Quantifying Effects of Clover Root Curculio (Coleoptera: Curculionidae) Larval Feeding on Biomass and Root Reserves of Alfalfa

Abstract

Alfalfa response to larval feeding of the clover root curculio (CRC), Sitona hispidulus (F.), was examined under controlled conditions. Nonlinear regression models were used to quantify reduction of plant biomass and total nonstructural carbohydrate root reserves based on taproot damage and CRC density. Root reserves, nodule dry weight, and number of nodules were most severely reduced by larval feeding, followed by dry weight reductions of other root components. Dry weight reductions of leaves, stems, and top growth were significantly correlated with larval taproot damage but were not significantly correlated with number of CRC recovered per plant. Taproot diameter was significantly and positively correlated with root reserves and plant dry weights, but this effect was independent of CRC density or damage. Results of a separate experiment indicated that the number of alfalfa root nodules damaged by first-instar CRC recovered from infested plants was much less than the number of intact nodules estimated to have been lost, based on a comparison of infested and uninfested plants. These results suggested that many nodules were consumed by older larvae rather than by first instars.