Journal ofAnimal Ecology (1982), 51,307-325 FORAGING BEHAVIOUR OF RHAGOLETIS POMONELLA, A PARASITE OF HAWTHORN (CRA TAEGUS VIRIDIS), IN' NATURE

(1) We examined the influence of Crataegus viridis fruit quality and density on the foraging behaviour of one of its parasites, the tephritid fly, Rhagoletis pomonella, in nature. (2) Individual female flies were released in trees harbouring: (a) no host fruit, (b) non-host fruit, (c) egg-infested, oviposition-deterring pheromone-marked host fruit, (d) varying densities of uninfested, unmarked host fruit. (3) Flies emigrated from trees within a narrow range of time if they did not discover fruit. (4) Flies never or rarely oviposited in non-host and marked fruit respectively, and in both cases emigrated from trees harbouring those fruit soon after examining the fruit. (5) Flies exhibited success-motivated search following discovery of and oviposition in uninfested, unmarked fruit. (6) Flies visited more fruit, oviposited more often and remained longer in trees harbouring high v. low densities of fruit clusters. (7) Flies emigrated sooner after the last egg they laid on trees harbouring high, v. low, densities of fruit clusters (Giving Up Time shorter). (8) Rhagoletis pomonella foraging behaviour is discussed in relation to current foraging theory