Abstract:
Anemotactic responses of the male oriental fruit fly Dacus dorsalis to 2,3,5
trimethyl pyrazine were studied using a horizontal wind tunnel. Various concentrations
of the chemical compound had significant effects on the behavioural activities
of the males but, very high concentrations of the chemical inhibited all their
activities. Maximum number of flies landed on the source in response to I0 u l of
the chemical. The flies showed an increase of flight activity (orthokinesis) in
response to the stimulation. In moving air, the flies apparently located the chemical
source using odour-modulated upwind anemotaxis. Two types of anemotaxis were
observed in the present study.i.e. positive anemotaxis (straight upwind flights) and
reversing anemomenotaxis (zigzagging upwind flights). Males performed both
types when the odour was presented as a plume, but exhibited only zigzagging
anemotaxis in the uniformly dispersed odour. A relatively lower concentration (l ul)
caused the flies to produce maximum number of zigzagging anemotactic flights
whereas a higher concentration (1Oul ) elicited the highest number of straight flights
in males. 2,3,5 trimethy I pyrazine had marked effects on males causing them to
orient towards the source (attraction) with the aid of upwind anemotaxis and to land (arrestment) on it.
