Efficacy of Two Entomopathogenic Fungi, Metarhizium brunneum, Strain F52 Alone and Combined with Paranosema locustae against the Migratory Grasshopper, Melanoplus sanguinipes, under Laboratory and Greenhouse Conditions.

Wahid H Dakhel,Stefan T Jaronski,Alexandre V Latchininsky

doi:10.3390/insects10040094

Abstract

Grasshopper outbreaks cause significant damage to crops and grasslands in US. Chemical control is widely used to suppress these pests but it reduces environmental quality. Biological control of insect pests is an alternative way to reduce the use of chemical insecticides. In this context, two entomopathogenic fungi, Metarhizium brunneum strain F52 and Paranosema locustae were evaluated as control agents for the pest migratory grasshopper Melanoplus sanguinipes under laboratory and greenhouse conditions. Third-instar grasshoppers, reared in the laboratory, were exposed up to fourteen days to wheat bran treated with different concentrations of each of the fungi alone or the two pathogens combined. In the greenhouse, nymphs were placed individually in cages where they were able to increase their body temperatures by basking in the sun in an attempt to inhibit the fungal infection, and treated with each pathogen alone or in combination. Mortality was recorded daily and presence of fungal outgrowth in cadavers was confirmed by recording fungal mycosis for two weeks’ post-treatment (PT). For combination treatment, the nature of the pathogen interaction (synergistic, additive, or antagonistic effects) was also determined. In laboratory conditions, all treatments except P. locustae alone resulted in grasshopper mortality. The application of the pathogen combinations caused 75% and 77%, mortality for lower and higher concentrations, respectively than each of the pathogens alone. We infer a synergistic effect occurred between the two agents. In greenhouse conditions, the highest mortalities were recorded in combination fungal treatments with a M. brunneum dose (60% mortality) and with a combination of the two pathogens in which M. brunneum was applied at high rate (50%) two weeks after application. This latter combination also exhibited a synergistic effect. Exposure to the P. locustae treatment did not lead to mortality until day 14 PT. We infer that these pathogens are promising for developing a biopesticide formulation for rangeland pest grasshopper management.

Highlights

Grasshoppers (Orthoptera: Acrididae) are important rangeland herbivores that compete with other wildlife and livestock for forage [1,2]
Because mortalities of grasshoppers over 16 d were less than 50% (Table 2), the median survival times (MST) for P. locustae alone, untreated control, and short-term exposure (STE)-low M. brunneum concentration (3DM1)
This is similar to the findings of the present study, which indicate that mortality of immature grasshoppers caused by feeding on P. locustae alone occurred only at d 16

Summary

Introduction

Grasshoppers (Orthoptera: Acrididae) are important rangeland herbivores that compete with other wildlife and livestock for forage [1,2]. Each year in western United States (US) grasshoppers consume more than 20% of rangeland forages, causing damage estimated at $400 million annually in. There are nearly 500 species of grasshoppers in the 17 US western states and over 100 grasshopper species in Wyoming [4,5]. A significant effort is needed to prevent damage to rangelands and crops, which is done by large-scale insecticide applications. More than 8 million hectares of rangelands and crops were blanketed by five million liters of broad-spectrum chemical insecticides at a cost of $75 million in the mid-1980s [7]. Insecticides are still broadcast in rangelands, with almost

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