Tag Archives: exoparasites

Information, Even If You Don’t Want It: Integrated Pest Management

One of the issues with which we struggle at the Triffid Ranch is a bit of a logical leap in what carnivorous plants can do. Based on phone calls, emails, letters, and incessant queries at shows and events, the logic starts with the given “Carnivorous plants attract, capture, and digest insect and other animal prey” and veers Immediately into “carnivorous plants will take care of my bug problem.” This leads to calls and queries. “My house abuts a stream, and the stream attracts mosquitoes. I need a pitcher plant to eat all of the mosquitoes.”  “My kids leave the door open all day, and we need a Venus flytrap to eat all of the flies they let in.” “My roommate won’t take out the garbage, so I need a flytrap to eat the flies on the garbage.” Sometimes this goes to extremes: “I saw ants at the end of the driveway, and I want to build a berm around my house and cover it with flytraps to get the ants.” Or my personal favorite and a reason why I refuse to return to one show at which I displayed plants in 2013, “Cool! Got anything that will eat bedbugs?”

To all of these, I try to explain, over and over, that while you can get great satisfaction in watching a Cape sundew digest mosquitoes, and even add Battle Boy sound effects to liven things up, one plant or even a thousand won’t get rid of every insect in your time zone. It’s not even a matter of picking wildly inappropriate plants, such as the people who ask repeatedly about using Venus flytraps to control fleas. (The simple answer: they won’t. Even sticky-trap carnivores such as sundews and butterworts may catch fleas, but they won’t break the life cycle.)  Besides, as entomologist and brilliant bug blogger Gwen Pearson notes, you’ll never bug-proof. your house. We lost the war against bugs, spiders, and other exoskeletal creepies about 400 million years ago, and barring a mass extinction that wipes out every arthropod (up to and including the millions of skin mites that eat dead skin cells on your body), we stand no chance of changing that.

That said, while wiping out pests is a lost cause, it’s possible to keep their depredations down to a dull roar. That’s the basic idea behind the concept of integrated pest management, which attempts to minimize horticultural chemical use by understand that complete annihilation is impossible, but cutting populations down to a dull roar isn’t. 

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“You are Number Six.”


For example, one of the more pernicious pests in most households this time of the year is a recent invader, having only been documented in large numbers since 2004. Since then, the shelf elf has been found in living rooms and bedrooms across the United States and Canada, never appearing in the same place twice during the holiday season, and resisting all attempts at capture or restraint. Not only will they return each year, but they have a propensity for breeding out of control, and all efforts at spaying and neutering have been complete failures. They also have a distinctive hive mind, reporting back to a central dominant individual known as a sinterklaas, thereby making efforts to collapse the hive structure nearly impossible. Recent reports suggest that they’re able to communicate with the sinterklaas from considerable distances, but whether this is by telepathy, by Extra Low Frequency vibrations through earth and water, or by pheromones or other vaporous output is unknown. What IS known is that they seem to be especially astute at viewing and modifying the behavior of children, merely by watching and waiting, and the intimation of a reward in exchange for those behavioral changes. Also unknown is the reason for initiating the behavior changes, but research suggests a model comparable to that of the pathogen Toxoplasma.

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“It’s an ugly planet, an Elf planet, a planet hostile to life as we know it!”

Thankfully, there are ways to deal with this menace using IPM, so let’s fire up the appropriate soundtrack and get going,.

The first and most obvious control, chemical, is problematic for multiple reasons. In fact, that problematic nature is why integrated pest management was founded in the first place, because the overuse of pesticides was becoming a significant issue in both farmlands and in residential areas. As a last resort, chemical repellents and poisons have their place, but be warned that most of the effective options for invasive elves also have negative effects on the human population. Butyric acid in aromatherapy bottles works sporadically as a repellent, but the enterprising and cost-conscious homeowner should consider making a custom mix of 75 percent potassium nitrate, 15 percent sulfur, and 10 percent charcoal, or an equal weight of gasoline and polystyrene foam. When ignited, both have an effect on local elf populations: when mixed up in sufficiently large quantities, the effects may be seen from low Earth orbit.

