Because the robots don't exist yet

Scientists say a species of non-stinging wasps can be trained in only five minutes [to react to the smell of explosives] and are just as sensitive to odors as man's best friend, which can require up to six months of training at a cost of about $15,000 per dog.

I can think of few better ways to get everyone to run away and generally avoid a suicide bomber than having a swarm of wasps clinging to him. This idea doesn;t work that way, but i'll bet it could.

If any mad entomologists and or botanists read this blog, please consider engineering a wasp feeding flower that smells like plastique and/or other roadside bomb material.

The "Wasp Hound" research by Lewis and University of Georgia agricultural engineer Glen Rains is part of a larger government project to determine if insects and even reptiles or crustaceans could be recruited for defense work. That project has already resulted in scientists refining the use of bees as land-mine detectors.

oh, good. Step it up then, bee season in baghdad is 365 days long and a lot of americans are dying for the lack. Or for some reason.