BATS, INSECTS AND PLANTS

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Mexican free-tailed bat (Tadarida brasilensis Mexicana)
Drawn from a photograph taken by Amanada Lollar, Bat World Sanctuary, Texas

Most of the world's one thousand plus bat species feed on insects. That is a positive endorsement for the much-maligned bat in our famine stricken world.

In 1992 McGavin estimated that insects destroy 10 to 20 percent of world food crops anually. In some areas three-quarters of food crops may be destroyed by insects.(6)

Samways (1994) writes that about 30 percent of crops are destroyed (despite application of pesticides), that some 200 species of insects are serious pests and that worldwide there can be 10,000 insect species that cause some crop damage. That number of species is about 1 percent of the described insect species of one million. The actual number of insect species could be from 2 to 10 million. (9)

Schoonhoven (2005)writes that there are 1000 insect species that damage crops in the United States and 9000 species worldwide. He states that less than 5 percent of those insects are serious threats which would be 50 insect species for the US and 450 species worldwide.(10)

Agricultural pesticides are expensive to develop and expensive to buy. They have undesirable effects on humans and other animals. Pesticides have not eradicated a single pest species.(6) Clearly, natural pesticides such as foraging bats are valuable.

Besides atttacking crops, some insects transmit dread diseases. Some insect larvae eat a variety of organic materials including buildings, furniture and books. In 1998 Peter McEwen, an entomologist, said "Insects are a scourge on humanity."(4)

IN DEFENSE OF INSECTS

Insects can present a very strong case for their appreciation and protection. That defense is, in part, as follows:

Insects pollinate many valuable food plants. In his introduction to The Forgotten Pollinators (1996) E.O. Wilson wrote:"Eighty percent of food plants worldwide depend on pollination by animals, almost all of which are insects." (1)

A 2006 report indicates that 35 percent of global food production is from plants which rely on animal pollination, including many fruit crops, vegetables, coffee and cocoa.(7) Without adequate numbers and species of insects, countries that are dependent on imports for these foods could experience shortages. "For example, the consumption of fruit in the EU outstrips production by 20%." (5)

For better or for worst, palm oil is an important world commodity. Samways queries: ". . . where might we find another weevil like Elaeidobius kamerunicus which has replaced hand pollination of oil palm to the value of US $13 million per year?"(8) Perhaps there is an insect that could be recruited to pollinate the passion fruit in Brazil's hand-pollinated commercial crops. Bees had the task but insecticides and loss of habitat have destroyed that work force. Of course, taking pollination employment from human workers would wreak economic disaster upon some of the human species.

Insects are an important link in many food chains. Some consumers at the top of the chain, human beings, include nutritious insects in their diets.

Insects help to recycle organic matter and prevent the countryside from disappearing under a drift of slowly decaying organic debris.

Insects produce silk, dyes, shellac, honey, wax and pharmaceutical products.

McGavin says that insects have contributed to the knowledge of:

• aeroengineering
• architecture
• ecology
• engineering
• evolution
• genetics (6)

While some insects prey relentlessly on man's food crops, other insects prey on those crop-eating insects. Evans and Eberhard wrote in their book, The Wasps, ". . .(it is) said of Hymenoptera (bees, wasps, ants) as a whole that man could scarcely survive without their assistance in regulating populations of plant feeding insects." (2)

In a general sense, McGavin states that the disappearance of honeybees alone would lead to " . . . rapid destruction of terrestrial ecosystems." (6)

Estimates of the total number of insect species ranges from one million to ten million.(9) The possible number of species and a conversion to insect biomass seem to attest to the importance of insects on earth. Whatever exists in such abundance must have a sizeable effect on the earth's biological functioning.

THE CONTRIBUTION OF INSECTIVOROUS BATS TO THE CONTROL OF CROP-EATING INSECTS
(HAVING ESTABLISHED, IN PART, THE IMPORTANCE OF INSECTS TO SURVIVAL OF THE EARTH)

The fact that over 700 species of bats prey on night flying insects is documented. The species of insects and larvae that prey on food crops is documented. It is more difficult to identify the specific insect species that are captured by specific bat species.

During the early years of bat research, bats could be killed or captured and euthanized and their stomach contents examined. That process is no longer condoned in British Columbia. (8)

Even when a direct approach was in use, insect species were difficult to identify. As Gardner said, " . . . the comminuted remains of insects and small vertebrates are usually difficult to identify, a problem intensified by the habit of many bats to discard, and often the only diagnostic, parts of their prey." (3)

Insect families can be identified from bat droppings by microscopic examination, whether the droppings are from a roost or from bats captured and eventually released. The same problem of insect identification to species exists. The insect remains in the droppings are a mish-mash of anatomical parts. DNA analysis is required to identify insect parts in bat droppings to species. (See articles 5 and 9 below.)

