An entertaining news item from the Wall Street Journal:
TUSCARORA, Nev. — The residents of this tiny town, anticipating an imminent attack, will be ready with a perimeter defense. They’ll position their best weapons at regular intervals, faced out toward the desert to repel the assault.
Then they’ll turn up the volume.
Rock music blaring from boomboxes has proved one of the best defenses against an annual invasion of Mormon crickets…the crickets don’t much fancy Led Zeppelin or the Rolling Stones, the townspeople figured out three years ago.
There isn’t any scientific evidence I can find that this will have any effect on the crickets. (Which, technically, are not crickets, but katydids.) But it’s got to be pretty darn entertaining to see!
Intriguingly, a million bucks for Mormon Cricket control was widely mocked in March as “Pork Barrel” spending in the budget. These are people who clearly haven’t seen the insects on the march as a giant swarm. It’s impressive.
When you have a 1-2 inch insect, and you measure density as >15 insects/square yard…that’s a lot of bugs.
What would you suggest for your repelling playlist?
Slim Whitman would be my obvious first choice…..
A brand new paper out in the journal Environmental Entomology describes a possible new method to trap the beetles, using chemicals that their host plant (Ash trees) release:
“In a field test comparing and combining Phoebe oil with Manuka oil, Phoebe oil-baited traps caught significantly more beetles than either Manuka oil-baited traps or unbaited traps.”
The full title of the paper is:
Development of a Host-Based Semiochemical Lure for Trapping Emerald Ash Borer Agrilus planipennis (Coleoptera: Buprestidae)
There is also some bad news in this same issue of the journal–evidence that Japanese Beetles feed plants grown under high CO2 conditions laid more eggs, and lived longer. Damn it.
“Females consuming elevated CO2 foliage laid approximately twice as many eggs as females fed foliage grown under ambient conditions….Although the precise mechanism is unclear, by altering components of leaf chemistry other than sugar content, elevated CO2 may increase populations of Japanese beetles and their impact on crop productivity.”
Also–if you see ads on this page (and you probably will) I have no connection with those. They seem to have multiplied out of control recently. I am investigating getting them stopped, or moving (UGH!) to a new host.
Oh! I just found out that a book I own is now online in an updated version:
Field Guide to Common Insect Pests of Urban Trees in the Northeast
Since it’s the time of year to look for these things, here’s the page on oystershell scales, which I have in abundance on my lilacs. Grrr.
Now is a great time to treat scales with dormant oil sprays. From that Extension publication:
“Proper timing is critical for success when using oils. Dormant oils should be applied in late March or April before leaves or flowers show signs of breaking dormancy; that is, before “bud break.” A common mistake is to apply ‘dormant’ oil sprays too early (on the first warm day in February or March) before insects are actively respiring and susceptible to the oil’s suffocating effects. Wait until as close to bud break as possible before applying oil sprays. “
As tiny animals that live widely dispersed, finding a partner of the proper sex and species to reproduce with is a problem for insects. How do they arrange a hook up?
Insects have solved that problem in a variety of ways, but sexual pheromones are one of the most common solutions. Pheromones are “chemicals emitted by living organisms to send messages to individuals of the same species.” The message transmitted doesn’t have to be about sex–there are lots of different kinds of pheromones–it’s just more appealing to human prurient interest when sex is involved
By making a species-specific blend of chemicals and releasing it into the air, insects are able to communicate over great distances. With sex pheromones, the message is usually from the female, and has the content “I’m here and ready to get it on, big boy!”
So, how do insect sex pheromones work?
Male moth antennae are exquisitely sensitive to even individual molecules of a female sex pheromone. (You can see an animation of what happens neurologically in a moth antenna when pheromone hits a receptor here, courtesy of UC Davis. Davis also has a movie of how male silk moths react to pheromone in a commonly used test apparatus.)
Reception of the pheromone triggers a series of behaviors in the receiver (male), leading to the two insects meeting and, hopefully, reproducing.
My illustration shows a theoretical situation.* The female (on the right) emits her pheromone from a gland, and the wind disperses it. Think of each pixel of color as an individual pheromone molecule. The more concentrated the pheromone, the darker the color.
Males fly upwind following a pheromone concentration gradient, and eventually find the female. (animation version here). Moving into of an area of lower pheromone concentration is a signal to turn, to try to follow the concentration as it increases.
This model makes a lot of assumptions–that the female is a stationary point, for example–but it’s a pretty good description of how the system generally works.
In fact, this simple system has been used in robotics to develop a robot that follows a smell to the source of a chemical leak!
How do synthetic pheromones muck up this process and provide insect control?
Many types of biological control in the last few decades have developed out of identifying and using an insect’s natural biochemistry and metabolism against itself. Insect sex pheromones are commonly marketed for control or monitoring of insect pests.
There are several ways that synthetic pheromones are used for insect control, but the one I’m interested in today is mating disruption. The theory is that if you saturate an area with pheromone, the males will be unable to follow a chemical trail, and will be unable to find the females. Males will also be attracted to the synthetic pheromone dispensers, and try to mate with them–with predictably unsatisfactory results for the male. Sometimes synthetic pheromone dispensers are combined with traps to kill the male insects, and really make sure no mating goes on.
No male + female = no eggs = no pest insect reproduction. It’s a type of insect birth control.
The beauty of the system is that it is specific to one species. A problem with pesticides or biological toxins are “off target” effects. You spray to kill the bollworms, and also kill all the predators that would help you out by eating the bollworms. Oh, and any butterflies and pollinators that happened to be in the area, too. Bummer.
Mating disruption involves very small amounts of a chemical, released in a small area, that results in lots of horny males and frustrated females of one species, and no fertilized eggs. Because males are so sensitive to the pheromones, micrograms are used, not pounds of active compound/acre. When it works, it’s been pretty awesome–pink bollworm and tomato pinworm are two success stories.
The problem is, mating disruption doesn’t always work 100% of the time. (What does, really, in any biological system?)
This is usually because while synthesizing a species’ pheromone is relatively easy with new molecular tools, understanding the complexity of a species’ behavior and ecological dynamics isn’t that simple. As we learn more about insects and their population dynamics, we continue to get better at figuring out why this works well on some insects, and not others. Entomologists also have seen evolution in action, as it’s turned out that insects have variation in their chemical blends, and are not as chemically monolithic as the model suggests.
All in all, it’s a fascinating system, and I’ll talk more about it tomorrow.
For additional info:
- Read a whole textbook chapter on sex pheromones!
- Visit the UC Davis chemical ecology site, and look at more cool movies and research
- A National Academy online book about pheromone communication in insects
*Disclaimer: the graphics and examples used here are for illustration only. Females don’t emit pheromone in a rectangle, and males are not a blue blob. If you can’t deal with this much abstraction in the purpose of communicating with lay readers, get a life. Or, make the graphics for me :p