Crop Pests & Diseases

Yellow stem borer (YSB) is a serious pest of rice throughout India and South East Asia. Stem borer occurs both in kharif and rabi seasons.
Moderate to severe incidence is noticed in nursery, planting to mid-tillering and panicle initiation stages. Heavy infestation results in 40-60 per cent yield loss.
Though considered predominantly as a monophagous pest, it has also has been reported from wild rice types, and other monocot weed plants present in the rice ecosystem.

DAMAGE SYMPTOMS

Symptoms of damage include presence of brown colored egg masses near leaf tip in nursery and early transplanted plants.
The egg masses are laid in oval patches of 80-150 eggs near the tip of leaf blade and they are covered with buff coloured hairs.
Tiny pale yellow larvae hatch out from the eggs in 5 to 8 days, enter the leaf sheath, feed for 2-3 days and then bore into the stem near the node.
Usually only one larva is found inside the stem. The larva grows for a period of 40 days and pupates inside the stem in a white silken cocoon for 7-11 days. The entire life cycle lasts for 35-50 days depending upon the environment. The adults do not feed and live for 4-10 days.

MANAGEMENT MEASURES

Use less susceptible varieties and adjust the dates of planting to evade the incidence of the pest.
Clip off the tip of the seedlings before transplanting and collect and destroyed stem borer egg masses present on the transplanted young rice plants
Soak the roots of the seedlings in 0.02 per cent chlorpyriphos for 12-14 hrs before transplanting to give protection from the attack of stem borer up to 30 days.
Avoid close planting and continuous water stagnation and pull out and destroy the affected dead heart tillers.
Set up light traps to attract and kill the moths.
Use  YSB pheromone lures and traps from 15 days after transplantation with lure replacement on 25, 46 and 57 DAT traps to monitor and manage stem borer males
Harvest the crop up to the ground level and disturb the stubbles to destroy the diapausing larvae and pupae.

Life cycle of Yellow stem borer (YSB),  Scirpophaga incertulas Wlk

 

  • This species is prevalent in many states across the country.
  • It is a serious pest in all the rice ecosystems, particularly in deep water rices.
  • The forewing of the female YSB moth is ochreous yellow to whitish with a black spot in the middle.
  • It has a wingspan of 24-36 mm.
  • Its abdomen is wide anal tufts are pale ochreous.
  • The adult male is smaller than female.
  • The forewings are gray or light brown in color and have two rows of black spots at the tip.
  • Sometimes the males are whitish yellow and spots on the forewing are not very clear.
  • Variation in the intensity of colour in the forewing and the size of the moth has also been observed.
  • Adults mate only once and up to 150 eggs are laid per female.
  • Each female lays 1-3 egg masses.
  • Egg masses are usually laid on leaf tips but they are also laid on the base of the stems.
  • The size of the egg mass also varies with the brood.
  • The egg mass of YSB is covered with pale ochreous (buff coloured) hairs from the anal tufts of the female.
  • Individual eggs are white, oval and flattened.
  • Egg period varies from 5-9 days and the newly hatched larvae disperse through silken threads and bore into the plant.
  • The first instar YSB larva is about 1.5 mm long.
  • A full-grown larva is pale yellow to yellowish green with brown head and prothoracic shield and measures 20 mm.
  • It feeds within the plant for more than 30 days and undergoes 5 -7 moults.
  • Usually only one larva is found in a tiller.
  • The number of moults and larval duration depends on the prevailing temperature.
  • Larval diapause is a common phenomenon.
  • The YSB pupa is whitish to pale yellowish green and measures about 12 mm long.
  • It is enclosed in a white silk cocoon.
  • Fresh cocoon is pale brown and turns dark brown with age.
  • The pupal period ranges from 6 -10 days.

File Courtesy:  Rice stem borers in India- species composition and distribution. Technical Bulletin No. XX,Directorate of Rice Research, Rajendranagar, Hyderabad - 500 030, A.P., India.
Photo Courtesy:  FIELD MANAGEMENT OF INSECT PESTS OF RICE - A READY RECKONER. Technical Bulletin No. 46, Directorate of Rice Research, Rajendranagar, Hyderabad - 500 030, A.P., India.

