Metarhizium: An effective, cheap, and environmental-friendly way to combat the pesky black rice bug

Dead rice black bug infected by Metarhizium anisopilae fungus. (IRRI)


Rice black bug (Scotinophara coarctata), locally known as itim na atangya, alitangya, or nangisit a bangaw (Ilokano), is a major pest of rice. Aside from destroying rice plants and causing severe crop loss, they are also notoriously known for their foul odor when they swarm around lamp posts during the full moon.

The rice black bug (Scotinophara coarctata). (URSchmidt/Wikimedia Commons)

The rice black bug feeds by sucking the sap of the rice plant’s stalks, leaves, and panicles. The rice panicles, or uhay in Tagalog, is the flowering part of the rice plant that holds the grains of rice. Infestation can also cause the rice panicles to go empty when they attack before grain development.

The rice black bug tend to infest poorly drained, densely planted, and irrigated or rainfed rice fields. Severe damage from this insect will result in a deadheart or wilting and death of the rice tillers. The rice tiiler, or suhi in Tagalog, is the secondary stem that grows from the main of the rice plant. Development of these parts are important in rice production because tillers produce their own flowering structures, hence significantly increasing the overall yield of the crop. However, when rice bugs feed on the stems of rice plants, they can damage the nodes where tillers emerge, which can reduce the number of tillers that grow from the main stem. Furthermore, they can cause bugburn, a rice black bug damage symptom where the leaves turn reddish brown. 

These damages will result in severe crop loss. According to the International Rice Research Institute (IRRI), ten black bugs per rice plant can cause losses of up to 35% on susceptible rice varieties. If left uncontrolled, the population of the rice black bug can quickly spread to the whole rice field as a single female can lay a mass of 40-60 eggs.

Ways to control rice black bug

To minimize the damage where there is a heavy infestation of black rice bugs, IRRI recommends using tolerant rice varieties such as R1314, IR44526, and C4 137. IRRI also suggests practicing synchronous planting in the barangays. Synchronous planting is a crop management technique in which all the seeds or seedlings of a crop are planted at the same time in a given area. It helps to reduce pests, as the crop plants are at the same developmental stage and can be more effectively managed using targeted control measures. 

For example, if a pest infestation occurs in a field with asynchronous planting or planting at different times, the pest population may be at different stages of development across the field, making it difficult to apply pesticides effectively. In contrast, synchronous planting can create a more uniform crop canopy and pest population, which can allow farmers to apply pesticides more effectively and efficiently.

It is also recommended to remove weeds that could serve as potential alternative hosts. Moreover, raising the water level for 1-2 days will submerge some of the rice bugs’ eggs and prevent them from hatching.

Farmers could also raise ducks and release them on the field before the planting season for them to feed on the rice black bugs. Setting light traps at night could reduce the population of rice bugs throughout the cropping season and during harvesting when the insects are actively searching for food. During the harvesting season, rice black bugs may become more active as they search for food sources. This is because as the rice plants mature and become ready for harvest, they start to dry out, and the sap flow decreases. The reduction in sap flow makes it more difficult for the bugs to find food, so they become more active in their search. 

Another way to control rice black bugs is to use a biocontrol (Biocon) agent called Metarhizium anisopilae.

The Metarhizium

Metarhizium anisopilae is the most effective locally available biocon agent to control rice black bugs. It is a green fungus that infects the rice black bugs when it makes contact with the insect’s body. It produces toxins that paralyze the pest that will eventually kill it. As the fungus develops on the pest’s dead body, it will start a new infection cycle for the other insect pests. This chain of events will effectively reduce the pest population by 30 – 68% in just seven days.

Dead rice black bug infected by Metarhizium anisopilae fungus. (IRRI)

The Metarhizium, in powder form, is applied through spraying or incorporated into the irrigation. The application should be done in the late afternoon because direct sunlight could kill the fungus. Each application contains 2.5 trillion spores which self-multiply in the field, thus, requiring it only to be applied two to three times each cropping season, unlike the use of chemical pesticides that require five to six applications. Furthermore, Metarhizium is also far less cheap than chemical pesticides.

The application of Metarhizium anisopilae is not only economical but environmental-friendly as well. Unlike chemical pesticides, it does not leave any residue and is perfectly safe for human health.

You may contact your Municipal Agriculture Office or Regional Crop Protection Center for more inquiries. 

Photo courtesy of IRRI

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