A devastating tropical and subtropical pest that's already considered one of the world's top invasive species just got a bit more troublesome.

The silverleaf whitefly (Bemisia tabaci) threatens a wide range of crops. Of the more than 20 known biotypes of this species, two of the most devastating are the B and Q biotypes. While the B type has been in the United States since its discovery in 1985, now type Q has been identified in 25 states.

For years, Agricultural Research Service (ARS) scientists in the Subtropical Insects Research Unit at Ft. Pierce, Fla.--led by entomologist Cindy McKenzie and molecular biologists Bob Shatters and Laura Boykin--have worked with collaborators on extensive studies of the B and Q biotypes.

Both types of whiteflies can reduce the yield of a broad range of agricultural, fiber, vegetable and ornamental crops. The aggressive B biotype arrived here from its native Middle East and Asia Minor range. It threatened agricultural production throughout the southern United States until new integrated pest management strategies brought it into check. Now, the Q type brings new challenges.

The newly arrived biotype was first detected in the United States in December 2004 on poinsettias from an Arizona retail outlet. Compared to the B biotype, Q is less susceptible to many pesticide types, which means there are fewer chemical options for its control. There is also concern that resistance to insecticidal controls may occur more rapidly in the Q biotype.

With the help of the ARS scientists, a Q biotype task force was set up to develop new control recommendations. Nationwide monitoring suggests that these improved recommendations are helping to slow or prevent the movement of the Q biotype into commercial vegetable fields. For now, rapid implementation of the new control strategies has greatly reduced control problems.

Detailed information about the task force and its findings is available online at: http://www.mrec.ifas.ufl.edu/LSO/bemisia/bemisia.htm.

ARS is a scientific research agency of the U.S. Department of Agriculture.