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Relative Population Density of Rice Borers and Their Natural Mortality

M. A. Islam
Entomologist
Bangladesh Institute of Biological Control, Sher-e-Bangla Nagar, Dhaka.

Abstract/ Executive Summary:

Chilo spp, were found most abundant in January-April and again in July-September of 1972-73 with relative larval population of 58.4-93.3 and 72.9-80.6% respectively. But Sesamia inferens Wik. was predominant in June and during October-December with relative larval density of 52.7% and 71.2-77.4% respectively. On the contrary, T. incertulas was predominant over others in May with 71.3% relative larval density. During the same period the larvae of Chilo spp, S. inferens and T. incertulas were parasitized to the extent of 44.4% (mainly be Sturmiopsis inferens Towns and Tropobracon schoenobii Vier), 41.2% (by Sturmiopsis inferens Towns) and 16.7% (bt T. schoenobii and Temelucha sp) respectively. While natural mortality was 41. 9, 27.1 and 37.5% respectively. It was, therefore, evident that the total effect of insect parasitism and other mortality factors played a very important role in suppressing the borer population in nature.

Keywords: Rice Borers , Population density, Natural mortality

Location: Bangladesh Rice Research Institute Farm at Joydebpur.

Start Date: 01-01-1972

End Date: 30-09-1973

Program Area: Pest Management

Commodity: Rice, Insects

Objectives:

To determine the total effect of insect parasitism and other natural mortality factors on the population of rice borer-larvae.

Methodology:

Borer-infested rice plants were regularly collected once a week from untreated rice fields throughout the year. One hundred such plants were collected each time. Every plant was carefully examined in the laboratory to record the relative number of different borer larvae and pupae present in the infested culm. Records of the naturally dead larvae or pupae for each borer species were also maintained to obtain data on the natural mortality of the borers caused by some unknown factors. All live borer larvae and pupae thus obtained were reared in the laboratory to record the rate of incidence of insect parasites under natural condition. These records were tabulated to show a trend of relative population density of different borer species and the total effect of insect-parasitism plus natural mortality of the borer larvae caused by factors other than insect-parasites in the existing situation of BRRI during the period under observation. In calculating the relative population density of different rice borers. all the available borer larvae and pupae in the infested plants were considered together as larvae.

Source of Information: Bangladesh Journal of Agriculture, Vol.2 (1), 1977

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

It was evident that the total effect of insectparasitism and mortality due to other factors including pathogenic cause on different borer larvae under natural condition was quite significant and vital for keeping the borer population down in nature. While natural mortality was 41. 9, 27.1 and 37.5%,respectively.

Knowledge Management: Journal