Photo 3. Damage ('deadheart') to rice stem by Chilo auricilius (damage to Scirpophaga innotata is similar).
Rice white stem borer
Scirpophaga innotata. A moth in the Crambidae.
Restricted. Southeast Asia, Oceania. It is recorded from Australia, and Papua New Guinea.
Rice, and wild rice. Whether or not the moth attacks sedge species has been questioned.
Symptoms are similar to those of other rice stem borers (see Fact Sheets nos. 408, 409, 410). Newly hatched larvae tunnel down the plant between the leaf sheaths, killing the shoot and causing 'deadhearts'. The stems are easily pulled out (Photo 3). Later, the feeding at the base of the panicles may prevent emergence, or result in white unfilled grain of those that have emerged, a symptom called 'whitehead' (Photo 4). Scirpophaga innotata is a tropical species, occurring in regions with distinct dry and wet seasons.
The eggs are laid in groups of about 100 near the tip of the leaf blade and covered with hairs from the tip of the abdomen. A week later the eggs hatch and the off-white larvae have a faint dark line along the back and brown heads. The larvae are at first greyish-white, and when fully grown are white to yellowish, 25 mm long. During diapause the larvae move down into the plant base, most reaching 3-5 cm below ground. Development takes from 20-30 days. Pupae are white, and pupation takes from 6 to 9 days. Adults are white; male wingspan is 18-22 mm, whereas the female wingspan is up to 33 mm (Photos 1&2). They are nocturnal.
In some situations the larvae of Scirpophaga innotata go through a resting stage or diapause. For instance, in a dry season, they remain in diapause until it is broken by more than 10 mm of rainfall. Generally, it takes at least 3 months for larvae to form a pupae. If diapause and pupation occur without interruption (as occurs with single long-maturity rice), then large numbers of moths emerge in a short, 2 week, period. In countries where rice is double cropped and then fallowed or land is planted to a secondary crop (maize, soybean, peanut), and short-maturing varieties are grown, the moth only goes through diapause in the dry season.
There are infestations of 10,000-20,000 ha a year in Indonesia, with some major outbreaks similar to those of 1990 when considerable yield losses were recorded. Australia, too, has reported high losses of summer crops (October to May). Losses are greatest if attacks occur during the flowering stage.
Look for deadhearts and whiteheads at the vegetative and flowering stages, respectively. Because of similarity with other Scirpophaga species attacking rice, identifications should be done by taxonomists with expertise in the Lepidopteran pests of rice. There have been instances when Scirpophaga innotata has been confused with Scirpophaga incertulas, which has a much wider distribution. Scirpophaga innotata does not have spots on the forewings.
Countries not yet infested by the rice white stem borer should consider all likely pathways for entry, and apply quarantine measures accordingly. It is a mjor pest of rice, in particular. Many countries throughout Asia, Africa, the Americas and Oceania are at risk. Pathways of introduction are likely to be via produce contaminated by pieces of stem of the hosts infested with larvae or pupae.
In general, the rice white stem borer is parasitised and predated by the same natural enemies as other rice stem borers. Egg parasities are important and include species of Telenomus, Tetrastichus and Trichogramma. Predators include generalists, such as rove and carabid beetles, aquatic bugs, and spiders.
Cultural practices are particularly important against the rice white stem borer as insecticide applications often give variable results, with even systemic products only effective during the vegetative, tillering, stage.
Modern rice varieties that are relatively thin-stemmed, short, high tillering, and early maturing, may result in less damage from stem borers generally. This aspect is important as well-grown, vigorous crops can withstand 20% deadhearts and 10% whiteheads before yield is affected. In the case of the rice white stem borer, early planting can improve management where the crop is planted at the beginning of the wet season.
The use of insecticides risks destroying natural enemies. Use only as a last resort:
AUTHOR Grahame Jackson
Information (and Photo 4) from Rice Knowledge Bank. IRRI. (http://www.knowledgebank.irri.org/training/fact-sheets/pest-management/insects/item/stem-borer); and CABI Scirpophaga innotata (white rice stem borer) (2017) Crop Protection Compendium. (www.cabi.org/cpc); and from Pathak MD, Khan ZR (1994) Insect Pests of Rice. IRRI/ICIPE. Photo 1 Biodiversity India. Rice white stem-borer moth. (https://indiabiodiversity.org/observation/show/370837). Photo 2 11ANIC-04905 CSIRO/BIO Photography Group, Centre for Biodiversity Genomics. (http://v3.boldsystems.org/index.php/Taxbrowser_Taxonpage?taxid=211612). Photo 3 Anderson S, Tran-Nguyen L (2012) Gold-fringed Rice Borer (Chilo auricilius). (Source: N. Sallam DAFF Biosecurity.) PaDIL - (http://www.padil.gov.au);
Produced with support from the Australian Centre for International Agricultural Research under project HORT/2016/185: Responding to emerging pest and disease threats to horticulture in the Pacific islands, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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