STUDIES ON ATTRACTION OF SIMULIUM-DAMNOSUM SL (DIPTERA - SIMULIIDAE) TO ITS HOSTS .1. RELATIVE IMPORTANCE OF SIGHT, EXHALED BREATH, AND SMELL

  • 1 January 1976
    • journal article
    • research article
    • Vol. 27  (4) , 455-473
Abstract
Four traps used in capturing hunting female S. damnosum s.l. are described: the slat trap, the enclosure trap, the fan trap and the sticky trap. In the forest a man hidden inside a trap, but removing his exhaled breath through a long hose, attracted 4 times as many flies as did an unbaited trap. When the man exhaled normally into the trap the number of flies taken rose again by a further factor of 4. CO2 gas, emitted from inside the trap attracted some 2/3 as many flies as a man exhaling normally inside the trap. In both forest and Sudan-savanna environments the catches of a man stationed on an open stretch of land and fully exposed to view while his exhaled breath was removed through a long hose, were not substantially lower than those of a man in a similar situation who exhaled normally. In the forest a motionless man, partly hidden among vegetation, attracted fewer flies than a moving man who was fully exposed to view when both men removed their exhaled breath through long hoses, and when they exhaled normally. In the forest a trap baited with CO2 gas (250 cm3/min) caught more flies than a similar, unbaited trap, but the performance of CO2-baited traps, as compared with that of human collectors, was highly variable. Catches in CO2-baited traps were uniformly low in the Sudan-savanna. In the forest, removal of olfactory substances from the human skin, by vigorous washing and application of petroleum jelly, or by wearing impermeable clothing, greatly reduced the numbers of flies attracted. No such reduction was observed in the Sudan-savanna. In the forest, clothes, worn by men for several days and then used as bait, attracted about 10 times as many flies as did similar, unworn clothes. Addition of CO2 gas produced a 4-fold increase in the attractiveness of worn clothes and an 18-fold increase in that of unworn clothes. No corresponding experiments were done in the savanna. Fan traps could become contaminated by human handling during the assembly and setting-up procedures, thus becoming attractive to flies. In the Sudan-savanna, the catches of men positioned in front of warm rock surfaces were lower than those of men stationed on cooler, sandy surfaces. This suggests that body heat may be an additional attractant factor. The results suggest that forest S. damnosum s.l. (presumably S. squamosum) females rely heavily on smell as an attractant and, to a lesser extent, on sight and exhaled breath. Smell appears to be the only obligatory attractant, and it can act by itself. This raises the possibility that a trap might be developed which incorporates only smell stimuli as bait. For savanna S. damnosum s.l. (presumably S. damnosum s.s.) neither smell nor exhaled breath appear to be important attractants, and some other factor, perhaps sight, appears to be the dominant attractant in this zone.

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