Host specificity of Megamelus scutellaris (Hemiptera, Fulgoromorpha, Delphacidae), a potential agent for the biological control of waterhyacinth

A.J. SOSA; H.A. CORDO; M.A. SZUDRUCK; M.C.HERNÁNDEZ; M. HILL

Canberra

Simposio; XI International Symposium on Biological Control of Weeds; 2003

The host range of Megamelus scutellaris was studied in the laboratory using two types of multiplechoice test (including and excluding water hyacinth), and one type of non-choice test. In the first multiple-choice test, plants other than Pontederiaceae were used, whereas in the second one only Pontederiaceae were used. For the non-choice test, five species and two varieties in the Pontederiaceae were included, and this test included maize and rice. These last two plants were included because they are host of many species of Delphacidae. Feeding damage was difficult to quantify, so the preference for each plant was indirectly measured using an index that related the number of insects on a given plant and the number of insects alive in the cage used. Mortality was also measured. When given a choice, M. scutellaris significantly preferred waterhyacinth to other plants and it did not show   preference to a particular plant when waterhyacinth was absent. The mortality after 48 hrs in the tests where waterhyacinth was present was significantly lower than those where waterhyacinth was absent. In the nonchoice trial, M. scutellaris reached the adult stage on only three plants: waterhyacinth, Pontederia cordata lancifolia and P. rotundifolia. However, nymphal mortality was lower, and the duration of the whole immature stage was  significatively shorter in waterhyacinth than on the other two plants. These results, along with the fact that, despite extensive surveys, M. scutellaris has been recorded from waterhyacinth in only Argentina and Brazil, indicate that the insect is monophagous and a safe agent to be introduced into other countries for the biological control of this weed.