OVIPOSITION SITE GUARDING BY MALE WALNUT FLIES AND ITS POSSIBLE CONSEQUENCES FOR MATING SUCCESS

Field studies showed that male Rhagoletis juglandis and R. boycei flie s guard egg-laying punctures (and the eggs within) on host walnut (Jug lans major) fruit and defend those sites from conspecific and heterosp ecific males. In field experiments with artificially punctured fruit, as well as field observations on unmanipulated fruit, males were consi stently more likely to be sighted and stayed longer on damaged fruit t han on undamaged fruit. On artificially punctured fruit, they consiste ntly spent more time in the vicinity of a puncture than expected by ch ance alone. Males together on damaged fruit were more likely to engage in contests over those fruit than males together on undamaged fruit. Copulations were consistently more frequent for either species on dama ged than undamaged fruit, both in observations of unmanipulated fruit and in artificial puncture experiments. Analyses which controlled for the longer male residence time on damaged fruit suggested strongly tha t copulations were consistently achieved at higher per capita rates on damaged than on undamaged fruit, indicating that puncture-guarding fu nctions to increase access to females. An exception to the pattern in male mating success was noted at a site where both species used host f ruit on the same trees. In this case, R. juglandis males were only sli ghtly more common on punctured fruit than on control fruit and male su ccess in copulation did not differ significantly between the two types of fruit. This anomalous result was apparently due to an almost absol ute advantage enjoyed by R. boycei males in on-fruit contests with R. juglandis males. A likely basis for improvements in mating success ass ociated with puncture guarding was a propensity for females to deposit eggs into existing punctures. Both in observations of unmanipulated f ruit and in artificial puncture experiments, females consistently atte mpted oviposition more often in damaged than undamaged fruit. In artif icial puncture experiments, both species at both sites deposited most clutches in damaged fruit. Mating generally took place as females init iated oviposition. The possible functions of puncture use by females a s well as alternative functions of puncture guarding by males are disc ussed.