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
Introduction
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
|
29
|
79
|
64
|
75
|
46
|
25
|
parasitoids immerged
|
5
|
2
|
4
|
28
|
4
|
0
|
Level of parasitism
|
17.24
|
2.53
|
6.25
|
37.33
|
8.69
|
0
|
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).
Conclusion
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.
References
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
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