Insights to the host range of the flea beetle Disonycha argentinensis Jacoby, 1992 (Coleoptera: Chrysomelidae), a candidate biological control agent of alligator weed in the U.S.A.

Abstract

Alligator weed, Alternanthera philoxeroides (Mart.) Griseb. (Amaranthaceae) is anaggressive invader in waterways and pastures throughout most of the southeastern U.S.A., andCalifornia. Three insect biological control agents have provided substantial control of aquaticA. philoxeroides in the warmer parts of its range in the U.S.A. However, these insects are lesseffective against A. philoxeroides in riparian-terrestrial habitats. In this study, the host specificityof 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 survivalonA. philoxeroides (0.55 ± 0.05) did not differ from A. maritima (0.35 ± 0.15), but developmenttime (days) from first instar to adult was faster on A. philoxeroides (21.78 ± 0.67) than onA. maritima (27.64 ± 0.70). No-choice oviposition tests showed that fecundity was higher onA. 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 speciestested. Collectively, these results indicate that the native A. maritima is within the ecologicalhost range of D. argentinensis and further tests (e.g., field studies) are necessary to determine ifpredicted non-target impacts will be transitory or persistent.