Well I agree that in general insecticides are overused. And herbicide weed killers and fungicide products too. But systemic just means it moves in the plant. Imidacloprid is a systemic very similar to nicotine. It's bad for some beneficial organisms like bees, but used properly isn't bad for human health. It works on a chemical pathway that insects have that we don't. I always try to use the most natural least toxic solution, and don't agree with the indiscriminate use of chemicals some people do, but at the same time modern science has created some pretty useful stuff, if we are smart about it, careful, follow directions and read labels chemical intervention is sometimes the best solution. Just my two cents :)

Not much except caterpillars bother brugs that are outside during the growing season. Spider mites and aphids are normally just an issue inside or in a greenhouse. You can try Neem or one of the insecticidal soaps. I control infestations on most plants with a strong blast of water from a hose. The only thing I treat with an insecticide are Broad mites. For those I use Forbid and/or Fluromite which are miticides and only effective against mites and white fly.

Rhizo, I did spray underside foliage too. When I trimmed the hedge they were flaying around and I was worried. I did not spray to the hedge because it has dense leaves and it'd be a bit difficult to spray properly. I let them stay there and on the other hand insecticides/pesticide are very expensive here. The plants are chilies and tomatoes mainly, chilies have a lot of flowers and tomatoes are also have flowers but I did not spray like I did on chilies. Now I have not found any whitefly and leafhopper on my chili plants. I do not know much about insecticide and pesticide, last year I had bad experiences with some insecticide since then I am very hesitated to use any of them. This season my plants are healthy and strong so I wish today's spray won't bring any undesirable result. Thank you for the questions and advice. Caelian Edited due to some missing sentences. This post was edited by chilliwin on Wed, Jul 3, 13 at 16:33

The adult whitefly is attracted to things yellow so some yellow sticky traps will work to capture the adults. The larva need a really moist soil to hatch in so the soil under the plants may be too wet and needs to be dried out. Bacillus thuringiensis - Israelenis, BTI, the same active ingrediant in mosquito dunks can also help control the larva.