Nitrogen and establishment of a beetle for biological control of the floating weed Salvinia in Papua New Guinea.
A population of 570 adult beetles (Cyrtobagous sp.) released onto plants of Salvinia molesta in field cages declined to 40 adults over 7 months, and increased to 3000 adults with weekly application of urea. On release from cages and in unsprayed controls, populations of the insect increased exponentially. It is suggested that there is a critical population density. Practical implications for biological control of weeds and management of crop pests are discussed.