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Square Abscission in California Cotton and the Stage Structure of Western Tarnished Plant Bug Populations

Andrew G. Zink and Jay A. Rosenheim


There is often a large amount of unexplained variability between the number of Lygus observed in a cotton field and the amount of damage the crop sustains. This study attempts to bridge the gap in our understanding by examining relationships between the stage structure of Lygus hesperus populations and overall damage to cotton squares. We sampled 38 fields of upland cotton during June through August of 2001-2003 in the cotton growing region of the San Joaquin Valley, CA. In these fields Lygus werecollected and counted in sweep samples and later identified to developmental stage. In addition, cotton plants were mapped for square retention, and squares were dissected to assess overall damage to anther sacs. A multivariate regression revealed that 4th and 5th instars are positively correlated with anther sac damage and negatively correlated with square retention. Adult Lygus are only marginally correlated with plant damage, and 1st through 3rd instars did not correlate with plant damage. Finally, subsampling at each of five sites within cotton fields in 2003 revealed that adult densities positively correlate with plant damage. This result opens up possibilities of managing Lygus on a site by site basis. Overall, our analyses suggest that late instars of Lygus hesperus are particularly damaging to cotton squares, having the largest impact on square abscission. Therefore it is important for field scouts and entomologists to pay close attention to these developmental stages when collecting Lygus in sweep nets.

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Document last modified 04/27/04