A HISTORY OF INSECT CONTROL BY BATS AS DOCUMENTED BY "BATS"
THE QUARTERLY PUBLICATION OF BAT CONSERVATION INTERNATIONAL
http://www.batcon.org

Bat Conservation International was founded by Merlin D. Tuttle in Milwaukee, Wisconsin in 1982 and subsequently took up permanent residence in Austin, Texas, USA. Merlin D. Tuttle is Founder and Executive Director of Bat Conservation International.

1. Makin, David and Dr. H. Mendelssohn, Insectivorous Bats Victims of Israeli Campaign, BATS, Vol. 2, No. 4, December 1985.

In 1958 Israel's 27 known species of insectivorous bats were protected. The Egyptian fruit bat (Rousettus aegyptiacus)was not protected. That fruit eating bat was apparently damaging ripe fruits in Israel's commercial orchards. To deter its activities roosting caves of mixed bat species were fumigated.

The insectivorous bat population plummeted, the Noctuid moth population, composed of several species, exploded. "Within 15 years, populations of insectivorous bats decreased by approximately 90 percent."

2. The Bats of Israel Yesterday and Today, BATS, Vol. 7, No. 4, Winter 1989-1990

This article reported that the insectivorous bat decline in Israel had continued and that the increase in Noctuid moth numbers had "required extensive chemical control."

3. Murphy, Mari, "Bats: A Farmer's Best Friend",BATS, Vol. 11, No. 1, Spring 1993

Tony Koch, an organic farmer in Oregon, encouraged bats to join his 54 species strong bird population to reduce pesticide use. Birds were accommodated with 800 boxes, bats with 21 multiple residence houses. The bats' insect target was to be Heliothis armigera, the corn earworm moth, a night flyer. Koch's pesticide spraying diminished from 13 times a year to two times a year. Since the bats joined the birds, corn earworms diminished from up to four a year on an ear of corn to zero.

John O. Whitaker, Jr. analyzed bat feces from Tony Roch's bat roosts and identified Diptera and small Lepidoptera. "Positively identifying individual species . . . is not possible from a fecal analysis."

*(NOTE: In later publications Heliothis armigera is identified as the Old World species of the corn earworm or cotton boll moth. Helicoverpa zea is the New World species.)

4. Whitaker, John O., Bats, Beetles and Bugs; More big brown bats mean less agricultural pests, BATS, Vol. 11, No. 1, Spring 1993

John O. Whitaker, Jr.,professor of life sciences at Indiana State University, stated that "In one summer season the 150 bats of an average midwestern maternity colony can easily eat 38,000 cucumber beetles, 16,000 June bugs, 19,000 sting bugs, and 50,000 leafhoppers." This tally was characterised as "very conservative" and omitted many other species.

Cucumber beetle adults forage on corn, spinach and vine plants. The larvae, corn rootworm, is more destructive. June bugs eat leaves, June bug larvae feed on roots. Leafhoppers siphon off sap and distribute diseases.

These insects can contribute from 40 to 100 percent of the diet of big brown bats.

5. McCracken, Gary F., Bats Aloft: A study of High-Altitude Feeding, BATS, Vol. 14, No. 3, Fall 1996

Gary McCracken calculated, based on the caloric needs of a Mexican free-tailed mother and pup, that " . . . a million nursing free-tailed bats eat about 10 tons (20,000 pounds)of insects every night." In the 1960's the largest maternity caves of Texas housed 100 million migratory Mexican free-tailed bats.

Corn earworm moths are a major agricultural scourge on corn and cotton. Do Mexican free-tailed bats feed on corn earworm moths that are migrating from Mexico en route to Texas and central North America?

Radar studies and radio microphones on weather balloons established that bats fly at altitudes from 600 to 3,200 to 10,000 feet (200 to 1000 to 3000 metres). McCracken says: "The (corn earworm) moths fly at the same altitudes as bats . . ."

In the 1996 efforts to establish Mexican free-tailed bats as a major predator on corn earworm moths evidence was being assembled from "nitrogen and carbon isotopic ratios of guano from Carlsbad and Eagle Creek Caves" and the development of " . . . a DNA marker that allows us to identify gene fragments from corn earworms in the feces of bats that have eaten these pests."

6. McCracken, Gary F., John K. Westbrook, Paul G. Schleider, The Virtual Bat;Digital deception repels insects and attracts hungry bats. BATS,Vol. 20, No. 1, Spring 2002

Some species of moths drop to the ground or abandon an area in response to bats' echolocation calls. Other research suggests that " . . . the risk of predation, as perceived by insects when they hear bat echolocation calls, can disrupt the mating and reproductive activities of the insects."

Paul Schleider, USDA, built a Virtual Bat which was " . . . programmed to produce a repeatedly randomized sequence of calls at the frequency, duration, and intensity of the real thing. The result sounds exactly like a large number of bats feeding on swarms of insects."

