Platygasterid parasitoids in rice and vegetables

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.