The cotton leafworm is an
important defoliating pest of cotton in Brazil, and occurs in all regions where
the crop is cultivated. The purpose of this study was to evaluate the effect of
larval densities of A. argillacea after different infestation periods on the yield components of four cotton
cultivars. The experiment was carried out in Pindorama, SP, Brazil, in the
2008/2009 growing season. The cultivars IAC-25, DeltaOPAL, Fibermax 966 and
Fibermax 993 were artificially infested with A. argillacea larvae at three times (30, 60 and 90 DAE) and four
densities (0, 2, 4, and 6 larvae per plant). The average boll weight (g), fiber
percentage (%), 100-seed weight (g) and yield (kg·ha-1)
were evaluated. With increasing infestation density of A. argillacea, the cotton yield of the cultivars decreased. The
presence of larvae significantly reduced the weight of 100 seeds of cultivar
Fibermax 966. Initial infestations reduced the boll weight of IAC-25 and
DeltaOPAL, while cultivars Fibermax 966 and Fibermax 993 were most affected by
late infestations. Early infestation compromised fiber percentage of cultivar
DeltaOPAL and late infestations were most harmful to cultivar Fibermax 966.
Early A. argillacea infestation
reduced the yield of DeltaOPAL, while infestations 60 DAE caused the most
damage to IAC-25, and the other cultivars were not affected by the moment of
infestation.