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

• Published in: Microbial ecology Vol. 86; no. 1; pp. 647 - 657
• Main Authors: Lopes, Rogerio Biaggioni, Faria, Marcos, Souza, Daniela Aguiar, Sosa-Gómez, Daniel Ricardo
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-07-2023; Springer Nature B.V
• Subjects: Animals; Azoxystrobin; Biomedical and Life Sciences; Caterpillars; Chemical damage; Conidia; Crops; Crops, Agricultural; Ecology; Effectiveness; Entomopathogenic fungi; Foliar applications; Fungi; Fungicides; Fungicides, Industrial - pharmacology; Geoecology/Natural Processes; Germinability; Glycine max; Impact damage; Infections; Infectivity; Invertebrate Microbiology; Larva - microbiology; Life Sciences; Metarhizium; Metarhizium rileyi; Microbial Ecology; Microbiology; Moths; Nature Conservation; Parasitism; Pesticides; Populations; Rust fungi; Soybeans; Spraying; Water Quality/Water Pollution; Soybean caterpillars; Microbial control; Compatibility; Entomophthorales
• ISSN: 0095-3628; 1432-184X
• DOI: 10.1007/s00248-022-02102-9

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.