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Alligator weed, Alternanthera philoxeroides (Mart.) Griseb. (Amaranthaceae) is an aggressive invader in waterways and pastures throughout most of the southeastern U.S.A., and California. Three insect biological control agents have provided substantial control of aquatic A. philoxeroides in the warmer parts of its range in the U.S.A. However, these insects are less effective against A. philoxeroides in riparian-terrestrial habitats. In this study, the host specificity of Disonycha argentinensis Jacoby, 1991, was investigated to determine its suitability as a biocontrol agent of A. philoxeroides in the U.S.A. No-choice and multiple-choice tests were conducted using 19 test plant species. Complete development of larvae took place only on A. philoxeroides and on a native plant, Alternanthera maritima (Mart.) A. St.-Hil. Larval survival on A. philoxeroides (0.55 ± 0.05) did not differ from A. maritima (0.35 ± 0.15), but development time (days) from first instar to adult was faster on A. philoxeroides (21.78 ± 0.67) than on A. maritima (27.64 ± 0.70). No-choice oviposition tests showed that fecundity was higher on A. philoxeroides (400.6 ± 115.2 eggs) than on A. maritima (93.5 ± 23.5 eggs), but egg viability (proportion) did not differ between A. philoxeroides (0.40 ± 0.14) and A. maritima (0.60 ± 0.19). In multiple-choice tests, D. argentinensis oviposited indiscriminately on all plant species tested. Collectively, these results indicate that the native A. maritima is within the ecological host range of D. argentinensis and further tests (e.g., field studies) are necessary to determine if predicted non-target impacts will be transitory or persistent. [ABSTRACT FROM AUTHOR]

Simple Summary: Exotic water primroses (Ludwigia spp.) are aggressive plant invaders in aquatic ecosystems worldwide. Management of exotic Ludwigia spp. is limited to physical and chemical control methods. Biological control, the use of insects to control exotic plants, is an alternative approach for the management of exotic Ludwigia spp. However, little is known regarding the natural enemies of these plants in their native range in South America. In this study, we investigated the biology and host range of a natural enemy, the flea beetle Lysathia flavipes, to determine its suitability as a biocontrol agent for exotic Ludwigia spp. in the USA. The beetle matures from egg to adult in approximately 20 days at 25 °C. Females lived approximately 86 days and laid 278–2456 eggs over their lifespans. No-choice development and oviposition tests were conducted using four exotic Ludwigia species and seven native USA plant species. The beetle showed little discrimination between plant species: larvae aggressively fed and completed development, and females laid eggs on most plant species regardless of origin. These results indicate that the beetle is not sufficiently host-specific for further consideration as a biological control agent of exotic Ludwigia spp. in the USA and further testing is not warranted. Exotic water primroses (Ludwigia spp.) are aggressive invaders in aquatic ecosystems worldwide. To date, management of exotic Ludwigia spp. has been limited to physical and chemical control methods. Biological control provides an alternative approach for the management of invasive Ludwigia spp. but little is known regarding the natural enemies of these exotic plants. Herein the biology and host range of Lysathia flavipes (Boheman), a herbivorous beetle associated with Ludwigia spp. in Argentina and Uruguay, was studied to determine its suitability as a biocontrol agent for multiple closely related target weeds in the USA. The beetle matures from egg to adult in 19.9 ± 1.4 days at 25 °C; females lived 86.3 ± 35.6 days and laid 1510.6 ± 543.4 eggs over their lifespans. No-choice development and oviposition tests were conducted using four Ludwigia species and seven native plant species. Lysathia flavipes showed little discrimination between plant species: larvae aggressively fed and completed development, and the resulting females (F1 generation) oviposited viable eggs on most plant species regardless of origin. These results indicate that L. flavipes is not sufficiently host-specific for further consideration as a biocontrol agent of exotic Ludwigia spp. in the USA and further testing is not warranted. [ABSTRACT FROM AUTHOR]