Drivers of Niphograpta albiguttalis establishment in the southern U.S.: Insights for water hyacinth biocontrol

The water hyacinth moth (Niphograpta albiguttalis) was introduced to the United States in the 1970s as a biological control agent for the invasive aquatic plant Pontederia crassipes. Although the moth established populations in several southern states, it failed to persist in California’s Sacramento–San Joaquin Delta. The reasons for this opposite outcome remain unclear. This study aimed to identify biotic and abiotic factors associated with N. albiguttalis presence and density along a latitudinal gradient (25°–32°N) in the southeastern U.S.
We surveyed 22 sites across five states, collecting data on water quality, plant traits, and co-occurring herbivores. Samples were collected using 30 × 30 cm quadrats, and individual petioles were measured for size, morphology, and toughness. Presence and herbivory by other biocontrol agents were recorded per petiole, and plant quality assessed through nitrogen and carbon analysis.
Moth presence was analyzed using a generalized linear mixed model (GLMM), while density was modeled with a Gamma regression restricted to sites where the moth occurred. Presence was positively associated with higher plant nitrogen content, higher latitude, and plants located in the interior of water hyacinth mats. Moth density increased with nitrogen-rich and softer plant tissues, as well as with latitude. Both nitrogen availability and latitude emerged as consistent drivers of establishment and abundance.
These findings suggest that environmental gradients and host plant quality jointly influence the success of N. albiguttalis. By identifying conditions that favor persistence, this study provides guidance for improving biocontrol strategies, particularly in regions like California where introductions have failed.