RESEARCH COMMUNICATIONS CURRENT SCIENCE, VOL. 112, NO. 11, 10 JUNE 2017 2312 *For correspondence. (e-mail: prabhusha2014@gmail.com) Generation and evaluation of nanoparticles of supernatant of Photorhabdus luminescens (Thomas and Poinar) against mite and aphid pests of cotton for enhanced efficacy Ramesh A. Kulkarni 1 , A. Prabhuraj 1, *, J. Ashoka 1 , S. G. Hanchinal 1 and Sharanagouda Hiregoudar 2 1 Department of Agricultural Entomology and 2 Department of Processing and Food Technology, University of Agricultural Sciences, Raichur 584 104, India Cell-free supernatant of Photorhabdus luminiscens was converted to nanoparticles (NPs) using a spray dryer fitted with ultrasonic nozzle. NPs were charac- terized by both scanning electron microscopy and zeta size analyser, and found to have average particle diameter of 89 nm. While converting to NPs, gum arabica @ 3% was used to eliminate hygroscopic property. Nanoparticulated supernatant exhibited superior pesticidal property against serious sucking pests of cotton, viz. Tetranychus macfarlanei and Aphis gossypii. On mites, NPs of P. luminiscens recorded lower median lethal concentration (LC 50 : 0.0001 ppm) compared to normal form (8.36  10 2 ppm) within 12 h of exposure. Similarly, on aphids, lower LC 50 (LC 50 : 0.0027 ppm) was recorded by NPs compared to normal form (LC 50 : 2.12  10 3 ppm). High mortality coupled with quick action emphasizes the potential of nanotechnology in enhancing the pathogenicity of a microbial pesticide. Keywords: Aphid, cotton, mite, nanoparticles, Photor- habdus luminescens. PHOTORHABDUS LUMINESCENS (Thomas and Poinar) is an endosymbiont of entomopathogenic nematodes (EPNs) Heterorhabditis spp. belonging to the family Enterobacte- riaceae in the gamma subdivision of purple bacteria. It is a non-spore forming, motile, bioluminescent, Gram- negative, facultative anaerobic bacterium producing an array of toxin complexes and enzymes. These extracellu- lar secretions have a wide range of insecticidal actions against both sucking and chewing arthropod pests of ag- ricultural crops. Some of the broad-spectrum toxin complexes include oral toxin complex proteins ( T c ), in- jectable toxin (makes caterpillar floppy 1 – mcf1), binary toxin (Pir AB) 1–5 and several enzymes, viz. chitinase, protease and lipase 6–8 . As a result, bacterial solution of P. luminiscens has been employed as topical pesticide against a wide range of insects like mite, aphid, mealy- bug, etc. 9–12 . Topical application of P. luminiscens in the form of spray is advantageous in terms of safety, potency and specificity compared to chemical spray, besides be- ing bio-degradable, providing a large and competitive market. However, to increase the efficacy of this bio- pesticide comparable to synthetic pesticides, it is quite essential to achieve the quick knockdown of the target pest. Nanotechnology offers a good opportunity to enhance the efficacy of such bio-molecules by decreasing the par- ticle size, thus increasing the surface-to-mass ratio com- pared to bulk equivalents. It also aids in developing superior bio-pesticide formulations comparable to chemi- cal pesticides. Surprisingly, few reports of conversion of bio-agents or their by-products are available to enhance the toxicological properties. Hence, in the present study an attempt has been made to improve the efficacy of ex- tracellular secretions of P. luminiscens by downsizing the particles through nanotechnological methods. The endosymbiotic bacterium, P. luminescens used in the present study was recovered from the local isolate of entomopathogenic nematode, Heterorhabditis indica from the soils of sugarcane cropping ecosystem during 2012–13. Identification of the bacterium was done through genome sequence studies which matched P. lu- minescens luminiscens (accession no. KP224437) to the extent of 85% through blasting at the National Center for Biotechnology Information (NCBI), USA. A loop full of symbiotic bacteria, P. luminescens from NBTA (nutrient bromothymol blue agar) medium was inoculated to sterilized nutrient broth (ca. 150 ml) under aseptic condition and incubated in biochemical oxygen demand (BOD) under ambient condition (28C and 85– 90% relative humidity) for 24–48 h. Stock solution hav- ing bacterial concentration of 10 10 cfu was prepared through serial dilution method and centrifuged at 4000 rpm for 20 min to get a supernatant solution. The cell-free supernatant (CFS) was collected in separate test tubes and dried using a spray dryer fitted with ultrasonic nozzle for the production of nanoparticles (NPs). Downsizing of any material mainly follows two approaches, viz. top-down and bottom-up, both of which use physical, chemical and biological methods to produce the NPs 13 . CFS was converted to nano-sized particles by physical method using spray dryer (Labultima, LU-222 advanced, Labultima, Mumbai; vertical co-current type with an evaporation rate of 1000 ml/h fitted with an ultrasonic nozzle). CFS of the bacterium was mixed with gum arabica (3%) as a binder to eliminate the hygroscopic property of the material by hand-stirring. Later, the thoroughly mixed solution was sprayed using a spray dryer fitted with an ultra sonic nozzle to convert into NPs by setting suitable parameters (Table 1). The CFS solution was first broken into small droplets using ultrasonic assisted atomizer. These fine droplets