Assessment-Based Pest Management and Busting Cockroach Bait Myths

Respected industry figure Professor Dini Miller shares her ground-breaking work on cockroach baiting from the USA. 

The inaugural Termite Professional Conference held in July hosted a special pre-conference event – An Evening with Professor Dini Miller. Prof. Miller was in Australia for the Top End Aussie Termite Tour and attending the conference as a delegate, so we were honoured she agreed to present and share her knowledge on German cockroach management and discuss the concept of Assessment-based Pest Management (APM). Here we summarise the key messages from her presentation.


Dr Phil Ridley, Director, Professional Pest Manager and Professor Dini Miller, Professor of Urban Pest Management, Virginia Tech University, USA


Integrated Pest Management (IPM)

IPM is widely talked about within the pest control industry, but rarely applied correctly. Indeed, Prof. Miller believes the use of IPM terminology does not really fit the pest control industry and that Assessment-based Pest Management (APM) provides a more relevant methodology that delivers practical results.


So, what’s wrong with IPM?

Integrated pest management as a concept was developed by the agricultural industry as a way of reducing insecticide applications, to better manage the risks around insecticide resistance (through avoiding excessive and unnecessary insecticide use). A key element of any IPM strategy is the need to monitor the pest levels and only apply insecticide once pest numbers reach an economically significant level. i.e. when the cost of spraying is less than the economic loss from not spraying. This means that in many cases, it is acceptable to have a low level of pests in a crop if the economic damage is insignificant. Of course, in an urban pest control situation, generally there is no ‘economically acceptable’ pest level, typically customers want zero pests!

Furthermore, Prof. Miller has observed that in the pest control industry, IPM terminology has morphed into a belief system that IPM is some sort of low toxicity or non-toxic pest control procedure. This appears to be a view held by many pest managers and their customers alike. Apart from being wrong and confusing, it doesn’t really help in developing practical treatment programs that deliver results.


Assessment-based Pest Management (APM)

Assessment-based Pest Management isn’t rocket science. It is actually the application of best practice. Before any treatment takes place, pest managers should carry out an inspection to identify the nature of the problem; specifically, identify the pest species present, the location of the pests, the level of pest pressure and the potential causes of the problem. Knowing this information allows an optimal pest management program to be designed and the appropriate products can be applied, to the necessary areas, at the correct levels.

However, with the cost and time pressures that commonly come into play, this important pre-treatment exercise is often rushed or even omitted altogether.

In applying Assessment-based Pest Management processes, the key word to emphasise is assessment. Ideally, this assessment involves collecting hard data – actual pest numbers – so accurate information about the infestation levels can be established. But to execute APM properly, it is important to continue this assessment over time. Only by continuing to assess the pest levels can pest managers gauge the effectiveness of their treatment, modify the program if necessary and demonstrate success to their customers.


Managing extreme German cockroach infestations

Prof. Miller carries out a lot of field trials on German cockroaches (and bed bugs) in low socio-economic, government-owned housing. These are apartment units with extreme German cockroach infestations and significant hygiene issues. The standard government pest control service allows only for a quick spray of product (generally a pyrethroid). Not only does this not work, but because of decades of spraying the same products every month, these repeat applications have resulted in high levels of insecticide resistance in the German cockroach populations.

Prof. Miller developed this APM methodology when she had the opportunity to carry out a research trial evaluating new bait formulations in government housing projects to determine what level of control could be achieved by using cockroach gel baits alone. This 30-day study provided an ideal opportunity to evaluate APM in practice.1

The first step in the study was to do a pre-trial assessment. Sticky traps were placed in three locations within each unit – above the sink, below the sink and behind the toilet. The traps were collected 24 hours later to determine which had the highest levels of infestation.


Two sticky traps full of cockroaches
These sticky traps are full after just one night in an apartment with heavy infestation


Highly infested units were selected for the trial and on day 1 each unit received 30 g of cockroach gel. When the apartments were assessed again on day 14 (using sticky traps), bait was then applied in quantities that varied depending on the level of infestation. Apartments with no trap catch received no bait, 7.5 g was applied in units with low level infestations, 15 g was applied to medium infestations, and 30–60 g was applied to those units that were the most heavily infested.


Typical sanitation at the housing sites


By day 30, the cockroach populations had decreased by 90-98% – and that was without asking the residents to clean up the rubbish, food or dirty dishes in their apartments! (Figure 1)


Figure 1: Effectiveness of using cockroach gel alone to control infested apartments (gel placements at day 0 and day 14)


Bait tacos!

