Intraspecific Competition in the Tephritid Fruit Fly Rhagoletis Pomonella

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 >1 larva developed per fruit. Multiple infestation also caused decreased size of pupae, which resulted in prolong 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 of host marking by females and monopolization of fruit by larvae may leave some fruit resources unexploited.