Platygasterid parasitoids in rice and vegetables
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Date
2003
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Department of Agricultural Entomology, College of Horticulture, Vellanikkara
Abstract
The survey was conducted in the rice fields of Ollukkara and
Madakkathara panchayats of the Thrissur district, Kerala during J line 2002 to January
2003. Six species of Platygaster namely, P. coorgensis (Mukerjee), P. inderdaadi
(Mukerjee), P. malabaricus (Mukerjee), P. minimus (Mukerjee), P. orzyae Cameron
and P. sasii Ushakumari have been recorded as pupal parasitoids of the rice gall midge
Orseolia oryzae (Wood-Mason). All the species except P. oryzae are new reports from
rice gall midge 0. oryzae (Wood-Mason). Parasitism by platygasterid parasitoids in
cecidomyiid galls, mealy bugs and white flies of vegetables was recorded during the
survey.
The species composition as well as seasonal and varietal variation in the
incidence of the parasotoids and the other relevant aspects of the study have bee
discussed.
P. coorgensis is 1.13 mm in length; antenna 10 segmented with five club
forming segments; notauli absent; submarginal vein present. P. inderdaadi is 1.21 mm
in length; antenna 10 segmented with five club forming segments, fourth segment
large sized; notauli absent; submarginal vein present.
P. malabaricus and P. minimus differ in case of notauli character. In
P. minimus notauli is present where as in P. malabaricus it is absent. P. oryzae is the
smallest among the six species studied i.e., 1.1 mm in length; antennal segments 10
with four club forming segments; notauli present and is faint, submarginal vein absent.
P. sash is the largest among the six species, 2 mm in length. It is the
solitary species while all others are gregarious, antenna 10 segmented with five club
forming segments, notauli distinct and submarginal vein present.
The peak Platygaster population was recorded in the 'virippu' season and
during the first week of September. In the 'mundakan' season, the maximum
population was observed during the second week of November. There is significant
difference in Platygaster populations between the two seasons, the 'mundakan'
season, showing significantly higher population of Platygaster parasitoids than in the
'virippu' season.
The maximum' per cent parasitism was observed during the third week of
September in 'virippu' season (25.69) and last week of October in 'rnundakan' season
(44.17) in both panchayats. The mean per cent parasitism in 'virippu' season was
20.67 and in 'mundakan' season it was 33.94. The per cent parasitism was found to be
significantly higher in 'mundakan' season.
Two types of Platygasfer were observed based on the number of
parasitoids emerging from the galls, namely, the solitary and gregarious types. The
solitary type is identified as P. sasii and the gregarious types are identified as
P. coorgensis, P. minimus and P. oryzae.
Seven species of other hymenopteran parasitoids also recorded from the
galls. They are Eurytoma sp. (Eurytomidae), Litus sp. (Pteromalidae), Neanastatus
cinctiventris Girault (Eupelmidae), Telenomus sp. (Scelionidae), one species of
Eucoilidae and two species ofMymaridae.
There was no gall fly infestation and platygasterid parasitoids in the rice
varieties studied during 'mundakan' 2002 season at RARS, Pattambi. During 'virippu'
2003, out of the 50 varieties' observed, gall infestation was seen in the varieties Red
Ponmani, CO-42, IET-13358, MTU-7 and Kuruva, but no Platygaster parasitoids
were recorded from these varieties.
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PG
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Citation
172168