Photo credit: Paden Johnson/University of Arkansas Division of Agriculture.
Researchers at the University of Arkansas Division of Agriculture have identified a previously undocumented plant defense mechanism in rice that traps and kills early-stage fall armyworm caterpillars, a finding that could influence future pest-management and crop-breeding strategies.
The discovery centers on rice spikelets, the structures at the end of rice panicles where grains develop. During flowering, the spikelets open to expose florets for pollination. Researchers found that hair-like structures known as trichomes lining the spikelets can trap fall armyworm larvae attempting to feed on the florets.
Scientists said floral scents emitted during flowering may help attract the caterpillars into the spikelets before the structures slowly close around them.
Balakrishnan, a doctoral researcher for the Arkansas Agricultural Experiment Station, said the discovery was unexpected and occurred while she was conducting separate research involving rice plants and fall armyworms. She said researchers began noticing caterpillars trapped and dead inside the spikelets during the experiment.
Experiments Confirm Trapping Mechanism
To better understand the phenomenon, Balakrishnan conducted four replication trials under the guidance of Rupesh Kariyat, associate professor of crop entomology and holder of the Clyde H. Sites Endowed Professorship in International Crop Physiology.
The experiments found that roughly 50% of week-old fall armyworm caterpillars became trapped and died inside rice spikelets while attempting to feed on florets. Similar results occurred even when rice leaves were present in the experimental enclosures.
Researchers also tested whether floral scents influenced caterpillar behavior. They found larvae showed a preference for flowering-stage panicles containing exposed florets over later-stage panicles in the dough stage, when spikelets remain closed as grain develops.
The study described the findings as preliminary evidence that spikelet trichomes may function as a defense mechanism protecting reproductive plant structures from herbivorous insects.
Kariyat said researchers still are studying whether the trapping effect is influenced by a combination of floral scents, trichomes, flower compounds and rice varieties.
Potential Implications for Pest Management
Researchers said the findings could eventually support development of alternative pest-management tools as fall armyworms continue developing resistance to insecticides in multiple production regions.
The research team collected and analyzed floral scent compounds emitted during rice flowering and suggested future work could examine whether increasing those volatile compounds might improve the plant’s natural trapping ability.
Kariyat said a naturally derived spray enhancing floral scent signals during flowering could potentially help attract more caterpillars toward the spikelets.
Researchers said the findings suggest rice plants may possess stronger natural defensive traits than previously understood, with floral scents potentially attracting caterpillars toward the spikelets where they become trapped.
Researchers also plan to study whether the mechanism functions similarly across different rice varieties and caterpillar species. Larger caterpillars with developed mandibles may be capable of escaping the spikelets.
For plant breeders, the findings may provide insight into naturally occurring insect defense traits that could eventually contribute to breeding programs focused on pest tolerance and reduced chemical dependence.
Discovery emerged from unrelated research
Balakrishnan initially began the work while studying whether a protein kinase involved in plant signaling could help rice tolerate stress during flowering.
Using fall armyworms as a biological test system, she observed that second-instar caterpillars migrated from rice leaves to flowering panicles within experimental enclosures.
Balakrishnan said earlier research had shown fall armyworms could feed on rice panicles, but closer examination revealed many of the caterpillars were becoming trapped and dying inside the spikelets rather than feeding successfully.
Kariyat said the discovery became one of the lab’s most significant and widely discussed findings.
Source: University of Arkansas Division of Agriculture, "Researchers document rice plants trapping and killing fall armyworm caterpillars"