Can Biflex Mikron Be Transferred Between German Cockroaches?

The repellent qualities of Biflex Mikron have been tested in a laboratory trial, with the results outlined here (part two of two). 

In the previous issue of Professional Pest Manager magazine, the results of a recent Australian trial were shared that answered the question: “Are Biflex Mikron treated surfaces repellent to German cockroaches?” The trial results showed quite conclusively that German cockroaches are not repelled by surfaces treated with Biflex Mikron, the newest dual-active formulation to the Australian market, from FMC.

With Biflex Mikron being a dual-active combination of pyrethroid (bifenthrin) and neonicotinoid (acetamiprid), FMC has been working to answer pest managers’ questions regarding the mode of action of Biflex Mikron, especially in regard to German cockroaches.

As a follow up to this first piece of research, a second question was posed: “Can Biflex Mikron be transferred from a treated German cockroach to untreated nestmates?”

To answer this question, FMC again engaged experienced pest researcher Scott Kleinschmidt from Australian Timber & Pest Research (ATP Research) to conduct a scientific trial. In the trial, a mix of German cockroach adults and nymphs were placed into 32 test arenas. Half of the areas had five cockroaches added and the remaining half had ten cockroaches added.


Petri dishes arranged in a grid
Test arenas with either one treated German cockroach (donor) per five or ten untreated nestmates (recipients)


In an area separate from the test arenas, several populations of German cockroaches were lightly misted with one of the following products (at recommended label rates, one treatment per population):

  1. Biflex Mikron (bifenthrin + acetamiprid)
  2. Temprid (beta-cyfluthrin + imidacloprid)
  3. Seclira (dinotefuran)
  4. Water

A single treated cockroach (donor) was then placed into a test arena containing either five or ten untreated cockroaches (recipients). Therefore, the trial consisted of four products at two different donor: recipient ratios (1:5 and 1:10), with four replicates for each treatment.

The cockroaches were free to roam within the test arena and interact with the treated cockroach as they wished. The trial was monitored for eight hours after treatment for the 1:5 ratio and 12 hours after treatment for the 1:10 ratio, with the number of dead or moribund cockroaches recorded at hourly intervals.

The results were both mixed and interesting at the same time. The 1:5 ratio produced similar results across the three chemical products, with all of them successfully transferring the active ingredients from the treated cockroach to the untreated nestmates. All the chemical products recorded close to 100% mortality during the eight-hour trial period, as compared to zero mortality in the water-treated population (Figure 1).


Figure 1: Results of German cockroach mortality after adding one treated cockroach to five untreated nestmates (average of four replicates)


In the 1:10 ratio, the chemical products achieved between 43- 73% mortality during the 12-hour trial period, as compared to zero mortality in the water-treated population (Figure 2). This highlights a somewhat limited transfer of active ingredient from the treated cockroaches to the untreated nestmates at this ratio.


Figure 2: Results of German cockroach mortality after adding one treated cockroach to ten untreated nestmates (average of four replicates)


That was the mixed part of the results. The interesting part was that the cockroaches that were still alive at the completion of the trial were all late-stage nymphs. This was interesting because normally the juvenile form of any animal is less robust and in need of more protection than the adult. However, a quick scientific literature review revealed numerous papers on the subject, including one published in Journal of Economic Entomology that found late-stage German cockroach nymphs more difficult to kill than the adults. This reduced susceptibility to insecticides in lateinstar nymphs occurred irrespective of weight differences, type of insecticide, or strain of cockroach.

This additional information changes how the results from Mr Kleinschmidt’s trial might be viewed. When he designed the trial, it was logical to include a mix of adults and nymphs. However, the exact number of adults and nymphs was not recorded. Therefore, the difference in level of mortality achieved by the chemical products, especially at the 1:10 ratio, may have more to do with how many late-stage nymphs were present than the actual effectiveness of the chemical itself.

This information has practical, real-world implications as well. If a pest manager conducts a treatment and soon afterwards the client complains of more cockroaches being present, it may not be a case of eggs hatching after the entire population has been controlled; it may be that the nymphs have survived and become adults, quickly resuming the breeding cycle. This emphasises the need to conduct as thorough a treatment as possible.