Sunday, February 3, 2013


Analysis of Egg Parasitoids of Rice Ecosystem of Intermediate Zone of Sri Lanka
S.Sujan1* and K.S. Hemachandra2
Department of Agricultural Biology, Faculty of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka

Insect pest is a main problem in all parts of Sri Lanka. Pest problem may be stimulated by favorable climatic factors to the pests. It must be controlled because it  causes for yield reduction in the rice field. Most dominant rice field pests are yellow stem borer (Scirpophaga incertulas), white stem borer (Scirpophaga innotata), Rice bug (Leptocorisa oratorius), Rice leaf folder (Cnaphalocrocis medinalis), Rice leaf butterfly (Melanitis leda), Rice skippers (Pelopidus mathias). These pests affect the rice plant in various parts in the various stages.Rice pests are controlled by applying various types of chemical, physical and biological methods. Biological methods are environment friendly method with low cost because it may be naturally exists in the fields. After   implementation they multiply naturally.  Egg parasitoids are good to bio control of pests because pest can be controlled before they damage the crop. Hence, it is important to know what species of egg parasitoids are present in our fields.

Materials and Methods
Research was conducted during May 2012 - August 2012 in the Department of Agricultural Biology, Faculty of Agriculture, University of Peradeniya.  This study is consisted of two parts. Field component was conducted in the fields belonging to Rice Research and Development Institute, Batalagoda. The Fields were selected based on availability of the pests, access and history of agrochemical application. The objective of this component is to collect egg parasitoids associated with rice pests.
Field collection eggs were incubated at the room temperature in the laboratory. Egg masses were examined under the microscope (x 40) and hosts were identified based on egg masses and eggs. Eggs were kept in individual vials until the emergence of the host or parasitoids. Vials were observed daily for emergence of the adults. Emerged parasitoids were kept in the vials until they die and they were examined under the microscope for possible identification.

Results and Discussion
Egg parasitoids of selected rice pests were collected from June to August 2012 in the paddy fields of Rice Research and Development Institute, Bathalagoda. Parasitoids were identified to species level as well as the family level by using the previously published identification keys.
Eggs of four rice insect pests were observed during the study for emergence of egg parasitoids. Paddy bug (Leptocorisa oratorius), Rice leaf folder (Cnaphalocrosis medinalis), Yellow stem borer (Scirpophaga incertulas) and Rice Horned catterpiller (Pelopidas mathias) were the hosts collected for emergence of parasitoids. Emerged parasitoids were Trichogamma spp., Gryon nixoni. and scelionidae wasp.  Scelionidae wasp was identified as egg parasitoid of Red horn caterpillar. It is most effective prevalent parasitoid of red horn caterpillar in kurunagela area. Trichogramma spp were identified in yellow stem borer eggs and Rice leaf folder egg and Gryon nixoni was identified as a paddy bug egg parasitoid.

Emerged parasitoids parasitism level was analyzed with the time to those 4 pest species.
Table 4.2  Level of parasitism (percentage) of paddy bug eggs by Gryon nixoni with sampling  time (June-August, 2012)

1st week
2nd week
3rd week
4th week
5th week
6th week
No of paddy bug eggs
parasitoids immerged
Level of parasitism

The level of parasitism was varied significant with the time (chi-square=36.500 df=5 p<0.01). Level of parasitism was increased with time until 4th week after it was reduced in the harvesting periods (Figure2).
Three species of egg parasitoids namely Gryon nixoni, Telenomus rowani, Trichogramma spp and unidentified egg parasitoids of Family Scelionidae were recorded. Gryon nixoni might be used to control paddy bug population and Telenourmus ruwani and trichogramma spp might be used to control the rice leaf folder and Trichogramma spp could be used to control the Yellow stem borer and Scelionids  might be used to control the Red horn caterpillar in the intermediate zone.

Arida,G.S. and Shepard,B.M. (1990). Parasitism and predation of rice leaf folder Marasmia patnalis (Bradley) and Cnaphalocrosis medinalis (Guenee) (Lepidoptera:Pyralidae) in Laguna province Philippines. J. Agric. Entomol.  7(2):113-118.
Gurr,G.M.,  Liu, J., Read,D.M.Y., Catindig,J.L.A., Cheng ,J.A., Lan ,L.P. and  Heong,K.L. (2010). Parasitoids of Asian rice plant hopper (Hemiptera: Delphacidae) pests and prospects for enhancing biological control by ecological engineering. Annals of Applied Biology ISSN 0003-4746: 149- 176

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