Role of glucosinolates in Brassica juncea on the Incidence and Development of Lipaphis erysimi and its Parasitoid Diaeretiella rapae

Abstract

Brassica juncea, the Indian mustard suffers from Lipaphis erysimi infestation to a great extent. The role of glucosinolates and its breakdown plant volatiles, time of sowing etc. seems to be related to the incidence and development of this aphid. The studies indicated that the parasitoid co-evolved along with the aphids to utilize the products of glucosinolates for the identification of the habitat of the host. These studies clearly specified the role of allyl isothiocyanate and hydroxyl indolyl isothiocyanate as kairomone. Under field conditions, aphid infestation and extent of parasitism was significantly higher at flowering stage than that on the vegetative stage. The qualitative and quantitative differences in the content of volatile aglucones of the cultivar and growth stages indicated that changes affected the extent of parasitism. It was observed that response of the parasitoid was higher towards the volatiles from the reproductive stage where the concentration of allyl isothiocyanate and hydroxyl indolyl isothiocyanatewas less than in the vegetative stage. The information generated during the investigations can be utilized to exploit the potential of biological control of the aphid when the population is still low so that the glucosinolates are not digested into aglucones by myrosinase, as these breakdown products play a very important role in attracting the aphids and the parasitoids towards the cultivars. It is also proposed that if the infestation of the aphid still increases then by parasitization of it by D.rapae can decrease its attack.