Toxicity and Pathogenicity Testing of the Insect Pest Control Fungus Metarhizium anisopliae

Abstract

Renewed interest in the use of Metarhizium anisopliae and its toxins for insect control prompted the following safety assessment. A neutral extract (methylene chloride, pH 7.2), derived from M. anisopliae cultures, was evaluated for toxicity and mutagenicity using aquatic animal bioassays and the Ames test. The average LC50 of the neutral extract obtained in static, acute 96-h tests conducted with </=24-h-old Mysidopsis bahia was 2.41 mg L-1. By partially purifying destruxins from the neutral extract, it was shown that destruxins alone were not responsible for the observed toxicity in mysids. The neutral extract was fetotoxic to developing grass shrimp, Palaemonetes pugio, and frog, Xenopus laevis, embryos; the LC50 values were 52 and 32 mg L-1, respectively. Eye spot abnormalities were observed in shrimp and frog embryos exposed to the neutral extract. In extract-exposed frog embryos, moderate to severe cranial, facial, and gut malformations were also observed. The neutral extract was toxic to juvenile mosquito fish, Gambusia affinis, at an LC50 value of 141 mg L-1. Adult female G. affinis surviving a 24-h exposure to 200 µg ml-1 of the neutral extract produced healthy broods. After 3 months, no mortalities or adverse effects were observed in adult G. affinis fed a diet partially composed of a freeze-dried M. anisopliae culture. The neutral extract did not show mutagenicity in the Ames test using strains TA98 and TA100 with and without metabolic activation by rat liver S9. Significant (p </= 0.05) mortalities were obtained when embryos of grass shrimp and inland silverside fish, Menidia beryllina, were exposed to the same lot of M. anisopliae conidiospores. Exposure of frog embryos to M. anisopliae conidiospores did not cause significant (p > 0.05) mortalities or malformations.

Agrobacterium -Mediated Disruption of a Nonribosomal Peptide Synthetase Gene in the Invertebrate Pathogen Metarhizium anisopliae Reveals a Peptide Spore Factor

“…Given this effect, it is appealing to consider that serinocyclins may play a protective role for the fungus in aquatic or highly humid environments since the compounds themselves are hydrophilic. For example, M. anisopliae ARSEF 2575 conidia have been reported to cause the death of embryos of inland silverside fish and grass shrimp (26,27) in safety assessments evaluating effects on nontarget organisms. How the behavioral effect of serinocyclin A on mosquito larvae relates to its role in the biology of M. anisopliae as a soil and plant-associated saprophyte and insect pathogen is still unclear.…”

Stable Chromosomal Inversion Polymorphisms and Insecticide Resistance in the Malaria Vector MosquitoAnopheles gambiae(Diptera: Culicidae)

“…However, it has been reported that the fungus may cause human keratitis (DeGarcia et al 1997). Other work has shown that the fungus can cause significant mortality of shrimp, frog and fish embryos exposed to conidia (Genthner et al 1994(Genthner et al , 1998. The latter effects, however, were not revealed in earlier studies where guppies, exposed to massive amounts of conidia, were not affected for periods up to two months (Roberts 1974).…”

Experimental evidence for the costs and hygienic significance of the antibiotic metapleural gland secretion in leaf-cutting ants

“…Metarhizium anisopliae is such a fungal pathogen (Genthner et al 1998 and references therein; Vilcinskas and Götz 1999) that has previously been isolated from many insects, including a number of species of Atta leaf-cutting ants (Humber 1992). M. anisopliae hyphae penetrate the cuticle by a combination of physical forces and the secretion of enzyme complexes (Hajek and St. Leger 1994;Boucias and Pendland 1998;Vilcinskas and Götz 1999).…”

“…Beauveria bassiana) have been extensively investigated for their usefulness as biological agents in insect pest control as an alternative to chemical insecticides (e.g. Diehl-Fleig et al 1988, 1993Genthner et al 1998;Jaccoud et al 1999;Vilcinskas and Götz 1999).…”