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The main objective of this study was to determine the suitability of using introduced hydrilla leaf-mining flies (Hydrellia pakistanae Deonier and H. balciunasi Bock) for the management of monoecious hydrilla (Hydrilla verticillata (L.f.) Royle). This was accomplished using a variety of procedures and experimental designs, including small container bioassays, development of a greenhouse-based fly colony reared exclusively on monoecious hydrilla, a larger tank study designed to evaluate short-term impact on both monoecious and dioecious hydrilla, use of small ponds to evaluate establishment in a more natural situation, evaluation of overwintering biology of the agents, and field releases to determine establishment success.

Information from unpublished reports, field, and greenhouse observations suggests that temperatures exceeding 29° C can cause reduced development and increased mortality of Megamelus scutellaris Berg (waterhyacinth planthopper), a biological control agent released for the management of Eichhornia crassipes (Mart. Solms). This document reports the results of an experiment conducted under greenhouse conditions designed to gauge temperature impacts to M. scutellaris survival and reproduction under fluctuating temperatures regimes. BACKGROUND: Waterhyacinth (E. crassipes) was first introduced into the U.S. in Louisiana during the International Cotton Exposition in 1884 (Center 2004). Since its initial introduction, the range of waterhyacinth has spread to include the southern and western regions of the United States and is expanding northward (U.S. Department of Agriculture/Natural Resources Conservation Service [USDA/NRCS] 2016). Waterhyacinth is capable of rapid growth and can quickly cover the water's surface thereby reducing light penetration to algae and submersed plants, lowering dissolved oxygen levels and pH, and ultimately leading to altered native species diversity (Getsinger et al. 2014; Center 2004; Villamagna and Murphy 2009). Mats of waterhyacinth have also been shown to obstruct waterways, impact irrigation and drinking water delivery, navigation, and recreation. Additionally, waterhyacinth has been documented as a human health hazard by increasing mosquito breeding habitats (Center 2004). NOTE: The contents of this technical note are not to be used for advertising, publication or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such products.

A complex of abiotic and biotic factors is known to impact the establishment and success of biological control agents. Experiments using the ephydrid fly Hydrellia pakistanae Deonier have demonstrated that hydrilla, Hydrilla verticillata (L.f.) Royle, containing low protein content appears to impact larval development time and the number of eggs oviposited per female. Eggs per female were over twofold higher for larvae reared on hydrilla containing 2.4-fold more protein. Mean adult female fly weight peaked when emergence is low (i.e. low crowding) and leaf protein content is high. The hydrilla biological control pathogen Mycoleptodiscus terrestris (Gerd.) Ostazeski also responds to plant nutritional condition. The nutritional status of hydrilla shoots affects M. terrestris vegetative growth, disease development and conidia and microsclerotia production. High protein content in shoot tissues was associated with a more than threefold increase in conidia production and maximum disease severity. In contrast, low protein content in shoot tissues stimulated a 3.7-fold increase in melanized microsclerotia, reproductive structures that are more persistent in the environment than conidia. These studies suggest that the nutritional condition of target plants cannot be excluded as an important factor in efficacy of biological control agents. Both agents responded to favorable conditions by reproducing prolifically, which ultimately resulted in increased host damage.

Waterhyacinth biological control research at the Engineer Research and Development Center (ERDC), Vicksburg, Mississippi is currently focused on the rearing and release of the delphacid planthopper, Megamelus scutellaris Berg (Hemiptera: Delphacidae), which has been in culture at the ERDC since 2010. Past failures to establish M. scutellaris were attributed to extreme summer temperatures at field sites; therefore, a putatively temperature-tolerant strain of this insect was obtained from field-established stock in Florida. This report details the performance of original and new strains of M. scutellaris in greenhouse rearing and field released colonies in 2015. INTRODUCTION: Waterhyacinth (Eichhornia crassipes (Mart.) Solms-Laub) is considered to be one of the world's worst weeds (Holm et al. 1977). It is an erect, free-floating herbaceous plant native to tropical South America (Gopal 1987). Waterhyacinth can grow rapidly and invade lakes, ponds, and rivers, creating impenetrable barriers and floating mats that impede water traffic and degrade aquatic ecosystems (Center et al. 2002). Herbicide management of waterhyacinth can be very costly. Since 1975, over $100 million has been spent on herbicide control of waterhyacinth in Louisiana alone 1. An alternative to using herbicides for waterhyacinth management has been the use of host-specific biological control agents.

Abstract:Research is being conducted by U.S. Army Engineer Research and Development Center (ERDC) scientists to identify naturalized and/or native herbivores of aquatic plants in an effort to develop alternative management strategies through an understanding of the agents' biology and ecology. Some of the native species showing promise as biocontrol agents include Altica spp. for water primrose, Donacia spp. for American lotus, and Euhrychiopsis lecontei for Eurasian watermilfoil control. Naturalized species with possibility include Cyrtobagus salviniae for common and giant salvinia, and Parapoynx diminutalis for hydrilla. Information is presented herein for selected native and naturalized agents that may potentially be used to impact and manage all types of aquatic and wetland plant species including introduced, naturalized, and native species. Native and naturalized insect herbivores and fungal pathogens discussed include: