Evaluation of Possible Pathways of Introduction for Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) from the Caribbean into the Continental United States
May 24, 2005
Center for Plant Health Science and Technology
Plant Epidemiology and Risk Assessment Laboratory
The objective of this risk analysis was to identify and evaluate possible pathways by which Scirtothrips dorsalis Hood may be introduced from the Caribbean into the continental United States. This analysis was requested from CPHST by Mike Shannon, State Plant Health Director of Florida.
S. dorsalis is a serious pest in numerous countries throughout the world. If introduced into the U.S., it would be expected to attack several crops of major economic importance. Its successful invasion of the continental U.S. would be aided by its great reproductive potential, extremely wide host range, and expected ability to survive and reproduce (at least part of the year) throughout almost the entire continental U.S. Permanent establishment would be especially likely in the southern U.S. and along the West Coast.
In the Caribbean, S. dorsalis is known to occur on St. Vincent, St. Lucia and Trinidad and Tobago. It has furthermore been confirmed for Suriname and has been intercepted from Jamaica.
An expert panel consulted for this analysis rated air passengers and permit cargo as the pathways most likely to introduce S. dorsalis from the Caribbean. They were also concerned about the mail pathway, as well as smuggling. About 6.5 million air passengers enter the U.S. from the Caribbean on an annual basis. Commodities that have a high likelihood of being infested with S. dorsalis are being imported from the Caribbean into areas of the U.S. where permanent establishment may be expected. No safeguarding measures are applied to these commodities.
Detection of S. dorsalis is extremely difficult, and distinguishing it from other thrips species is basically impossible for non-experts. Increased inspection alone is therefore not very likely to prevent its introduction. Based on our analysis, it furthermore seems likely that S. dorsalis will eventually enter the U.S. through wind-borne dispersal from the Caribbean region. We therefore consider it very important that strategies for early detection and treatment in the U.S. be developed. At the same time, efforts to lower S. dorsalis population levels on currently infested Caribbean islands could help slow down the spread of this pest to other islands and to the U.S.
Our analysis resulted in the following recommendations: Conduct surveys for S. dorsalis throughout the Caribbean region in order to determine where the pest occurs and where mitigation strategies need to be applied; conduct regular surveys for S. dorsalis in the U.S., especially in locations where introduction is most likely (in order to increase the likelihood of early detection); develop educational initiatives for U.S. Cooperative Extension Experts, as well as for CBP and PPQ port inspectors; require appropriate treatments on commodities imported from the Caribbean that are known S. dorsalis hosts; develop better sampling methods and detection equipment and make them available to port inspectors.
Table of Contents
A. Objective 5
B. Background 5
C. Expected consequences of introduction into the continental U.S. 6
Host range 6
Areas of potential establishment in the U.S. 9
Potential economic impact 12
Potential environmental impact 13
D. Evaluation of potential pathways of introduction 14
E. Summary 27
F. Recommendations 27
G. Acknowledgements 28
H. Appendices 29
Appendix 1. Hosts of S. dorsalis. 29
Appendix 2. Scirtothrips species intercepted at U.S. ports of entry between January 1, 1985 – April 20, 2005. 41
Appendix 3. Commodities imported between October 1, 2001-February 14, 2005 from Caribbean countries where S. dorsalis has been confirmed. 45
Appendix 4. Agricultural commodities imported into the U.S. between October 1, 2001 and February 14, 2005 from the Caribbean. 50
Appendix 5. Questionnaire distributed to Expert group. 80
Table 1. Interceptions of S. dorsalis from origins in the Western Hemisphere between January 1, 1985 and April 20, 2005 (USDA-APHIS-PPQ 2005c). 6
Table 2. Total number of air passengers entering the U.S. from various Caribbean countries during the fiscal year 2004. (Bureau of Transportation Statistics 2005)
Table 3. Shipments of confirmed hosts of S. dorsalis from Caribbean countries where the species is known to occur (USDA-APHIS-PPQ 2005a). 20
Table 4. Total counts of forward trajectories which passed over nearby regions, from a start point of St. Lucia (13°53' N, 60°68' W). 26
Table 5. Length of time it took for forward trajectories to reach the border of nearby regions, from a start point of St. Lucia (13°53' N, 60°68' W). 26
Figure 1. Predicted number of S. dorsalis generations per year in the continental U.S. and Mexico (based on a generational requirement of 281 DD and a base and upper development temperature of 9.7°C and 33.0°C, respectively). 9
Figure 2. Generational potential outside of the predicted cold temperature exclusion boundary (areas where the minimum daily temperature reaches -4ºC or below on 5 or more days per year) for S. dorsalis in the U.S. and Mexico. 10
Figure 3. Acreage of peppers, eggplant and tomatoes grown per county in 2002 (overlaid with a cold temperature exclusion boundary where the minimum daily temperature reaches -4ºC or below on 5 or more days per year). 11
Figure 4. Acreage of 34 S. dorsalis hosts3 grown per county in 2002 (overlaid with a cold temperature exclusion boundary where the minimum daily temperature reaches -4ºC or below on 5 or more days per year). 11
Figure 5. Average of the risk ratings scored from the Expert Opinion Questionnaire for the air passenger, cargo, express mail, mail and smuggling pathways. 18
Figure 6. Number of agricultural shipments that arrived from the various Caribbean countries between Oct. 1, 2001 and Feb. 14, 2005 (USDA-APHIS-PPQ 2005a). 22
Figure 7. Number of Caribbean agricultural shipments that entered the U.S. between Oct 1, 2001 and Feb 15, 2005 in areas where permanent establishment of S. dorsalis is likely to occur. 23
Figure 8. HYSPLIT analysis showing the paths and altitudes of trajectories at starting heights of 100m (▼), 200m () and 500m (○) above ground level, from St. Lucia (13°53' N, 60°68' W) on 9/1/04. 25