The Determination of Numbers of Leatherjackets in Sample Turves

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Abstract
A method of determining numbers of leatherjackets (larvae of Tipula oleracea group) on sample turves, 12 inches square, the hot water process, is described. This consists in driving leatherjackets to turf surface by means of heat carried by water rising through turf. From mid-Oct. until the 1st prepupae occur, usually in June, the hot water process brings up all leather-jackets inhabiting turf, i.e. 100% efficiency. After prepupation starts in the population and until emergence is complete, usually Sept., efficiency drops, but not more than 5-10%. Hot water process has been used to check efficiency of St. Ives method of determining leatherjacket numbers. The latter method consists in bringing leatherjackets to the surface by means of an irritant emulsion of orthodichlorobenzene poured on turf in the field after cutting grass close. Leatherjackets surface from 15 seconds to 13 minutes after application of St. Ives fluid. If left alone, some re-enter turf, and others remain on surface for up to 20 minutes. Hence observation must be continuous for 10-15 minutes after applying the fluid, and leatherjackets must be counted and picked off as they surface. Efficiency of St. Ives method is about 85% from Nov. to May, then falls steeply to near zero in July. Experiment suggests that doubling the strength or volume of fluid should increase efficiency of the method a little, but this requires confirmation.

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