This is taken from the excellent 'Practical Hints for the field Lepidopterist'by J.W. Tutt,a good x-mas present to yourself and can be got from Pennine Books(link on the right of screen) run by P.Talbot.Also the new edition of Skinner is out soon.
Sugaring should be attempted side by side with sallowing. It sometimes happens that when sallows are unattractive moths may be taken at sugar, and vice versa. We are indebted to Alderson for some excellent notes on "sugaring" (Ent. Rec., i., p. 140). He states that he always uses coarse brown sugar, when procurable, but has found old black treacle quite as effective. Blackberries, gathered when ripe, and boiled down with sugar, form an excellent substitute, and is especially attractive to the Xanthiids. When laying the sugar on, it is advisable to add a little rum (methylated spirit, jargonelle, and other substitutes are also used by various collectors), every dozen trees or so, rather than to mix the whole previous to starting. It is also desirable to commence in sufficient time to allow finishing the last tree on the round before dusk, the first hour being as a rule the most productive. A long thin line (the width of the brush) almost to the foot of the tree is better than a small patch, one advantage of the former method being that the insects are not clustered so closely, and fewer escape, especially if one commences by throwing the light first at the bottom of the tree. On a windy night the majority of the moths are frequently on the lowest part of the sugar, the upper portion being almost deserted, whilst those Noctuids that fly nearest the ground are much more likely to be attracted. It is also always worth while to sugar a quantity of small-limbed trees, as these frequently pay well when the bare trunks of large trees are little patronised. It is advisable, too, to shake the brush over low-growing shrubs, and also to carefully let a drop of sugar fall on the centre of thistle and other composite flowers, or to sprinkle a little over the flower-heads of Eupatoriur. Be careful also to keep at work on the same ground, the moths appear to congregate more on a round that is continually worked, and the trees kept constantly sugared. Changing ground does not usually prove particularly productive, especially for the first few nights, besides, the fact that more sugar is required on a new round is important, an old round wanting very little to freshen it up. Boxes should always be ready when renewing old sugar, as many species, early on the wing, will be found already at the bait, and, the spirit having evaporated from the latter, these early-comers are usually exceedingly wary.