Impact of Metarhizium robertsii on Adults of the Parasitoid Diachasmimorpha longicaudata and Parasitized Anastrepha ludens Larvae

SIMPLE SUMMARY: The Mexican fruit fly Anastrepha ludens is a polyphagous pest that infests at least 32 tropical and subtropical plant species of different families. A. ludens is native of Mexico, and is distributed from Northern Mexico to Central America. Integrated Pest Management (IPM) programs build upon the Sterile Insect Technique (SIT) and biological control agents (parasitoids and microbial pathogens), two eco-friendly sustainable control strategies, which are highly relevant in organic farming. In our laboratory study we evaluated the efficacy of fungal pathogens and intraguild predation (IGP) risk of one strain of Metarhizium robertsii and another of Metarhizium anisopliae, when used in conjunction with the braconid parasitoid Diachasmimorpha longicaudata. Our results show a reduced negative effect of M. robertsii on D. longicaudata adults, and a low IGP risk when D. longicaudata-parasitized larvae were exposed to Metarhizium strains. Our study is important for organic, tropical fruit growers because it shows that M. robertsii and D. longicaudata are promising biocontrol agents for organic farming in Veracruz, Mexico. ABSTRACT: Biological control of the Mexican fruit fly, Anastrepha ludens, is mainly carried out by releasing parasitoids, such as Diachasmimorpha longicaudata, and by applying entomopathogenic fungi (EPF), such as Metarhizium anisopliae, Beauveria bassiana, or Isaria fumosorosea, which can be applied to the soil or dispersed using infective devices. The combined use of two or more biocontrol agents could improve A. ludens control, but IGP between natural enemies, if it occurs, may have negative effects. We evaluated the effects of EPF on D. longicaudata. First, we determined the susceptibility of adults of D. longicaudata to strains of EPF (Metarhizium robertsii strain V3-160 and M. anisopliae strain MAAP1). We also evaluated the infection of these two fungi on A. ludens larvae parasitized by D. longicaudata. Finally, we determined sub-lethal effects on adults of D. longicaudata that emerged from larvae that had been exposed to low concentrations of M. robertsii. Both fungi caused moderate mortality to D. longicaudata adults. There were no adverse effects on the longevity of parasitoids that emerged from parasitized larvae exposed to M. robertsii. Based on these results, we argue that M. robertsii has the potential to be used for biocontrol of A. ludens, with limited risk to D. longicaudata adults.