- N H G Jacobsen1 and E du Plessis2
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1Division of Nature Conservation, Private Bag X209, Pretoria 0001
2Department of Physiology, Medical School, University of the Witwatersrand, Johannesburg 2001 - 1990
Fruit bat damage in litchi orchards in the Transvaal was studied during 1972-1977. Two species were involved, namely Epomophorus wahlbergi and Rousettus aegyptiacus, but the latter predominated. Each bat consumes 8-9 litchis per night. On occasions up to 2 200 Rousettus bats entered an orchard, consuming up to 309 kg of litchis per night. Damage was found to be localised and less than that estimated by the fruit growers. Various control measures were tested, but only mist nets proved to be effective in curtailing numbers.
Summary:
- The study, conducted between 1972 and 1977, assessed damage caused by two fruit bat species in Transvaal litchi orchards: predominantly Rousettus aegyptiacus (Egyptian fruit bat) and Epomophorus wahlbergi.
- Each bat consumes 8-9 litchis per night, with up to 2,200 Rousettus bats in an orchard consuming up to 309 kg of litchis in a single night.
- Damage was localized and less extensive than estimated by farmers; some orchards showed no damage while neighboring ones did.
- Bats select ripe litchis, remove the skin, and consume the flesh, often wasting fruit by dropping whole litchis.
- Rousettus aegyptiacus forage up to 24.5 km from caves to orchards, arriving about 20-40 minutes after sunset.
- Control methods tested included shooting, noise deterrents, lights, scent repellents, predator calls, and mist nets.
- Shooting and noise/firecrackers were ineffective or counterproductive as bats quickly resumed feeding.
- Scent repellents and ultrasonic sounds did not deter bats effectively.
- Predator calls initially disrupted feeding but bats quickly adapted and resumed normal feeding.
- Mist nets were the only effective control measure tested, capturing significant numbers of bats but being labor-intensive and requiring repositioning to maintain effectiveness.
- Harvest timing affects damage; harvesting nearly ripe fruit reduces bat attacks.
- Fruit bats are considered a nuisance mainly affecting small producers and home gardens, not a major threat to commercial production.
- The bats play an important ecological role in seed dispersal and pollination, making widespread destruction undesirable.
- Control efforts should be localized and economically justified; large-scale eradication is neither feasible nor recommended.
- Collaboration across regions would be necessary for effective control of migratory bat populations.