One of the side developments that arose from this trial was the development of the ‘bait taco’ application technique. Applying dots of gel in a heavily infested apartment would be very time consuming, given the quantity of bait that would be required. It would also be difficult to measure how many of these dots of gel had been consumed. The solution was the ‘bait taco’, a 0.5 g line of gel applied on a small square of greaseproof paper that had been folded into a taco. Not only did using these bait tacos allow for quick, easy placement, it was also easy to assess how much bait had been eaten.



Long-term German cockroach management

The results from the initial 30-day trial led to a year-long trial in multiple locations, using 60 units at each trial site. After the pre-trial assessment, the day 1 treatment was a little different to the previous 30-day trial. Units with low numbers of cockroaches were untreated – they became the control units. The other units were graded according to three levels of infestation, with the lowest level receiving 7.5 g of gel, the middle level, 15 g of gel and the highest level of infestation, 30 g of gel. The apartments were then evaluated on day 14 with the units treated again, applying increasing levels of gel depending on the level of infestation, with no gel applied to apartments with a zero-catch count in the traps, to 60 g of gel applied to the units with over 500 cockroaches in the traps.


Professor Dini Miller holding a sticky trap full of German cockroaches
Sticky traps are key to assessment-based pest management of German cockroaches


The process of monitoring and baiting continued every 30 days for over a year, with the level of bait applied varying according to trap count. Importantly, the bait products were rotated every 90 days to avoid any bait aversion or resistance developing. Vacuuming was included as part of the treatment to clear up dead cockroaches.


Wall infested with cockroaches
German cockroach infestations were so heavy, large numbers of cockroaches were seen in the open during the day – and were controlled only using baits and no hygiene measures!


The results!

Irrespective of the products used, the populations were largely controlled within 2-3 months and the populations remained under control (90%, 99% and 100% at the three housing locations) for the duration of the trial (over a year), (Figures 2 & 3).


Figure 2: Control program using Vendetta Nitro, Optigard, Maxforce Magnum and Advion Evolution in rotation


Figure 3: Control program using Optigard and Advion Evolution in combination


This was despite the fact that the study started during the summer months; there was no pre-treatment preparation; and residents did not clean their apartments prior to the bait application. Therefore, there were plenty of alternative food sources for the cockroaches. The other interesting observation, that flew in the face of expectations, was that there was no evidence of movement of cockroaches between apartments. Once the population in an apartment was under control, there appeared to be no new arrivals from untreated neighbouring apartments.


Cockroach treatment myths – busted!

BUSTED: Insecticide sprays are necessary to get on top of extreme German cockroach infestations. Cockroach gels on their own can do the job.

BUSTED: It’s essential to clean the site and remove competing food sources for the baits to work. Leaving the site undisturbed can be beneficial to ensure fast bait uptake.

BUSTED: German cockroaches will re-invade from neighbouring apartments. Not necessarily. And how do we know this? APM – Assessment-based Pest Management.


An important tip offered by Prof. Miller: you should not disturb the cockroaches and then try to feed them i.e. don’t do a big clean up and don’t spray with insecticide prior to applying bait. Applying the bait near hotspots and current feeding sites will get the fastest bait uptake. The cockroaches may even start consuming the tacos while that are being prepared, literally before you even put them in place.


Dini Miller, PhD Professor Dini Miller

Professor and Urban Pest Management Specialist Department of Entomology, Virginia Tech, USA

Dini M. Miller is a Professor at Virginia Tech, and the Urban Pest Management Specialist for the state of Virginia. Dr. Miller is an internationally recognised expert in the area of urban pest management, particularly German cockroach and bed bug biology, behaviour, and control. Dr. Miller has won numerous awards for her work in urban entomology including the pest control industry’s Crown Leadership Award, the Entomological Society of America’s (Eastern Branch) Distinguished Achievement Award in Extension, and the Virginia Pest Management Industry Stewardship Award.


1 Miller, D.M and Smith, E.P (2019). Quantifying the Efficacy of an Assessment-Based Pest Management (APM) Program for German Cockroach (L.) (Blattodea: Blattellidae) Control in Low-Income Public Housing Units: Journal of Economic Entomology, Volume 113, Issue 1, February 2020, Pages 375–384.

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