THE OLFACTORY BEHAVIOUR OF LUCILIA SPECIES (DIPTERA) UNDER NATURAL CONDITIONS

Using an apparatus of the 'two-choice' type under field conditions, it has been demonstrated that a wool-factor forms an important part of the mechanism whereby female Lucilia sericata may be attracted to sheep. The 'wool-factor' could not wholly be replaced by ammonium- or sulphydryl-type attractants. L. sericata was strongly attracted by the combination of ammonium carbonate/indole with sheep wool but less strongly attracted when ethyl mercaptan/hydrogen sulphide was used with sheep wool. L. caesar and L. illustris, on the other hand, were not markedly responsive to the ammonium-type attractants but were strongly attracted by the sulphydryl mixture used either alone or in combination with sheep wool. Temperature is an important element in the oviposition stimulus. The amount of oviposition by L. sericata was increased when substances known to induce oviposition were exposed at 30-40 degrees C. Sheep wool kept moist and incubated at approx. 38 degrees C. under field conditions for 3 weeks did not attract L. sericata and oviposition did not occur on such wool. This suggests that bacteria normally present on the wool fibre as distinct from the skin, do not play an important part in rendering sheep susceptible to blowfly attack.