Careful use of Nuvan strips

It may never be as big a seller as Vogue,
but the CDC's Morbidity and Mortality Report
covers some interesting news for PMPs.

The Morbidity and Mortality Weekly Report from the Centers for Disease Control will never make Amazon.com's Best Sellers in Magazines List.  In fact among all the subscriptions I receive, I'd be hard-pressed to think of one with a less appealing title. But sometimes this report has very useful information for entomologists and pest management specialists. This week's Notes from the Field feature looks at statistics concerning acute illnesses associated with Pest strips containing the insecticide dichlorvos (DDVP).

For anyone unfamiliar, dichlorvos is the active ingredient in (among other products) Nuvan™ Prostrips™, a slow release pesticide formulation for control of bed bugs, "flies, gnats, mosquitoes, moths, silverfish, cockroaches, spiders, beetles, earwigs and other pests".  Dichlorvos looked like it might have seen the last of its days a few years back, at least partly because of its acute toxicity. It is a holdover from the era of organophosphate insecticides, and like all OPs, it acts as an acetylcholinesterase inhibitor.  But dichlorvos has a unique property: its relatively high volatility makes it useful as a fumigant.  And thanks to its effectiveness against bed bugs, dichlorvos now appears to be staging a comeback.

Dichlorvos kills pyrethroid-resistant bed bugs. But it can also hurt people if not used carefully as described in the label. The CDC study reports on 31 acute DDVP pest strip–related illness cases recorded from seven U.S. states and Canada from 2000 to 2013 (more cases undoubtedly occurred that were not part of this study). Most of the illnesses resulted from using the product in commonly occupied living areas (e.g., kitchens and bedrooms), in violation of label directions. According to the report, "Although 26 of the 31 cases involved mild health effects of short duration, five persons had moderate health effects."  Illnesses included neurological, respiratory and gastrointestinal symptoms. Effects due to dichlorvos overexposure usually resolve themselves completely, according to the study; but make no mistake--this insecticide should be used with care.

The report concludes that in order to prevent dichlorvos-related illnesses, the public should be educated on correct use of pest strips, and how to control insect pests using safer pest control methods.  I would add that it's important for professionals to be reminded of the safe use of these products and the importance of reading the fine print on dichlorvos labels.

Some key label points to remember about Nuvan and similar strips:

• Do not over-apply.  One 16 gm strip is sufficient for treating 100 to 200 cubic feet.  Having said that, do your technicians know how to estimate cubic feet?  A typical 6' by 12' by 8' walk-in closet is approximately 575 cubic feet (a simple multiplication of length x width x height) and would require 3 to 5 strips--6 would be an over-application.
• Around the home, strips may only be used in closets, wardrobes and cupboards, storage units, garages, attics or crawl spaces. Other sites outside the house are also listed on the label.
• Do not use in kitchens or food prep or storage areas where unwrapped food may be exposed.  Kitchen utensils should not contact the strips.
• Pets and children should not play or sleep where strips are in use, nor should the strips be used in any room where humans are likely to spend more than four hours a day. An important sidenote here: most of the illnesses (65%) reported in the CDC paper occurred when exposures exceeded four hours per day.

If you or your technician encounters a customer using dichlorvos strips, you owe it them to make sure they understand the risk of the product and use it only after carefully reading and following the label.

And if you'd like to receive the Morbidity and Mortality Report for it's occasional pesticide and pest-related stories, you can subscribe here. 

Is your customer left holding the bag?

Bagged items following an insecticide treatment for bed bugs. 

One of the great conundrums of bed bug service is what to do with the mounds of clothing, shoes, electronics, books, papers and other personal items that must be bagged prior to, or during, a bed bug treatment. These items are potentially infested with adults, nymphs and bed bug eggs, and should not be returned to the home until all bed bugs inside are killed. So what to tell the customer?

Clothes are usually the least troublesome bagged item, because they can be run through the washer or drier.  But many bagged personal items are not appropriate for the laundromat.  What can be done for non-washable items that might harbor bed bugs?

Heat

There are several options for treating "hard items" like books and electronics.  Heat is one of the best choices, because bed bugs don't do well in heat. A study by Stephen Kells and Michael Goblirsch from the University of Minnesota, showed that bed bugs exposed to rising temperatures for two hours began to die at around 104 degrees F, though eggs were not greatly affected by this temperature.  Both adults and eggs were  killed immediately by exposure to 122 to 131 degrees F, respectively.  The authors concluded that bed bugs in a room could be eliminated by heating all parts of a room to 122 degrees F for an hour, a guideline followed by most heat treatment companies today.

These same heat treatment guidelines can be used for heat-treating hard or soft goods in garbage bags.  The cheapest and easiest way to accomplish this is through solar heat during the summer months.  People have used this method for many years, especially in tropical areas where mattresses and clothing can conveniently be bagged and placed in the sun all day to kill bed bugs.  My summer intern and I attempted to replicate this approach in 2012 by bagging 7 lbs of soft goods in both clear and black plastic bags on a summer afternoon with an ambient outdoor temperature of 95 degrees F.  We put the bags on pavement at mid-morning and monitored temperatures within the bags through the afternoon. Thermometer readings in the clear plastic bags easily exceeded the lethal temperature for the minimum one-hour exposure; however black plastic bag contents never exceeded the one-hour lethal temperature required to kill all adults and eggs.  We found that even when daytime air temperatures stayed under 90 degrees, clear bags can heat soft goods sufficiently to kill bed bugs.

