Silicon amendments may provide sustainable control for rice water weevil

A Masters student at Louisiana State University is seeking a more sustainable way to manage rice water weevil, by amending soils with silicon to strengthen the plant. He is also this year’s winner of the Friends of Southern IPM Graduate Student award in the Masters category.

Rice water weevil is a tiny insect that feeds on the rice plant’s leaves as an adult. After mating, females lay their eggs at the base of the plant. Larvae feed on the roots. The larval feeding on the roots potentially interferes with the nutrient uptake, thereby, weakening the plant. Root damage can cause yield losses through decreasing panicle densities, number of grains, and grain weight. Rice growers use insecticides to control rice water weevil.

James Villegas holds a rice plant starting to tiller. Credit: Lina Bernaola, LSU

LSU student James Villegas, now beginning his doctoral work, has been studying the effects of soil silicon amendment on rice water weevil density. Silicon is added to the soil as a fertilizer, but it has the added benefit of making the rice stalk stronger.

“Silicon increases the hardness of plant tissues, so it’s harder for insects to feed on the plants,” Villegas says. “Several countries in Asia have been amending their soils with silicon to manage rice insect pests.”

Silicon acts as a mechanical barrier to insect feeding because it requires the insect to use more force to penetrate the stem. In an experiment to test how silicon affected penetration force for rice stem borer, Villegas found that silicon-treated plants required a higher force for stem penetration than did untreated plants.

Villegas hypothesized that silicon amendments might lower rice water weevil density. Several studies have shown that silicon reduces rice stem borer damage, but the effect on rice water weevil density has not been proven. The amendments do help with yield, however.

Force gauge to measure stem hardness.

Field experiments were conducted at H. Rouse Caffey Rice Research Station in Crowley, Louisiana. Because many of the test plots may have initially high silicon content, Villegas says that additional silicon did not yield definite pest management results for rice water weevil.

Whiteheads due to stem borer feeding at reproductive stage of rice. Credit: James Villegas

“In some plots, we saw there were less weevil larvae in silicon treated plots, and in other plots, it’s the same as in the untreated plots,” Villegas says. “We also assessed whiteheads, which are unfilled panicles caused by stem borer feeding at the reproductive stage of rice. We saw in some plots there were fewer whiteheads in the silicon treated plots, but in other plots, it wasn’t different.”

Villegas surmises that the reason for the differences could be that the soil already has so much silicon that amending it doesn’t change anything.

As a result, he and advisor Michael Stout will be taking their experiment to two locations outside of the rice research station.

“We’ve located two places where silicon levels in soil are potentially really low,” Villegas says. “We expect that we’ll see a more significant result compared to what we’ve seen at the rice station.”

Villegas collects adult rice water weevil

He also plans to examine weevil-tolerant varieties and see if silicon improves their tolerance to the rice pest complex. Currently, there are no rice varieties that possess high levels of resistance to rice water weevil. An effective match could lower insecticide use.

Originally from the Philippines, Villegas specialized in molecular biology and biotechnology as an undergraduate. After graduating with a bachelor’s degree in life sciences, Villegas began delving into rice viruses in the Philippines and worked on a project experimenting ecological engineering practices in rice farming. For his masters, he specialized in integrated pest management and plant-insect interaction.

Villegas will be recognized for the Friends of Southern IPM Award during the Southeastern Branch of the Entomological Society of America meeting in March.

Although Villegas will focus on another cropping issue for his doctoral studies, he plans to continue working on the rice water weevil project. He hopes that the addition of silicon will add an important pest management tool for rice growers.

“Amending soils with silicon can improve rice tolerance to insect pest,” he says. “We thought that if we could find a good soil for this to be used, it might decrease insecticide use.”

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