Occurrence Patterns and Control Methods of the Rice Water Weevil

The rice water weevil is an internationally recognized agricultural plant quarantine pest. It first occurred in the Americas, and the countries in Asia where it occurs include Japan, South Korea, North Korea, and others. The place where the rice water weevil was first discovered in China was Tanghai County, Hebei Province, in 1987.

The area where the rice water weevil was first discovered in our province was Ji'an City in the Tonghua region in August 1993. At present, this pest occurs to varying degrees in most areas of Heilongjiang Province.

I. Degree of damage caused by the rice water weevil

The rice water weevil mainly damages rice, and also damages some grass family plants. Both the adults and larvae of the rice water weevil damage rice. The adults feed on the mesophyll of young tender rice leaves, leaving the epidermis. The larvae feed on roots, feeding inside and on rice roots. Larvae in the 1st to 3rd instars bore into and feed on the roots, and after the 4th instar they crawl out of the rice roots and bite and feed on the root system. After the root system is bored and eaten, it turns black or rots, and the rice plants are prone to lodging in the wind. In fields where the pest occurs, yield is generally reduced by 20%. In fields with severe rice water weevil occurrence, yield reduction can reach 50-70%.

II. Living habits of the rice water weevil

The rice water weevil is a semi-aquatic insect. This insect has both bisexual reproduction and parthenogenetic reproduction types (adults can undergo parthenogenesis). The rice water weevils occurring in China are all of the parthenogenetic reproduction type. Adults overwinter in rice straw, rice stubble, grass family weeds around paddy fields, and in the soil of field ridges. Overwintering-generation adults begin to revive and become active in spring when the temperature reaches about 10°C. After reviving, they first feed on the new leaves of grass family crops, and after rice is transplanted they enter the paddy fields to cause damage.

III. Characteristics of the rice water weevil

This pest has strong stress resistance, tolerates starvation, tolerates low temperatures, has a high reproduction rate (each adult can lay 50-75 eggs), and has a wide host range.

The rice water weevil spreads quickly. This pest can crawl, is good at flying, and can swim. It can spread through water flow, air flow, and vehicles.

IV. Control methods for the rice water weevil

In areas where the rice water weevil has not occurred, its introduction into the local area must be controlled. Plant quarantine laws and regulations should be strictly followed. Do not introduce seeds from epidemic areas, and do not transport rice straw and rice straw products from epidemic areas or occurrence areas.

Control measures in occurrence areas:

1. Reasonable fertilization. Fertilization should be based on soil testing, supplementing whatever is deficient. Excessive nitrogen fertilizer tends to cause an increase in pest population density.

2. Remove weeds. In autumn, winter, and spring, weeds around paddy fields should be removed or burned, so that the pest loses its overwintering sites and is directly eliminated.

3. In view of the phototaxis of adult rice water weevils, black light lamps can be set up near paddy fields for trapping and killing.

4. Chemical pesticide control. Chemical pesticides that have currently been screened out with relatively good effects on controlling the rice water weevil include: Daolefeng, Weidao emulsifiable concentrate, Xiangchongjing, Shachongshuang, and others.

In terms of control methods, joint control should be carried out with villages and towns as units, and the "four unifications" should be achieved. That is, unified organization, unified purchase of pesticides, unified timing of pesticide application, and unified inspection. This helps improve the control effect. The timing of control should be based on the local actual situation. Generally, overwintering-generation adults are controlled from June 5-10, and the new generation of adults is controlled in early August.