Sometimes biocontrol doesn't work

The article by Natalie Theron on urban insect conservation on page 122 in the September 2010 issue of Veld & Flora strikes the right chord, but the list of “biofriendly” remedies she proposes for the management of garden household insects is puzzling. A saucer with vinegar for mosquito control and dried orange peel in the cupboard for fish moth control? A wax candle to keep maize and rice free from weevils? I wonder if there are references to scientific papers to back these claims? As she writes from an academic institution on would expect so, but I have my doubts. Perhaps she could test these remedies scientifically for a research project.
As I am a keen gardener and have insect conservation at heart, I go about it a little differently. My first approach is control by hand, If snails, slugs, chafers (beetles eating holes in the leaves of roses or plectranthus) weevils (beetles eating the edges of leaves of agapanthus) or hawk moth larvae on your arums and impatiens are your problem, walk through your garden at night with a torch and collect them by hand. What you then do with them, is up to you: squeeze them, step on them or release them a distance away.
There are a number of insects that cannot be controlled without insecticides. Amongst them are the lily borer in your clivias, cutworms in your seedlings, false codling moth on your oranges or pomegranates and fruit flies on your peaches. For these highly effective insecticides with very low mammalian toxicity and used in very low concentrations are available, like Ripcord. The trick is not to apply a cover spray, but to direct the spray only at the plant that is affected or even the individual fruits that you want to protect.
If you want to use a remedy that is based on anecdotal evidence, use one that has a scientific basis.Thus 2 teaspoonfuls of Sunlight Liquid and 2 of bicarbonate of soda in 5 liters water, sprayed twice 10 days apart, evidently is effective against the woolly whitefly that attack our citrus trees in gardens. Here one can speculate that the Sunlight Liquid dissolves the waxy covering of the insects with the result that they dry out and die.
Jan Giliomee, Stellenbosch