Brown Pant Hopper (BPH), Nilaparvata lugens (Stål) (Homoptera: Delphacidae), feeds on rice plants (Oryza sativa L.). BPH are among the most important pests of rice, and rice is the major staple crop for about half the world's population. They damage rice directly through feeding and also by transmitting two viruses, rice ragged stunt virus and rice grassy stunt virus. Up to 60% yield loss is common in susceptible rice cultivars attacked by BPH. The BPH are distributed in: Australia, Bangladesh, Bhuthan, Burma (Myanmaar), Cambodia, China, Fiji, India, Indonesia, Japan, North and South Korea, Laos, Malaysia, Nepal, Pakistan, Papua New Guinea, Philippines, Sri Lanka, Taiwan, Thailand, and Vietnam. Their host plant other than rice is Leersia hexandra.

Biology

The brown plant hopper is dimorphic, with fully winged 'macropterous' and truncate-winged 'brachypterous' forms. The macropterous forms are potentially migrants and are responsible for colonizing new fields. After settling down on the rice plants, they produce the next generation in which most of the female insects develop as brachypters and males as macropters. Adults usually mate on the day of emergence, and the females start laying eggs from the day following mating. Brachypterous females lay 300 to 350 eggs, while macropterous females lay fewer eggs. The eggs are thrust in a straight line generally along the mid-region of the leaf sheath. Eggs hatch in about six to nine days. The newly hatched nymphs are cottony white, and turn purple brown with in an hour; they feed on plant sap. They undergo five instars to become adults.

Damage

BPH [3] infest the rice crop at all stages of plant growth. As a result of feeding by both nymphs and adults at the base of the tillers, plants turn yellow and dry up rapidly. At early infestation, round, yellow patches appear, which soon turn brownish due to the drying up of the plants. This condition is called 'hopper burn'. Temperature is a critical factor in the life activities of the insect. The hatchability and survival rate are the highest around 25°C. Eggs are very sensitive to desiccation and soon shrivel when the host plant starts wilting. The population growth of brown plant hopper is maximum at a temperature range of 28 to 30°C.
Excessive use of urea as nitrogenous fertilizer and insecticides can lead to outbreaks by increasing the fecundity of the brown planthopper, and by reducing populations of natural enemies.In 2011, the Thai government announced an initiative to address brown planthoppers that included restricting the use of outbreak-causing insecticides including abamectin and cypermethrin - the decision was supported by the International Rice Research Institute (IRRI). IRRI also outlined recommendations in an action plan to help smartly manage planthopper outbreaks. In December 2011, the IRRI held a conference in Vietnam to address the threats of insecticide misuse and explore options for mitigation.

Predators

Predators of this insect include the spiders Pardosa pseudoannulata and Araneus inustus. In some cases, BPHs lay eggs in the rice seed beds (also known as rice nurseries) shortly before transplanting, so enter the field in this manner.
Differential mortality of predators and hoppers does not appear to be the primary factor for resurgence. Some insecticides evidently increase the protein content of BPH male accessory glands, and thereby increase planthopper fecundity. Some insecticides increase the amount of amino acids and sucrose available in the phloem of rice plants, and thereby increase BPH survival.

Management and Control

Rice varieties with resistance to BPH, e.g. IR64, are important for preventing outbreaks. However, in areas with low insecticide use, high levels of BPH resistance are not usually necessary.Chemical mutagenesis can significantly increase or decrease BPH resistance levels of rice. Some chemical insecticides, e.g. imidacloprid, can affect the gene expression of rice and thereby increase susceptibility to BPH.
In an attempt to make BPH control more species-specific, researchers are trying to develop methods of turning off specific BPH genes for digestion-, defense- and xenobiotic metabolism. Many novel genes for these functions have been detected in tissue from BPH intestines.
Some plant lectins are antifeedants to BPH and if properly formulated may have the potential to protect rice from BPH.

Impact of Climate Change

Research indicates that BPH nymphs are already living at the upper limits of tolerable temperatures. This suggests that climate warming in tropical regions with occasional extremely high temperatures would limit the survival and distribution of BPH.

1. The nymphs and adults suck sap from the basal portions of the plants, insert eggs into, leaf sheath or mid ribs and inject some toxins.
2. Cumulative effect of all these results in premature yellowing of leaves leading to dying. Later the plant dies.
3. Drying of plants occurs in isolated circular patches which coalesce and the entire the field dries up causing hopper burn.
File Courtesy:    RARS, Karjat                         Photo Courtesy:  Mr. Y. Kondal Rao (DRR)