Chilli Thrips, Scirtothrips Dorsalis: A Potential Threat to Cotton Production in the USA

The chilli thrips, Scirtothrips dorsalis Hood is a serious pest of various vegetable crops, cotton, citrus and other fruit and ornamental crops in its principal range of southern and eastern Asia, Africa, and Oceania where it is known to kill newly emerged seedlings, severely distort leaves and scar the surface of fruits of its favored hosts. Detection of S. dorsalis larvae and adults in fresh vegetation is difficult due to their thigmotactic behavior and tiny stature (< 2mm in length).  Eggs are deposited within plant tissues and may take a week for larval emergence. Consequently, chances of transportation of S. dorsalis through state, regional and international trade of plant materials for all life stages are high.  Within five years of its introduction into the U. S., S. dorsalis has become established in 30 Florida counties, 8 counties in Texas with several positive reports of interception in New York, Alabama, Louisiana and California. Studies involving host preference, age specific abundance, within plant distribution and seasonal abundance of S. dorsalis were conducted to evaluate its pest status on cotton. Cotton was found to be the most preferred host plant among the three hosts (cotton, peanut and pepper) evaluated. Highest abundance of S. dorsalis was reported on 1-5 week old cotton plants with a maximum damage rating of 3.8 out of 5. No damage was observed on 8 and 9 week old cotton plants. Studies to determine within plant distribution of S. dorsalis showed abundance of S. dorsalis was significantly higher on upper young leaves of cotton compared to middle and basal leaves. Significantly high abundance of S. dorsalis larvae and adults were reported in the months of July and August.  Our results indicate that if given the opportunity, this pest could be a threat to cotton production in the United States.