An Evaluation of Resistance to the Black Vine Weevil, \u3cem\u3eOtiorhynchus sulcatus\u3c/em\u3e (F.), in Taxus and Rhododendron

Resistance to the black vine weevil, Otiorhynchus sulcatus (F.) in in rhododendrons was examined on the basis of leaf type. Indumented (hairy) and lepitode (scaly) rhododendrons were compared to glabrous (clear leaf) rhododendrons for feeding damage and egg production. A screening study of Taxus cultivars for resistance to the weevil was also conducted. Weevil preference for rhododendrons was tested in an open bed by measuring leaf damage and by counting larvae on the roots at the end of the study. Weevils were also confined on individual plants and leaf damage, frass production, and egg production were measured each week. The preference study showed that indumented and lepitode rhododendrons had less feeding damage than glabrous rhododendrons. However, there were wide differences within groups. The confined study showed that indumented rhododendrons generally had less leaf surf ace removed than the lepidote and glabrous rhododendrons. The frass production results showed few differences by leaf group. The indumented cross R. smirnowii x R. yakusimanum supported the lowest egg production and was significantly different from all rhododendrons tested. The indumented rhododendrons R. smirnowii and R. yakusimanum were significantly different from the glabrous rhododendrons in the number of eggs produced by weevils confined to these hosts. All Taxus varieties had high mortality from feeding by the black vine weevil and no weevil resistance was demonstrated