Bats’ Economic Services

Roberto Forte, Adriel Sierra & Helio Quintero

The appearances of bats tend to make us feel very unrelated to them. It is hard to think of a social or economic beneficial of bats to humans, since for century they have been associated to blood sucking vampires and more recently as potential reservoir hosts and vectors of diseases or parasites (Klimpel & Mehlhorn, 2014). Bats are highly diverse worldwide, showing astonishing morphology, lifestyles feature and feeding behaviors that are related to their importance in ecological functions such as pest control, seed dispersal and soil fertilization. During the Tropical ecology course during a lecture and field night observation, we were introduced to the bat’s high diversity in Panama and its importance. Based on our interest and curiosity we decided to explore and discuss the functional importance of bats to human economy and health, in order to break current negative view to these organisms.

Bats as effective pest management

Recent studies (Kolkert et al., 2020; Whitaker Jr & Odegard, 2019) in insectivorous bats sustain their potential as crop’s pest controls. This service of control of plagues can be valued in trillions of dollars globally through the decrease of crops damage, reduction of the use of chemicals, and increasing the yield. It is estimated that a bat can eat 30%-100% of its body weight in prey every night. Bats like to feed on places where there is an abundance of prey, such as areas in crops where there is an outbreak of plague (Kolkert et al., 2020). Advances in molecular methods have facilitated the precise identification of the diet of these bats, thus allowing them to establish predator-prey interactions. Kolkert et al., (2020) applied the Metabarcoding methodology to identify how diverse the insectivorous community was in transgenic cotton crops and what type of insects (benefits or pests) are consumed by bats. The study evaluated the effectiveness of insectivorous bats as plague controllers through the investigation of their diets. Bats were captured at the limits of cotton plants by using mist nets and harp traps. They were placed in bags and kept until the next nightfall. Fecal pellets (2-8) were removed from each of the trapped bats. A total of 58 individuals from 7 different species of insectivorous bats were captured. Of the total of individuals captured, only in 24 the sex was identified, 50% male and 50% female.

Figure 1. View of Phyllostomidae (Artibeus jamaicencis) bat captured in Gamboa on the STRI Laboratory.

Kolkert et al., (2020) stated that the most prefer insects by bats included: Lepidoptera (moths), Coleoptera (Bettles), Homoptera/Hemiptera (true bugs), Orthoptera (grasshoppers amongst others), Diptera (flies), Araneae (spiders) and Ixodidaes (ticks). Moreover, they concluded that moths are in important component of bat’s diets; however, bats determine what to eat based on the availability of food.  For instances, Cicadellids where an important component of bat’s diet when they were most available. Cicadellids contribution to bats diet in September was very limited (up to 1.5%), this behavior corresponded with the low availability of Cicadellids during this month. Similarly, insects such as beetles and true bugs were consumed in less quantity during September. Another conclusion reached by Kolkert et al., (2020) was that small insects (such as flies) with less energy in relation to the energy expended by them during the predation process were captured in lower amounts even when vastly available. Species of flies of greater size were the most preferred.

Bats guano as a source of fertilizers

Bats feeds on various sources from fruits, insects, fish, mammals and blood. One interesting fact is that most bats often have a special place where they eat and consequently defecate, accumulating massive amount of fecal matter (guano) in a single place. Due to this behavior people have taken advantage to collect large amount of guano to fertilize poor soils for agriculture. Guano is rich in nitrogen, phosphorous and potassium which are principal components for plant growth making them an inexpensive natural resource for local agriculture. Guano was used extensively around the globe before the production of artificial fertilizers in 1915. In the 1800s century mining for Guano cause the destruction of bat caves and consequently reduction in guano production in Peru after the monopolization of the resource. Extensive mining of guano in caves can negatively impact bats caves in various ways and the ecosystems it beholds. This critical situation made the International Union for Conservation of Natures (IUCN) in 2014 to create sustainable mining policies. Sustainable extraction of guano in developing countries could be a solution to boost local agriculture where buying artificial fertilizers represent a relatively big expense causing negative incomes in their local productivity.    

Bats pollination to improve tequila production

The mention that bats are great pollinators is often accompanied by images of them visiting flowers in the forest or somewhere distant without establishing a direct connection with the applicability of their role to our daily lives. An example that shows us how these winged companions, in exercising their natural function, are capable of affecting our economy is the relationship of some species of Mexican bats with agave plants (Agave sp.), responsible for generating tequila. These bats are one of the main pollinators of agave (Trejo Salazar et al., 2016), however, due to the techniques that some producers use for their cultivation, agave populations have low genetic diversity (since they do not allow them to flourish and the production of more agave is carried out asexually) (Eguiarte et al. 2013), this makes the crops a vulnerable target for the attack of pathogens and as a side effect can reduce the availability of food for these nectarivores bats. A fairly novel method proposed to solve both problems lies in allowing at least 5% of the agaves in one hectare to flourish, thus giving, on average, nectar to 89 bats per night. Taking into account the amount of agave hectares in Mexico, it was estimated that this could represent food for more than two million bats per month and at the same time increase the genetic diversity of both agave crops and wild populations of the genus that are also threatened by their low levels of genetic diversity (Trejo Salazar et al. 2016). The producers who have adopted these measures are benefited with a label that certifies that their tequila is “Bat-friendly” (figure 2), which gives them an added value to their product while supporting the conservation of two wonders of this world, bats and tequila.

Figure 2. Logo of bat-friendly tequila Project.

References

Eguiarte, L. E., Aguirre-Planter, E., Aguirre, X., Colín, R., González, A., Rocha, M., & Souza, V. (2013). From isozymes to genomics: population genetics and conservation of Agave in México. The Botanical Review, 79(4), 483-506.

Klimpel, S., & Mehlhorn, H. (2014). Bats (Chiroptera) as Vectors of Diseases and Parasites. Facts and Myths. Springer, 1-187.

Kolkert, H., Andrew, R., Smith, R., Rader, R., & Reid, N. (2020). Insectivorous bats selectively source moths and eat mostly pest insects on dryland and irrigated cotton farms. Ecology and Evolution, 10(1), 371-388.

Trejo-Salazar, R. E., Eguiarte, L. E., Suro-Piñera, D., & Medellin, R. A. (2016). Save our bats, save our tequila: industry and science join forces to help bats and agaves. Natural Areas Journal, 36(4), 523-530.

Whitaker Jr, J. O., & Odegard, D. (2019). Food of the Free-Tailed bat, Tadarida Brasiliensis, from congress avenue Bridge, Austin, Texas. The Southwestern Naturalist, 64(1), 20-22.