Optimizing Western Flower Thrips Management on French Beans by Combined Use of Beneficials and Imidacloprid.

Johnson Nyasani,Sevgan Subramanian,Hans-Michael Poehling,Rainer Meyhöfer,Sunday Ekesi,Nguya Maniania

doi:10.3390/insects6010279

Abstract

Western flower thrips (WFT), Frankliniella occidentalis (Pergande), is an important pest of vegetable crops worldwide and has developed resistance to many insecticides. The predatory mites Neoseiulus (=Amblyseius) cucumeris (Oudemans), the entomopathogenic fungus Metarhizium anisopliae (Metsch.), and an insecticide (imidacloprid) were tested for their efficacy to reduce WFT population density and damage to French bean (Phaseolus vulgaris L.) pods under field conditions in two planting periods. Metarhizium anisopliae was applied as a foliar spray weekly at a rate of one litre spray volume per plot while imidacloprid was applied as a soil drench every two weeks at a rate of two litres of a mixture of water and imidacloprid per m2. Neoseiulus cucumeris was released every two weeks on plant foliage at a rate of three mites per plant. Single and combined treatment applications reduced WFT population density by at least three times and WFT damage to French bean pods by at least 1.7 times compared with untreated plots. The benefit-cost ratios in management of WFT were profitable with highest returns realized on imidacloprid treated plots. The results indicate that M. anisopliae, N. cucumeris, and imidacloprid have the potential for use in developing an integrated pest management program against WFT on French beans.

Highlights

French bean, (Phaseolus vulgaris L.) (Fabales: Fabaceae), is the second most important horticultural export crop after cut flowers in Kenya, constituting nearly 24% by volume and value of all fresh horticultural exports [1]
In the first planting period the interaction between treatment and sampling time on the number of adult western flower thrips (WFT) recorded on French bean plants was not significant by RM-analysis of variance (ANOVA) (F35,144 = 0.636, p = 0.940)
The results of the present study indicate that M. anisopliae, N. cucumeris, and imidacloprid have the potential for use as components in developing an integrated pest management program against WFT on French beans

Summary

Introduction

French bean, (Phaseolus vulgaris L.) (Fabales: Fabaceae), is the second most important horticultural export crop after cut flowers in Kenya, constituting nearly 24% by volume and value of all fresh horticultural exports [1]. Attacks by various pests and diseases remain a limiting factor for French bean production and marketing [2]. The main pests attacking French beans are thrips, whiteflies, aphids, and the bean fly [2]. The western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is considered to be one of the most important pests affecting French bean production [2,3,4]. Farmers commonly use synthetic chemical pesticides to control pests and diseases on French beans. WFT is difficult to control with insecticides because of its cryptic feeding habit, ability to pupate in the soil [5], and fast development of resistance to the commonly used synthetic chemical insecticides [6,7]. Biological control could be a major component of IPM programs of WFT [9]

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Conclusion