New research refines thrips colony management

Thrips can cause significant damage to greenhouse plants, and biological control options are becoming increasingly popular with growers. Maintaining biological control agent populations beyond the initial release in a greenhouse can be challenging. New UF/IFAS research investigates how to manage poinsettia thrips with predatory thrips and how to keep predators alive through multiple life cycles.

Predatory insects are used to help control a variety of greenhouse pests. Keeping the voracious appetite of these arthropods in check can be difficult, and their long-term survival is important to successful pest control. New UF/IFAS research provides management strategies to help biological control agent populations thrive.

"There is growing concern about the use of chemical pesticides for pest control, which has led to increased interest in the use of predatory and parasitic insects to control greenhouse pests," said Erich Schoeller, a postdoctoral researcher at the UF/IFAS.

“Unfortunately, we lack excellent alternatives to chemical control options for many greenhouse pests. It is often a game of trial and error to discover the best predator to deal with a particular pest. Something that works great for one pest might not work for another."

There are thousands of species of thrips that feed on plants. This study investigated ways to manage Echinothrips americanus , also known as poinsettia thrips, a globally important pest of many greenhouse-grown crops.

“Thrips are a particularly big problem for greenhouses, and poinsettia thrips are a pretty big thrips species,” Schoeller said. "We were looking for a really big predator for a really big pest."

The research team studied to Franklinothrips vespiformis Crawford, a generalist predator with a large appetite.

"I was surprised at how effective this predator was in a short time," Schoeller said. “We went from high pest densities to almost nothing within just two weeks of releasing the predatory thrips.”

These results were seen in many crops, including kava, poinsettia, and industrial hemp.

The predator's intense appetite is excellent for controlling pests, but once all available prey within the greenhouse has been eaten, they often starve to death. The researchers wanted to know if they could feed the insect a supplemental diet of brine shrimp eggs or cysts to maintain their populations during times of low prey population.

Many studies over the years have tested this method by feeding pollen, other insect eggs, and artificial diets to predators, but many of the diets tested are too expensive to implement in large-scale operations.

Brine shrimp eggs are commercially available and are often used as fish feed. They have been tested globally as a complementary feed for biological control agents with some consistent positive results over the last five years. However, scientists had not tested the suitability of a diet of brine shrimp eggs on this predatory species.

Turns out thrips like eggs. But not just any brine shrimp egg will work. The used cysts are specially processed and sold by a commercial insectary in Israel. Once the pest populations had been consumed by the predatory thrips, the researchers saw them complete additional generations only when the supplemental food source was provided.

"What's exciting is that we proved we could keep these predators in the greenhouse longer by feeding them," Schoeller said.

This saves growers money, so they don't have to buy predators repeatedly. It is more affordable to feed insects than to build a new colony. However, growers do not have much access to these predators. Predatory thrips are not yet commercially produced, but UF/IFAS entomologists at the Mid-Florida Research and Education Center in Apopka are working on ways to make them more widely available.

"We're hoping to find a way to rear them en masse, using the same feeding methods used in this research," Schoeller said. "Now that we know how to feed them cheaply, this is a possibility."

The researchers hope to refine the feeding process. Currently, the diet is shared among the crops inside the greenhouse. Not only is this labor intensive, but in humid climates the presence of food on the crop for long periods can cause mold to occur.

“We are adjusting how we feed these predators because our current process is not ideal,” Schoeller said. "We think we have a solution to this problem by creating feeding stations inside the greenhouse so that supplemental feeds don't need to be applied directly to the crop, but we're still working on that."

More good news: In additional research trials, these predatory thrips show potential to control other pests, including whiteflies, spider mites, and chili thrips.

"Knowing how to breed these predators is helpful, especially as we see that they have the potential to control other pests beyond our study species," Schoeller said. "This is really exciting for the future."

This work was a collaboration between UF/IFAS entomologist Lance Osborne, USDA research entomologist Cindy McKenzie, and funded by the Floriculture and Nursery Research Initiative, USDA APHIS, Farm Bill, and the Osborne NIFA Research Project. Invasive Species in High Value Crops Grown in Protected Culture.

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