Perhaps only the parsnip webworm gets less respect. An age-old enemy of the parsnip, the webworm is one of very few insects able to overcome the plant’s chemical defenses. The tenacious parsnip webworm has followed the weedy version of the parsnip in its transit from its ancestral home in Eurasia to Europe, North America and – most recently – New Zealand.
The long association of the parsnip (Pastinaca sativa) and parsnip webworm (Depressaria pastinacella) offers a unique window on the complex interaction of plant and insect enemies, according to a study appearing this week in the Proceedings of the National Academy of Sciences. And the recent appearance of parsnip webworms in New Zealand, more than 100 years after the parsnip first arrived there, offers the best view yet of how these species influence one another.The research team, led by University of Illinois entomology professor and department head May Berenbaum, made two key findings. First, the researchers found, the New Zealand parsnips had significantly lower levels of certain chemical defenses than parsnips growing in Europe and North America, where webworms are a constant threat. Second, the New Zealand parsnip webworms were dramatically affecting the plant’s ability to reproduce. The webworm caterpillars eat the parsnip flowers and burrow into their stalks.
“In certain populations affected by webworms, 75 percent of the plants were completely devoid of any reproductive parts,” said Art Zangerl, a senior research scientist in the department of entomology and co-author on the paper. “The affected plants were contributing zero fitness, which is really dramatic. We don’t often see that.”
Fitness is a measure of a species’ ability to successfully reproduce. Environmental factors that reduce the fitness of an organism – by, for example, destroying all of its offspring – can influence the course of its evolutionary trajectory. Survivors less susceptible to that environmental factor, or selective agent, enjoy a reproductive advantage, contributing more offspring, and more of their genetic attributes, to subsequent generations.
In New Zealand, the newly arrived parsnip webworms are a major selective agent, Zangerl said, wiping out a majority of the flowering parsnips.
The altered chemical defenses of New Zealand parsnips are probably allowing the webworms to feast on most of the plants in any given locale, Berenbaum said.
The parsnip’s chemical defenses normally include a good dose of furanocoumarins, a class of organic compounds that can be toxic to insects that eat the plant. While the parsnip webworm has evolved to tolerate large doses of furanocoumarins in its diet (it can eat up to 5 percent of its body weight of these toxins) the chemicals do limit its capacity to inflict damage.
What isn’t clear is whether the absence of parsnip webworms in New Zealand for more than 100 years allowed the parsnips to let down their guard, Berenbaum said.
“Parsnips have been in New Zealand since the 19th century,” she said. Absent an aggressive enemy like the webworm, the parsnip had no reason to keep producing large amounts of furanocoumarins.
“It could be simply that the parsnips have had 100 years to relax,” Berenbaum said.
Other factors may explain the lower levels of certain furanocoumarins, however, she said. It could be that the parsnips that were first brought to New Zealand had less of these chemicals to begin with. Or perhaps the soil or climate influenced their evolution.
The appearance of parsnip webworms in New Zealand offers an appealing research opportunity, Berenbaum said. The researchers will be able to measure any changes in plant chemistry that result from the webworm infestation.
“Here, we’re looking at one variable, and it’s the insect,” she said. “The soil is essentially the same as it was 10 years ago. The climate is more or less the same.
“The neighboring plants are the same. The only variable is the insect and we have shown that the insect is a selective agent.”
Berenbaum and Zangerl have spent several decades studying the co-evolution of the parsnip and its webworm.
In the late 1990s, they studied pre-1900 museum specimens of parsnips collected in the U.S. They found that the furanocoumarin compound sphondin – produced in high levels in parsnips growing in the U.S. today – occurred at low levels or not at all in the oldest museum specimens. Early colonists brought parsnips to the New World in the early 17th century, but the parsnip webworms did not arrive for another two centuries. The webworms have difficulty metabolizing sphondin.
This suggested that the plants ramped up production of sphondin in response to the webworm infestation, the researchers concluded.
These findings have implications for those hoping to manage invasive weeds by importing the insects that attack them in their native land, Berenbaum said. While such strategies may appear to be effective initially, the plants may be able to adjust to the insect threats over time by upping their chemical defenses. Only time, and more data collected in New Zealand, will determine if this occurs, and if it does, how quickly the plants can respond, she said.
M.C. Stanley, of the University of Auckland, New Zealand, was a co-author on the study.
This research was supported in part by a seed grant from the National Science Foundation.
Editor’s note: To reach May Berenbaum, call 217-333-7784; e-mail: email@example.com.
Diana Yates | University of Illinois
Solving the efficiency of Gram-negative bacteria
22.03.2019 | Harvard University
Bacteria bide their time when antibiotics attack
22.03.2019 | Rice University
DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.
The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...
Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.
The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...
Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.
Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.
A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...
Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.
"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...
11.03.2019 | Event News
01.03.2019 | Event News
28.02.2019 | Event News
22.03.2019 | Life Sciences
22.03.2019 | Life Sciences
22.03.2019 | Information Technology