The second control, mechanical, applies to most traps, grinders, zappers, or pitfalls. Repeated vivisections of shelf elves reveals no vital organs or internal structure particularly susceptible to anything other than overwhelming force, and documented sightings exist of shelf elves recovering and attacking immediately after crushing or flattening that would kill most Earthly life. With this in mind, further research continues with finding all-inclusive mechanical controls that can anticipate and neutralize shelf elves before the sinterklaas can give them new orders. The choice of mechanical control is up to the one applying it: from personal experience, while American, Chinese, and Australian controls are have their advantages, Russian controls are low-maintenance, exceeingly durable in multiple environments, and extremely effective.

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“Elbow rocket…NOW!”

This leaves the obvious and logical choice: biological controls. Since shelf elf study really only started a decade ago, many “facts” about their behavior, reproduction, natural history, and evolutionary history are little more than assumptions, and are forcefully disputed. One of the most disputed involves predators in their original environment before coming in contact with humans. Due to their lack of internal structure, which leads some palaeontologists to make comparisons to the extinct Ediacara faunas of the Vendian Era (Crusher, Franklin, & Shaw, 2010), nothing other than highly contentious fragments exist in the fossil record, and genome sequencing has been stymied by a complete lack of sequenceable DNA (Banner, 2011; Richards, 2012; Hoshi, 2012). One thing is certain, though: in multiple tests in captivity, a wide variety of predators actively attract, capture, consume, and digest shelf elves (Logan, West, & Furter, 2015). No widespread field tests on predator selection have been done to date, and the understandable concern is that any effective introduced predator may itself become an invasive species, as demonstrated with the introduction of the cane toad (Bufo marinus) in Australia (Benway, 1959; Duke, 1971).

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One very promising avenue of biological control involves the use of exoparasites, which utilize host organisms during stages of their life cycle. Again, the largest concern involves whether the exoparasite stays with one host or utilizes multiple host species. An equally vital concern, based on recent studies, is whether shelf elves will evolve changes in structure or behavior to bypass parasitism, causing the exoparasite to seek out new host species or become extinct. Using cicadas as a model, extreme predation or parasitism may cause shelf elves to spread out infestations over multiple years, in an attempt to keep parasites from depending upon them every holiday season. Alternately, shelf elf emergence may start earlier in the year: reports of shelf elves being spotted as early as July may be examples of this new behavior.

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“It has a funny habit of shedding its cells and replacing them with polarized silicon.”

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“I could lie to you about your chances, but you have my sympathies.”

Due to the challenge of the shelf elf life cycle, with large populations accumulating only in the month of December, the secret may be in finding a combination parasite/predator. A predator that subsists through the rest of the year either in hibernation or on the occasional early emergence, only to reproduce during the height of the shelf elf cycle, may be the only effective way to get populations into something approximating control.

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“Its structural perfection is matched only by its hostility.”

In some cases, while biological controls may seem to be the best option, the available biological controls may be organisms that may themselves become pests under the right conditions: for instance, Asian ladybugs becoming pests in vineyards when they feed on ripening grapes and taint the resultant wine. Sometimes the best option is to use several types of control organisms, especially when needing to ensure that one species doesn’t become a threat with increased numbers.

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Finally, one remaining option is now available due to advances in technology. A possible alternative to wiping out the shelf elf may involve introducing organisms that outcompete it for available resources, such as food or nesting sites. In many areas, the beneficial Bench Mensch has made inroads into shelf elf habitat, but future control may involve a combination of mechanical and biological controls. A competitor that can remain in hibernation for years or even centuries between shelf elf infestations, with an active resistance to retaliation, and a built-in weakness should it become a pest: the future is here.

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“Shiny and chrome!”

Tales From The Ranch: Introducing Dasymutilla klugii

While wandering around the ranch, the Czarina and I ran into an old friend, well, enemy, from my adolescence. We were tromping around close to the bank on the Brazos river, and spotted and surprised a rather interesting lizard. While circling around to get a photo so I could ID it later, she suddenly exclaimed “What the hell is THAT?” In a small sapling was what initially appeared to be a rust-colored ball of fluff, and the fluff was moving. That’s when we had a reminder that cowbirds weren’t the only parasites on the ranch.

