAIN, Barcelona
Project start date: October 2016 - Project end date: October 2017
Project number: 2016-028
Beneficiary: Associació Per A L’estudi I Al Divulgació Del Medi Ambient Galanthus

Crop losses caused by agricultural pests are and have always been an important worry for farmers. However, there are many natural predators such as bats that are able to regulate naturally an important part of these pest species.
If they are not kept under control, agricultural pests can threaten crop viability, producers’ livelihoods and even their ways of life. The industrialization of agriculture has led to a simplification and degradation of agricultural spaces and habitats (agro-ecosystems), which in turn has resulted in a weakening or disappearance of populations of natural predators able to control agricultural pests in a natural manner. The restoring of the functioning of these agro-ecosystems, which would permit them to act once again as balanced natural systems, is the key to achieving healthier, more ecological and sustainable agricultural production. The creation of appropriate spaces where bats can shelter and breed in agricultural areas may well become a cheaper and more ecological way of biologically reducing plague species. 

In the past decade, the key role played by bats in the control of agricultural pests has become much better known. Despite calculations that, if bats suddenly disappeared from North America, it would be necessary to invest 3.5 billion dollars annually in pesticides to maintain agricultural yields, the general public is largely ignorant of this function. In Thailand, the effects of bats on rice production demonstrate that bats guarantee alimentary security for 26,000 people annually due to their ability to reduce crop loss. Bats are present on all the continents inhabited by humans and so appropriate management aimed at preserving and enhancing bat populations could ensure a decrease in agricultural plagues in almost any part of the world.
In recent years, the Galanthus Association and the Granollers Natural Science Museum have carried out a series of experiments in the Ebro Delta (NE Iberian Peninsula) in which the use of artificial bat boxes has led to an increase in bat populations in an area of paddy fields. At the same time, there was also a fall in the numbers of the striped rice borer, one of the main rice pest species in this region, which meant a saving of around €45/ha in chemical treatment. 
This experiment reveals that it is possible to improve bat populations in agricultural areas and that such improvements can lead to a reduction in levels of agricultural plagues — or, at least, in those plague species that have a winged nocturnal stage. The next step is to extend this type of biological control to other types of crop and environments. The project presented here is aimed at studying the factors that determine the success of measures taken to enhance bat populations, and under what circumstances bats act as effective controllers of pest species (rice borers and mosquitoes) associated with rice cultivation.

This project has twin objectives. Firstly, it aims to improve understanding of how local environmental conditions affect the way that bats control agricultural (moths) and human (mosquitoes) plagues associated with rice cultivation. Secondly, it examines what type of environmental conditions are required if populations of bats linked to rice cultivation are to be improved by providing bat boxes. Both lines of work are essential if this biological control system is to be implemented successfully in other regions.

This project will be conducted in the rice fields of the regions of Alt and Baix Empordà (Girona, Spain). The experimental design consists of comparing the paddy fields where bat boxes have been installed with others of similar characteristics (in terms of size and surrounding landscape) where no habitat improvements for bats have been carried out. In both cases, the evolution of the populations of bats and the target pest species (mosquitoes and rice borers) is monitored. At the same time (but at a certain distance to avoid influencing the comparative study), bat boxes will be placed around rice paddies in as many different environmental settings as possible in an attempt to determine under what circumstances the placing of boxes is most successful.
One challenge to be overcome is the public perception of bats, which in western culture continues to be negative. An explanation of the ecosystem services they provide is an essential step in helping to popularize bats, although a parallel campaign designed to increase public awareness of these mammals is also required if their populations are to be respected. The second main challenge is linked to the methodology: how can we overcome the fact that many vital environmental variables may as yet be unidentified and so will not be included amongst the tested variables, or may be very difficult to measure. Some of these variables could have an unexpectedly important effect on bat and/or the studied pest populations, and this possibility must be taken into account when analysing the data generated and drawing conclusions.
This experiment will tackle for the first time a fundamental question that will shed more light on a generalized application of this biological control methodology: how to determine under what specific circumstances bat populations can be enhanced by installing bat boxes for breeding. A better understanding of the relationship between habitat and successful box-occupation will enable us to not only optimize the placing of bat boxes in the future but also to appreciate more fully what other habitats and landscape elements favour the presence of bats and, thus, what other improvements in the environment should be sought. 

The main objective of this project is to obtain enough robust scientific data to be able to publish our results in specialized scientific journals, thereby encouraging the application of the knowledge gained in other agricultural areas in the Mediterranean.
We also hope to help raise local rice farmers’ awareness of the virtues of ecological pest control methods and hope likewise that the towns and villages affected by the mosquitoes originating from rice fields will choose to employ our methodology as part of their regular pest control procedures.
We anticipate that our methodology will provide data that will enable us to determine with confidence under what conditions high bat-box occupation rates can be achieved in agro-ecosystems, thereby making it exportable to other regions and crops.
An awareness-raising campaign directed at the general public aimed at explaining the viability of ecological pest-control methods will also be set up.

The project, which received a grant from The Nando Peretti Foundation, Delegació a Catalunya will run for four years (2016–2019) to give time for changes to occur in bat populations in areas in which boxes have been installed, and to guarantee that the impact of bats on pest populations are large enough to be measurable. 

This project aims to improve understanding of the conditions required for improving bat populations in rice-growing areas in the Mediterranean region, and to evaluate the threshold beyond which bats start to act as effective controllers of pest species (rice borer moths and mosquitoes) associated with rice production. The data generated will enable us to increase the possibilities of success when this biological control system is implemented in other areas and regions, and will also provide important guidance for applying such techniques in areas outside the Mediterranean.