Host utilization by the walnut fly, Rhagoletis juglandis (Diptera : Tephritidae)

Rhagoletis juglandis Cresson is a specialist that deposits its eggs into th e husks of developing walnut fruit. Like other walnut infesting flies in th e R. suavis group, R. juglandis actively superparasitizes its larval hosts. However, little is known regarding the degree to which hosts are reused an d the ecological context under which host reuse occurs. This field study ex amined the pattern of host utilization by R. juglandis and how fruit variab les such as volume and penetrability affect the degree that hosts are reuse d. Fruit on four of five study trees were synchronously infested and within 2-2.5 wk all fruit on these trees were infested. Fruit on a fifth tree wer e significantly less penetrable than those found among the other trees in t he study and this may explain why fruit on this tree were rarely used throu ghout the season. Walnut hosts were commonly multiply infested and reuse of hosts occurred in as few as 1-2 d after first infestion. Infestation level s within fruit appeared to stabilize 4-5 d after fruit were first used. Fru it volume was positively correlated with both the number of punctures on ho sts and the infestation levels within hosts that had been infested for eith er 1-2 or 4-9 d. Large fruit were infested more quickly than small fruit, a lthough this trend was stronger on some trees than others. Finally, despite a size-penetrability correlation among two of the ave trees, penetrability itself did not explain either which fruit were preferentially used through out the season or the infestation levels within fruit.