AREA-WIDE POPULATION-DYNAMICS OF SILVERLEAF WHITEFLY (HOMOPTERA, ALEYRODIDAE) AND ITS PARASITOIDS IN THE LOWER RIO-GRANDE VALLEY OF TEXAS

The population dynamics of the silverleaf whitefly (SLWF), Bemisia arg entifolii Bellows and Perring (= sweetpotato whitefly, B. tabaci Bioty pe ''B'', [Gennadius]), and its endemic parasitoids (mostly Encarsia s pp. [Aphelinidae]) were monitored in a heterogeneous cropping area, co nsisting of cotton, cantaloupe and kenaf(tall fiber crop). To assess t he suitability of the whitefly for areawide pest management, we compar ed estimates of population densities using different sampling methods and determined the effects of agronomic practices on the whitefly and parasitoid populations. There was no correlation between adult SLWF es timates using sticky traps and those counted directly on the leaves. H owever, counts of immatures using disk subsamples were found to be goo d predictors of whole leaf counts. SLWF counts were law in cotton, unt il the han est period of cantaloupes, which may have triggered migrati on from cantaloupe to cotton. The determinants of emigration from cott on were less clear. High numbers of adults were migrating well before harvest or the application of a defoliant, One likely contributing fac tor in triggering whitefly migration was leaf senescence. Despite rath er high adult densities sampled in kenaf, populations of immature SLWF were low, suggesting that it is not a preferred host. Parasitoid popu lations were high in the kenaf fields, causing 20 to 80% parasitism an d suggesting that kenaf could serve as a reservoir of natural enemies within a larger cropping system, Parasitism in cotton was less than th at in kenaf, usually at -10 to 15%. Encarsia spp, sampled on sticky tr aps indicated significant activity of the adults in the cotton and ken af fields, and much lower numbers in the cantaloupe. Because it is a d ispersive and polyphagous pest, areawide suppression of SLWF must incl ude the consequences of farming practices and cropping patterns in het erogeneous fields, especially when they are under different management .