Multiple Crossed Generations, a novel method to evaluate the performance of a thrips on two invasive species of Ludwigia (Onagraceae)

FALTLHAUSER, ANA C.; SOSA, ALEJANDRO J.; HERNÁNDEZ, M. CRISTINA; CABRERA WALSH, GUILLERMO

Engelberg

Simposio; XV International Symposium on Biological Control of Weeds; 2018

CABI

Ludwigia grandiflora subsp. hexapetala (Hook. & Arn.) G.L. Nesom & J.T. Kartesz and L. peploides subsp. monteviensis (Spreng.) Raven are two invasive weeds of South American origin that have been taken as ornamentals to different regions. In France, L. g. hexapetala is considered as the worst invasive aquatic weed. In the USA, these plant species alter aquatic environments by obstructing lakes, ponds, irrigation canals and other sensitive wetlands. In 2007, FuEDEI began the search for natural enemies of L. g. hexapetala highlighting Liothrips ludwigi Zamar as the most promising candidate. In host specificity tests, L. ludwigi was highly specific for L. g. hexapetala and L. p. montevidensis and was able to persist on both species, completing their development. Both of these species coexist as invasive plants in the USA, France, England, Belgium, Italy and the Netherlands. Therefore, the objective of this work was to evaluate the performance of L. ludwigi on these two species to improve management strategies in a more efficient and safe way. When confined to the laboratory for host specificity testing (either in the native range or quarantine), potential biological control insect agents are reared only on the target weed for multiple generations. If the insect is influenced by the plant on which the previous generation was reared, the results can be biased. Understanding this effect is important in order to correctly interpret the experimental results and to study potential biological control agents in particular. Hence a novel method called Multiple Crossed Generations was developed to evaluate the survival and fecundity of L. ludwigi that was reared on L. g. hexapetala for several generations. The mortality and fecundity recorded indicated a better performance of the thrips on L. p. montevidensis. The interaction between crossed generations was not significant suggesting that, except on a specific combination, maternal effects did not influence the results.