Bella moths use venom to attract mates. Scientists are closer to discovering how – Research News

Pyrrolizidine alkaloids are as bitter and poisonous as they are difficult to pronounce. They are produced by several types of plants and are among the leading causes of death in livestock.

Plants containing these alkaloids have made it very clear that they do not want to be consumed, but that has not deterred the bella moths (Utetheisa ornatrix). These day-flying moths eat exclusively the alkaloid-laden leaves and seeds of rattlesnake plants. They then use the venom to guard their eggs and deter predators in later stages of life. They even use it to make pheromones that attract mates.

How exactly bella moths and related species evolved the ability to safely consume pyrrolizidine alkaloids remains unknown.

In a new study published in the journal PNAS, researchers sequenced the bella moth genome, which they used to pinpoint specific genes that may confer immunity against these toxins. They also sequenced the genomes of 150 museum specimens – some of which are more than a century old – to determine where the bella moths and their close relatives came from. Finally, they scoured genetic data for clues that could help explain how bella moths’ intricate wing patterns evolved over time — the first study of moths or butterflies to do so using dry specimens from museum collections.

“We managed to demonstrate that you can use museum specimens to answer genetic questions that would normally require complicated laboratory techniques,” said co-author Andrei Sourakov, collections coordinator at the McGuire Center for Lepidoptera and Biodiversity at the Florida Museum of Natural History. “This opens a window for future research of this kind.”

Eggs are particularly vulnerable to predation. To avoid being eaten, bella moths inject their eggs with a harmful alkaloid.

The caterpillars of the Bella moths are brightly colored and packed with toxins.

Bella moths collect most of their toxins while eating plants as caterpillars. They retain this venom through metamorphosis and into adulthood.

Bella moths have an ancient and unique wing pattern symmetry that makes them easy to distinguish from their close relatives.

Sourakov has been studying bella moths for 15 years and said sequencing the species’ genome was the natural next step in the research he has conducted so far. Many of the insights he gained during that time came from his work with college and high school students, helping them conduct short experiments, analyze data for science fairs, and interpret the results in peer-reviewed articles.

In one such project, a student was trying to determine the average lifespan of adult bella moths and accidentally stumbled upon the Methuselah of the moth world. “To our great surprise, they can live up to 50 days, which is six times longer than the average moth,” Sourakov said.

Longevity is not a critically important trait in most moth species. Many breed once and die shortly afterwards, either from aging or predation. But bella moths are not limited by the latter, making it more likely that genes that ensure longer lifespans will be beneficial and passed on to the next generation.

“It makes sense that something that is chemically defended would live longer, because even if they are caught, the predator usually lets go and the moth can continue to fly around.”

Bella moths live across much of eastern North America, Central America and the Caribbean and are often active during the day. Instead of using the darkness as a shroud to avoid predators, bella moths make a point of being seen. Their wings are covered in radiant pink, pearl, onyx and sulfur yellow scales, which birds and carnivorous insects can easily see from a distance. Any predator unlucky enough to catch a bella moth quickly corrects its mistake.

“Banana spiders will cut them out of their webs,” Sourakov said, adding that wolf spiders and birds will do their utmost to avoid them. “If caught, they produce a frothy liquid that tastes bad and consists almost entirely of alkaloids.”

When ready to mate, females release a plume of aerosolized alkaloids from the plants they ate as caterpillars. Males are attracted to this scent, which they follow to its source. There they perform a short but elaborate ritual in which they gently touch the female’s head with two fluffy and retractable structures that closely resemble dandelions. Each filament in these structures is laced with pyrrolizidine alkaloids.

Male bella moths inflate two retractable air sacs called coremata when trying to attract a mate.

When bella moths perceive themselves as a danger, they secrete a frothy ball of venom from their upper abdomen, which serves as a warning to predators.

Alkaloids are found in the stems and leaves of bella moths’ favorite foods, but are especially concentrated in the seeds, which caterpillars specifically seek out.

If the female decides that the male has sufficient quantity and quality of alkaloids, the pair will mate. When he’s done, the male leaves behind a parting gift called a spermataphore, which contains sperm and, yes, more alkaloids. The female will use this and alkaloids from her own supply to infuse the resulting eggs with toxins. This type of biparental egg protection in insects is rare. In fact, when it was first observed in 1989 among adult bella moths, it was the only known example of a male moth or butterfly investing chemical resources in its offspring.

Bella moths can avoid the ill effects of pyrrolizidine alkaloids by using a special enzyme that oxidizes the molecule, making it harmless. However, if a predator eats a moth, the process is reversed and the alkaloid regains its potency.

Pyrrolizidine alkaloids probably first evolved as a defense mechanism in plants, which then became a commodity for moths. Sourakov and his colleagues wanted to know how bella moths acquired this detoxifying enzyme and how they maintained it during a millions-year arms race between plant and moth.

The authors discovered that bella moths have not one but two copies of the gene that codes for their unique detoxifying enzyme. They may have acquired the second through a process of gene duplication, in which other species, including many plants, developed new traits.

They also found two copies of a gene partially involved in antioxidant production and defense. Sourakov suspects that these genes may be related to both bella moths’ ability to detoxify alkaloids and their remarkable longevity.

“Certain types of stress on biological systems result in longer lifespans. It could be that the interaction that bella moths have with alkaloids is not only why it makes sense for them to live a long life, but also one of the mechanisms behind it.”

Jing Zhang, Qian Cong, Jinhua Shen, Leina Song and Nick Grishin of the University of Texas Southwestern Medical Center and Winnie Halllwachs and Daniel Janzen of the University of Pennsylvania are also authors of the study.

Funding for the research was provided in part by the Welch Foundation (Grant Nos. I-2095-20220331 and I-1505), the National Institutes of Health (Grant No. GM127390), and the Cancer Prevention and Research Institute of Texas (Grant No. RP210041 ).

Source: Andrei Sourakov, [email protected]
Media Contact: Jerald Pinson, [email protected], 352-294-0452