Cotesia glomerata (Hymenoptera: Braconidae): A Potential Biocontrol Agent for Large White Butterfly, Pieris brassicae (Lepidoptera: Pieridae)

摘要

Biotic stresses are among the several constraints that limit realization of full yield potential of oilseed Brassica crops. Although mustard aphid, Lipaphis erysimi (Kaltenbach) continues to pose serious threat to oilseed Brassica and is a major production constraint, the large white butterfly, Pieris brassicae (Linnaeus) is also emerging as an important pest. In the Punjab province, this species was earlier restricted to vegetable Brassicas only, however, for the past few years continuous occurrence is being reported on oilseed Brassicas . The pest is a voracious feeder and inflicts heavy damage to the leaves and inflorescence. In this part of the country, it generally starts infesting oilseeds Brassicas from 4th Standard Meteorological Week (SMW) and thereafter, the population remains upto the crop maturity. Observations at Punjab Agricultural University, Ludhiana, India have recorded larval population as high as 106.6 larvae/plant. Such a high incidence resulted in plants practically devoid of leaves, flowers and developing pods with only twigs left intact. In the event of lack of food even the twigs were scratched by larvae on some of plants. Since, P. brassicae is of regular occurrence on vegetable Brassicas, the possibility of a tritrophic interaction in oilseed Brassicas cannot be overruled. Native parasitoids/predators can prove to be a good component of biological control programmes, especially in area wide pest management. Therefore, three years study during 2007-08, 2008-09 and 2009-10 crop seasons was carried out at Punjab Agricultural University, Ludhiana to find out potential parasitoids/predators of this pest. For this 10 egg masses and 50 grown up larvae were collected at weekly intervals and brought to the laboratory. These egg masses and larvae were kept until hatching and adult emergence, respectively, in glass jars to record emergence of parasitoid, if any. Field observations were also made to record for any predator feeding on eggs or larvae. While no egg and pupal parasitization was recorded during the three crop seasons, larval parasitization ranging from 6 to 86% was recorded during different SMWs. In 2007-08 crop season 37% larval parasitization was observed while in 2008-09 and 2009-10 it was about 53% each. Of the 600 larvae collected, 46.3 were parasitized. The parasitoid recovered was identified as Cotesia glomerata . Parasitization was recorded after 8th SMW till the population lasted on crop. Although, P. brassicae is causing substantial damage to the crop but, a considerably high level of larval parasitization by C. glomerata occurs under unsprayed field conditions. This native parasitoid can prove be an important component of area wide pest management programmes especially in the biological control of P. brassicae .