Dasymutilla klugii

That fuzzball is most likely a female Dasymutilla klugii, commonly known as a velvet ant. Velvet ants are members of the family Mutillidae, part of the same superfamily of insects that includes wasps, stinging ants, and hornets. The velvet ants are flightless wasps found through North America, but they’re rarely seen by most people. It’s not that they’re incredibly rare, but that a combination of rough habitat and a tendency to stay away from human habitations means that they’re not encountered all that often.

More velvet ant

Eric Grissell’s book Bees, Wasps, and Ants: The Indispensable Role of Hymenoptera in Gardens still qualifies as one of the best general interest books on wasps published in the last fifty years, and even it doesn’t have all that much on velvet ants. That lack of knowledge is due to their being poorly studied. What’s known for certain is that they tend to be exoparasites of exoparasites. Many species take advantage of hunting wasps’ industriousness by waiting until a mother wasp digs a nesting gallery, gathers paralyzed prey to feed her young, and lays an egg atop said host. The velvet ant sneaks into the gallery while the mother wasp is away and lays its own egg next to the wasp’s egg. The velvet ant larva hatches first, and it first eats the wasp egg and then the host before pupating and emerging as an adult velvet ant. Other than that, it’s known that the females are flightless while the males are winged, and the females pack an impressive sting, to the point where they’re also called “cow-killers” or “mule-droppers”.

Dasymutilla klugii

Obviously, I wasn’t insane enough to test the stories, because I tend to pay attention to warnings along the lines of “much more painful than a bee sting”. I settled for watching it scramble through the sapling, desperately looking for something that it couldn’t quite find, before leaving it to go about its business.

And how was this an old friend/enemy? Being a kid of the northern US, my views on Texas were based on reading, particularly a copy of the book Poisonous Dwellers of the Desert by Natt N. Dodge that had been left at my house by a friend when I was nine. By the time I was thirteen, I had read that book to death, regaling everyone with horror tales of cone-nosed bugs, puss caterpillars, the multiple species of scorpion and dangerously venomous spiders to be found in the Chihuahuan and Sonoran Deserts. After I informed a honeybee-stung neighbor that scraping out the sting is much better than pulling it out, she asked me how I knew this, and I merely pointed to the paragraph in question. At that point, nobody in the family questioned me about the arthropodal horrors we’d encounter in North Texas, even after my mother was playing solitaire on the floor of our new living room in Flowermound and put down the 10 of hearts atop a bark scorpion that was checking out the neighborhood. (Two days later, she found another in a huge crock bowl she used for making popcorn. That one became the basis for my first experiment in encasing a scorpion in epoxy, but that’s another story.)

Anyway, the summer of 1980 not only brought us the hottest summer in North Texas history, only possibly exceeded by the droughts of record of 1952 and 2011, but it brought out all sorts of critters. At the time, I lived on the edge of a huge subdivision that was under construction through the year, and honed my then barely existent tracking skills by chasing down the multitude of new animals that I’d never before encountered. One of these was a similar ball of fluff, and I knew well enough about not letting it sting. What I didn’t know is that velvet ants also bite. HARD. I yelled and flung it as far away as I could before it could reacquire a stinging target, and that was the last velvet ant I would see for nearly one-third of a century. And so it goes.

Tales From The Ranch: And now for the horror

And before poor Dave gets into his head that I’m going to stop joshing him, I have to share the story of the ceiling fan birdnest. The area around the ranch is habitat for the black-tailed gnatcatcher (Polioptila melanura), and they spend most afternoons and evenings snagging as many insects as they can manage. When not hunting, they spend their time watching us crazy humans, mostly to take advantage of the situation.

Black-tailed gnatcatcher

“Taking advantage of the situation,” in this case, refers to using appropriate human structures to facilitate their own nestmaking. Specifically, they like using the house located on the property, particularly the big open deck on the back. Shortly after arriving at the ranch for the last big family gathering, my sister-in-law found this nest atop a ceiling fan over the deck, and a quick peek showed that it had eggs and at least one hatchling.

Gnatcatcher nest

Getting up to the nest to observe further had issues, the least of which was the lack of head clearance above the ceiling fan blades. Tilting the blades to get a better view risked knocking the nest off the fan. In the end, my nephew Bruce and I settled for putting cameras up to the nest, taking whatever pictures we could, and backing off before the parents came back. After doing so, we had a bit of a surprise.

