At densities found in nature, competition among larvae of the frugivorous fruit fly Rhagoletis pomonella (Diptera: Tephritidae) was pronounced. In fruits of Crataegus mollis, a small native host of the fly, survivorship dropped sharply when >!larva developed per fruit. Multiple infestation also caused decreased size of pupae, which resulted in prolonged maturation of females and lower daily fecundity. Our findings suggest that interference competition occurs among rival R. pomonella larvae within the same fruit and that older larvae may be competitively dominant. In most instances, when 2 d separated the introduction of two larvae into unpicked fruits of Crataegus oxyacantha, a very small ornamental hawthorn, the first larva pupated while the subsequent larva failed to complete development.Rhagoletis pomonella marks its oviposition site with a contact pheromone. The amount of pheromone deposited following a single egg-laying in C. mollis fruit was sufficient to deter most females from laying more eggs. By avoiding marked fruits in which a larva is already developing, a female may conserve eggs and add measurably to her fitness.Because most C. mollis fruits can support more larvae to puparium formation than they actually do, it appears that the strategy ofhost marking by females and monopolization of fruit by larvae may leave some fruit resources unexploited.

Evidence is presented demonstrating that associative learning during oviposition in Crataegus or apple hosts can significantly influence the propensity of apple maggot flies to accept or reject these hosts in future encounters. The data suggest that within resource patches of a given host type there may be an enhancement of foraging efficiency.

1 Although management of the oriental beetle Anomala orientalis (Waterhouse) by mating disruption shows promise across a range of agricultural systems, relatively little is known about aspects of the reproductive biology of this species relevant to its management. We studied the effects of delayed mating on several aspects of the oviposition behaviour and biology of the oriental beetle using females mated in the laboratory at 4 -13 days posteclosion. 2 Females exhibited a gradual decline in fecundity with increased age at mating that was largely a function of a decline in duration of the oviposition period, as well as lower female fertility: females mated at 11 days were less likely to lay any fertile eggs. However, egg fertility did not vary with female age at mating. 3 Because mating delay did not affect longevity, females mated at older ages experienced decreased oviposition periods; however, females laid more eggs per day with increased age at mating, which partially offset shorter oviposition periods. 4 A mating delay of ³ 6 days relative to females mated within the first day of reaching sexual maturity resulted in an approximately 35 -50% lower mean fecundity. 5 These results suggest that, for mating disruption to be a successful management tool for the oriental beetle, mating must be prevented rather than delayed. We compare the findings of the present study with the published research on delayed mating in moths and discuss the importance of these results in relation to management of the oriental beetle using female sex pheromones.