Bc. Legaspi et al., AREA-WIDE POPULATION-DYNAMICS OF SILVERLEAF WHITEFLY (HOMOPTERA, ALEYRODIDAE) AND ITS PARASITOIDS IN THE LOWER RIO-GRANDE VALLEY OF TEXAS, Journal of entomological science, 32(4), 1997, pp. 445-459
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
.