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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Publications at this Location » Publication #420730
Research Project: Integrated Weed Management and Restoration Strategies to Protect Water Resources and Aquatic and Wetland Ecosystems of the Far Western U.S.

Location: Invasive Species and Pollinator Health

Title: Life history and host range characteristics of Paracles azollae Berg, 1877 (Lepidoptera: Erebidae), a herbivore considered for biological control of invasive Ludwigia spp. (Onagraceae) in the United States

Author
item FRIEDMAN, MARIELLE - US Department Of Agriculture (USDA)
item Reddy, Angelica
item PRATT, PAUL - Former ARS Employee
item GREWELL, BRENDA - Former ARS Employee
item HARMS, NATHAN - Us Army Engineer Research And Dvelopment Center
item CIBILS-STEWART, XIMENA - Instituto Nacional De Investigacion Argropecuaria, Urugary
item CABRERA WALSH, GUILLERMO - Fuedei
item FALTHAUSER, ANA - Fuedei

Submitted to: The Pan-Pacific Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2025
Publication Date: 10/6/2025
Citation: Friedman, M.H., Reddy, A.M., Pratt, P., Grewell, B.J., Harms, N.E., Cibils-Stewart, X., Cabrera Walsh, G., Falthauser, A. 2025. Life history and host range characteristics of Paracles azollae Berg, 1877 (Lepidoptera: Erebidae), a herbivore considered for biological control of invasive Ludwigia spp. (Onagraceae) in the United States. The Pan-Pacific Entomologist. 101(3):243-255. https://doi.org/10.3956/2025-101.3.243.
DOI: https://doi.org/10.3956/2025-101.3.243

Interpretive Summary: Exotic water primroses (Ludwigia spp.) are disruptive plant invaders that are degrading aquatic ecosystems worldwide. The management of these plants has been limited to physical and chemical control methods. An alternative approach to managing Ludwigia spp. is biological control: the use of insects to control exotic plants. However, little is known of 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 from Uruguay, the moth Paracles azollae, to determine its suitability as a biocontrol agent of exotic Ludwigia spp. in the USA. Development and oviposition tests were conducted using four exotic Ludwigia species and seven USA native plant species. The moth matures from egg to adult in approximately 51 days at 25 °C with a total of 6-8 larval instars. The adult female moths live an average of 9 days and are highly fecund, laying an average of 597 eggs in their short adult life. Paracles azollae did not exhibit a high level of host specificity: larvae fed and completed development on all target weeds and four of seven native plant species tested and did not differentiate between target weeds and most native species in multiple-choice tests. These results indicate that the moth is not sufficiently host-specific to be considered a biological control agent of the exotic Ludwigia spp. in the USA and further testing is not warranted.

Technical Abstract: Exotic water primroses, Ludwigia spp. (Onagraceae), invade aquatic ecosystems worldwide. Management of these plants has been limited to physical and chemical control methods, but alternative approaches are needed, including classical biological control. However, little is known regarding the natural enemies of these exotic plants in their native South American range and whether any are sufficiently host-specific to be used as biological control agents in invading regions. Herein, the biology and host range of Paracles azollae Berg, 1877 (Lepidoptera: Erebidae), a moth associated with Ludwigia spp. in Uruguay, was studied to determine its suitability as a biological agent of exotic water primroses in the U.S.A. Larval no-choice and multi-choice tests were conducted using four exotic Ludwigia species and seven native U.S.A. plant species. The number of larval instars ranged from 6–8 and generation time from egg to adult was 51.1 ± 5.9 days at 25 °C. Females are short-lived (9.0 ± 2.3 days) but highly fecund, with a lifelong fecundity of 597.3 ± 338.8 eggs. Paracles azollae did not exhibit a high level of host specificity: larvae fed and completed development on all target weeds and four of seven native closely related species tested and did not differentiate between target weeds and most native species in multiple-choice tests. Results indicate that the host range of P. azollae is unacceptably broad to be considered for biological control of exotic Ludwigia spp. in the U.S.A. and further consideration is not warranted.