"Nick Maclaren" wrote: There are two mechanisms. One is that it washes
off their waxy coat
that protects them from dehydration, and the other is that it clogs
the pores through which they breathe. I believe that it is primarily
the former, but I could be wrong.

For this reason, pretty well any soap-like liquid will work

Insects are very susceptible to dehydration. For the same reason, fine
dust, although often completely inert, is a very effective insecticide
which works by mechanically scratching the wax cuticle, destroying its
integrity and causing the insect to then dehydrate (borax dust is still a
recognised and very persistent insecticide, provided it is used in dry
situations). Animals and particularly birds take dust baths, partly for
this reason, the other being the dry cleaning effect (c.f. dry "shampoos"
for people in a hurry).

I also suspect that the effect detergent has on altering surface tension
might contribute, possibly by interfering with respiration.

Finally, IME, insects do tend to lose their grip on plants sprayed with
washing-up liquid and I think a reasonable proportion that fall to the
ground may die in situ, be easier for predators to find or go off to
another plant.

I have controlled aphids on houseplants by spraying with very dilute Fairy
Liquid and then washing them off under a running tap or (with larger
plants) hosing them down on the lawn. It might take a few go's but it can
work very well.


- Tom.