Many people are surprised that, when it comes to heating, clear plastic bags are superior to black. We've all been taught that black absorbs heat; however in this case the greenhouse heat-trapping effect is more powerful than bag color. The greenhouse effect happens when the short visible and UV wavelengths pass through the clear bag and begin heating the objects inside. The same plastic keeps the radiant heat produced by light inside the bag. Black plastic doesn't let much visible light through, so greenhouse heating effect is minimal. Hence clear is hotter than black (and tinted windows do keep a car cooler in the summer, as Texans will tell you). A second important advantage of using clear bags in bed bug work is that the customer can see what items are stored in the bags, for easier retrieval.

Temperatures from the middle of clear and opaque black plastic bags set
outdoors on a clear summer day with a maximum ambient temperature of
95 degrees F. Note that only temperatures in the clear bag exceed the lethal
temperature for bed bug adults and eggs. M. Merchant, unpublished data.

Clearly, solarization provides one simple, fast and inexpensive solution for dis-infesting personal belongings during the summer.  To make sure that lethal temperatures are reached, I suggest using a relatively inexpensive wireless (or wired) weather monitor with thermometer capabilities, in the middle of whatever items are in need of treating.

Cold

But what if it's not summer, or you live in areas where outdoor temperatures just aren't that hot? Another option is cold.  Unfortunately, cold is not a very fast or effective treatment for bed bugs.  Simply putting items in the refrigerator freezer is not a guarantee of lethality.  Dr. Dini Miller, at the recent bed bug summit in Denver, CO, reported that five bed bugs (out of 200 bed bugs) in a vial she stored in a refrigerator freezer for TWO YEARS recovered on removal from the cold. Granted, colder temperatures do kill bed bugs eventually, but cold is not a reliable or fast method to disinfest bags.

Fumigants

The final option for killing hidden bed bugs is use of fumigants.  Fumigants are insecticides in gas form, and hence have the potential for penetrating many substances to kill hidden pests. Nuvan™ Prostrips placed in plastic bags is a fumigant option used by many PMPs.  These strips were tested as a means of controlling bed bugs in infested items by Dini Miller's Virginia Tech lab.  While dichlorvos, the active ingredient in Nuvan™ Prostrips, is toxic to bed bugs, it's ability to provide 100% control was limited in the Virginia tests.  The only time Dr. Miller's group was able to document 100% bed bug adult and nymph mortality was with hard goods when bags were held for 14 days (significantly longer than the 48 hour "minimum" time recommended on the label). Miller's lab concluded that dichlorvos is a slow dispersing fumigant and that the limited air flow in closed bags makes it difficult for dichlorvos to reach bed bugs in small crevices of enclosed items. Soft goods were much more difficult to treat with fumigants because of more limited air flow through clothing and fabrics.

Another bed bug fumigant tested by Miller's lab, and now being actively marketed for use in bags, is Cirkil®.  The Cirkil® active ingredient is neem oil, a plant-based extract with a good safety record and the cachet of being a natural product.  Terramera, Cirkil's manufacturer, has just published a new protocol for using the product that they refer to as "Rag in a Bag". The method involves spraying the undiluted product on a rag and placing it with the items to be treated in plastic bags. The protocol is based on Miller's research that showed that one treated rag could effectively fumigate a bag with hard goods in 3 days.  One big drawback of the Cirkil product, according to some who have used it, is the strong, lingering odor of the product.  If you are interested in this product, I suggest you try it on a small scale to assess the odor issue before subjecting clients to a potentially smelly product.

Lastly, carbon dioxide has been suggested as a means of controlling bed bugs in plastic bags. Dr. Changlu Wang from Rutger's University has tested placing commercially available dry ice pellets in plastic bags to kill bed bugs. As I reported in an earlier blog, Wang found that 3 lbs of dry ice in a 42 gallon (3 mil-thick) garbage/yard waste plastic bag was sufficient to suffocate all stages of bed bugs in up to 22 lbs of clothes, when held for 24 hours. This amounts to a cost of approximately $4 to disinfest 22 lbs of clothes or other items that would fit in the bag.  Sounds like a great option, except that the U.S. EPA considers carbon dioxide to be an insecticide and discourages its use for safety reasons. Indeed, CO2 can be toxic in high enough doses, and several leaking bags in a bed room (all bags will leak) or other closed living space could certainly elevate gas levels into the range of health concern to humans. Until the EPA gets this figured out, I am reluctant to recommend use of dry ice as a bag treatment.

Patience

So where does that leave the average bed bug client?  As we've seen, heat, cold and fumigants all have their place, but their usefulness can be limited.  If none of these options works, the client may be left holding the bag--literally.

But even when the only option appears to be waiting, the wait isn't forever. Bed bugs without access to blood will eventually starve. But how long does it take to kill bed bugs?  Current research on bed bug longevity suggests that 3-5 months is long enough to starve bed bugs.  This is a long time, but not an impossible task, especially for personal items that are not immediately needed. For this reason, it may be a good idea to suggest to your clients that they store items together that do not need to be used quickly. It may be possible to use some of the methods listed above on higher priority bags and let the rest just sit. And items that are needed immediately can be individually inspected and/or washed if you are unsure whether there might still be live bed bugs hidden within.  This option is probably good for children's toys that cannot be placed in the wash.

When storing bags, keep in mind that the warmer the temperature, the shorter the lifespan of starving bed bugs. A warm bed bug respires faster, consequently using up its energy stores more quickly. If you keep bagged items at 70 degrees or higher it should be safe to remove items after three months.  But if they've been stored at slightly cooler temperatures, you may want to keep those bags shut a little longer. Putting bags in an unheated shed or closet outdoors might not be the best solution if those bags are needed within 5-6 months. Remember the bed bugs that survived the freezer for two years?

If your company conducts bed bug control with insecticides, the question of what to do with bagged items is critical. Because each client and job is unique, it's up to you as a professional to advise your customer what their best options are for handling those important personal items.  After all, no one wants to be left holding the bag--especially one full of bed bugs.