QUESTION:
In some cases diatomaceous earth is a very reasonable option in my work. It seems like it should be a “non-repellent” but I’m not crystal clear. Repellent or not? Can I use this for pharoah ants or German roaches in combination with baits and/or Phantom?
ANSWER:
The use of insecticide dusts is making a nice reappearance in professional pest management, and I will summarize some information that was in a 2009 trade magazine article. A study by Romero, Potter, and Haynes at the Univ. of Kentucky tested several dust products on bed bugs, and their results were very interesting. Very briefly they got the best results with a silica gel/pyrethrum/PBO dust with 100% kill of all bed bugs within 72 hours, including resistant strains of these insects. Second place was Diatomaceous Earth (DE) which gave 100% kill but took 10 days. Surprising to them was that Tempo Dust killed 100% of the bugs within 24 hours, and topped their list.
There does not appear to be any inherent repellency from contact with these sorptive and desiccant dusts, but if the dust is applied too heavily it may become “physically” repellent – the bugs just don’t want to rest on a heavily dusted surface or wade through a barrier of dust material. As one industry consultant stated it 30 years ago “if you can see the dust on the surface after you applied it IT WAS TOO MUCH”. It is our tendency, and comfort level, to be able to see the result of our application, and a we may believe that a nice, even, visible layer is just perfect. In reality, this is an over application and detracts from the effectiveness. These dusts should be just excellent for ants and roaches too, and should be applied into closed voids as part of the overall strategy for their management. Even a nearly invisible layer of the dust allows particles to adhere to the lower surfaces of the bugs that walk over them or rest on them, and sorptive dusts like silica gel (Drione, Tri-Die, and others) also may have an electrostatic charge to them that helps them attach to the insect.
If there are any bugs that may be harder to kill with dusts, and this is just my thinking, perhaps it would be those that are very hairy, such as some spiders. The hairs could keep the dust particles away from the exoskeleton, and since these are abrasive materials that need to scratch into the exoskeleton to be effective this could be a problem. But, smooth-bodied insects like bed bugs, roaches, and ants should be highly susceptible to the dusts. There are 2 huge advantages to using the inorganic dusts like silica gel and DE – extremely low hazard to people and pets and many years of residual effectiveness. As long as they are applied to a dry surface the dust particles remain available to the bugs that touch that surface at some point in time. This is perfect for wall voids and interior voids of equipment or furnishings that are okay for dust to be in (do NOT dust the inside of a computer!!). Also appropriate for within the enclosed box spring of a bed, around the edges of floors behind molding or carpet edges, and carefully within deeper crevices.
The disadvantage to dusts is their visibility, especially when over-applied. Even though their toxicity to people is almost nil, just the presence of a “pesticide” can spark fear in uninformed people, so your customers need a little education and discussion on what you plan to use in their home. Bottom line is that dusts have an excellent role in control of many structural pests and DE should be non-repellent if it is applied discreetly. The one dust that is NOT effective on bed bugs is boric acid dust, but it should be very good for roaches and ants. Boric acid must be ingested and bed bugs have no ability to do this.
Contrary to things you read on that darned Internet boric acid is NOT a desiccant and does not kill by plugging the breathing openings on bugs. It is toxic only by ingestion. And just to pontificate a bit more on MISinformation on the internet, boric acid also is NOT non-toxic, is NOT safe to use around children, is NOT toxic to “all” insects, does NOT attack their nervous systems, is NOT a “drying agent” to insects’ bodies, is not absorbed through their exoskeletons, and is not the “secret” ingredient in professional products. I picked up every one of these tidbits of disinformation from a single website that was promoting boric acid as the non-toxic alternative to pesticides. We have a big job to do as professionals to help our customers learn the facts about our products and our profession, and to overcome the junk they can find on the internet.
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