Pest Control Keys

Scientists from the University of the Basque Country and the Doñana Biological Station examined a group of cave-dwelling bats (Miniopterus Schreibersii) in the Sierra de San Cristóbal, in Puerto de Santa María, Cádiz.

During August and September, the swarm kills about 60,000 moths each night. Bats play an important role in combating agricultural pests. This is the conclusion reached by the University of the Basque Country (UPV/EHU) and the Doñana Biological Station (CSIC) in a new study in which they examined the diet of a colony of cave bats (Miniopterus Schreibersii), which lies in a cave in the Sierra de San Cristóbal in Puerto de Santa María (Cádiz).

Miniopterus Schreibersii It is the most sociable cave bat species in Europe and forms colonies of up to tens of thousands of individuals. It is also an important flyer and can reach a range of more than 30 km from its hiding place. The San Cristóbal colony in particular had a number of 3,000 to over 7,000 individuals during the study period. The colony is known to hunt as far south as Doñana National Park.

This large colony can exist and sustain itself in an area so humanized by the characteristics of the species that forages in open spaces.“said Carlos Ibáñez, researcher at the Doñana Biological Station.
This means it is independent of the type of plant substrate and also has great mobility.“.

According to Ibáñez: “Although the environment is highly humanized, it is heterogeneous and provides sufficient alternative resources over time“. Two thirds of the area is intended for a variety of agricultural crops and urban areas. The rest consists of natural vegetation areas including protected areas such as the Bahía de Cádiz Natural Park and the southern area of ​​the Doñana National Park.

Analysis of bat nutrition

The study is based on DNA analysis of prey remains in bat guano samples using super barcodes. As a result, the scientific team identified just over 160 species of arthropods in the diet of these bats, 39 of which are considered pests.

Most of its diet consists of 24 species, 11 of which are pests, mainly moths, which in the caterpillar stage attack various crops and forests (pine forests, oak forests and cork oak forests).

These species also include green stink bugs, which infest cotton and many fruits and vegetables. Two disease-carrying prey items were also found in the diet of these bats. One of them is the common mosquito Culex pipiens, which transmits the West Nile fever virus and is reportedly infecting people in the region. The second is the grasshopper Neophilaenus campestristhat transmits the phytopathogenic bacteria Xylella fastidiosais considered the greatest global threat to agriculture in Europe.

Consumption of agricultural and forestry pests

The composition of the diet changes throughout the year due to the availability of different prey. The most commonly consumed insects, in turn, are associated with a variety of habitats and crops. This means that bats use a variety of available hunting environments and change them over time. Therefore, while foraging, bats may attack successive population explosions of pests attacking different crops or forests.

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After identifying the species eaten by the bats, the team calculated the bats’ pest consumption, taking into account daily food intake, colony size, and the proportion of each prey species’ diet at each site. In total, this colony consumed 1,610 kg of insect pests from May 11th to October 10th. More than 90% correspond to 10 species.

To understand the meaning of these numbers, the research team focused on the specific case of the processionary moth caterpillar (Thaumetopoeapityocampa), a common pest in pine forests.

In the study area, pine forests only accounted for less than 3% of the area used by the colony. Pine forests mainly form small forests and even occupy gardens in urban areas. The largest masses are found at distances of more than 25 km, for example in Doñana National Park.

The processionary, in turn, has only one reproductive cycle per year, which means it is only available for a limited period of time.

In this region, the maximum number of flights takes place in the second half of August to the first half of September. “During these weeks they were by far the main prey and appeared in more than 90% of the samples despite the small area of ​​the pine forest.“, commented Carlos Ibáñez.
During these days the colony reaches its maximum size of 7,200 individuals, partly due to the incorporation of the young, which begin to fly independently during the month of July, but also to the incorporation of individuals from protected areas further east.“. The increase in population could be due to the large number of processionary moths.

It is estimated that the colony eats up to 6 kg of moths per day during these days. Since each moth weighs 0.1g, this means there are about 60,000 processionary moths or imagos. In the entire season, the bats would destroy approximately 173 kg of processions (equivalent to 1,730,000 moths). Since there are about 10,000 hectares of pine forest, about 173 imagos per hectare are destroyed.

This colony is protected by law. M. Schreibersii It is a sensitive species (CEEA) and the protected area is in the Natura 2000 network with ZEC code (ES120030 Cuevas de la mujer y de las Colmenas). “However, this does not ensure long-term preservation.”explained researcher Carlos Ibáñez.

Threats include the possible change in the use of the enclave, the protection of the cavities in which it winters, such as the Hundidero-Gato and Motillas complexes, the increasing pressure from active tourism activities inland and the strong wind force on farms in your vital area.”

reference:

Joxerra Aihartza, Nerea Vallejo, Miren Aldasoro, Juan L. García-Mudarra, Urtzi Goiti, Jesús Nogueras, Carlos Ibáñez. “Aerospace-foraging bats forage seasonally in different habitats.”. Scientific reports 2023, 13:19576; Scientific reports

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