Influence of Rice Stem Borer Sex Pheromones on The Behaviour of Its Egg Parasitoids

The egg parasitoids Trichogramma japonicum Ashmead (Hymenoptera: Trichogrammatidae), Tetrastichus schoenobii Ferriere (Hymenoptera: Eulophidae) and Telenomus dignus (Gahan) (Hymenoptera: Scelionidae) are key biotic factors that regulate stem borer population. Augmentation and conservation of these parasitoids is an essential component of Integrated Pest Management (IPM) strategies for stem borers. Similarly, use of sex pheromone technology either by monitoring or mass trapping is also gaining momentum in managing rice stem borers. The synergistic effect of indigenous blends of sex pheromone (YSB and YSB-PSB) on the behaviour of egg parasitoids of stem borer was studied through olfactometer assay. Among the three egg parasitoids tested T. dignus exhibited greater response for a longer period, to its host YSB sex pheromone compound (Z)-11 hexadecenal + (Z)-9 hexadecenal at 0.5 μl treatment dose with an attraction index (AI) per cent of 19.36 followed by T. japonicum (10.76) and T. shoenobii (6.35). The treatment doses at 1.0 and 2.0 μl resulted in lesser orientation. Similarly, for individual compound, (Z)-11 hexadecenal had elicited little attraction to all parasitoids studied. The YSB-PSB sex pheromone compound comprising (Z)-11-hexadecenal, (Z)-11-hexadecenol, (Z)-11- hexadecenyl acetate, and (Z)-9-hexadecenal, irrespective of treatment doses and parasitoid species, resulted in lesser or poor attraction. Results revealed that host synthetic YSB pheromone at lower concentration attracted and retained egg parasitoids for a longer period and elicited as a synomone and kairomone kind of source.