Prof. Greg Loeb Protects Plants From Pests With Natural Predators

Entomology professor leads an effort to develop inexpensive, environmentally friendly methods of controlling pest populations in agriculture...


By Nicolas Ramos via the Cornell Daily Sun, 2/27/13

Insect infestations can wreak havoc on crops, and are traditionally controlled through pesticides producing unwanted environmental and ecological side effects. Prof. Greg Loeb, entomology, studies the interactions between plants and insects in an effort to develop inexpensive, environmentally friendly methods of controlling pest populations in agriculture.

Plants create their own energy through photosynthesis, so they are considered primary producers at the first trophic level – or position – in the food chain. Herbivores, which include most of the problematic insects in agriculture, are primary consumers, and are placed at the second trophic level. The third trophic level is made up of secondary consumers, or carnivores that eat the herbivores, according to Loeb.

One of Loeb’s main projects is studying tri-trophic interactions, or how plants in the first trophic level and predators at the third trophic level affect one another.

“We are trying to understand what benefits the plant provides to natural enemies and the potential costs there might be to the plant,” Loeb said. “In the case of our system, we have a good idea of the benefits the predators are providing to the plants.”

Loeb has shown that small hairs on grape leaves can influence predatory mites that live on the plants. These predatory mites provide a crucial benefit to the plant: They feed on the pest mites that eat the plants and cause damage.

“We want to promote the beneficial insects and the predatory mites, as a way to better manage the pests that feed on the plants,” Loeb said.

In collaboration with a geneticist, Loeb is working to determine the mechanisms by which certain plant morphological traits influence predatory mites. Through the process of marker-assisted selection, researchers can identify positive traits in different grape varieties.

Loeb is also investigating whether or not a positive morphological trait is correlated with a negative trait. According to Loeb, if there is an association between two traits, researchers must be careful to decouple the good trait from the bad trait before attempting to promote a particular morphology in a plant.

“By promoting positive morphological traits, we can enhance the natural enemies of the pest mites and indirectly increase the role of the plant in its own defense,” Loeb said. “Miticides can be very expensive and can be disruptive, so the ultimate goal would be to reduce the monetary and environmental costs of chemical control in the grape commodity.”

Loeb is also working with Heather Connelly grad to examine whether scientists can use natural means to increase ecosystem services in strawberry production. Ecosystem services are services provided by organisms in the environment that are beneficial. These include things such as pollination and decomposition, which are conducted by a wide variety of organisms.

Loeb and Connelly are looking at ways to augment pollination and biological control in strawberry systems by adding plant diversity.

By adding native perennial wildflowers to the strawberry fields, the flowers provide nectar and other resources to pollinators and parasitoids, or insects that lay their eggs in other insects. A particular parasitoid, the braconid wasp, lays its eggs in the body of the tarnished plant bug, a pest in strawberry fields that damages the fruit. Adult braconid wasps feed on nectar, so their presence poses no threat to the crops.

“The idea is that parasitoid wasps will move into the strawberries once we put wildflowers in proximity and attack the tarnished plant bugs,” Loeb said.

The braconid wasp is sensitive to insecticide, but it is very effective at biological control. By providing a habitat to the braconid wasp, researchers are simultaneously reducing their use of insecticides and regulating populations of tarnished plant bugs.

Wildflowers can also benefit pollinating insects, which are important for the size of the strawberries. Although strawberries can self-pollinate, the size of the fruit is larger if insects pollinate the plant.

“We are looking to see how we can increase the activity of native bees,” Loeb said. Part of this project is to see how landscape affects the addition of the wildflower resources.

“Certain landscapes may be more amenable to this manipulation, so we are looking to see what kinds of environments the addition of wildflowers would work best in,” Loeb said.

Loeb co-teaches ENTOM 3200: Grape Pest Management in the fall semester.

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