Effects of Adult and Larval Cyrtobagous salviniae on the Floating Weed Salvinia molesta

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Abstract
(1) Experiments were conducted in field cages to assess the effects of adult and larval Cytrobagous salviniae Calder and Sands (Coleopotera: Curculionidae) on Salvinia molesta D.S. Mitchell (Salviniaceae) growing under different conditions of temperature and availability of nitrogen. (2) Adult C. salviniae fed on meristematic tissues in buds and on young leaves and roots (probably meristematic tissue) of S. molesta. Larvae tunnelled through buds, rhizomes and roots. (3) Destruction of meristematic tissues was compensated for by increased development of buds, but compensation was complete only at high levels of nitrogen availability. (4) Adult feeding for 14 days did not reduce relative growth rate (RGR) of ramets or of whole plant weight. Though roots were destroyed by adults, compensatory growth maintained the RGR of root weight. (5) The plant was not able to compensate for ramets killed through larvae destroying vascular tissues. RGRs were reduced by 0.0018 ramets per ramet per day and 0.0014 g per g per day by each larvae present during the period from hatching to pupation, on plants initially containing seven ramets and four buds.