By: Michelle Klug
Photos provided by: Lance Osborne

While Americans everywhere enjoy plump, juicy tomatoes straight from the Florida sunshine, they may not know that a papaya plant wasp is helping to keep their beloved red vegetables disease free.

Florida is the dominant supplier of fresh tomatoes in the eastern United States, with 29 thousand acres devoted to tomato production in 2009-10 and a total revenue impact of over $1.64 billion annually, according to Alan Hodges, IFAS agriculture economic analyst.

However, the sunshine state’s prized cash crop is often prone to disease. One known culprit, Tomato Yellow Leaf Curl Virus (TYLCV), occurs when an infected silverleaf whitefly (Bemisia tabaci) feeds on tomato plants and spreads the virus. Named for the yellowing and curling of the leaves, TYLCV causes a drastic decrease in tomato yield and may even kill the plant.

"Most greenhouse growers will just cut that plant out and destroy it immediately," said IFAS Researcher Lance Osborne. "It’s a very severe problem."

Osborne, researcher at the Mid-Florida Research and Education Center in Apopka, has found that Papaya plants host a small wasp that attacks this infectious whitefly and acts as a biocontrol, a naturally occurring control mechanism.

"The Encarsia sophia is a little, tiny wasp – almost the size of the head of a pin," Osborne said. It’s in the environment, it’s flying all over Florida – people just don’t know it’s there."

Osborne said that the wasp does not attack people or other insects and is even specific in the kind of whitefly it feeds on.

The method Osborne and post-doctoral scientist Yingfang Xiao tested was the Banker Plant System, a specific type of biocontrol that involves intentionally placing plants that host parasitoids within range of unwanted pests for a natural control system.

To test this system, Osborne reared colonies of the predator wasp and the unwanted silverleaf whitefly, as well as a harmless whitefly (Trialeurodes variabilis). This harmless whitefly only lives on papaya plants and is essential in getting the wasps established to papaya plants before they can be used as a biocontrol. Wasps feed on the papaya whiteflies and they increase in number. After the papaya whiteflies and wasps were properly established to papaya plants, they were placed in the vicinity of tomato, cucumber, eggplant and many ornamental plants.

Results showed that the harmless whitefly stayed on the papaya plants (demonstrating that it is no risk to other plants), the infectious silverleaf whitefly preferred the tomato plants and the parasitic wasp, E. Sophia, effectively eliminated many diseased whiteflies feeding on tomato plants – proving that utilizing the Banker Plant System can act as a natural control agent for this serious pest of over 900 host plants.

Cindy McKenzie, entomologist for the USDA Agricultural Research Service, had previously determined that papaya plants are not a host for TYLCV – a crucial step in the implementation of these plants in the banker plant strategy. Papaya plants proved to be a valuable reservoir for beneficial parasitoids that feed on unwanted pests.

As well as leading the way for a more sustainable production process, this biocontrol strategy helps to solve a common pesticide problem.

"In our industry, one of the biggest problems we have is pesticide resistance," Osborne said.

Insects such as the silverleaf whitefly become resistant to insecticide chemicals and farmers are left with fields of unproductive plants.

"It allows us to back off of the 100 percent dependence we had on pesticides - That’s the number one benefit of this, "Osborne said.

Use of pesticides can impede the natural pollination process by killing off natural pollinators.

"If you have to use insecticides, it will impact your bumble bees and the pollination process," Osborne said. "Tomato plants must be pollinated in order to produce fruit. It’s very expensive to send people through the greenhouse and not as effective as using bumble bees."

Osborne said this study applies to greenhouse farming and outside crop systems, as well as smaller gardens.