Medium Selection and Effect of Higher Oxygen Concentration Pulses on Metarhizium anisopliae var. lepidiotum Conidial Production and Quality Saul Tlecuitl-Beristain • Gustavo Viniegra-Gonza ´lez • Gerardo Dı ´az-Godı ´nez • Octavio Loera Received: 31 July 2009 / Accepted: 15 December 2009 / Published online: 29 December 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Rice and oat flours were analyzed as media for the production of conidia by M. anisop- liae var. lepidiotum. The presence of peptone increased conidia yield regardless of the substrate used; however, the highest yield was achieved on oat flour media. The effect of oxygen on conidia production using oat-peptone medium was also studied at two levels: Normal atmosphere (21% O 2 ) and Oxygen-rich pulses (26% O 2 ). Maximum conidia production (4.25 9 10 7 conidia cm -2 ) was achieved using 26% O 2 pulses after 156 h of culture, which was higher than 100% relative to conidial levels under normal atmosphere. Conidia yield per gram of biomass was 2.6 times higher with 26% O 2 (1.12 9 10 7 conidia mg -1 ). Conidia quality parameters, such as germination and hydrophobicity, did not show significant differences (P \ 0.05) between those treatments. Bioassays parameters, using Tenebrio molitor adults, were analyzed for conidia obtained in both atmospheres and data were fitted to an exponential model. The specific mortality rates were 2.22 and 1.26 days -1 , whereas lethal times for 50% mortality were 3.90 and 4.31 days, for 26% O 2 pulses and 21% O 2 atmo- sphere, respectively. These results are relevant for production processes since an oxygen increase allowed superior levels of conidia by M. anisopliae without altering quality parameters and virulence toward Tenebrio molitor adults. Keywords Metarhizium anisopliae  Oxidative stress  Virulence  Tenebrio molitor  Conidial quality Introduction The fungus Metarhizium anisopliae is considered as an alternative for agricultural pest control. One limiting factor for its use as a biocontrol agent is the production of biomass and conidia in large-scale on artificial substrates [1]. Recently, cultivation methods have been optimized for the production of M. anisopliae conidia on natural substrates such as sugar cane bagasse [2], rice, sorghum and barley [3], and even insect cadavers like Coptotermes formosanus [4]. Artificial substrates have also been used including yeast extract-enriched Potato Dextrose Agar (PDA) [5–7], yeast extract-enriched Sabouraud Dextrose Agar (SDA) [4], and Malt S. Tlecuitl-Beristain  G. Viniegra-Gonza ´lez  O. Loera (&) Departamento de Biotecnologı ´a, Universidad Auto ´noma Metropolitana-Iztapalapa, CP 09340 Iztapalapa, Mexico, DF, Mexico e-mail: loera@xanum.uam.mx G. Dı ´az-Godı ´nez Universidad Auto ´noma de Tlaxcala, Center for Biological Science Research, Tlaxcala, Tlaxcala, Mexico 123 Mycopathologia (2010) 169:387–394 DOI 10.1007/s11046-009-9268-7