Diaspidid scale insects on imported fruit are a substantial risk Richard Stouthamer and Joseph Morse Department of Entomology, University of California, Riverside
USDA finding: Living scales present on fruit for consumption do not pose a substantial risk Finding by USDA-APHIS 1986 Reason: How can scale insects move from fruit to trees? Assumptions Scale crawlers are the only stage that can disperse and settle Live only a short time (cannot move very far walking) Method of dispersal generally by wind
Life Cycle
Avocado Production in California Approximately 27,500 ha (68,000 acres) with an annual crop value of $300-400 million First commercial planting in 1908, no regular/ severe arthropod pest problems until 1990 USDA imposed a quarantine on seed-containing avocados in 1914 (avocado seed weevil, avocado seed moth) As of 25 Feb. 1997, Mexican avocados allowed to enter 19 northeastern U.S. states, Nov.-Feb. In 2001, allowable states expanded to 31, season 15 Oct. to 15 Apr. 1 Feb. 2007, all 50 states opened to shipment year round
Diaspididae on Mexican Avocados Entering CA USDA-APHIS - as of 2000, avocado fruit have been added to the list of commodities which do not require action when armored scales are intercepted on commercial shipment Armored scales seen on fruit soon after Mexican avocados when allowed into California 1 Feb. 2007 Science Panel meeting May 2007 requested by CDFA due to high levels of scales seen, untenable differences between CDFA policy (fumigate exotic scale loads or not enter CA), Homeland Security/APHIS (ignore) As of 28 March 2008 APHIS expanded no action policy to all consumption commodities
Blythe Border Station Sampling Sampled 1 carton per truck from 102 trucks that entered CA on seven 4.5-day periods 9/20/08-1/7/09 9 species found, 8 are thought to be exotic to California Live eggs or crawlers found in 84/140 cartons (60%) 92% of cartons had live scales; 2/140 cartons had no scale Most common scale was Abgrallaspis aguacatae (new species named 1/09) Data extrapolated to the whole truck, all fruit entering CA
Abgrallaspis aguacatae Abgrallaspis aguacatae Abgrallaspis aguacate Acutaspis albopicta Diaspis miranda Diaspis nr. miranda (thin cover) Hemiberlesia lataniae (CA) Hemiberlesia sp. nr lataniae (MX) California red scale (CA)
Multiplex PCR technique for rapid identification of the diaspidid scales on Avocado Rugman-Jones, P.F. et al.(2009) Rapid, molecular identification of armored scale insects (Hemiptera: Diaspididae) on Mexican Hass avocado. Journal of Economic Entomology 102:1948-1953.
Results of border sampling
How many scales come into California? Species No Fruit Live Scales Live + dead scales Live eggs and crawlers Total in our samples 7,343 A. aguacatae 4,694 18,890 1,781 Other scales 553 5,427 730 Total 5,247 24,317 2,511 Extrapolated total for California for 8 months from Sept 2007-April 2008 67 million A. aguacatae 42 million 156 million 14 million Other scales 5 million 52 million 5.6 million Total 47 million 208 million 20 million Morse, JD et al 2009. High Levels of Exotic Armored Scales on Imported Avocados Raise Concerns Regarding USDA APHIS Phytosanitary Risk Assessment. Journal of Economic Entomology 102: 855-867
Where do they go in California? Packing houses for repacking and distribution to retail Several of these packing houses are located in the middle of avocado orchards
Concerns Regarding Mexican Scales Law of Truly Large Numbers With a large enough sample, rare events are likely to occur (e.g., woman who won the New Jersey lottery twice) Chance that they establish simply because of the huge numbers should be substantial How do crawlers disperse to find places to settle? Short distance walking and settling close to mother Long distance by wind dispersal Tested their ability to be blown by the wind Appeared to be able to hang on to perches despite high wind speeds How could they hang on so well?
Scale crawler on elytrum of coccinellid beetle
Phoretic transport of crawlers by insects in the lab Do crawlers climb on other insects? Allowed Cryptoleamus beetles to walk on lemon leaf (5.5 cm* 5.5 cm) with 50-100 crawlers for one minute or five minutes Mean number of crawlers per beetle after: One minute: 1.2 crawler Five minutes : 1.5 crawler Conclusion: Crawlers will climb on host insects, similar results on houseflies, drosophila and ants
Can they be transported to new hosts and settle?- YES Magsig-Castillo et al 2010. Phoretic dispersal of armored scale crawlers. Journal of Economic Entomology 103: 1172-1179
Will they remain attached when insects fly?- YES Confine crawlers with 100 beetles in vial Open vial collect 50 beetles upon release, determine crawler number Allow 50 beetles to fly in small room to window Fly at least two meters, most likely more Collect beetles at window after 20 or 60 minutes Determine crawler number
Do insects transport crawlers in the field? - YES Place a squash producing crawlers with malaise traps around squash Collect insects from ethanol and search for crawlers Control experiment throw a large number of crawlers into the upright part of the malaise trap: results no crawlers reach the ethanol trap Field experiments from 0-8 crawlers per trap per week Still need to determine how many crawlers demount their host before the host falls in the ethanol
USDA-APHIS should reconsider their finding that scale insects on fruit pose a low risk Scales insects arrive alive in CA 8 months a total of ~22 million living crawlers/eggs Phoresy allows them to cover longer distances They end up in packing houses in close proximity to Avocado groves Obviously avocados grow there, presumably the climate is also suitable for the scales So they are there in large numbers, have a way to make it from dumpsters with culled fruit to the grove by phoresy Since large numbers come in, there should be a good chance that both males and females will settle and be able to find each other so that populations can establish Solution clean up the fruit before it is shipped
Acknowledgements: Molecular Expertise: Dr. Paul Rugman-Jones Taxonomy Expertise: Dr. Gillian Watson Scale Processors: Lindsay Robinson, Alan Urena, Pamela Watkins, Heavenly Clegg, Lorena Baste-Pena CDFA Assistance with Blythe Border Station samples: Gary Leslie, Michael Hoffman & Inspectors; Dennis Day, Abraham Sandoval, Phillip Tennefos and Rosalia Villa Funding: California Avocado Commission