J Appl Entomol. 2020;00:1–9. wileyonlinelibrary.com/journal/jen | 1 © 2020 Blackwell Verlag GmbH Received: 14 February 2020 | Accepted: 26 February 2020 DOI: 10.1111/jen.12747 ORIGINAL CONTRIBUTION Kairomones effect on parasitic activity of Trichogramma japonicum against rice yellow stem borer, Scirpophaga incertulas Ramasamy Kanagaraj Murali-Baskaran 1 | Jandrajupalli Sridhar 1 | Kailash Chander Sharma 1 | Lata Jain 1 | Sengottayan Senthil-Nathan 2 | Wayne Brain Hunter 3 | Jagdish Kumar 1 | Pankaj Kaushal 1 1 ICAR-National Institute of Biotic Stress Management, Raipur, Chhattisgarh, India 2 Division of Biopesticide and Environmental Toxicology, Sri Paramakalyani Centre for Excellence in Environmental Science, Manonmaniam Sundaranar University, Alwarkurichi, India 3 United States Department of Agriculture, Agriculture Research Service, U.S. Horticultural Research Laboratory, Fort Pierce, FL, USA Correspondence Ramasamy Kanagaraj Murali-Baskaran, ICAR-National Institute of Biotic Stress Management, Raipur 493 225, Chhattisgarh, India. Emails: rcrkm2013@gmail.com; rk.baskaran@icar.gov.in Funding information ICAR-National Institute of Biotic Stress Management, Raipur Abstract The yellow stem borer (YSB), Scirpophaga incertulas, is a borer pest of low-land rice in tropical regions of the world, reducing production and productivity. Chemical con- trol of YSB is challenging and often less effective due to its cryptic larval feeding behaviour inside the rice culm. Biological suppression of YSB, using egg parasitoid, Trichogramma japonicum, has been well demonstrated. Kairomones, that are interspe- cific, play a vital role in deciding biocontrol efficiency of egg parasitoid against lepi- dopteran pests. However, the mechanisms involved in terms of emission of long- and short-chain volatile chemicals from YSB and its by-products and YSB damaged rice plants in attraction to T. japonicum to locate eggs of YSB are still poorly understood. In order to trace out the volatile compounds responsible for attraction of egg parasi- toid, the hexane extract of YSB female whole body and acetone extract of YSB dam- aged rice culm were subject to GC-MS analyses. Out of 20 chemicals, four chemicals belonging to carboxyl, alkane and saturated fatty acid [n-hexadecanoic acid (palmitic acid), tetradecane, octadecane, n-octadecanoic acid (stearic acid)] from female YSB hexane extract and three sesquiterpenoids (β pinene, α pinene and caryophyllene) from YSB damaged rice plant extracts were detected in greater concentrations. In laboratory assays with the synthetic form of seven chemicals, three, n-hexadecanoic acid, n-octadecanoic acid and octadecane, were promising in enhancing the parasitic activity of T. japonicum on YSB eggs from 26.4% to 92.6% at 200 ppm, 27.3% to 96.5% at 500 ppm and 23.6% to 82.8% at 500 ppm, respectively, in contrast to un- treated eggs (87.3% at 7 th day after exposure) and hexane washed eggs (16.7% at 7 th day after exposure). Evaluation of these compounds revealed the key chemical cues of biocontrol potential (n-hexadecanoic acid, n-octadecanoic acid and octadecane) for enhancing egg parasitism activity of T. japonicum on YSB eggs. KEYWORDS biocontrol, crop protection, Hymenoptera, Lepidoptera, parasitoid, pest control, semiochemical