Fly Attraction Reduction - So FAR, So Good!

Except for winter cress (which is, by the way, a tasty “wild edible”), the weeds in the garden have stopped growing, and I have a time to plan for next year’s garden to be so much better than this year’s. This is why I like autumn, no overwhelm of weeds.

Another good thing is no houseflies.  I have developed a whole new appreciation for and engagement with houseflies, now that these creatures are a part of our WERF High Quality Biosolids Research Project.  But that doesn’t mean I need to like them.

Houseflies have a hugely important and negative impact on humankind, but are mostly ignored. Why so?  I head to the Internet for see what connection, if any, has been forged between the housefly and cultural arts. Hmmm, interesting! Yoko Ono produced a video work in 1970 named “Fly,” in which according to Wikipedia, the source of all truth, a camera records in close-up the movement of a house fly over a naked woman, in a critique and parody of male sexual desire. The 1986 horror film “The Fly” had a scientist mis-quide his “telepod” and consequently began a merge of his DNA with that of a housefly, causing his very alarming transformation.  In 2010, an episode of “Breaking Bad” was titled,  “Fly,” in which the principal character is a housefly that threatens to contaminate a batch of illicit drugs; said housefly was a masterwork of a pre-eminent visual effects firm, Entity FX.  A photo essay strikes the most positive chord. The Purpose of Flies and Art of the Fly  posts some stunning photographs, though none I would hang in my office.

Houseflies may someday have a hugely positive impact.  In my Biosolids in the News last December first, I reported, mostly facetiously, on the paper by Drs. Zheng and Zhou, “Antibacterial potency of housefly larvae extract from sewage sludge through bioconversion” that housefly maggots can totally stabilize biosolids and then harvested for extraction of immensely valuable antibiotic enzymes. Perhaps even more persuasive is the prospect that the housefly holds the key to future advances in immunotherapy treatment of disease (Fly genome could help improve health, environment.)

My new found respect for the housefly is in discovering how very far from benign this creature is. Over ail, the housefly is not just a nuisance when it ceaselessly flies around the picnic lunch, it is a major vector of food-borne, diarrheal disease throughout the world. It inhabits all continents, except for Antarctica, and is classified as synanthropic, meaning it benefits from its association with the “somewhat artificial habitats that humans create…”

In last December’s blog, I featured the work of Dr. Ludek Zurek and his doctoral students that has connected biosolids to housefly propagation, which is a nuisance for our profession. Further, he has drawn a link between livestock operations and the spread of antibiotic resistant genes from that livestock pool.  This year, Dr. Zurek is part of the WERF High Quality Biosolids research project, so valuable are his insights.

The WERF project interest in the housefly is in its potential for advancing the definition of “Vector Attraction Reduction (VAR).” The three legs of the Exceptional Quality stool are compliance with pollutant concentration standards, demonstration of a Class A (PFRP) “Pathogen Reduction” process and, of interest here, documentation of VAR. VAR is the wobbliest of the three legs.  Back at the early days of the Part 503 regulations, with the release of the “White House” document “Control of Pathogens and Vector Attraction in Sewage Sludge,” EPA challenged us all with this: “The responsibility to eventually develop additional vector attraction reduction test protocols lies with the scientific community and the sewage sludge industry.”

At long last, we are on the road to new methods.

I argue here that the only “vector” for which “reduction” in “attractiveness” is meaningful with respect to biosolids is the housefly. No other potential vector of pathogen spread is at work with biosolids… neither the cockroach or mosquito is active around biosolids, and the other flies swarming biosolids are not carriers of human pathogens. The housefly is it. My opinion is that a goal for biosolids management ought to be, specifically, "Fly Attraction Reduction," not more generally-speaking "Vector Attraction Reduction."

Of course, the High Quality Biosolids research project is about more than VAR or flies. The project also examines odors, plant response, aesthetics and similar attributes of biosolids product performance. But interestingly, and not really coincidentally, qualities of biosolids that cause “fly attraction” are the same ones that are seemingly poor measures of “high quality biosolids.”

What attracts houseflies generally?  Houseflies are attracted to putrescible organic matter, such as fresh manure, rotting vegetables, and poorly stabilized biosolids. A 100 year old USDA publication, titled simply “Farmers Bulletin 679, House Flies,” lays out these attractant materials pretty concisely.

But what precisely about biosolids might attract houseflies?  Here we get to use 21st Century science. House Flies and Pig Manure Volatiles: Wind Tunnel Behavioral Studies and Electrophysiological Evaluations  actually measures the volatile emissions that are most attractive to houseflies: “…volatiles eliciting responses from female antennae were butanoic acid, 3-methylbutanoic acid, dimethyldisulfide, dimethyltrisulfide, dimethyltetrasullide, phenol, benzeneethanol, indole, and 3·methylindole.”

As one of the participants in the dawning of biosolids odorant research, I recognize some of these compounds.   The paper by Matt Higgins and others, presented at the 2003 WEF specialty conference, “Mechanisms of Volatile Sulfur Compound and Odor Production in Digested Biosolids,” identified some of these very same compounds in the odors emanating post-centrifugation from biosolids cake. Perhaps the human nose is exquisitely sensitive to the same odorants as the housefly.

Entomologists have also established that houseflies are attracted to material with characteristics suitable for successful egg-laying. Flies look for a substrate that consists of fermenting organic matter with a “not-too-wet and not-too-dry” moisture content (say 30% solids), with sufficient protein and of a moderate temperature.  Sounds like most dewatered digested cakes I’ve met.

The housefly is one of those ubiquitous inhabitants of our world to which we seldom pay serious attention.  I suspect many of us who have worked with biosolids have had situations of startling invasion by houseflies, yet have not connected that incident to Part 503 VAR regulations. Now, with our research project we have the opportunity to deploy several new tools and technologies to objectively measure attributes that key in to actual vector attractiveness.

Stay tuned as our research explores real measures of VAR... So FAR (Fly Attraction Reduction), so good!