Tech Notes

Demand® CS and Insect Repellency

Demand® CS and Insect Repellency
 
Within the pest management industry there is a perception that ants are repelled by pyrethroid insecticides. This view suggests that ants would not cross pyrethroid-treated areas, and that ants would subsequently find an entry point around the treated zone. While not accurate, this opinion has led some pest management professionals (PMPs) to the assumption that pyrethroids are not effective for controlling ants.
 
What is repellency?
With regard to insects, repellency is defined as “a negative chemotactic response which causes orientated directional movement away from the chemical stimulus.” Or, in other words, insects try to avoid repellent chemicals.
 
The concept of repellency for insecticides is really about the speed with which the insecticide kills the pest insect. Fast acting insecticides like the pyrethroids generally kill exposed ants in less than 10 minutes. This prevents the ants from forming a recruitment trail for other ants to follow and inhibits recruitment to food sources making it appear that surfaces treated with pyrethroids are repellent.
 
Why is repellency important in pest control?
If insects are repelled away from a treated surface before picking up a lethal dose of insecticide, the treatment may be less effective. Insects that have contacted  a pyrethroid insecticide may display hyperactivity which is a result of the product’s irritancy. Because the insects’ erratic movements may carry them away from treated surfaces, this hyperactivity may appear to be repellency.
 
Is Demand® CS repellent?
Two laboratory tests, one with imported fire ants (Solenopsis invicta) and the other with Pharaoh ants (Monomorium pharaonis) demonstrate that ants are not repelled from surfaces treated with Demand CS.
 
Imported Fire Ants Choice Study
In the first trial, imported fire ant workers were placed in an arena containing two unglazed ceramic tiles. One tile was treated with Demand CS, and the other was treated with water. The arena construction ensured that ants were in contact with a tile at all times. The time spent on the treated tile or untreated tile was recorded for a period of five minutes.
 
The results show that there were no significant differences between times spent by the foraging workers on a tile treated with Demand CS compared to a tile treated with water. As a check, a separate arena with two tiles only treated with water was compared to the test arena. The same pattern of behavior was seen in the control arena as the test arena; no preference for either tile in either arena. This clearly indicates that a surface deposit of Demand CS is not repellent to imported fire ant workers.
 
Pharaoh Ants Choice Study
In another trial, whole colonies of Pharaoh ants, containing workers, queens, and larvae, were placed in an arena containing a water source. In each arena, ants were presented with two food sources located equidistant from the colony. One of the food sources was surrounded by a residual treatment of water, and the other was surrounded by the test substances.
 
Test substances evaluated included:
1) Demand CS (applied at 0.06%)
2) Farnesol (ant repellent)
3) Suspend® SC (deltamethrin, a non-encapsulated pyrethroid, at 0.06%)
4) Water (control)
 
Assessments of the number of worker ants that crossed the treatment bands were made every 20 minutes. These numbers were used to calculate the relative proportions of foraging ants in each arena that chose to cross the test chemical barrier, or the water- treated barrier, to reach food.
 
This test was repeated six times for every treatment combination. These data were averaged and subsequently divided into three time groups: 0-40 minutes, 41-80 minutes and 81-120 minutes.
 
In the initial forage and recruitment phase of the test (0-40 minutes), there was little difference in the proportion of ants choosing to cross either a residual deposit of Demand CS or water to reach food. The initial time group showed 49.3% of the foraging ants crossing the Demand CS barrier, compared with 50.7% crossing the water barrier. This was almost identical to that in the water:water control, where ants split 46.5% : 53.5% between the two food sources.
 
These results suggest that Demand CS has no repellent effect.  Similar behavior was seen for the Suspend SC treatment further demonstrating that ants are not repelled by pyrethroid insecticides. When faced with the choice of crossing a farnesol-treated barrier or water treated barrier to reach food, no ants crossed the farnesol barrier, thus confirming the highly repellent nature of this


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