Biologists have successfully mapped out the genome of the red milkweed beetle, uncovering a range of genes associated with plant feeding and various biological traits. They sequenced and constructed the complete genome of the host-specialist milkweed beetle, *Tetraopes tetrophthalmus*. In their research, they compared certain genomic features with a related species, the host-generalist Asian longhorned beetle (*Anoplophora glabripennis*), which is an invasive species that targets a variety of trees crucial to the forestry industry. Understanding how the common red milkweed beetle can safely consume a toxic plant provides valuable insights into the ecological, evolutionary, and economic implications of interactions between insects and plants from a genomic standpoint.
Understanding how the common red milkweed beetle can safely consume a toxic plant provides valuable insights into the ecological, evolutionary, and economic implications of interactions between insects and plants from a genomic standpoint.
Even though the relationship between red milkweed beetles and milkweed plants has been researched for nearly 150 years, a scientist from the Arkansas Agricultural Experiment Station collaborated with colleagues from the University of Memphis and the University of Wisconsin Oshkosh to achieve something unprecedented: they curated the beetle’s genome and associated plant-feeding genes as well as other biological traits.
With funding from the National Science Foundation, they sequenced and assembled the entire genome of the host-specialist milkweed beetle (*Tetraopes tetrophthalmus*). They then analyzed various genomic characteristics in comparison to a related species — the host-generalist Asian longhorned beetle (*Anoplophora glabripennis*), known for its invasive nature and ability to feed on numerous tree species critical to forestry.
Their study, titled “Functional and evolutionary insights into chemosensation and specialized herbivory from the genome of the red milkweed beetle,” was published this summer in the *Journal of Heredity* by the American Genetic Association.
“From a biological perspective, there are many connections that indicate how the long-standing relationships between milkweed beetles and their toxic milkweed hosts should affect the biology of both,” stated Rich Adams, who is one of the main authors of the study. “However, up until now, no one had put together a complete milkweed beetle genome, which now allows researchers to explore numerous intriguing questions at the intersection of insects and plants.”
Adams is an assistant professor of agricultural statistics within the department of entomology and plant pathology for the University of Arkansas System Division of Agriculture. He is also part of the Center for Agricultural Data Analytics, a new initiative at the experiment station, and teaches statistics courses in the Dale Bumpers College of Agricultural, Food and Life Sciences.
Scientific Progress
For over a century, milkweeds and milkweed beetles (genus *Tetraopes*) have been significant in research concerning ecology, evolution, developmental biology, and biochemistry of toxins, according to Adams. They also highlight interesting cases of co-evolution patterns between insects and plants. This refers to how plants and insects evolve concurrently throughout their interactions, explained Adams.
The research team discovered that the red milkweed beetle has a notable increase in genes related to the ABC transport family, which might assist them in consuming milkweeds and storing toxins within their tissues. Milkweeds are well-known for their toxic latex, which disrupts the sodium, calcium, and potassium balance vital for heart cell function. Adams indicated that this genome sheds light on the specific genes the beetle has adapted to thrive while interacting with its toxic milkweed hosts.
“Milkweeds produce highly harmful substances known as cardiac glycosides among other toxins,” Adams noted. “For many insects consuming milkweeds, these toxins can impair their sodium-potassium pumps. However, this beetle has developed mechanisms to not only withstand these toxins but also to retain them, offering protection against potential predators.”
The study also identified variations in the genes linked to smell, taste, and the metabolic enzymes that break down plant cell walls. Adams pointed out that this provides a fresh viewpoint for investigating the ecology and evolution of specialized plant feeding in longhorned beetles and other beetle species that feed on plants.
Implications for Agriculture and Human Health
These findings could enhance our understanding of the genetic factors that influence agricultural and forestry pests and how they manage to feed on plants while avoiding control measures. While most animals that digest woody plant material depend on gut microbes to decompose plant cell walls, many plant-eating beetles lack this capability.
Adams explained that numerous plant-feeding beetles, including longhorned beetles, have gained the ability to break down plant cell walls through horizontal gene transfers from microbes. By examining the variety of proteins encoded in beetle genomes, scientists can gain insights into the genetic foundations of beetle biology, evolution, and diversity, as well as their interactions with plants.
“Nature has produced an astonishing variety of genes and genomes that we have yet to fully decode,” Adams remarked. “Grasping this diversity has excellent potential to benefit agriculture, forestry, and human health. Herbivorous beetles face significant challenges while feeding on plants without their metabolic enzymes, since they cannot eat effectively without those enzymes.”
In addition to examining the genomic DNA of the milkweed beetle, the team also collected RNA from the antennae of male and female red milkweed beetles to increase understanding of how they locate mates and food through chemosensory processes.
“Gaining more insight into chemosensory biology — how an organism perceives its surroundings, such as identifying a host plant or potential mate — has widespread relevance for understanding insect-plant interactions, which are critically important to agriculture and forestry,” Adams added.
The RNA profile generated serves as the first transcriptomic resource for *Tetraopes*. A transcriptome encompasses a collection of genes that have been transcribed into RNA molecules expressed in particular tissues or sets of cells.
While DNA provides the gene sequence, RNA delivers a more detailed representation of the gene and its activity, including how frequently the gene is produced, according to Adams.
Co-authors of the study include Terrence Sylvester (also a lead author) and Rongrong Shen, postdoctoral researchers at the University of Memphis, along with Duane D. McKenna, the William Hill Professor in the department of biological sciences and director of the Center for Biodiversity; Matthew A. Price, who formerly worked at the University of Wisconsin Oshkosh and now is at the University of Hawaii at Manoa; and Robert F. Mitchell, who previously worked at the University of Wisconsin Oshkosh and is currently an associate professor in the department of entomology at Pennsylvania State University.
The research was funded by National Science Foundation grants DEB-1355169 and DEB-2110053.
