There is nothing Aceria malherbae likes more than a field of delicious bindweed. The microscopic gall mite basically loves to die in a kind of “favorite food”.
Nibbling for tiny nibbles, the mite eats the weeds from the moment they hatch and for the rest of their life. It is a slow process for the mite and for landowners and homeowners eager to cause bindweed death. But it is effective.
Bindweed is the second most in-demand ingredient in the Palisade Insectary’s arsenal, according to Dan Bean, director of the Insect Center at 750 37.8 Street.
It is not a secret agent, although the mite and its comrades-in-arms work quietly, the inconspicuous James Bonds and deadly enemies of certain plants or beetles.
Their headquarters in Colorado is unremarkable, across from peach plantations and just a few blocks from downtown Palisade. Unless someone already knows the insect, “they’re not going to trip over us,” said Bean. The insect is “a curiosity”.
Weevils, mosquitoes, beetles, wasps, and fungi make up the insect’s nearly 20 biological control agents sent on long-term missions across Colorado.
“For Mack, it’s Holly,” said Bean. It’s the weeds along the Yampa River in Dinosaur National Monument to the weeds in Cortez.
“We’re trying to cover every square inch of the state,” said Bean. “But Mesa County will definitely get the best out of us because it’s our home.”
The insect is part of the Colorado Department of Agriculture and it started in the mid-1940s when the peach industry in the Grand Valley was attacked by a pest from Asia.
The oriental fruit moth threatened to ruin orchards as several generations of its larvae fed on the growing branches of the peach trees and then on their fruits, damaging trees and devastating fruits.
The day’s chemical controls weren’t effective, so a biological control agent was sought, Bean said.
Step inside Macrocentrus ancylivorus, a stingless wasp affectionately known as the Mac. Mac was found to target the moth’s larvae specifically by laying its eggs inside the larvae. The eggs hatch, destroying the larvae from the inside out – the insect was set up as a manufacturing facility for Mac, Bean said.
Mac is not doing well in winter, so the insect continues to raise around 1–2½ million Mac pupae annually because the moth is still active in the valley, he said.
Every spring, local peach growers come to the insectarium to fetch packed lunches of Mac dolls to place in orchards where they hatch and get to work.
“It’s about the balance of nature,” said Bean. “We take this balance of nature and use it for pest control.”
AIM OF THE PEST
Organic control is about control, not extermination, said Bean.
There are weeds and pests, many of which originated overseas, that have made themselves comfortable in Colorado. Biocontrol finds the natural enemies of these weeds or pests and turns them into biological control agents, he said.
If an active ingredient is to be released, it is subjected to all possible laboratory tests to ensure that it does not harm the ecology. During these tests, he’s given the option to eat peaches, alfalfa, and all kinds of other farm crops, “and they may not make it,” Bean said. “They do not go out if they were feeding on an agriculturally important plant, not even with suboptimal feeding.”
So, an agent’s response to eating its target plant is to dig harder for that plant, Bean said.
When they find it, their work continues. If they don’t, “then they will starve,” he said.
Populations of biocontrol agents are increasing and booming in proportion to their goals. So if the tamarisk tree, for example, seems to be having a good year, so is the tamarisk beetle.
The tamarisk tree is at home along the western Colorado Rivers, but it shouldn’t be there.
The plant from Eurasia is a water eater, displaces native plants and even changes soil chemistry so that native plants cannot thrive.
In 2005, the tamarisk beetle’s appetite for the leaves of the tree was combined with local efforts to tear the plant out or to combat it with chemical agents.
Brought to the United States from Europe and Asia, the tamarisk beetle is a specialized feed eater, meaning the only thing it eats is tamarisk, Bean said.
The insect was key to raising the beetles and working with agencies across Colorado for the widespread release of the beetles. It continues to monitor the beetles’ progress and breed them for research and keep them ready when a government agency needs them.
But the beetle’s influence on the tamarisk is becoming more and more apparent, said Bean.
An average of 30% of tamarisks in western Colorado from Cortez to Rangely have died from the beetle, Bean said. In some areas it is around 50%.
“We think it’s a mature project,” said Bean.
In thirty years, the tamarisk may not be eradicated, but it will be a lot less of a problem, he said.
“That wouldn’t have happened without introducing one of its native herbivorous enemies,” said Bean.
While Mac is active in the orchards and the tamarisk beetle defoliates the tamarisks, there are other bio-control agents the insect makes available to the public and state agencies such as the Bureau of Land Management, the US Forest Service, and Colorado Parks and Wildlife.
There is a gall mosquito and a gall wasp for Russian knapweed. There is a seed cap weevil and a root-boring weevil for diffuse and spotted knapweed. There is a flea beetle for milkweed and rust fungus for Canada thistle.
However, according to Mac, the most sought-after pathogen of the insect is currently the connective herb gall mite. “Everyone knows (bindweed) and has it in their garden,” said Bean.
As the mite feeds on the weeds, its leaves and tendrils begin to look bunched and shriveled, and it stops blooming. Over time, the mites will kill the plant.
For people who can’t or don’t want to use a chemical agent against connective herbs, the mite is an option to better control them, he said.
“There are numerous reasons why we cannot rely heavily on chemicals as we have in the past,” said Bean. Chemicals are poisonous. Insects and weeds become resistant to it.
But you can’t tell people to stop using chemicals unless you can give them other options, he said.
FIND MORE AGENTS
The insectarium also has Madagascar hissing cockroaches housed in a tank inside the insectarium, but their main job is to get people’s attention at farmers markets and festivals.
Bean is confident that the insect’s biocontrol agents will do more PR in the future.
If anything, he expects the demand for only current agents to increase and for new agents to rise when research declares them options.
He wants agents to be found against the codling moth, which is a problem for apple growers, and the cherry fruit fly, which is responsible for the maggots in cherries.
Experiments are currently underway by the U.S. Department of Agriculture on an agent to attack the emerald ash borer that has invaded ash trees in the Front Range and the U.S., he said.
He has also spoken to people interested in better controlling the seeds of the Russian olive tree.
“There’s no shortage of targets and no shortage of biological controls,” said Bean. “We have our work to ourselves.”