Effects of adult and larval Cyrtobagous salviniae on the floating weed Salvinia molesta.
Experiments were conducted in field cages in Queensland to assess the effects of adults and larvae of the curculionid Cyrtobagous salviniae on Salvinia molesta growing under different conditions of temperature and availability of nitrogen. Adults 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. Destruction of meristematic tissues was compensated for by increased development of buds, but compensation was complete only at high levels of nitrogen availability. Adult feeding for 14 days did not reduce relative growth rate of ramets or of whole plant weight. Though roots were destroyed by adults, compensatory growth maintained the relative growth rates (RGR) of root weight. The plant was not able to compensate for ramets killed through larvae destroying vascular tissues. On plants initially containing 7 ramets and 4 buds, RGRs were reduced by 0.0018 ramets per ramet per day and 0.0014 g per gram per day by each larva present during the period from hatching to pupation.