Impact of insecticides on the efficacy of entomopathogenic nematodes against the diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae) on cabbage in northern Benin

Brice G. Sinhouenon,Hugues Baimey,Rufin Dossou,Regis B. Ahissou,Laura Wauters,Bruno Schiffers,Wilfrida Decraemer

doi:10.25518/1780-4507.18134

Abstract

Description of the subject. The article deals with the study of compatibility of entomopathogenic nematode (EPN) species with insecticides currently used against diamondback moth (DBM) Plutella xylostella (L.) in northern Benin Objectives. The aim of this work was to determine the impact of five insecticides on the efficacy of entomopathogenic nematodes against DBM larvae. Method. Infective juveniles (IJs) of two EPN species (Steinernema sp. 83a and Heterorhabditis sonorensis KF723827) were exposed to five insecticides used against P. xylostella larvae in Djougou for 48 h. The number of surviving nematodes was used to infest DBM larvae. The experiment was carried out under laboratory and semi-field conditions. Results. The bioassays carried out in laboratory showed that the survival rate of nematodes exposed to KARATE 2.5 WG, LAMBDA SUPER 2.5EC or neem oil ranges between 95% and 98%. In the treated plots, Steinernema sp. 83a was the most virulent with the highest P. xylostella mortality (87% at 50 IJs·cm-2 after 24 h) while only 35% larval mortality was recorded for H. sonorensis applied at the same dose. Population density of nematodes which penetrated DBM larvae reached 9 ± 3I IJs·larva-1 for H. sonorensis KF723827 and 6 ± 2 IJs·larva-1 for Steinernema sp. 83a. In cadaver of DBM, nematode reproduction did not appear to be affected by the contact with insecticides. Conclusions. Based on our research, we conclude that the three insecticides did not affect EPNs efficiency and could be used in combination against DBM.

Highlights

The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), is the most destructive insect pest of cruciferous plants throughout the world (Sarfraz et al, 2006; Syed et al, 2012)
This study provides the first evaluation of efficacy of Entomopathogenic nematodes (EPN) against DBM larvae in West Africa
Results from the IJs doses screening showed that DBM larvae are highly susceptible to infection by EPN at 50 and 100 IJs.cm-2, this implies that DBM larvae were favorable hosts of the two EPN species tested and that the symbiotic bacteria associated with the nematodes are lethal to the larvae

Summary

Introduction

The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), is the most destructive insect pest of cruciferous plants throughout the world (Sarfraz et al, 2006; Syed et al, 2012). Management costs and yield losses are estimated up to US$ 4-US$ 5 billion (Zalucki et al, 2012). In Benin, the DBM causes considerable economic losses to cabbage and other crops such as egg-plant, black mustard, broccoli, kale, radish, turnip and watercress (James et al, 2010). In West Africa the control of this pest lies mostly on synthetic hazardous insecticides (James et al, 2010). Zalucki et al (2012) suggested that greater efforts at implementation of integrated pest management (IPM) would reduce insecticide inputs considerably, reducing health problems, negative environmental impacts and saving many millions of dollars annually

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Conclusion