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Biodiversity and Quantification of Natural Biological Control in Coastal Rice Agroecosystem

Dr. Md. Mohasin Hussain Khan
Professor
Department of Entomology, Patuakhali Science and Technology University, Dumki, Patuakhali-8602, Bangladesh

Abstract/ Executive Summary:

The study was conducted for monitoring biodiversity of natural biological control agents associated with rice pests and to quantify the insect pests and natural enemy incidence in T. aman rice field. The abundance of several insect pests and their natural enemies was influenced by different growth stages of rice plant. Among insect pest species, green leafhopper and short horned grasshopper were found high in abundance while other insect pests were low in relation to rice growth stages. Among natural enemies, damsel fly, spider and ichneumonid were high in abundance while mirid bug, lady bird beetle and ground beetle were low in relation to rice growth stages. The highest abundance of insect pests was found at vegetative stage and lowest at tillering stage. The abundance of natural enemies was also higher at vegetative stage compared to other stages. Abundance of insect pests and their natural enemies were more in high yielding rice variety and accession No. 20 as compared to local rice cultivars. The incidence of insect pest was the highest at Patuakhali sader and incidence of natural enemies was the highest at Bauphal. The diversity index, evenness and richness index was found highest in rice-banana habitat and lowest in rice-rice monoculture habitat.

Keywords: Biodiversity, Rice, Insect pest, Natural enemies, Abundance

Location: Four locations of Patuakhali district viz., Dumki, Bauphal, Mirjagong and Patuakhali sader

Start Date: 00-07-2010

End Date: 00-01-2011

Program Area: Pest Management

Commodity: Insects

Objectives:

To quantify the insect pests and natural enemy incidence in coastal rice agro ecosystem.

Methodology:

Four locations of Patuakhali district viz., Dumki, Bauphal, Mirjagong and Patuakhali sader were selected to carry out survey programme. Surveys were done in 10 randomly selected farmer’s rice fields of each location and PSTU farm. Different rice varieties were included in this study at PSTU farm. Data were collected from the different growth stages of rice seedling till harvest during July 2010 to January 2011. The total developmental period of rice plant was divided into five growth stages viz., seed bed, seedling, medium tillering, vegetative and panicle initiation stage. The insect pests of rice and their natural enemies were observed and collected by using a fine nylon cloth sweep net (30 cm diameter) and an aspirator. In each field 10 double sweeps were made to collect the insect pests and their natural enemies. Sampling was done at 7 days intervals at the above mentioned growth stages during morning hours at all study fields on all sampling dates. Ten samples were taken in every growth stage of rice plant for recording insect pests and natural enemies. Immediately after collection, the samples were kept separately in labeled polyethylene bag.To study the relative abundance and species diversity of pests and natural enemies, the study site was also selected considering the diverse habitat of non-rice crops like banana, vegetable, homestead etc along with rice. Four types of rice fields were selected in each location. These were: (a) rice field adjacent to banana field, (b) rice field adjacent to vegetable field, (c) rice field adjacent to homestead and (d) rice field adjacent to rice field.

Relative abundance of insect pests and natural enemies was calculated using the following formula:

Total no. of each species

Relative abundance (%) = _________________________ × 100

Total no. of all species

Species diversity

According to the Shannon-Weaver Index of Diversity was calculated (Shannon and Weaver, 1963). The index is expressed as-

H= - ∑ Pi log Pi

i= 1 Where, Pi = the proportion of individuals in the ith species and

ST= the total species

[ Pi =_______ ; ni = the number of individuals observed for each species and

N N = the total number of individuals in each study area].

Source of Information: Research report

Article Link (Online Journal):

Funding Source:

1.	Budget: 20,000/ (Twenty thousand)

Total Budget (Tk.) : 20,000/ (Twenty thousand)

Achievement/Findings:

The study has provided information on different aspects of pests and natural enemies in coastal rice agro ecosystem. The ability to quantify diversity in this way is an important tool for biologists trying to understand community structure. The study thus will help in saving significant amount of revenues through controlling rice pests by conserving biological control agents with minimum use of insecticides and also in saving the yield loss by major insect pests of rice. Further study should be done involving an extensive survey of natural enemies of the pest followed by detailed ecological studies in boro and aman seasons. Studies of rice insect pests and their natural enemies should be a continuous part of a research programme, both to identify important natural enemies and to promote practices that enhance their conservation.

Knowledge Management: Journal, Report/Proceedings