Rethinking German Cockroach Control

The current approach to cockroach control in low-income, multi-unit housing is not working, said Dr. Dini Miller, an urban entomologist at Virginia Tech. Tenants continue to deal with ongoing infestations of the pests, even at properties under contract with professional pest control companies.

That’s why Miller urged pest management professionals to “try something totally different,” such as the methodology she field-tested at three housing complexes in Richmond and Hopewell, Va., and Rocky Mount, N.C.

The results of the study, which took place from May 2017 to September 2018, surprised even Miller. She found that German cockroaches can be eliminated from the most-infested multi-unit housing using an assessment-based approach, an appropriate amount of gel bait as the only means of control, and without requiring residents to empty cupboards or remove clutter before treatment.

“We have had miraculous results where we’ve basically gone from summer cockroach trap counts of 800 to 1,000 roaches in a single night to one or zero,” said Miller.

A NEW APPROACH. First, Miller assessed the level of cockroach infestation in each unit overnight using large Lo-Line sticky traps. The results determined how much gel bait she applied in each unit.

An apartment with a trap count of one to 50 cockroaches got 7.5 grams of bait (a quarter of a tube). A count of 50 to 100 cockroaches got 15 grams (half a tube of bait), and a count of more than 100 roaches received 30 grams (one tube) of bait. Miller assessed all test apartment units two weeks after initial baiting and every 30 days thereafter. Units with more than 500 cockroaches were treated with two tubes of bait (60 g); units with 100-459 cockroaches received one tube of bait; units with 50-99 cockroaches received half a tube of bait (15 g); and units with 1-49 cockroaches received a quarter of a tube of bait (7.5 g).

Bait was applied to the creases of 2-inch-by-2-inch squares of wax paper that had been folded on the diagonal, forming a bait “taco” so that the cockroaches had direct access to the bait as shown in the photo above. Note that the baits were not pressed closed. Miller placed several wax paper tacos in each cabinet, behind stoves and refrigerators, underneath microwaves and even slipped them into stacks of mail where the roaches were harboring.

The wax paper wrap let Miller put bait in hard-to-treat places (e.g., within stacks of clutter) as well as give the pests a “clean dinner plate” where surfaces were dirty, covered in food debris or contaminated by old bait or repellent spray.

The cockroaches really loved eating out to the wax paper (Cut-Rite brand wax paper, which is used for baking) and would often eat right through it — and Miller was able to easily remove any bait residues that were not consumed. (Miller said leftover bait residue is a real problem; she regularly finds old bait that was applied like “caulk” in the 1990s in public housing units.)

Four different gel baits were used in the study: Bayer’s MaxForce Magnum was applied at the Richmond, Va., complex (30 apartments); MGK’s Vendetta Nitro in the Hopewell, Va., complex (21 units); and Syngenta’s Advion Evolution and Optigard gel baits in the Rocky Mount, N.C., complex (30 units). “So far every bait has worked well being applied this way,” said Miller.

Within 60 days, she achieved a 90 percent reduction in trap catch, even in June with summer cockroach populations actively growing. She continued to trap “onsie-twosies” in units for some time after the initial knockdown, treating these as low-level infestations.

Over the 16 months, Miller assessed units monthly and found that cockroach populations did not rebound the next summer. “It looks like once they’re gone, they’re actually gone,” she said of the pests.

“WE’VE GOT TO ROTATE.” At the Rocky Mount Housing Authority, Miller also documented the results of bait rotation, which can help prevent bait aversion and insecticide resistance in German cockroach populations. Bait aversion is when cockroaches develop a dislike for certain sugars or food ingredients in the bait matrix and refuse to eat it.

RESISTANCE IS PHYSIOLOGICAL. Resistance is also prevalent in these German cockroach populations. They have been treated with every insecticide available for decades.

Cockroaches in public housing facilities have “very malleable genetics” and using the same control products year after year contributes to these problems, said Miller. “We need to avoid resistance like the plague,” she added. In the study Miller rotated use of the two Syngenta gel baits, which have different active ingredients and modes of action, every three months to match the life cycle of the pest. The 30 units saw “a total wipeout” of the cockroach population with none caught in follow-up traps through June; “that’s huge,” Miller said.

