A Strong Relationship Between Oviposition Preference and Larval Performance in a Shoot-Galling Sawfly

Abstract

To investigate the relationship between oviposition preference and offspring performance we tested three hypotheses about the oviposition behavior of Euura lasiolepis: (1) the preference hierarchy hypothesis that Euura had an oviposition preference based on shoot lengths; (2) the larval survival hypothesis that the preference hierarchy corresponded to the suitability of shoots for larval survival; and (3) the flexibility hypothesis that the preference hierarchy changed as resource availability changed. The oviposition preference hierarchy of Euura lasiolepis, a shoot—galling sawfly, for plant shoots of different lengths strongly corresponded with the rank of shoot lengths for larval survival. The oviposition preference hierarchy was related to shoot growth; the more rapidly a shoot was growing the higher the probability that an oviposition site on a shoot would be attacked. Larval survival was highest on long shoots on young ramets. The probability of shoot abscission was negatively related to shoot length, and Euura in galls on abscised shoots invariably died. Intraspecific interactions and willow clone identity, independent of shoot length and ramet age, had relatively small influences on larval survival. The oviposition hierarchy was flexible; if long shoots were not available shorter shoots were accepted for oviposition. Shoots were always attacked in order of length, so that a strong relationship between preference and performance was always maintained.