Establishment in Australia of two insects for biological control of the floating weed Salvinia molesta

Abstract

In attempts at the biological control of S. molesta in Australia, the curculionid Cyrtobagous sp. was released at 8 sites and became established at 7 of them. At these 7 sites, air temperatures ranged from < 0.degree. C to > 45.degree. C and the mean concentration of N in S. molesta ranged from 1.18-1.82% of dry weight. Establishment was effected by releasing 200 adults, and the shortest time for extensive damage to be caused to the weed was 4 mo. Cyrtobagous sp. dispersed in undamaged S. molesta at rates of a few meters per month. The pyralid Samea multiplicalis Gn. was released, and became established, at 3 sites and spread at least 170 km north and south in 20 mo. At the sites colonized, air temperatures ranged from less than 0.degree. C to more than 45.degree. C and the mean N concentration in S. molesta ranged from 1.34-3.30% of dry weight. Establishment was effected by releasing 800 larvae, and the shortest time for extensive damage to be caused to S. molesta was 3 mo. Contrasts in the biology and ecology of the 2 spp. of insects are discussed briefly as is competition between them for food. In late 1983, Cyrtobagous sp. had achieved control of S. molesta at 5 sites, while Samea multiplicalis had achieved control at none. S. multiplicalis might perform better in locations which experience maximum temperatures lower than those in the present distribution.