While baits are on eof the most effective methods of controlling cockroaches, their success is not guaranteed--here are some reasons cockroach baits fail.
Cockroach infestations come in all shapes and sizes, and so too then, do the many different ways to control them. One of the most effective and popular methods is baiting. And while there are thousands (millions?) of successful cockroach bait treatments performed every year, there are plenty of accounts in which baits fail as well. Why is that the case?
During NPMA’s PestWorld 2012, Dr. Ted Granovsky gave a presentation on 12 factors that may contribute to bait failure, ranging from human error to cockroach bait aversion, as well as everything in between. Granovsky, president of Granovsky Associates, an urban and industrial entomological consulting firm, showcased field tests and research illustrating 12 reasons that cockroach baiting can leave PMPs scratching their heads (Editor’s note: Granovsky referred broadly to the German cockroach during his presentation).
1. Consumer Products.
According to Granovsky, many products that clients keep under their kitchen sinks — cleaning products, for example — can have an adverse effect on baits placed by the pest management professional. “You go in, you put out the baits, they seem to work, but then because of some cleaning agents, you’ll get contamination,” he said.
And it’s not just cleaners — paint, water, grease and more, can all have adverse effects. Particularly when using a dry bait, Granovsky said, water contact can create problems.
Interestingly, many of those household cleaning products can work as a contact-killing agent, Granovsky added, citing a 2003 paper by Rebecca Baldwin, of the University of Florida, titled “The toxicity of household cleaners to urban pests,” which documented how household surface cleaners can have high mortality if sprayed directly onto the pest. (Of course, many other household products kill pests on contact as well. But those aren’t the sorts of products PMPs use because, well, they’re professionals!)
Structural issues, like piping, site complexity and excessive humidity can impact the effectiveness of baits.
The size of the cockroach population is a factor. If a large enough population can consume all of the bait in a bait station, those stations will turn into “condos” once the bait is gone, Granvosky said. As well, the population level of the infestation can greatly impact the success of baits. A larger population of cockroaches can require more bait, which may work — but it becomes increasingly cost-prohibitive for the PMP.
Locations of the infestation also can vary from residential homes to larger housing developments. In short, a “one-size-fits-all” approach to baiting is sure to bring about failure.
3. Bait Components.
PMPs need to know their bait in order to successfully apply it, Granovsky said. Baits contain inert ingredients, an attractant, a liquid, a humectant, a fixative, the active ingredient and preservatives.
PMPs need baits that flow well — Granovsky used an example of one particular bait that was “nearly impossible” to apply because of the amount of liquid and humectant. “That creates an issue for us in the field,” Granovsky said. “We can’t have baits that don’t flow well. Some haven’t made it to market because of a very simple thing like that.”
4. Active Ingredients.
Abamectin, boric acid, dinotefuran, imidicloprid, indoxacarb, hydramethylnon...the list goes on. PMPs are faced with a variety of products when it comes to cockroach baits, and different actives abound, Granovsky said.
This range of actives can have varying results, Granovsky said. He cited his own 2007 laboratory study in which he tested 2,500 field-collected roaches of different sexes, using 15 different baits, with no alternate food source presented in the experiment. Results ranged from one bait obtaining 77 percent control over the course of a single day, to another bait achieving less than 3 to 4 percent control in the same period of time, Granovsky said. This being a lab test, even more variation can occur out in the field.
As well, baits may not work in the same location more than once. “If we go back to the same places, reuse the same products, the same combination, at the same apartment — we may not get the same results,” Granovsky said. “You might get aversion, adaptation, resistance — something. Those cockroaches that still survived may have passed something on.”
5. Inert Ingredients.
As with actives, cockroaches can adapt and respond differently to inert ingredients within baits, rendering them less effective in some cases. He referenced lab data that showed four different hydramethylnon products tested on roaches ranged from 60 to 80 percent mortality.
Granovsky also referenced a recent study conducted at North Carolina State University (see related story on page 69) by Dr. Coby Schal that sheds light on cockroaches’ aversion to glucose, a popular material used in roach baits. Schal’s work was published in the journal Science in May and North Carolina State’s research finds this aversion has a genetic basis and it eventually spreads to offspring, resulting in increasingly large groups of cockroaches that reject glucose and any baits made with it.
6. Bait Types.
Gel bait, granular bait, bait stations, dusts and more. The type of bait you’re using in an account, regardless of active ingredient, can impact control, Granovsky said.
He pointed to a study in which three forms of the same active ingredient were used in different trials in different forms: a dust, a gel bait, and an aerosol. The results for the three are quite different.
7. Cockroach Behavior.
Cockroaches are capable of building up behavioral resistance as well — this relates to the potential for cockroaches to develop an aversion to glucose, as noted in item #5. For instance, Granovsky cited a study in which scientists were able to circumvent this problem by swapping the glucose — used in baits to stimulate feeding — with fructose. This also has to do with…
8. Genetic Aspects.
Any particular strain of cockroach can be genetically different — these roaches pass down different traits to their offspring, which can result in a wide variety of aversions, etc. “You can get a real variation of roaches,” he said. “Even from [roaches] in your own area, relating to bait material, you can have resistance within [different] populations.”
As well as aversion, cockroach populations can build up resistance to various bait products, in that it will take a stronger dose of an active ingredient to be effective on a particular cockroach.
9. Life Stage.
How old are the cockroaches? Whether a PMP is dealing with roaches in the nymph stage vs. the adult stage is important. While smaller/younger cockroaches will require less bait, a larger/adult cockroach will require more bait in order for the product to provide the same level of control, Granovsky said. This also relates to the sex of the cockroach, leading to... (see reason #10, page 74).
