UDMessenger

Volume 13, Number 2, 2005


Connections to the Colleges

Insect rebels have a cause

Entomologist Doug Tallamy, professor in the College of Agriculture and Natural Resources, studies what he terms “the rebels of the insect world.”

Those rebels are assassin bugs (Rhynocoris tristis), common beneficial insects found worldwide, which get their name from their food-stalking habit. Assassin bugs wait in ambush for unsuspecting insect pests, then seize and poison their prey with unparalleled speed. This hunting activity alone makes the insects fascinating to study, Tallamy says, but he is particularly interested in the assassin bugs’ less characteristic insect behaviors.

“Rhynocoris assassin bugs stand out because of their atypical insect behavior. They are the rebels of the insect world, with three nontraditional insect traits,” he says. “The first is that the adults of the species care for and guard the fertilized eggs, a truly rare phenomenon among insects.”

The second peculiarity, which Tallamy says is even more rare, is that the adult guardians are the males of the species. “This paternal-care trait is seen in few animal species and known in only 11 other insect lineages,” he says.

The third trait that sets Rhynocoris apart is its tendency to remain on one type of plant—Stylosanthes—for its entire life, from gestation to mating to death. “We believe this behavior in particular explains why this species has paternal care,” Tallamy says. “If an entire species is restricted to one type of plant, females will be able to find guarding males easily.”

Assassin bugs are in the family Reduviidae, and Tallamy and his graduate students are focusing on the genus Rhynocoris, which contains 170 species. For easy identification and observation, the scientists have separated the assassin bug colony into male/female pairs in small containers containing food, water and a branch of the specific plant on which they live.

“We’re testing the hypothesis that paternal care in assassin bugs is a sexually selected trait. Males guard eggs because females find guarding males more attractive than males without eggs. Egg-guarding males, therefore, get more matings,” Tallamy says. “This has never before been demonstrated in any insect species.”

The insect behaviorist says he believes that because of the male assassin bug’s paternal-care role, he maximizes opportunities to mate with multiple females. By protecting the fertilized eggs, the males become sexually attractive to the females, who will search them out in order to mate.

The small colony of assassin bugs in Tallamy’s Townsend Hall laboratory isn’t sufficient to accommodate all the experiments he needs to prove his hypothesis.

“This colony came from Uganda, where preliminary research was done,” he says, adding that he and his graduate students spent January in South Africa to conduct an additional month of research. “Africa is where the Rhynocoris genus occurs. It is much easier to conduct our tests there, where we can replicate our findings in the field.”

Tallamy also plans to develop a phylogenic (ancestral) tree of all the Rhynocoris species, a project he has undertaken with Anthony Cognato at Texas A&M University. Their database will allow them to determine which Rhynocoris species are most closely related.

“Using DNA sequences to trace the paternal-care trait in assassin bugs, we can find out whether paternal care evolved once or several times in the lineage. We will also be able to correlate the behavior with environmental variables,” Tallamy says.

“From this evidence, we can extrapolate the causes of paternal behavior to other animals, even humans.”

—Jean Ruiter, AS ’03