Toxicity of neem oil to Bemisia tabaci biotype B nymphs reared on dry bean

Patricia Valle Pinheiro,Jaison Pereira De Oliveira,José Carlos Seraphin,Eliane Dias Quintela

doi:10.1590/s0100-204x2009000400004

Patricia Valle Pinheiro, Jaison Pereira De Oliveira + Show 2 more

Open Access

https://doi.org/10.1590/s0100-204x2009000400004

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Abstract

The objective of this work was to determine the most susceptible nymphal stage of Bemisia tabaci biotype B to neem (Azadirachta indica A. Juss.) oil applied to dry bean (Phaseolus vulgaris L.) in a screenhouse. A solution of commercial oil (Dalneem) extracted from neem seeds was sprayed directly on each nymphal instar at 0, 0.1, 0.25, 0.5, 1 and 2% concentrations for lethal concentration (LC) determination, and at 0, 0.5 and 1% concentrations for lethal time (LT) determination. The number of living and dead nymphs was recorded five days after spraying for LC determination, and daily during six days for LT determination. The LC50 estimated for fourth instar nymphs occurred at 0.56% concentration. For all instars, LC50 and LC95 were estimated at 0.32 and 2.78% concentrations, respectively. The estimated values of LT50 at 1% concentration were 2.46, 4.45, 3.02 and 6.98 days for the first to fourth instars, respectively. The LT50 occurred at five days for 0.5% and at four days for 1% concentration in all instars. A mortality rate of over 80% was observed on the 6th day for the first to third instars at 1% concentration. The first three nymphal stages were more susceptible to neem oil when compared to the fourth nymphal stage.

Highlights

Bemisia tabaci (Genn.) is a polyphagous and multivoltine insect pest responsible for high economic losses in many crops, due, in part, to the transmission of plant-pathogenic viruses
In the first experiment nymphs mortality for all nymphal stages of B. tabaci biotype B increased as neem oil concentrations increased (Figure 1), indicating a contact dosage-dependent toxic effect on B. tabaci nymphs
A phytotoxic effect was observed on dry bean leaves treated with neem oil at concentrations higher than 2%

Summary

Introduction

Bemisia tabaci (Genn.) is a polyphagous and multivoltine insect pest responsible for high economic losses in many crops, due, in part, to the transmission of plant-pathogenic viruses. Twenty different whitefly (B. tabaci) biotypes have currently been reported worldwide, named according to their native occurrence (Lima et al, 2000; De Barro et al, 2006). Biotype B is considered the most aggressive because it was distributed over various regions of the world (De Barro et al, 2000). In Brazil, large agricultural areas are successively single-cropped with whitefly host plants, such as beans, soybeans and cotton. In cropping systems like these, the intensive usage of agrochemicals to control whitefly eliminated the natural enemies of this insect as well, favoring the selection of resistant whitefly individuals (Morales & Anderson, 2001).

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