Eyes on the whiteflies
Out of the 1500 species of whiteflies worldwide, over 75 have been reported in Florida. These small white insects can cause direct and indirect damage to a broad variety of plants in the ornamental and vegetable industries. Whiteflies cause direct damage by removing the sap from the host plant. They excrete honey dew which creates a perfect resource for sooty mold development giving the affected plants a dark moldy appearance. Indirect damage can also be caused when the whitefly species vectors plant viruses.
A spotlight lover
There is a particular whitefly that is a continuous topic of conversation, Bemisia tabaci. There are multiple biotypes of B. tabaci and a couple of them are of major agricultural importance as these can be devastating for many crops. In Florida, B. tabaci Biotype A, an indigenous species of the new world, has narrow host range, seemingly, it lacks the potential to transmit viruses and up until the mid/late 1980’s was rarely a concern. With the introduction of the B biotype (a.k.a Silverleaf Whitefly) in 1985, things started to get more complicated for vegetable growers and plant producers. Unlike Biotype A, the invasive Biotype B has more than 500 host plants and has the ability to transmit more than 100 plant viruses. One of the major consequences of the establishment of Biotype B in Florida was the introduction of Tomato Yellow Leaf Curl Virus (TYLCV). This virus can eliminate fruit production if the plants are infected at an early age. Since the 1990’s, growers have been battling this pest and TYLCV which continue to impact vegetable production primarily solanaceous crops (tomatoes, eggplants, etc.). Because of the harmful effects Biotype B can have, the management of this pest is highly dependent on the use of insecticides which can give rise to insecticide resistance. Things got even more complicated back in 2004 where a new biotype was reported in Arizona. Bemisia tabaci Biotype Q (a.k.a Sweetpotato Whitefly). This new biotype quickly made its way into Florida where it was first detected in 2005 in retail nurseries. As well as Biotype B, Biotype Q is capable of transmitting plant viruses and also has a broad host range (although it has not been found yet on vegetable production except for sweet potato). What is concerning about Biotype Q is that this species is even less susceptible to the major classes of insecticides used for whitefly control. Therefore, concerns about insecticide resistance are even greater. This implies that the typical chemical control strategies used for whitefly control will not work effectively resulting in great production and economic losses. But B. tabaci story doesn’t end here. Biotype Q was restricted in greenhouses and nurseries for the last ten years after its first detection in Florida until last year, when multiple reports of Biotype Q outside of the greenhouses and nurseries triggered an alarming situation for Florida’s agriculture. The establishment of biotype Q in the field and open landscapes could be a nightmare for growers, landscapers, and home owners because of its natural potential to be resistant against commonly used insecticides. The task force with collaborations among University of Florida, U. S. Department of Agriculture and Division of Plant Industry has already established to stop the further spread of Biotype Q in Florida.
What to do?
Biotypes B and Q, are one of the major threats to agriculture and the landscaping industry in Florida. Both are morphologically identical and can be distinguished only with a molecular test. What is relevant about distinguishing among the two biotypes, is what strategy to follow to manage them. It is fundamental to understand the biological and ecological differences to approach their management more effectively. Cases like Biotype Q remind us of the importance of Integrated Pest Management (IPM) where multiple approaches are dedicated to managing pests. IPM is particularly important when insecticide resistance renders chemical control futile. To keep a close eye on B. tabaci, different institutions are partnering to accurately identify this whitefly’s biotypes and monitor the spread. Locally, whitefly samples for identification can be submitted to the whitefly identifier, Dr. Zee Ahmed at Division of Plant Industry. Please contact us at the UF/IFAS Extension office in Alachua County if you have questions about how to sample or manage whiteflies in your crops, ornamental production or landscape.
Acknowledgement: Dr. Zee Ahmed, Division of Plant Industry.