A New Entomopathogenic Fungus, Aspergillus Oryzae XJ-1and Its Application Potential In Control Of Locusts

Plagues caused by Locusta migratoria have led to severe damage and great economic losses world wide. The negative side-effects of synthetic insecticides used in locust control stimulated interest in the development of biological control agents. So, it is necessary to explore new agents to control the L. migratoria. The pathogenicity, taxonomic status, safety to human beings and mass production of a new pathogen isolated from Xinjiang province against L. migratoria were studied, and we considered that this new pathogen may have biocontrol potential against L. migratoria. Details are as follows:Ⅰ. The pathogenicity and identification of Aspergillus sp. XJ-1A preliminary identification of a fungus isolated from a dead grasshopper which collected from Xinjiang grassland, Northernwest of China, suggested that this fungus belongs to the genus Aspergillus, and named as Aspergillus sp. XJ-1. The Koch’s postulates were following conducted. The isolated fungus was inoculated into healthy L. migratoria, and then dark yellow fungus grew out of the cuticle of the dead locusts after incubating under the moist environment. The fungus growing on the cadavers was isolated and cultured on CA medium, resulting in light-yellow and olive-green colonies. Similar cadavers incubated in moist petri dishes were produced when healthy L. migratoria were treated with the fungus cultured on the CA medium. Fungus growing on the new cadavers had similar morphological features with the fungus growing on the old cadavers mentioned above after isolation and culture on CA medium again, and both them were Aspergillus sp. XJ-1. These results indicated that this fungus is an entomopahtogenic fungus of locusts. Lots of vegetative haphae were observed in the tissue of infected locusts. A BLAST search of GenBank revealed a99%similarity between its internal transcribed spacer (ITS) sequence and those of three species, Aspergillus oryzae, Aspergillus flavus and Aspergillus parvisclerotigenus, which are on the same branch of the Flavi section of the genus Aspergillus in a phylogenetic tree. Eventual analyses of morphological features indicated that Aspergillus sp. XJ-1belonged to A. oryzae, named as Aspergillus oryzae XJ-1. A. oryzae has been used in oriental food fermentation production for more than2000years, so from the standpoint of safety to human beings, A. oryzae XJ-1may have biocontrol potential against locusts.II. The virulence and toxin analyses of A. oryzae XJ-1The median lethal concentrations of A. oryzae XJ-1against L. migratoria were3.31×108,1.72×107and7.24×106conidia/ml after10,13and15days post-inoculation, respectively, according to bioassay results. The results of inoculation by oral and injection showed that the metabolism of the A. oryzae XJ-1contained no toxic subtances to the locusts. Aflatoxin B1detection by ELISA demonstrated that A. oryzae XJ-1was a non-aflatoxin B1producer. From the standpoint of virulence and safety, A. oryzae XJ-1may have biocontrol potential against L. migratoria. Ⅲ. Solid state fermentation of A. oryzae XJ-1Some conditions associated with solid state fermentation of A. oryzae XJ-1were optimized according to a basic fermentation formula designed based on the experiences. The results showed that the best fermentation temperature of A. oryzae XJ-1is35℃; there was no significant difference between the growth rates of A.oryzae XJ-1grown in sunlight and dark; the best water content of the medium was60%; the glucose, yeast and minerals in the basic fermentation formula had no significant affects on the spore yield of A. oryzae XJ-1; the best proportion of bean pulp and corn starch was9%:5%; the maxumum spore yield of A. oryzae XJ-1reached4.1×109spores/g of dried medium after growing in a medium optimized for6days. From the standpoint of spore yield, A. oryzae XJ-1may have biocontrol potential against locusts.