First establishment of the planthopper Megamelus scutellaris Berg 1883 (Hemiptera: Delphacidae) released for biological control of water hyacinth in California

Authors: Moran, Patrick; PITCAIRN, MICHAEL - California Department Of Food And Agriculture; VILLEGAS, BALDO - California Department Of Food And Agriculture

Submitted to: Pan Pacific Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2015
Publication Date: 4/1/2016
Citation: Moran, P.J., Pitcairn, M.J., Villegas, B. 2016. First establishment of the planthopper Megamelus scutellaris Berg 1883 (Hemiptera: Delphacidae) released for biological control of water hyacinth in California. Pan Pacific Entomology. 92(1):32-43. doi: 10.3956/2016-92.1.32.

Interpretive Summary: Water hyacinth is a floating aquatic weed from South America, introduced as an ornamental over 100 years ago in the southern U.S. and around the world in the tropics and subtropics, because it produces interesting-looking inflated leaves that allow the plant to float, and because it produces attractive purple and yellow flowers. Water hyacinth is now one of the world's worst invasive weeds, capable of reproducing via vegetative 'clones' or buds, doubling its population size in as little as 8 days, and covering thousands of acres of the water surface in over 50 countries. Dense mats of water hyacinth prevent recreational and commercial navigation, impede water flow and pumping for agriculture and drinking water supply, reduce light and oxygen below the water surface, and outcompete native aquatic plants. Herbicides and mechanical removal are commonly used to control water hyacinth, but these methods are expensive and do not provide long-term control. Biological control of water hyacinth, using insects that feed and damage water hyacinth and can survive and reproduce only on this plant in the field, has reduced the severity of water hyacinth invasions in parts of the southeastern U.S. and in the tropics worldwide, but new insect species from South America are needed to increase biological control impact. In the Sacramento-San Joaquin Delta and Sacramento River watershed of northern California, a planthopper from Argentina, Megamelus scutellaris was released in this study at three sites by the California Department of Food and Agriculture and the USDA-ARS, and its ability to establish populations, disperse and have impact determined over three years (2012-2015). The planthopper established a population at only one site, in Folsom, California in the watershed of the American River, which drains into the Sacramento River. Densities of the planthopper increased between 2012 and 2015 and varied seasonally from less than 1 per plant to 9 or more planthoppers per plant, with peak densities occurring in late summer each year. The planthopper dispersed 40 to 50 meters per year in 2014 and 2015 and by June 2015 had colonized most of the water hyacinth available at the site. Plants on which the planthoppers had been feeding since 2012 had 27% fewer live leaves and about 40% less leaf and shoot crown weight than did plants at the other end of the site, into which planthoppers dispersed in 2014-2015. However, seasonal and random variation in growth makes it difficult to conclude that the planthopper is having impact, and further evaluations are needed. This study demonstrates the first successful estsablishment of the planthopper M. scutellaris in the western U.S.

Technical Abstract: Water hyacinth (Eichhornia crassipes (Martius) Solms-Laubach) is a non-native, invasive floating aquatic weed in the Sacramento San Joaquin Delta and associated river watersheds of northern California. Prior efforts to control water hyacinth biologically in this region have not led to sustained control. The South American planthopper Megamelus scutellaris Berg, permitted and released first in the southeastern U.S., was released at three sites in the watershed from 2011 to 2013, leading to establishment at one site in the American River watershed in Folsom, California. Planthopper populations consisting of nymphs (2/3rd or more of total counts) peaked in late summer each year between 2013 and 2015, reaching densities of six to nine planthoppers per plant by 2015. M. scutellaris dispersed about 50 m per year from the point of release between 2013 and 2015. A 27% decline in proportion live leaves per plant occurred in the area of release between 2012 and 2015, and plants in this area had about 40% less live above-water biomass than plants in another area of the site into which planthoppers dispersed in 2014-2015, but impact could be obscured by inter-annual and within-site variability in plant growth unrelated to planthopper release. This study documents the first establishment of M. scutellaris on water hyacinth in the western U.S.