Grass Host Preferences of Listronotus bonariensis (Coleoptera: Curculionidae)

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Abstract
Host plant preferences for feeding and oviposition by adult Listronotus bonariensis (Kuschel) were determined in multiple-choice experiments in the field and laboratory using 19 grasses. Feeding intensity was negatively correlated with fiber (cellulose + hemicellulose + lignin) content of foliage, possibly indicating an effect of leaf toughness on feeding. Oviposition preferences were correlated with feeding intensity; 29-86% of the variation in egg numbers per plant was accounted for in numbers of feeding scars on these plants. Numbers of eggs deposited in the plants were negatively correlated with the density of intercostal silica deposits (inclusive of trichomes) in the abaxial surface of the grass sheaths. A causal relationship between silicification and oviposition preference was confirmed in a pot experiment where increased silica uptake and deposition reduced egg-laying on two ryegrass cultivars. The dispersion of eggs in the various grasses also was apparently related to the density and distribution of intercostal silica deposits and trichomes on the sheath. Feeding and oviposition on ‘Grasslands Nui’ ryegrass, Lolium perenne L., were reduced by plant infection by the endophytic fungus Acremonium lolii Latch, Christensen & Samuels. In the absence of A. lolii infection, ryegrass cultivars of L. multifiorum L. parentage were preferred over L. perenne cultivars. These results are briefly discussed in relation to breeding of forage grasses.