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Whitefly and whitefly-borne viruses in the tropics : Building a ... - cgiar

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Conclusions <strong>and</strong> Recommendations<br />

CHAPTER 3.14<br />

Conclusions <strong>and</strong> Recommendations<br />

Despite over 40 years of research on<br />

Bemisia tabaci (Gennadius)<br />

(Homoptera:Aleyrodidae) as a pest <strong>and</strong><br />

vector of plant <strong>viruses</strong>, this <strong>whitefly</strong><br />

species cont<strong>in</strong>ues to cause<br />

considerable damage to food <strong>and</strong><br />

<strong>in</strong>dustrial crops <strong>in</strong> Mexico, Central<br />

America <strong>and</strong> <strong>the</strong> Caribbean. B. tabaci<br />

first became a pest of cotton<br />

(Gossypium hirsutum L.) <strong>in</strong> Middle<br />

America, <strong>and</strong> <strong>the</strong>n a major vector of<br />

plant <strong>viruses</strong> <strong>in</strong> common bean<br />

(Phaseolus vulgaris L.) <strong>and</strong> tomato<br />

(Lycopersicon esculentum Mill.)<br />

plant<strong>in</strong>gs throughout <strong>the</strong> region. The<br />

expansion of non-traditional crops <strong>in</strong><br />

<strong>the</strong> 1980s, ma<strong>in</strong>ly vegetables for<br />

export, fur<strong>the</strong>r aggravated <strong>the</strong> problem<br />

by provid<strong>in</strong>g more reproductive hosts<br />

for <strong>the</strong> <strong>whitefly</strong> pest <strong>and</strong> a higher<br />

dem<strong>and</strong> for pesticides. The<br />

<strong>in</strong>troduction <strong>in</strong> <strong>the</strong> early 1990s of a<br />

more aggressive <strong>and</strong> polyphagous<br />

biotype (B) of B. tabaci <strong>in</strong> <strong>the</strong> Americas<br />

fur<strong>the</strong>r jeopardized past efforts to<br />

control this pest.<br />

In this region, <strong>whitefly</strong>-<strong>borne</strong><br />

gem<strong>in</strong>i<strong>viruses</strong> (begomo<strong>viruses</strong>) are<br />

more prevalent dur<strong>in</strong>g <strong>the</strong> dry months<br />

of <strong>the</strong> year (November through April),<br />

when B. tabaci populations encounter<br />

more favourable wea<strong>the</strong>r. The area<br />

planted to crops such as melon<br />

* Centro Internacional de Agricultura Tropical<br />

(CIAT), Cali, Colombia.<br />

Francisco Morales*<br />

(Cucumis melo L.), common bean,<br />

tomato, eggplant (Solanum melongena<br />

L.), cucurbits <strong>and</strong> sweet <strong>and</strong> hot<br />

peppers (Capsicum spp. L.) has been<br />

reduced greatly or completely<br />

ab<strong>and</strong>oned dur<strong>in</strong>g this period of <strong>the</strong><br />

year because of <strong>the</strong> frequent outbreaks<br />

of whiteflies <strong>and</strong> <strong>whitefly</strong>-<strong>borne</strong> <strong>viruses</strong>.<br />

The development of B. tabaci from a<br />

harmless <strong>in</strong>sect to a major pest is<br />

closely related to <strong>the</strong> <strong>in</strong>troduction <strong>and</strong><br />

<strong>in</strong>tensive use of pesticides after <strong>the</strong><br />

Second World War. Pesticide abuse<br />

rema<strong>in</strong>s a major factor <strong>in</strong> B. tabaci <strong>and</strong><br />

begomovirus epidemics <strong>in</strong> this region.<br />

Whiteflies are known to develop<br />

resistance to <strong>in</strong>secticides, <strong>the</strong> frequent<br />

use of which elim<strong>in</strong>ates natural<br />

predators of B. tabaci. It is not<br />

uncommon to see farmers spray<strong>in</strong>g<br />

<strong>in</strong>secticides on susceptible crops every<br />

o<strong>the</strong>r day <strong>and</strong> even daily, up until<br />

harvest time, <strong>in</strong> open defiance of food<br />

safety regulations. The high levels of<br />

pesticide residues <strong>in</strong> tomato, pepper,<br />

common bean, eggplant <strong>and</strong> o<strong>the</strong>r<br />

vegetables attacked by B. tabaci<br />

disqualifies <strong>the</strong>se products for sale <strong>in</strong><br />

<strong>in</strong>ternational markets <strong>and</strong> constitutes a<br />

serious health hazard for <strong>the</strong> millions<br />

of rural <strong>and</strong> urban consumers <strong>in</strong> <strong>the</strong><br />

region, where produce is not tested for<br />

toxic residues.<br />

But <strong>the</strong> ma<strong>in</strong> reason for <strong>the</strong><br />

persistence of <strong>the</strong>se pest problems is<br />

<strong>the</strong> lack of qualified technical<br />

assistance for farmers, particularly<br />

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