Olfactory and visual cues guiding plum curculios (Coleoptera: Curculionidae) to host plants
The plum curculio, Conotrachelus nenuphar (Herbst), is a major pest of stone and pome fruit in eastern North America. I determined generalized olfactory and visual cues guiding plum curculios to host plants as a first step in the creation of a reliable monitoring trap for this important tree fruit pest.
Olfactory attraction of overwintered adults to volatiles from extracts of McIntosh apple tissues was evaluated in the laboratory using a still-air dual choice bioassay system to determine the most attractive odor sources. For hexane-extracted or water-extracted volatiles from McIntosh apple tissues (twigs, leaves or fruit) at seven phenological stages of development (pink through 5 weeks after bloom), greatest numerical responses were recorded to volatiles from extracts made between bloom and 2 weeks after bloom.
This same laboratory bioassay system was used to evaluate the influence of barometric pressure on degree of olfactory discrimination by adult females; response indices used as a measure of discrimination were significantly and positively correlated with barometric pressure.
Olfactory attraction of overwintered adults to individual volatile components of unripe plum odor was evaluated in the laboratory and in the field using baited boll weevil traps placed on the ground beneath the canopy of unsprayed apple trees. Two compounds, ethyl isovalerate and limonene, were significantly attractive in both laboratory bioassays and field experiments.
Olfactory attraction of overwintered adults to volatiles released from same- and opposite-sex conspecifics alone, synthetic grandisoic acid alone, wild plums alone, or combinations of live single-sex conspecifics or grandisoic acid with plums was observed in the laboratory. Females may produce a sex pheromone attractive to males, but in general both male and females were strongly attracted to host plum volatiles and only mildly attracted to conspecific odors or synthetic grandisoic acid, with little evidence for synergy or enhancement of host plum odors when combined with conspecific odors or synthetic grandisoic acid.
Laboratory, semifield, and field experiments were conducted to determine the most visually-stimulating and acceptable version of a branch-mimicking trap (PVC cylinder topped with an inverted screen funnel) to capture adults in the canopy of host fruit trees. Tall cylinder traps (50 cm tall x 6 cm diam) coated with flat black latex paint were significantly more visually stimulating than cylinder traps of lesser height and/or different diameter. Lining inverted screen funnels with paper cones and joining cylinders to inverted screen funnels with wooden inserts increased surface acceptability of traps.
I conclude that a reliable monitoring trap for adult plum curculios should be baited with attractive host fruit volatiles, and a trap placed in the canopy of fruit trees should include visual cues provided by a supernormal branch-mimicking cylinder.