Dorylus orientalis
Crop: Generalist, but can seriously damage vegetable crops including potato and Cole crops
Why is it a problem? Red ants live in the soil and can feed on the roots and tubers of a wide variety of plants. They make holes on the surface of potato tubers, (chewing damage ) reducing tuber yield as well as market quality. They can also kill seedlings of a diverse range of plants, including Cole crops.
Where and when is it a problem? Red ants are mainly a problem at lower elevations (about 600 m asl), where they can be a serious problem across significant areas. There have also been sporadic reports of red ant damage farms at higher elevations, such as near Talo, Punakha (2,300 masl).
IDENTIFICATION
Adult: Red ants are large and look like wasps. Worker ants are sterile females that are 3-6 mm long and have no functional eyes. The queen is brown and wingless. Males are reddish-brown to dark brown and have two membranous wings.
SYMPTOMS
Red ants make holes on the surface of potato tubers. Damaged plants wilt (quite similar to that caused by bacterial wilt) and can eventually die. Initially, wilting will be temporary, occurring during the day and then recovering. Ants should normally be found in association with affected plants.
Confusion with other pests: Other harmless ant species can be present in fields, but red ants are the only ones that will be closely associated with roots and tubers. Red ants can also be superficially confused with termites, which are also harmless. White grub also cause surface feeding damage to potato tubers, but the holes caused by white grubs are much larger.
BIOLOGY
Lifecycle: Red ants are social insects with a queen, female workers, and males. They live in a nest, usually built 1.5–2 m under the ground. Subterranean worker ants forage for food along underground trails.
Dispersal: Adults have winged forms.
When can damage be expected? Once established, red ants can become a serious problem in a field.
Hosts: Red ants can feed on the underground stems, tubers, and roots of a wide range of plants, including potatoes and cole crops.
MANAGEMENT PRACTICES
Red ants are one of the pests in Bhutan that has received little research. Hence, there are currently no recommended management practices for this species in Bhutan. Red ants are also a serious problem in Nepal and are relatively well studied there. Management practices developed there are provided below but have not yet been tested in Bhutan.
On-farm monitoring
The presence of red ants can be indicated by wilted plants and damaged tubers, and confirmed by the presence of red ants around affected roots. Locating the actual nests is very difficult.
Effect of variety
Unknown.
Non-chemical management
- Soil drenching and foliar spray of fermented extract of leaf and tender stem of Yucca sp. and Urtica dioca (stinging nettle) were effective to control red ants in potato field (Bhandari, 2011).
- Flooding of fields may work but is often impractical when crops are not being grown in rotation with paddy rice.
Chemical management
- The lowest tuber infestation was achieved with three applications of chlorpyrifos 20 EC at 5 ml/lit of water around the root zone, beginning 45 days after potato tuber sowing and spaced 10 days interval (Dash, 2016). Check this link for more information: https://www.researchgate.net/publication/262529571_Development_of_Management_Stratigies_against_Red_Ant_Dorylus_Orientalis_Westwood_of_Potato?_esc=publicationCoverPdf&el=1_x_3&enrichId=rgreq-1f91aea019da337c8e883cbb7a7ba1fe-XXX&enrichSource=Y292ZXJQYWdlOzI2MjUyOTU3MTtBUzozMjg1ODMzNzQ0OTE2NTFAMTQ1NTM1MTc4OTc1Nw%3D%3D
Version: NPPC 2022. Red ant V1.0. Bhutan Pest Factsheet. www.PestsofBhutan.nppc.gov.bt. Date produced: 15 December 2022. Contact: nppcsemtokha@gmail.com
Image acknowledgements: NPPC.
