Most good garden shops will sell derris and pyrethrum.
There are many different makes of both and mixtures of the two are stronger than either when used separately. They are capable of killing caterpillars and a range of different pests such as aphids and others which are listed on the bottle.
They are sometimes mixed with lindane and other organo-chlorine compounds and these ... are not organic.
Derris is sometimes available as a dust ‘derris dust’ and is very effective against the fleabeetle which eats holes in the leaves of brassica plants and radishes.
Do not let this substance trickle into your fishpond as it began as a Malaysian fish poison.
Also, if you keep bees and have to spray anything in flower, use pyrethrum or nicotine in the evening and it will ...be harmless by the time your bees start work in the morning.
Safe General Pesticides - Grow Organic Vegetables for a Healthier Life Style!