Factors affecting oviposition rate in the weevil Rhinocyllus conicus on non-target Carduus spp. in New Zealand.

Abstract

AbstractAdults of the nodding thistle receptacle weevil, Rhinocyllus conicus (Froehlich) (Coleoptera: Curculionoidae), oviposit on developing thistle flower buds. Larval feeding on the receptacle prevents seed development. The weevil is known to attack several thistle species, but has clear preference for nodding thistle, Carduus nutans L. The effects of plant characteristics on oviposition preference and/or the size of emerging adult weevils were examined on winged and slender-winged thistles (Carduus tenuiflorus Curtis and C. pycnocephalus L., respectively). The results indicate that larger, higher seed heads on larger plants are preferred for oviposition. Larger seed heads supported the development of larger adults. This paper is part of a study looking at ecological aspects of non-target effects of thistle biological control in New Zealand. Nodding thistle flowers over an extended period of time but the two winged thistle species offer additional oviposition opportunities three to four weeks before nodding thistle flowers. The adults emerging from the winged thistle species are likely to establish a second generation, enabling this normally univoltine weevil to sustain seasonally prolonged attack on nodding thistle. Thus, proximity in space, combined with separation in time of closely related weed species, potentially enhances the performance of the oligophagous R. conicus as a biocontrol agent of all three thistle species.