Gnatcatcher nest contents

If you’re observant, you’ll note that the hatchling inside the nest, while still blind and helpless, is considerably larger than its eggs. You may also note that the eggs aren’t the same color. That’s because both the hatchling and one of the eggs both belong to a brown-headed cowbird (Molothrus ater), which is also common to the area. Cowbirds get their name because of their otherwise encouraging habit of picking ticks and other pests from cattle, bison, and other big herd animals. Since bison herds are migratory, the cowbirds evolved to take advantage of other birds’ instincts and parasitize them. The mother cowbird arrives at a nest while the parents are gone, lays one to two eggs, and moves on, reasonably assured that the foster parents will lay on the clutch and feed the hatchlings as they emerge. Gnatcatchers seem to be particularly susceptible, with reports of 100 percent parasitism of all gnatcatcher nests in surveyed areas.

This led to quite the spirited debate. My sister-in-law argued for scaring off the gnatcatchers so the cowbird chicks would starve, being offended by the idea that the cowbirds were parasites. I argued instead for leaving well enough alone, because at least this way the gnatcatcher eggs wouldn’t be a complete waste. Besides, being very much unlike my own family, I could appreciate the cowbird chick’s situation. We left that weekend with the nest intact, and I suspect that I might see one of the cowbirds the next time I visit, inexplicably relieved that we left it alone. And so it goes.

“The first thing I’m going to do when I get back is get some decent food.”

Every time I come across new behavior among parasitoid and exoparasitic wasps, I figure that I’ve read it all. They can’t get any more surreal and horrifying than the one before, can they? And then a friend passed on the story of Polistes dominulus and Xenos vesparum: the former is a European paper wasp, and the latter is a parasitoid fly. Neonate flies that turn their hosts into anarchic wasp queens: that reminds me of a song about a distant relation of mine.

Review: Bees, Wasps, and Ants by Eric Grissell

(A bit of context. This blog features regular reviews of books, horticultural products, and interesting related items, under this proviso. All items reviewed will be purchased by the reviewer in advance, at full retail price, in order to prevent any conflict of interest. Information about upcoming releases is greatly appreciated, but receipt of advance copies or samples will be announced well in advance and will not influence the final review. The world has enough Jeff Craigs and Maria Salases as it is.)

Bees, Wasps, and Ants: The Indispensable Role of Hymenoptera in Gardens
by Eric Grissell. Timber Press, 2010. 335 pp., $27.95 US. ISBN-13: 9780881929881

I came across gardening in a very roundabout way, and I can credit one book as being my awakening to the possibilities. That book, discovered in a pile in the Natural History section of the local Half Price Books, was The Hunting Wasp by John Crompton. Before starting that volume, my attitude toward wasps was the same as with most humans: duck and wave your arms around your head if one approaches, and rush for the can of Raid when it retreats. Considering how sensitive I am to honeybee venom, I thought I had a good reason to keep up that attitude.

Well, that was before John Crompton. Without him, I never would have learned exactly how valuable wasps are in the garden, and in fact elsewhere. Honeybees can pollinate flowers, but they do nothing against common garden pests. With the exception of vertebrates, pretty much every gardener’s nemesis has a parasitoid or exoparasite wasp that uses it as a host. Tomato hornworm caterpillars, houseflies, spiders large and small, cicadas, and even praying mantises are all prey. The more social wasps such as paper wasps may not capture and paralyze prey, but they still do their part: I currently have a paper wasp nest on the back porch, right over my head when I’m repotting plants. Considering how much damage they do to the annual green looper plague every spring, anyone who wants to spray my paper wasps will have to go through me first.

That’s the biggest thing that Crompton’s book taught me: we’re taught our basic responses to wasps, and they’re a matter of conditioned fear, augmented by the pain of the very occasional sting. Wasps should be respected, yes, especially by those with allergies to their venom. However, a lot of what’s seen as wasp aggression is really little more than curiosity, abetted by our conditioning to react in a certain way to certain insect shapes and colors. What’s funnier is that this conditioning is one of the big factors in keeping male wasps alive, as they have no sting and are completely harmless to humans.

