5 Questions with Alexander Ko

Alexander Ko, Ph.D., Bayer Pest Practices Team
1. When it comes to German cockroach control, what is your stance on a combined-arms approach that leverages both baits and sprays?

I firmly believe that an integral component of pest control in field environments is the use of multiple tools and control tactics to ensure effective remediation of pests. In the case of German cockroaches, I recommend that sprays, baits, dusts, and even vacuums are all brought to bear to reduce the likelihood of resistance development.

2. Why should I use multiple tools if my current tool works just fine by itself?

While using a single tool with a single active may be easier, when this is done continually it will not be as effective in the long run compared to a control strategy that combines the strengths of multiple tools. That said, I’ve spoken with many pest control operators who expressed concerns that pesticide sprays might deter cockroaches from approaching and eating cockroach bait placements. So, Bayer reached out to academia to conduct an experiment to test that hypothesis.

3. What did the experiment with baits and sprays entail?

Sabita Ranabhat and Changlu Wang in the Department of Entomology at Rutgers University conducted an experiment to understand whether a type 2 pyrethroid spray (such as Suspend PolyZone) would deter cockroaches from approaching and feeding on bait placements.

The experiment was conducted over the course of seven days with three treatments using blank Maxforce Impact cockroach bait (i.e., cockroach bait without active ingredient):

  1. Treatment 1: Water sprayed onto both blank baits
  2. Treatment 2: Suspend PolyZone sprayed onto both blank baits
  3. Treatment 3: Suspend PolyZone sprayed onto one blank bait while the other was sprayed with water

One gram of blank cockroach gel bait was placed on each stainless steel platform, and the platforms were sprayed with either Suspend PolyZone (0.75 fl oz per gallon, 0.03% deltamethrin) or water until the point of runoff. Once the platforms were dry, they were placed into the experimental testing arena with 50 cockroaches (30 large nymphs, 10 adult males and 10 adult females).

Throughout the duration of the study, the cockroaches were regularly given rodent chow and water so that they could eat as desired and did not need to approach bait placements to feed. They were then monitored for mortality at regular intervals.

The Rutgers University experiment included harborage (the brown tent), baits and spray.
4. What were the results of the experiment?

At each observation period, average mortality caused by Treatment 2 (93%) was significantly higher than that caused by Treatment 3 (65.6%), suggesting mortality was a result of greater exposure to treated areas. Bait consumption data indicates that cockroaches were not repelled by the insecticide residue, and that most of the mortality occurred within one day of treatment.

5. What conclusions did you draw?

This was an experiment to demonstrate that not all insecticide sprays will deter German cockroaches from approaching and consuming cockroach bait placements. Suspend PolyZone — a type 2 deltamethrin pyrethroid spray — caused high mortality of German cockroaches, and the applications did not deter cockroaches from eating Maxforce Impact bait.

July 2019
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