Behaviour of the oriental fruit fly, Dacus dorsalis, Hendel (Diptera:Tephritidae)

The role of pheromones in the behaviour of the Dacus dorsalis and the biological significance of the parapheromone (methyl eugenol) in the male sex pheromone communication system have been investigated. These compounds could have possible application in controlling this pest. Three bioassay techniques, a horizontal wind tunnel, an olfactometer and a still air bioassay chamber have been used for the behavioural studies. The activity pattern of the male and the female were investigated. A clearly-defined circadian rhythm of mating activity was observed. The mating activities of males and females were restricted to the `dusk' period under low light conditions (10-22 lux). The male released the sex pheromone which attracts the female. The source of the sex pheromone is the male rectal gland associated with the posterior ventral region of the rectum. Males and females start mating at about five days after eclosion from the pupa. Females show high responsiveness and the males show maximum pheromone release at between 10 and 20 days after emergence. Previous mating does not diminish the ability of males to remate but after the first mating the female responsiveness to male pheromone ceases for a few days. Behavioural activities of the male and female associated with mating occur near the top of the plant in semi-natural conditions. The principal site of assembly for mating is the under-surface of the leaves, and copulation is initiated on the foliage but not on the fruit. Both males and females were assayed against identified chemical components of the male sex pheromone: 2,3,5 trimethyl pyrazine elicited very high activation, attraction (short-range and long-range) and arrestment in males. The rhythm of responsiveness of males to this chemical component was inversely related to the circadian rhythm of mating activity. Female responses to the same compound were lower and positively related to the circadian rhythm of mating activity. Only the pyrazine induced ovipositor probing behaviour in females, a behavioural pattern which is associated with mating behaviour. N-3 methyl butyl acetamide elicited high activation of females. The mixtures of the sex pheromone components elicited higher responses in females during `dusk' than they did during the day. Highly significant levels of response of males and females to the male sex pheromone were found indicating the presence of substances in the pheromone which play a behavioural role as a part of a pheromone in normal courtship and in male-male interactions. Gas chromatography and mass spectroscopy revealed three component peaks in the sex pheromone extract of males fed on methyl eugenol. These have been identified as caryophyllene, α caryophylene and 1,2 benzenedicarboxylic acid butyl methyl ester. Chemical analysis indicated several component peaks of substances more volatile than any compounds previously identified in the aeration extract of male sex pheromone. Tentative identification of the compounds have been made.