Increased and sex-selective avian predation of desert locusts Schistocerca gregaria treated with Metarhizium acridum.

Wim C Mullié,Robert A Cheke,Albertinka J Murk,Stephen Young,Abdou Baoua Ibrahim

doi:10.1371/journal.pone.0244733

Abstract

The entomopathogenic fungus Metarhizium acridum in oil-based formulations (Green Muscle® (GM)) is a biopesticide for locust control lacking side-effects on biodiversity, unlike chemical insecticides. Under controlled conditions, GM-treated locusts and grasshoppers attract predators, a complementary advantage in locust control. We assessed avian predation on a population of desert locusts in northern Niger aerially sprayed operationally with GM with 107 g viable conidia ha-1. Populations of adult locusts and birds and vegetation greenness were assessed simultaneously along two transects from 12 days before until 23 days after treatment. Common kestrels Falco tinnunculus and lanners F. biarmicus were the predominant avian predators. Regurgitated pellets and prey remains were collected daily beneath "plucking posts" of kestrels. Locusts started dying five days post-spray and GM had its maximum effect one-two weeks after the spray, with 80% efficacy at day 21. After spraying, bird numbers increased significantly (P<0.05) concurrent with decreasing desert locust densities. Locust numbers decreased significantly (P<0.001) with both time since spraying and decreasing greenness. Before spraying, kestrel food remains under plucking posts accounted for 34.3 ±13.4 prey items day-1, of which 31.0 ±11.9 were adult desert locusts (90.3%), reducing post-spray to 21.1 ±7.3 prey items day-1, of which19.5 ±6.7 were adult desert locusts (92.5%), attributable to decreased use of the plucking-posts by the kestrels rather than an effect of the spray. After spraying, kestrels took significantly (P<0.05) more larger female (75-80%) than smaller male (20-25%) locusts. Avian predation probably enhanced the impact of the GM on the desert locust population, especially by removing large adult females. No direct or indirect adverse side-effects were observed on non-target organisms including locust predators such as ants and birds. These substantial ecological advantages should also be considered when choosing between conventional chemical and biopesticide-based locust control.

Highlights

Most locusts, including the desert locust Schistocerca gregaria, are usually controlled by synthetic pesticides such as the organophosphates fenitrothion, chlorpyrifos and malathion, e.g. during the 2003–2005 desert locust upsurge [1] and during the present desert locust outbreak in Eastern Africa, the Arabian peninsula and SW Asia with over 2 million hectares being sprayed between 1 January 2019 and 31 March 2020 [2]
The results showed that Green Muscle1 containing the entomopathogenic fungus Metarhizium acridum had strongly reduced locust numbers starting about five days after spraying (Table 2), without any negative impact on acridivorous bird numbers (Table 3) which continued feeding on locusts, including impaired individuals
An increase of acridivorous birds in plots treated with entomopathogens against grasshoppers has been reported before [18, 38]. This is in sharp contrast with reports from application of synthetic pesticides such as chlorpyrifos and fenitrothion, widely used for desert locust control

Summary

Introduction

Most locusts, including the desert locust Schistocerca gregaria, are usually controlled by synthetic pesticides such as the organophosphates fenitrothion, chlorpyrifos and malathion, e.g. during the 2003–2005 desert locust upsurge [1] and during the present desert locust outbreak in Eastern Africa, the Arabian peninsula and SW Asia with over 2 million hectares being sprayed between 1 January 2019 and 31 March 2020 [2] These pesticides, if applied correctly kill sprayed locusts within hours, they kill or debilitate natural enemies of locusts, such as birds [3] and insects including Coleoptera, Hymenoptera and Diptera [4, 5]. A second strain of M.acridum (EVCH 077), marketed as NOVACRID, was registered in November 2019 by the Comite Sahelien des Pesticides for use in the Sahel

Methods

Results

Conclusion