Potential Impact of Chemical Fungicides on the Efficacy of Metarhizium rileyi and the Occurrence of Pandora gammae on Caterpillars in Soybean Crops

Abstract

Entomopathogenic fungi may play a crucial role in the regulation of caterpillar populations in soybean crops, either through natural occurrences or applied as mycopesticides. In the present work, we reported the naturally occurring entomopathogenic fungus Pandora gammae attacking the caterpillar Chrysodeixis includens, with infection rates in field trials ran in two consecutive years in the 10-35% range. As many chemicals are potentially harmful to entomopathogenic fungi, this work aimed to investigate the potential impact of two chemical fungicides (azoxystrobin + benzovindiflupyr and trifloxistrobina + prothioconazole) used to control soybean rust (Phakopsora pachyrhizi) on the natural occurrence of P. gammae and Metarhizium rileyi, as well as the efficacy of the latter fungus applied as different formulations against the soybean caterpillars Anticarsia gemmatalis and C. includens. Under laboratory conditions, fungicides used at field-recommended rates had a considerable negative impact on the germinability of M. riley on the medium surface, and all tested formulations did not protect conidia from damage by these chemicals. This harmful effect also impacted host infectivity, as the larval mortality owing to this fungus was reduced by 30-40% compared to that of the fungicide-free treatments. In field trials conducted in two subsequent years, unformulated and formulated M. rileyi conidia applied to soybean plants produced primary infection sites in caterpillar populations after a single spray. Spraying unformulated or formulated M. rileyi conidia following fungicide application on plants did not affect host infection rates over time. Moreover, the use of M. rileyi-based formulations or chemical fungicide did not interfere with the natural infection rates by P. gammae on its host, C. includens. Although a higher degree of exposure to non-selective fungicides can negatively affect fungal entomopathogens, a single foliar application of fungicides may be harmless to both M. rileyi and P. gammae in soybean fields. Additionally, this work showed that naturally occurring wasps and tachnids also play an important role in the regulation of A. gemmatalis and, notably, C. includens, with parasitism rates above 40-50% in some cases.

Potential for Use of Species in the Subfamily Erynioideae for Biological Control and Biotechnology

“…However, partial ITS sequences (ITS2 region) were used to genotype the species of Strongwellsea and describe several new species of this genus [ 128 , 129 , 131 , 132 ]. Pandora formicae , P. gammae , P. kondoiensis , P. neoaphidis , P. nouryi , and Zoophthora radicans have also been genotyped with ITS sequences [ 86 , 173 , 174 , 175 , 176 ]. Some species have information available for genes encoding elongation factor 1-alpha, RNA polymerase II subunits ( RPB1 and RPB2 ), mitochondrial small subunit ribosomal RNA, white collar-1 protein, beta-tubulin ( btub ), elongation factor 1 alpha-like protein ( efl ), cell division control protein 25 ( CDC25 ), chitin synthase ( CHS3 ), chitin deacetylase ( CHD1 ), chitinase 1 ( CHI1 ), endochitinase ( CHT1 ), triacylglycerol lipase ( LIP2 ), glucan binding protein ( GBP1 ), subtilisin-like protease precursor ( SPR2 ), polyketide synthase ( PKS ), triacylglycerol lipase precursor ( LIP1 ), trypsin-like serine protease precursor ( TRY1 ).…”

Natural Prevalence, Molecular Characteristics, and Biological Activity of Metarhizium rileyi (Farlow) Isolated from Spodoptera frugiperda (J. E. Smith) Larvae in Mexico

“…Metarhizium rileyi (Farlow) Kepler, SA Rehner, and Humber (formerly Nomurea rileyi ) (Hypocreales: Clavicipitaceae) is a cosmopolitan pathogen that infects many species of Lepidoptera [ 10 , 17 , 18 ]. Natural epizootics of this fungus have been reported in several noctuid pests [ 19 , 20 , 21 , 22 , 23 ], including S. frugiperda [ 24 , 25 , 26 , 27 , 28 ]. Although M. rileyi has been recognized as an effective control agent to complement integrated pest management strategies [ 10 ], its efficacy in causing mortality is isolate-specific [ 5 ].…”