The importance of long-term post-release studies: insect-plant monitoring and public awareness of water hyacinth management in Dique Los Sauces, Argentina

FALTLHAUSER, ANA C.; JIMÉNEZ, NADIA L.; RIGHETTI, TOMÁS; SALINAS, NICOLAS A.; MC KAY, FERNANDO; CORDO, HUGO A.; HILL, MARTIN; SOSA, ALEJANDRO J.

Puerto Iguazú

Simposio; XVI International Symposium on Biological Control of Weeds; 2023

FuEDEI y CERZOS-CONICET

Several key components of classical biological control (CBC) programmes are necessaryto assess not only the success of the management strategy (e.g., post-release monitoring)but also to help prevent future reintroductions or resurgences of the invasive species (e.g.,public awareness). Water hyacinth, Pontederia crassipes (Mart.) Solms (Pontederiaceae)is an aquatic plant naturally distributed in the north-eastern region of the Del Plata basinin Argentina. Reproduction and spread is largely vegetative, however prolific seedproduction is a source of new or re-infestations. In the 1960s it was introduced into theDique Los Sauces reservoir located outside of its native range in La Rioja Province, asemi-arid region in western Argentina where it became invasive. The natural enemy,Neochetina bruchi Hustache (Coleoptera: Curculionidae) was intentionally introduced in1974 to control the weed in the reservoir. To assess the success of this CBC programme,a long-term post-release study has been conducted. Between 1965 and 2023, wemonitored plant coverage on the water body, estimated N. bruchi densities, and quantifiedthe associated damage by reanalysing previously published data and incorporating newfield sampling. We also conducted an anonymous online survey to the local communityto analyse their knowledge and perception about this programme. Water hyacinth’scoverage fluctuated from its first record in 1965 (maximum coverage, 90%) until thecomplete control of germinated plants in 2018. The plant population decline wasaccompanied by an increase in the weevil population. In 2023, a few newly germinatedplants were recorded following a severe drought that exposed water hyacinth’s seed bank.In our survey, out of 325 respondents, only a small group of mostly middle-aged andelderly people knew that the restoration of the water surface had been achieved througha management strategy and even fewer were aware of the biological control approachtaken. Respondents who had a positive perception about biological control were moreaware about the management plan than respondents who had neutral or negative opinions.Neochetina bruchi has played a key factor in the complete control of P. crassipes. Theintrinsic dynamic of these populations, the dormant seed bank and the lack of publicawareness support the need for long-term post-release evaluations including outreachcampaigns to ensure a sustainable successful management programme.