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.

Authors: Reddy, Angelica; Juarez, Caroline; Pratt, Paul; Moran, Patrick; Grewell, Brenda; HARMS, NATHAN - Us Army Engineer Research And Dvelopment Center; CIBILS-STEWART, XIMENA - Instituto Nacional De Innovacion Agraria (INIA); SOSA, ALEJANDRO - Fundacion Para La Investigacion Agricola Danac; CABRERA-WALSH, GUILLERMO - Fundacion Para La Investigacion Agricola Danac; FALTLHAUSER, ANA - Fundacion Para La Investigacion Agricola Danac

Submitted to: The Pan-Pacific Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2024
Publication Date: 6/28/2024
Citation: Reddy, A.M., Juarez, C.M., Pratt, P.D., Moran, P.J., Grewell, B.J., Harms, N.E., Cibils-Stewart, X., Sosa, A., Cabrera-Walsh, G., Faltlhauser, A. 2024. 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.. The Pan-Pacific Entomologist. 100(2):136-147. https://doi.org/10.3956/2024-100.2.136.
DOI: https://doi.org/10.3956/2024-100.2.136

Interpretive Summary: Alligator weed (Alternanthera philoxeroides) is an aggressive plant invader in waterways throughout most of the southern U.S.A., including California. Three insect biological control agents have provided substantial control of aquatic alligator weed in the warmer parts of its range in the U.S.A. However, these insects are less effective against the plant in riparian-terrestrial habitats. In this study, the host specificity of a flea beetle, Disonycha argentinensis, was investigated to determine its suitability as a biocontrol agent of terrestrial alligator weed in the U.S.A. No-choice and multiple-choice tests were conducted using 19 test plant species. Complete development of beetle larvae took place only on alligator weed and on a native plant, seaside joyweed (Alternanthera maritima). Larval survival on alligator weed (0.55 ± 0.05) did not differ from seaside joyweed (0.35 ± 0.15), but development time (days) from first instar to adult was faster on alligator weed (21.78 ± 0.67) than on seaside joyweed (27.64 ± 0.70). No-choice oviposition tests showed that egg laying was higher on alligator weed (400.6 ± 115.20 eggs) than on seaside joyweed (93.5 ± 23.5 eggs), but egg viability (proportion of eggs that hatched) did not differ between alligator weed (0.40 ± 0.14) and seaside joyweed (0.60 ± 0.19). In multiple-choice tests, beetle adults oviposited indiscriminately on all plant species tested. Collectively, these results indicate that flea beetle is not sufficiently host-specific for further consideration as a biological control agent of alligator weed in the U.S.A. and that further testing is not warranted.

Technical Abstract: Alligator weed, Alternanthera philoxeroides (Mart.) Griseb. (Amaranthaceae) is an aggressive invader in waterways throughout most of the southern U.S.A. including 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 terrestrial 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. (Amaranthaceae). 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 ± 115.20 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 D. argentinensis is not sufficiently host-specific for further consideration as a biological control agent of A. philoxeroides in the U.S.A. and that further testing is not warranted.