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Some Ecological Aspects of Rice Bug (leptocorisa Spp.) in Bangladesh

Z. Islam
PSO (Ex.)
Entomology Divison BRRI, Gazipur 1701 Consultant Crop and Environmental Sciences Division (Entomology) International Rice Research Institute, Philippines Tel: +14169278424 email: irri@cgiar.org Web: www.irri.org & Ex. Head, Entomology Division, BRRI, Gazipur 1701 Bangladesh Email: zislam51@yahoo.ca

Nur Ahmed
CSO & Head
Entomology Division BRRI, Gazipur 1701

M. Haq
CSO (Ex.)
Entomology Division BRRI, Gazipur 1701

Nadira Afsana
SO (ex.)
Entomology Division BRRI, Gazipur 1701

N M M Haque
SSO (Ex.)
Entomology Division BRRI, Gazipur 1701

Abstract/ Executive Summary:

Some aspects of the ecology and management of rice bugs (RB), Leptocorisa spp. (Alydidae: Hemiptera,) were studied in a continuous rice cropping system at the experimental farm of the Bangladesh Rice Research Institute, Gazipur, Bangladesh. Some observations were also made in farmers' fields in the Tangail district. Four rice grain sucking insects, viz., Leptocorisa oratorius (Fabricius), L. acuta (Thunberg), Riptortus linearis (Fabricius) (Alydidae: Hemiptera), and Pygomenida bengalensis (Westwood) (Pentatomidae) were found in the farm. Leptocorisa spp. were most abundant (93.0%) while the presence of the other two species was negligible (7.0%). L. oratorius (59.2%) was relatively more abundant than L. acuta (40.8%). Their abundance was highest in the boro (dry season) followed by upland aman (monsoon rice), upland aus (summer rice), irrigated aus, and irrigated or lowland aman rice crops. Rice bug abundance appeared to be higher in the upland situation than the lowland or irrigated situations in the aus and aman seasons. In 10 out of 26 (38.6%) rice seasons the RB population exceeded the ETL (10 bugs/20 rice hills), especially in late planted crop fields. Time series data indicated that the boro season was more prone to RBs and once in four years populations might reach higher levels causing significant yield loss. It was observed that during the rice-free winter period RB took shelter in nearby forests in high concentrations in some areas of Tangail. The use of fertilizers at higher rates (100:60:60:10 kg NPKS/ha) positively influenced the RB incidence in one out of five experiments. The results indicated that application of insecticide as a prophylactic measure, hand picking of bugs or the use of straw tepee for predator conservation had no effect on RB populations or on grain yield. Curative application reduced RB populations but failed to increase grain yield. It was estimated that at the reproductive phase of boro crops about 20% of RB eggs were destroyed by the parasitoid Cryan nixoni (Masner) (Scelionidae: Hymenoptera).

Keywords: Rice, Leptocorisa spp., Abundance, Over-wintering, Egg-parasitism

Location: BRRI farm and Kapashia, Gazipur, Basail and Gatail, Tangail

Start Date: 00-00-1996

End Date: 00-00-2001

Program Area: Pest Management

Commodity: Insects

Objectives:

To study some aspects of the ecology of the rice bugs (RB) in a continuous rice cropping system in Bangladesh. Emphasis was given to the study of the relative abundance of the two Leptocorisa species, abundance pattern of RBs in successive rice crops, observation on over-wintering populations, determination of the extent of egg parasitism, and the influence of higher doses of chemical fertilizers and some control techniques on bug populations and grain yield.

Methodology:

Most of the experiments and observations were carried out in the experimental farm of BRRI, Gazipur, Bangladesh in order to determine composition of the species. RBs were sampled at the reproductive stage of boro crop in 1999. Bugs were collected by sweep-netting over a two-week period in May and identified at species level. Abundance of RBs in different rice crops situations at the BRRI farm was monitored at weekly intervals from 1996 to 2001. Abundance was estimated by counting RBs on 20 random rice hills each week. Some observations were made on the over-wintering RB populations during the rice free season during winter of 2000 and 2001 in some areas of the forests at Basail and Gatail, Tangail and Kapasia, Gazipur. Incidences of RBs were observed visually also by sweep-netting. A sample of paddy grains of BRRI dhan32 variety was collected from a farmer's house near the forest area where RBs were present in high numbers during the winter. Weight of head rice, broken rice, bran and husk were measured. Grains were cooked to compare cooking time, colour and taste with uninfested rice of that variety. Rice bug eggs were collected at the reproductive phase of boro in 1999 and 2001. Field collected eggs were reared and observed on daily on the emergence of rice bug nymphs and parasitoids and examined carefully to determine status of each egg viz., hatched, parasitized or infertile. The parasitoids were identified at species level. Five experiments were conducted during 1995 and 1996 to evaluate the influence of a high dose of fertilizer; and the effects of different control techniques such as prophylactic use of insecticide, mechanical control (hand picking) and predator conservation by straw tepee on the RB populations and grain yields. All these experiments were conducted using RCBD with four replications and a unit plot of 5m x 8m. One treatment received NPKS at a higher dose (100:60:60:10 kg/ha) and all other treatments received NPK fertilizers at standard dose (80:40:40 kg/ha). Phosphamidon 100SL (prophylactic treatment) was applied at 0.85 l/ha at different DAT during boro, aus and aman. At ETL, bugs were handpicked from plots as mechanical control. Rice bug populations were estimated by counting bugs on 20 random hills/plot at different DAT during boro, aus and aman. Grain yields were estimated from 20 m2 (4m x 5m) crop cuts/plot. Another experiment was carried out during boro in 1999 to quantify the effects of the gradients of rice bug density on yield component and grain yield and crop was established in a series of 2x2 m plots by transplanting BRRI dhan29 seedlings at 20 x 20 cm hill spacing. No pesticide was used. At the flowering stage, adult RBs were confined on rice hills at the rate of 0, 1, 2, 4 and 10 per hill/plot by the use of a nylon mesh cage. Another set of rice hills was randomly selected and marked to serve as natural infestation or untreated control. The trial was carried out using RCBD with 10 replications.

Source of Information: Bangladesh J. Entomol 13 (1): 85-96; 2003.

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Rice bug economic threshold level (ETL) has been readjusted as one rice bug in every two hills at reproductive stage.

Knowledge Management: Journal