10. Males vs. Females.
This can make a big difference in bait effectiveness, Granovsky said. Females are slow and tend not to feed as much while pregnant, and they can exhibit much lower mortality rates than male cockroaches. Granovsky cited his own lab work in which female cockroaches showed 0 percent mortality after four days with one particular bait.
11. Technician Variables.
As Granovsky put it: “This is a biggie.” One tip Granovsky said PCOs can use to ensure their technicians are properly inspecting while treating for roaches is to look at the technician’s knees — are they dirty? If so, that technician likely has been on the floor, getting “down and dirty,” thoroughly inspecting for a roach problem.
“Are they really getting to where the roaches are?” Granovsky asked. “If the technician doesn’t go there, he can’t put the bait where it needs to go.” As opposed to applying sprays, Granovsky said that technicians working with cockroach baits need to be savvy.
He added that to ensure a technician is making a thorough bait application, it’s up to managers to get out into the field and teach the proper techniques. Being involved with technicians and their training is certainly a factor that affects baiting success, Granovsky said.
A proper inspection is an important part of this process. It could be that baiting is not the most effective way to handle a cockroach problem, depending on the population.
12. Client Behavior.
Client behavior will have an effect on your control efforts, Granovsky said. One aspect is client awareness; in the past, a client’s threshold for cockroaches in their residence may have been much higher than it is now that a professional has been on site to rein in the problem. One cockroach sighting after a treatment may prompt a call to your office, Granovsky said.
There also is the aspect of the client’s behavior in keeping with recommendations made by a PMP. Cleanliness can be a major factor, as is excessive clutter, such as cardboard boxes being kept in a pantry where cockroaches may hide, Granovsky said.
In all, baiting is a nuanced process that can take a good amount of finesse and expertise, with plenty of factors playing into whether or not a program is successful. But at the end of the day, as Granovsky noted, there are plenty of options from which to choose. And, he said, “Roaches are just downright fun.”
The author is associate editor of PCT magazine.
North Carolina State Research Sheds New Light On Glucose Aversion in Cockroaches
Sugar isn’t always sweet to German cockroaches, especially to the ones that avoid roach baits.
In a study published May 24 in the journal Science, North Carolina State University (NCSU) entomologists show the neural mechanism behind the aversion to glucose, the simple sugar that is a popular ingredient in cockroach baits. Glucose sets off bitter receptors in roach taste buds, causing roaches to avoid foods that bring on this taste-bud reaction. This aversion has a genetic basis and it eventually spreads to offspring, resulting in increasingly large groups of cockroaches that reject glucose and any baits made with it.
In normal German cockroaches, glucose elicits activity in sugar gustatory receptor neurons, which react when exposed to sugars like glucose and fructose – components of corn syrup, a common bait ingredient. Generally, roaches have a sweet tooth for these sugars.
“We don’t know if glucose actually tastes bitter to glucose-averse roaches, but we do know that glucose triggers the bitter receptor neurons that would be triggered by caffeine or other bitter compounds,” says Dr. Coby Schal, the Blanton J. Whitmire Distinguished Professor of Entomology at NCSU and the corresponding author of the paper. “That causes the glucose-averse roach to close its mouth and run away from glucose in tests.”
In the study, the researchers conducted tests on the roach tongue, the paired mouth appendages called paraglossae. The tests showed the unexpected electrophysiological reactions that glucose stimulates both sugar and bitter receptor neurons, confirming behavioral tests that showed roaches quickly fleeing from glucose when presented with it.
But it’s not just a sugar aversion. Roaches exposed to fructose were happy to partake of its sweetness.
Glucose-averse roaches that were forced to taste glucose refused to ingest the sugar, akin to a child who spits out her bitter-tasting food. Normal cockroaches, meanwhile, were happy to eat glucose. Researchers learned this by combining the glucose with food coloring and watching it get ingested or rejected by the normal or glucose-averse roaches, respectively.
Study co-author Dr. Jules Silverman, the Charles G. Wright Distinguished Professor of Entomology at NCSU, discovered glucose aversion and described its inheritance pattern more than 20 years ago. “It is extremely gratifying that we now understand the neural mechanism that underlies this unusual, yet adaptive, behavior,” he said.
There is a cost, however, to cockroaches with glucose aversion. In the absence of glucose-toxicant mixtures, glucose-averse cockroaches grow more slowly than normal roaches in laboratory settings where there are no nutritional stresses. “Now we want to understand how this trait persists in nature, where the food supply is probably limited,” Silverman said. “Cockroaches have to adapt to a varied and unreliable food supply, and glucose-aversion places an additional restriction on obtaining adequate nutrition.”
Schal says the pest control industry has focused mostly on learning about how pests gain resistance to the insecticides themselves. This paper, however, shows cockroaches’ behavioral resistance to certain types of food — in this case, glucose.
“Most times, genetic changes, or mutations, cause the loss of function,” Schal says. “In this case, the mutation resulted in the gain of a new function — triggering bitter receptors when glucose is introduced. This gives the cockroach a new behavior which is incredibly adaptive. These roaches just got ahead of us in the arms race.”
Ayako Wada-Katsumata, a NCSU senior research scholar, performed most of the experiments and is the first author of the paper. She is now investigating whether roaches can learn to associate glucose with specific odors and thus use their memory to ignore baits that contain glucose. The research was supported by the National Science Foundation, the U.S. Department of Housing and Urban Development, and the Blanton J. Whitmire Endowment at North Carolina State. — Source: North Carolina State University News Service
Editor’s note: PCT’s Brad Harbsion sat down with Schal for a podcast regarding his findings. To access the podcast visit http://bit.ly/12fgbxR.