Toxic cocktail creates a buzz

QUESTION How does a fly spray kill bugs? THOSE who have used fly spray will have noted a specific reaction preceding the insect’s demise. First, it speeds up its activity, next all of its movements appear to become chaotic and then, usually, it ends up lying on its back, legs writhing in the air, buzzing furiously before it finally expires.

Most fly sprays contain a class of neurotoxins called pyrethroids, with names such as tetramethrin, cypermethrin and imiprothrin, often combined with a chemical called piperonyl butoxide.

Fly nerves emit a transmitter chemical called acetylcholine, which binds to receptors on the muscles and activates them. An enzyme called acetylcholinesterase breaks down acetylcholine and thus terminates the signal.

Pyrethroids work by inhibiting this enzyme, thus causing the muscles go into tetany — involuntary contraction. this explains the wild flight.

Eventually, the fly becomes unable to move its abdomen backwards and forwards to move air in and out of its body, so it can’t oxygenate its hemocele, the bag of blood inside the fly, so it asphyxiates.

Pyrethroids are also toxic to beneficial insects, such as bees and dragonflies, and to fish.

Dr Ian Smith, Cambridge.

QUESTION A common misconception is that sushi mans ‘raw fish’. In fact, it means ‘sour rice’. What other words are commonly mistranslated? FURTHER to the earlier answer, there are a number of ‘ false friends’ in Spanish. A direct translation of seguro de continente often yields ‘contents insurance’; but when the phrase is correctly translated, it means ‘building insurance’. educado is commonly mistaken to mean ‘ educated’, when it actually means ‘polite’. harry Schofield, Ipswich, Suffolk.