The Colorado potato beetle (Leptinotarsa decemlineata) may be controlled with chemical pesticides, however over time, the insects frequently acquire insecticide resistance to these substances.

The development of a novel pesticide employing the RNA interference technique shows promise for control since it prevents the beetles from getting rid of a defective protein.

Samuel Pallis, a graduate student at the University of Maine at Orono, along with principal investigator Andrei Alyokhin, Ph.D., and researchers Brian Manley, Ph.D., Thais Rodrigues, Ph.D., Ethann Barnes, Ph.D., and Kenneth Narva, Ph.D. of GreenLight Biosciences in North Carolina examined the impact of the RNA insecticide Ledprona on Colorado potato beetle mobility and reproduction.

Given that it is based on the biological molecule double-stranded RNA, Ledprona is categorized as a “biopesticide” (dsRNA). The manufacturer, GreenLight Biosciences, trades under the brand Calantha. Due to the dsRNA it contains, ledprona was one of the first pesticides to use the gene-silencing method known as RNA interference (RNAi). Ledprona inhibits the development of an enzyme that facilitates protein cleavage in Colorado potato beetles. When this enzyme is blocked, metabolites build up and, if left unchecked, eventually cause death.

“Ledprona has a new mode of action, unlike any other insecticide. The majority of insecticides target some kind of protein inside their target pests. Ledprona, on the other hand, prevents a protein from being synthesized by targeting mRNA,” Alyokhin mentioned.

Ledprona has already been tested in the field and proven to be deadly against Colorado potato bugs. Pallas and colleagues concentrated on examining Ledprona’s possible impacts on adult mobility, pup survival, and reproduction. The Aroostook Research Farm of the University of Maine in Presque Isle, Maine, is where the Colorado potato beetles employed in the study were first discovered.

The researchers employed wind tunnels that led to potato leaves used as an attractant to assess the insects’ adult mobility. They created a line within the tunnels and timed how frequently and quickly insects placed inside the tunnels crossed the line. In the mobility tests, Ledprona-treated foliage was provided to the treatment group of beetles, whereas distilled water-treated foliage was administered to the control group.

Late-stage fourth instar larvae were fed under one of three conditions: foliage treated with a low concentration of Ledprona, foliage treated with a high concentration of Ledprona, or foliage treated with distilled water to test survival until pupation. Every day until each individual had pupated or perished, they examined the containers.

The number of eggs deposited, the percentage of eggs that hatch into larvae, the number of egg-laying occasions during 24 hours, and the duration before egg masses started hatching were all considered reproductive indicators in the study. Beetles in the treatment group received foliage that had been treated with a low concentration of ledprona, whereas beetles in the control group received foliage that had been treated with distilled water.

In their mobility study, Pallis and colleagues discovered that after three days of feeding, there was no significant treatment effect on the number of beetles crossing the line in the wind tunnels, but after an additional four days, there was a significant decrease in the number of beetles crossing the line.

“Fewer treated beetles survived through pupation. The ones that did survive, however, completed their pupation as quickly as the untreated beetles,” Alyokhin added.

However, Ledprona had a noticeable impact on Colorado potato beetle reproduction. When sexually mature, the group of immature females who consumed the foliage treated with Ledprona laid considerably fewer eggs, had significantly fewer eggs that hatched and experienced significantly fewer egg-laying episodes. Females in the treatment group also had noticeably extended incubation periods before eggs hatched. Significantly fewer sexually mature females produced eggs when the foliage was treated with ledprona.

“In the field of pest management, there should be a switch in mentality from a perennial quest for a silver bullet solution that is supposed to take care of a problem once and for all, yet never does, to a quest for good components of integrated pest management systems. I think that Ledprona can be such a component,” Alyokhin concluded.

During the 2023 growing season, Alyokhin’s team will start examining how Ledprona affects Colorado potato beetles in industrial potato fields.

The Colorado potato beetle (Leptinotarsa decemlineata), a pest of potatoes and other members of the nightshade family, causes about USD500m in crop losses globally each year.