Submitted to: Biocontrol Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/6/2011
Publication Date: 8/2/2011
Citation: Hernandez, M., Brentassi, M., Sosa, A.J., Sacco, J., Elsesser, G. 2011. Feeding behaviour and spatial distribution of two planthoppers Megamelus scutellaris (Delphacidae) and Taosa longula (Dictyopharidae) on water hyacinth. Biocontrol Science and Technology. 21(8):941-952. Interpretive Summary: Among the planthoppers under study as potential biocontrol agents for water hyacinth, an aquatic weed and a problem on the East and West coasts in the United States, two of them seemed to use the same tissues as food. They feed on sap from the plants by inserting their mouthpart in the vascular bundles. The saliva they inject in this process solidifies forming a salivary sheath which remains in the plant tissues. These pathways of the salivary sheath were detected with compound microscopy and histological techniques. These structures are evidence of the feeding site in the plant tissues. Different techniques and experiments were used to test if the two insects were competitors among themselves for food or for the place in the plants. The results showed that both species of planthoppers obtain the sap from the same vascular tissues, but they use different parts of the plant to settle, probably avoiding in this way the interspecific competition. They could be used together as potential agents for biocontrol. Part of this research was collaborative work between the USDA-ARS-South American Biological Control Laboratory and Universidad de La Plata, Argentina.
Technical Abstract: Megamelus scutellaris Berg (Delphacidae) and Taosa (Cuernavaca) longula Remes Lenicov (Dictyopharidae) are specialist planthoppers that feed and reproduce on the invasive aquatic weed, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae). They overlap geographically in several regions of South America and may therefore interact and compete for food and microhabitat. Preliminary observations indicated that both species do not feed on the same part of the plant. We hypothesized that they partition the resource; hence, we studied (1) the feeding mechanism at the tissue level, and (2) the spatial distribution of both species on the water hyacinth plant. Salivary sheaths were detected through histological sections of plant tissues using light microscopy. The location of either planthopper species on the plant was recorded when in the presence or absence of the other species. Both species produced true salivary sheaths, mostly branched (M. scutellaris: 82%; T. longula: 84%), ending in phloem (M. scutellaris: 56%; T. longula: 52%), and xylem tissues (M. scutellaris: 24%; T. longula: 28%). They resided on different parts of the water hyacinth plant even when they didn’t coexist; nymphs of T. longula occurred primarily on the back side of the leaf laminas, while nymphs of M. scutellaris occupied the basal zone of the petioles. This study shows that these planthoppers complement each other and could be used in combination as control agents for water hyacinth. Further experimental studies and field observations are necessary to quantify interactions.