Several species of Cicadellid and Delphacid bugs
Why is it a problem? Leaf hoppers and plant hoppers are sap-sucking insects that at high densities can desiccate and ultimately kill rice patches of rice plants (called hopper burn). However, it rarely if ever requires management in Bhutan. Some species can also transmit viruses, but rice viruses, although present, are currently not considered to be important in Bhutan.
Where and when is it a problem? There are several species in Bhutan. Hopper burn is rare and reported cases are of small patches, typically up to a few terraces in size. One patch of 2-3 acres was reported in Trashiyangtse in the early 1990s. This was caused by the white-backed plant hopper. There is currently no data available from lower elevations where rice is less important. It is expected that hoppers will be more common there, as might viruses.
Only the four most commonly encountered hoppers on rice are described below.
Brown plant hopper (Nilaparvata lugens)
- Adults (4-6 mm in size) are ochre-brown in colour dorsally and deep-brown ventrally. All males are winged but females can either have full-sized or truncated wings. Adults typically feed near the base of tillers.
- Nymphs are brown.
- Eggs are crescent-shaped, white and inserted into the midrib or leaf sheath.
White-backed plant hopper (Sogatella furcifera)
- Adults (about 3 mm long) are yellow-brown to black, with a typical white spot on the middle of the thorax. All males are winged but females can either have full-sized or truncated wings. The forewings have a characteristic dark brown mark at the tip of the clavus.
- Young nymphs are creamy-white but as they mature, they develop distinct dark-grey and black markings on their abdomens.
Green leaf hoppers (Nephotettix sp.)
- Adults are bright green.
- Nymphs are more yellowish-green.
Zigzag leaf hopper (Recilia dorsalis)
- Adults have a very characteristic zigzag pattern on their forewings.
Adults and nymphs suck plant sap. The resulting feeding damage predisposes the plant to fungal diseases. They also secrete honey dew secretions which encourages the growth of sooty moulds.
Severe infestations can result in “hopper burn”, the yellowing, browning and drying of the plant as a result of feeding by large numbers of hoppers. Older leaves turn progressively yellow from the tip to the midpoint of the leaf, then gradually dry up and die. Hopper burn typically begins in patches but can spread rapidly as the hoppers move from dying plants to adjacent plants. It normally does not appear until the crop reaches the milk or dough stage. In its vegetative stage rice can tolerate high hopper densities without any obvious damage symptoms. In severe cases hoppers can cause total crop loss.
Confusion with other pests: Only the four species of hoppers that are most likely to be encountered in Bhutan are described here. The hopper burn symptoms could potentially have other causes so it is important to confirm the presence of high densities of hoppers on or near affected plants. There may also be sooty mould at the base of the plant in the case of at least some hopper species. In most cases specialists are required to confirm species identifications.
Lifecycle: Both nymphs and adults suck the sap from their hosts. Generation times can be rapid, so they can pass through many generations in a year, and populations can build up rapidly under optimal conditions.
Dispersal: Adults fly. Females of some species have a short-winged (flightless) stage and a winged stage which normally forms later in the season. Some species are migratory, and can travel great distances.
When can damage be expected? Outbreaks are rare and isolated. In other countries hopper outbreaks have been associated with the development of irrigation systems to allow year-round rice cropping (thus continuous hopper build-up), excessive fertilizer usage that results in higher hopper populations, and the use of insecticides that kill natural enemies.
Hosts: Hoppers typically feed on wide range of grass species. The brown plant hopper feeds only on rice, while Nephotettix nigropictus prefers other grass species to rice.
Management methods can differ between species of hopper, and with the size and timing of the outbreak. Please contact NPPC for specific advice in the event of a serious outbreak.
Monitoring for hoppers should be part of regular pest scouting within the rice crop. Estimate the number of hoppers per hill (plant) across about 10 plants. Shake each plant vigorously and count the hoppers that fall into the water. Management may be needed if average hopper densities are greater than ten per hill.
Effect of variety
Studies elsewhere show that varieties can differ in resistance but this has not been studied in Bhutan.
- A range of management methods have been developed in other countries where hoppers are more serious. Some of these require considerable effort so may not be justified in Bhutan.
- Best practice use of nitrogenous fertilizers, such as split application.
- Manage grassy weeds and remove volunteer rice plants to help prevent some hopper species from existing between rice crops.
- Crop rotation can provide effective control in areas where one rice crop per year is grown.
- Use recommended planting spacings. Close spacing induces populations of some hoppers to build up.
- Hoppers have many important predators and parasitoids that help keep populations in check. This should be protected through minimising pesticide use.
- Minimise the use of pesticides as over-use can result in rapid pest resurgence as a result of the destruction of natural enemies
- Spraying of damaged plants will be ineffective if hoppers have already moved away.
- Apply chemicals only if the insect population reaches 10 hoppers per hill. Spray (dimethoate at 2 ml per 1 litre of water) where the hoppers are. Only patches where hoppers are dense need to be sprayed.
Image acknowledgements: Rice knowledge Bank, IRRI