The Role of Males in Host-Fruit Selection by Females of a Walnut Infesting Tephritid (Diptera) Rhagoletis zoqui

Abstract

Rhagoletis zoqui Bush flies have a mating system in which males guard and defend walnut fruit-hosts from other males and mate, apparently without courtship, with females as they arrive to oviposit. Hypothetically, female selection of a particular fruit may be due to the quality of fruit for larval development (previously determined by guarding males), the quality of the male upon the fruit as a mate, or both, but this is not clear. We performed an experiment to determine if R. zoqui females or males select the fruit to oviposit or guard based on its quality for larval development (i.e., size, sugar-content [brix] or hardness), or following male-mediated cues such as chemical residues, related to prior fruit occupation by the male during guarding. Fruit choice by R. zoqui females and males were examined under semi-natural conditions on caged branches of English walnut trees, Juglans regia L., growing in the highlands of south-central Mexico. A single male or female was allowed to select a fruit and was then removed. An individual of the opposite sex was then introduced to the same branch and presented with the opportunity to choose among the same array of hosts. The pattern of fruit choice was consistent, with female choice on the basis of male presence, suggesting that males left a chemical cue that persisted in their absence. No fruit quality differences were detected between selected and non-selected fruit. Fruit features selected by females and males matched almost exactly, although males rarely select the same fruit as females. We conclude that females preferentially selected fruit previously occupied by males although additional studies are required to determine the cues used by R. zoqui for oviposition resource selection by both females and resource guarding males.