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Density Dependent Parasitism of Trichogramma Zahiri

Md. Nazmul Bari
Senior Scientific Officer
Entomology Division, BRRI, Gazipur-1701

Dr. Mahbuba Jahan
Professor
Department of Entomology, BAU, Mymensingh-2202

Abstract/ Executive Summary:

Density dependent parasitism studies it showed that the rice hispa egg parasitism increased significantly with the incresing number of parasitoid. The average number of rice hispa egg parasitism/parasitod decreased from 12.7 to 4.98 when parasitoid number increased from 1 to 4 in a small arena with fixed number of host.

Keywords: Density, Parasitoid, Host, Interact, Rice

Location: BRRI, Gazipur

Start Date: 01-07-2010

End Date: 30-06-2011

Program Area: Pest Management

Commodity: Rice

Objectives:

To evaluate how the parasitoid T. zahiri interact with the host availability

Methodology:

The study was conducted by allowing variable number of eggs to be parasitized by different number of parasitiods. Four numerical groups of hispa eggs having 10, 20, 30 and 40 eggs in a group were placed in different test tubes (size 23X 8 cm²) and were allowed to be parasitized for 24 hours by 1, 2, 3 and 4 parasitoids respectively maintaining a ratio of 1:10. Both the ends of the test tube were covered by the black cloth except the area where the eggs were present. Dark shedding forced the parasitoid to remain active around lightened area where host eggs were available. Again, 20 rice hispa eggs were kept in each of different test tubes and exposed for 1, 2, 3 and 4 parasitoids separately for the parasitism for 24 hours. Removing the parasitoids after the stipulated time the test tubes with the parasitoid eggs were kept in the laboratory at about 25°C. After 5-6 days of parasitization, the individual eggs were placed separately in individual 5 ml vial which were then kept in the laboratory till the emergence of the parasitoids. The unhatched eggs were dissolved in Carbol-xylene and Alcohol (1:10) for 24hr and checked under microscope either the eggs were parasitized or not. Four cohorts of 10 parasitoids were used in each trial. Thus every trial had 40 replications and the experiment was conducted in completely randomised design (CRD).

Source of Information: Internal Review Workshop, 2010-11

Article Link (Online Journal):

Funding Source:

1.	Budget:
2. Bangladesh Agricultural Research Council	Budget:

Total Budget (Tk.) :

Achievement/Findings:

The parasitism of T. zahiri varied significantly with the dependent of two host densities. Results of two experiments with similar and variable parasitoid host ratio showed that density of host per parasitoid influenced the rate of parasitism. In the 1st experiment mean parasitization was higher only in parasitoid and host (1 parasitoid/10 host egg) combination. On an average 7.90 eggs were parasitized when one parasitoid released per 10 rice hispa egg. When 20, 30 and 40 rice hispa eggs were offered to 2, 3 and 4 parasitoids respectively 6.58, 6.37 and 5.93 eggs were parasitized per parasitoid respectively which were statistically identical. Although the parasitoid-host ratio was similar but a slight difference in parasitism was evident. Thus it was indicated that the mean number of host parasitized by the individual parasitoid was affected to a little extent due to mutual interference. It was found from the 2nd study that average parasitism efficiency per parasitoid decreased when more than one parasitoid released in a fixed number of host. Mean number of rice hispa egg parasitism decreased from 12.7 to 4.98 when parasitoid number increased from 1 to 4 in a small arena with fixed number of host (20 RH egg). Thus it was clearly indicated that mutual interference happened by the parasitoid T. zahiri on the ratio of host and parasitoid.

Knowledge Management: Report/Proceedings