Author: Richard Stouthamer and Joseph Morse

February 2007, avocados from outside the U.S. were allowed into California for the first time. During the first months of importation, CDFA inspectors at the border between Arizona and California found several species of armored scale insects on avocados imported from Mexico, that were not known to occur in California nor anywhere in the U.S. The detection of these scales on the fruit was not deemed to be important by USDA-APHIS because they had determined that scale insects on fruit in general pose a low risk of population establishment (this is in contrast with scale insects found on imported plants). Partially because of the presence of these scales on avocado and concerns expressed by CDFA and the CAC, this determination was reexamined at a USDA-APHIS science panel in May 8-9, 2007. Following the panel meeting, USDA-APHIS did not change their risk assessment and maintained that armored scale insects pose little risk with this policy affecting all imported fruits and vegetables (all “commodities for consumption”). The low risk associated with living scales on fruit was based in part on the fact that adult female scale insects are sessile and establishment of new populations would need to rely on the movement of the tiny, short-lived, first instars (crawlers) that were thought to mainly move about by walking short distances (< 4 feet) or by being blown around by the wind. We were asked by the CAC initially to determine which scale species were present and how many were present on the imported fruit. We established a sampling program, and developed a quick DNA-based method for the accurate identification of the species present on the fruit, and observed that huge numbers of living scales were imported on Mexican avocados (> 60 million during our initial 8 month sampling period). Many of the species were not known from the U.S. One of the species was even new to science. Next we investigated how crawlers disperse and in contrast to dispersal mainly by wind or walking, we found that crawlers hitchhike along with flying insects and could be transported long distances. Thus crawlers present on fruit do have a method of long-distance dispersal. We have published all of these findings in short order because USDA-APHIS largely considers research data published in refereed journals as possible reasons to revise a pest risk assessment. USDA-APHIS is presently re-examining their previous pest risk assessment and this revision is scheduled to be finished by December 2011.