The result? When the Virtual Bat was parked in experimental plots of corn and cotton there was up to 50 percent reduction in moth activity compared to controls. There was also an increase in bat activity.

7. Kiser, Mark and Selena, Cultivating Bats; BCI Research explores airborne alternatives to pesticides. BATS, Vol. 20, No. 1, Spring 2002

Frank and Teresa Bibin were losing 30 percent of their Georgia pecan crop to the hickory shuckworm (Cydia caryana)annually. They erected 11 bathouses which accommodated up to 3000 bats and shuckworm moth numbers have declined to "only a few". In 3 years they "found minimal evidence of shuckworm larvae or damage".

In 2002 Bat Conservation International was sponsoring two long-range projects to amass hard evidence supporting "effectiveness of bat houses for pest reduction on organic farms."

Rachel Long, University of California, found that "central California pear orchards near major bat roosts suffered only 5 percent damage from codling moths, while damage to orchards more than two miles away increased to 60 percent."

8. Long, Rachel, Protecting Cotton; Bats attack pests over Australian cotton farms, BATS, Vol. 22, No. 4, Winter 2004

Narrabri, New South Wales, Australia: "The major pest of cotton in Australia is the cotton bollworm."

Rachel Long observed the activities of six species of insectivorous bats foraging for moths over cotton fields. The majority of the bat activity was over fields that were "adjacent to irrigation ponds with old-growth trees". Bat activity was reduced over fields ". . . completely cleared of native vegetation for miles around."

Rachel Long observed moths diving and departing when bats arrived.

More research is required as a comparison of bat activity with the numbers of bollworm eggs on cotton plants was indecisive. Drought conditions reduced bollworm activity. More research is required. However, the value of roosting trees for insectivorous bats near insect decimated cotton crops was clearly established.

9. Lopez-Damian, Leonardo J., Protecting Mexico's Corn;Bats help keep pests at bay, BATS, Vol. 25, No. 4, Winter 2007

Mexico depends on their corn crop for the population's bodily sustenance and employment. A study is in progress to ". . . document the Mexican freetails' role in reducing corn pests."

The insect culprits are the cotton bollworm (Helicoverpa zea) and the armyworm moth (Spodoptera frugiperda).

This study aimed to document the Mexican freetailed bats' diet by capturing bats and collecting their droppings.

1500 bats were captured on return from their night foraging, their droppings collected and analyzed. Forty insect families representing 15 orders were identified from fecal samples. From the three subject caves the order Lepidoptera (moths and butterflies) "accounted for approximately 63 percent of total volume of the Mexican free-tailed bat diet . . ."

"Our next step is DNA analysis of a subset of fecal samples to document the bats' consumption of specific crop pests."

10. Kalka, Margareta, New Respect for Tropical Bats; Demonstrating the value of insect-eating bats, BATS, Vol. 26, No. 2, Summer 2008

Margareta Kalka worked in Panama forests and on Panama cacao plantations.

Kalka worked with Elisabeth K.V. Kalko on an earlier study. That study showed
" . . . that almost 50 percent of prey items, mostly plant-eating insects, would not have been detected by traditional methods of bat-diet analysis."

In this study Kalka used a netting system for plants with bat-excluded plants, bird-excluded plants and controls. Ten weeks of observations established that bat-excluded plants were populated by 153 percent more insects than their control plants, non-bat-excluded plants. Bird-excluded plants were populated by 65 percent more insects than were their controls.

Visually, bat-excluded plants were three times more damaged than bat- control plants. Bird-excluded plants were two times more damaged than bird-control plants.

Kalka observed that an analysis of bat feces does not identify the soft bodies of caterpillars and immature insects. In her work with Elisabeth Kalko they established that " . . . plant-eating insects account for more than 70 percent of the diet of the common big eared bat (Micronycteris microtis), a leaf gleaning, caterpillar-eating bat, in a tropical lowland forest in Panama."

In a different study on a cacao plantation, Kalka fashioned 90 tables from cacao leaves and attached them to the branches of 45 trees. Caterpillars were detained on the tables by Tanglefoot.

Half of the tables were controls. The remaining tables were loaded for birds at sunrise and reloaded for bats at sunset.

"Predation rates were more than three times higher at night than during the day . . ."

11. Williams-Guillen, Kimberly, Bats and Birds' A potent team for coffee plantations, BATS, Vol. 26, No. 2 Summer, 2008

Kimberly Williams-Guillen investigated the efficacy of bat gleaners on a coffee plantation in southern Mexico.

Williams-Guillen identified 15 species of insectivorous bats on the site.

Williams-Guillen and her assistants counted the insect populations of 88 coffee plants during two eight week experiments. They had no-bird plants and no-bat plants.

Bats and birds both controlled insect populations. The effect of birds was greater than bats during the dry season. The effect of bats was greater than birds during the wet season.

NOTE: Both of the research projects above, Numbers 10 and 11, have been published in Science, a leading scientific journal.