NO COOPERATION? NO EXCUSE. Miller did not ask residents of the buildings “to clean up or disturb their cockroaches in any way” before treatment and still “the effect has been amazing.”

Moving the contents of cabinets and other clutter likely scares the roaches deeper into harborage areas. Plus, PMPs are never satisfied with how tenants prepare their units anyway, she said.

Miller began using the wax paper because initially she wasn’t allowed to ask residents to clean up their units and she didn’t have the time or enough clean places to apply 60 grams of bait. “We’d just have them all over the place. It would be ridiculous,” she said of the standard, quarter of a dime-sized placement. With the no-prep approach, the cockroaches remained calm and had bait delivered right to them in the wax paper.

Residents were grateful not to have to dismantle their homes and vacate the premises for hours, like required after traditional spray treatments. And because residents were present, Miller could ask them where they’d seen cockroaches, which helped guide her bait placement, and urge them to hold off on spraying over-the-counter roach control products for several days after she placed the bait. Miller continued to engage residents by asking how the program was working during follow-up assessments.

“There are a million reasons why the residents need to clean up but cockroach control is not one of them,” said Miller. Blaming residents is an excuse; one the industry has used for 50 years, she said.

FUNDAMENTAL CHANGES NEEDED. Two big challenges exist to implementing this methodology.

The first is that everyone — PMPs, property managers, tenants — is “married to this idea of spray” for cockroach control and that has to change, said Miller.

Spray is fast to apply and cheap compared to bait, depending on the product chosen, but waving around a pesticide wand for three minutes in a unit is not going to get rid of the cockroach population.

This leads to the second challenge: PMPs are under-bidding social housing properties. At one building where Miller field-tested her methodology, the pest management company was charging half of what a previous provider charged seven years ago. And while that might make a salesperson’s monthly quota, it certainly doesn’t give the technician the time needed per unit to do the job correctly.

Neither do low bids deliver customer service. Property managers and housing agencies may go with the cheapest price but they (and their tenants) are getting nothing for their money. All three complexes in the study were being treated for roaches, reminded Miller, and “to have 1,300 roaches in a single apartment in a single night that I can take out with a single sticky trap… how well is the pest control being applied there?”

It has become an issue of social justice. “We’re talking about human beings here,” said Miller. Middle-class white people wouldn’t stand for it; a restaurant would be shut down with great fanfare yet “this is completely ongoing in our public housing situation,” she said.

HOW TO MAKE IT WORK. It is possible for pest management professionals to follow Miller’s assessment-based cockroach control protocol in the field and keep costs in check.

She recommends that PMPs get a separate contract to monitor all the units first. Do this in October/November when the cockroach populations have naturally decreased and are at their lowest.

Use the largest sticky traps so you can determine which units have more cockroaches; small traps may quickly fill up to capacity, making it hard to determine differences in the levels of infestation. Instead of counting each roach trapped, technicians can visually estimate whether the catch represents a low, medium or high infestation. Take photos of trap catches and share with apartment managers, who generally avoid knowing how many units they have infested with cockroaches and the depth of their infestation, “so nobody can be in denial,” advised Miller.

From this data, identify the top 25 percent of the most infested units. Work on these units monthly or biweekly (December-February) following the protocol for the next three months. In heavily infested units, it takes about 15 minutes to assess traps and place 60 grams of bait in wax paper squares.

From March to May, move on to the medium-infested units for three months. Then move to the minimally infested units.

After the first year, monitor all the units again to determine how to divide them up for treatment.

Additional pointers: Use a black marker to make lines on bait tubes at 7.5 gram intervals so technicians apply accurate amounts of bait. Sticky traps that do not catch roaches in a 24-hour assessment period can be reused. Miller urged PMPs to follow the protocol specifically. “Don’t deviate because it works,” she said.

The author is a frequent contributor to PCT.