When it comes to books on members of the insect order Hymenoptera, the vast majority focus on the bees. Lots and lots on traditional honeybees, with maybe some mention of carpenter bees, mason bees, and sweat bees as a sidenote. Most books on ants are intended for grade-school students, and they’re discarded about the time the reader has to deal with carpenter ant damage to a house or Argentine fire ant infestations in the yard. Wasp books pretty much begin and end with Crompton and with Jean-Henri Fabre’s The Hunting Wasps, now nearly a century old. And on the wasp cousins the sawflies? Not a peep, outside of basic insect pest guides.

Part of the reason for that lack of care, obviously, is bad public relations. Bee folklore and mythology range the width and breadth of the planet. (How many of you know that the name “Melissa” is ancient Greek for “bee”?) Ants at least get the Aesop’s fable on the ant and the grasshopper. Ants and bees get cutesy Pixar movies made about them. The closest to popular respect given to wasps? A begrudging comment on how the life cycle of the title creature in the film Alien had a basis in the real-life habits of certain exoparasite wasps.

Yeah yeah, sure sure. The wasp’s world is a horrifying one compared to that of humans, and it’s not hard to see the comparisons. (Last year, I came across an unopened silkworm coccoon hanging from a maple tree, and found inside the coccoon a mummified silkworm with two tiny holes in its body from where wasp larvae, implanted as eggs before the caterpillar started spinning, had gnawed their way out before pupating within the coccoon. I couldn’t help but murmur “Alien life form, dead a long time. Fossilized. Looks like it grew out of the chair.”) That’s just part of the story. Most wasps are essential pollinators, as the adults only consume nectar and other sweets (this explaining why they’re always attracted to spilled juice or soda), and they’re often manipulated themselves, as with wasp orchids. Furthermore, each parasitoid (young develops within the host’s body) or exoparasite (young develops outside) wasp species has a specific host, and those can range from aphids to cicaidas. I was recently lucky enough to view two tarantula hawk wasps searching for prey, and as their name implies, their chosen hosts are tarantulas and other extremely large spiders. Crompton himself was impressed by one species of wasp that attacks and paralyzes praying mantises, and he described these wasps as being like a human mother who has decided that the only food fit for her children is grizzly bear. (With both tarantula hawks and mantis hunters, the wasps don’t always win their battles.)

It takes a special love to research a book on wasps and their preferred hunting methods, and I was afraid I’d hit the point where the only way I was going to find a book with the information I sought was by writing it myself. Thankfully, research entomologist Eric Grissell beat me to it, and in so doing, gave me a lot of ideas for future arrangements. For instance, he described going from butterfly to wasp garden by setting up a solar-powered water pump with a 5-gallon bucket as a well and covering the top with rocks that would get splashed during the heat of the day, encouraging wasps and bees to gather water without a chance of drowning. Considering the number of bees and wasps converging on my Sarracenia pots for water during the summer heat, this is going to be an essential addition to the garden come next spring.

And then there are the photos. Crompton’s and Fabre’s books are a bit lacking in illustrations, and thankfully Bees, Wasps, and Ants is thoroughly and copiously augmented by beautiful color photos. When the photos can make me appreciate the beauty of ants, this says something.

As a final note, one of the best reasons to buy this book lies with the insects even more disrespected than wasps. Learning about sawflies was intriguing enough, but for years, the only information I could find on the local velvet ants was that (a) velvet ants were solitary wasps, (b) the females are wingless, and (c) their sting packed a powerful enough punch that they’re referred to throughout Texas as “cow-killers”. (I haven’t seen one since 1980, but after narrowly missing being stung, I don’t plan to test its ranking in the Schmidt Sting Pain Index to make sure.) That right there made this book indispensable, as now I can get co-workers and family members to alternate between oohing in wonder and making vague squicking sounds when reading about braconid wasps on tomato hornworms. I was even able to make the Czarina’s head go “pop” when describing the color of tarantula hawk antennae as tango, and she definitely wasn’t expecting to learn about colors and historical significance from a discussion of wasps.

“I could lie to you about your chances, but you have my sympathies.”

Longtime readers of my Gothic Beauty gardening columns might already know of my fascination of and respect for the strategies and tactics of exoparasitic wasps. The common analogy comparing the life cycle of the typical hunting wasp to the title creature in Alien, while accurate, is also very simplistic. Using the ladybug exoparasite Dinocampus coccinellae as an example, pray that hunting wasps never see chordates as possible hosts.