The consequences of the introduction of invasive plants for the diet of herbivorous insects have been little explored in nature where, potentially, abiotic and biotic factors operate. In this study we examined the larval performance of two Neotropical Danaini butterflies when using either a native or an exotic Apocynaceae species as host plant in both field and laboratory experiments. Hosts greatly differ in their amount of latex exudation and other physicochemical traits, as well as in the amount of evolutionary time they have interacted with herbivores. First, herbivore performance on the hosts was investigated under laboratory conditions. Larvae of both Danaini species took more time to develop on the exotic host; larval survivorship did not vary between hosts. Second, first instar survivorship on both hosts was evaluated in two field sites, one site per host. To do so, in both sites half of the larvae were bagged (protected against both abiotic and biotic factors) while the remainder were non-bagged (exposed). The interaction between larval exposure with the use of the exotic host reduced larval survival. We concluded that the combined effects of host plant traits and abiotic factors reduced survival of herbivores in field conditions. Therefore, the performance of herbivores when using hosts of different origins should be considered together with the multiple ecological factors found in natural environments, as these factors can modify the result of plant-herbivore interactions.

Performance data were collected in field and laboratory experiments, described in detail in the main text of the manuscript.

Larval survival under laboratory conditions was compared through Fisher's exact test between host plants and Danaini species. Larval development time and forewing length were analyzed for their normality and homoscedasticity by Shapiro-Wilk and Bartlett's tests. Forewing length for both Danaini species showed normal distribution and was compared between host plants using unpaired Student’s t-tests. Larval development time did not show normal distribution and was compared between host plants using the Mann-Whitney test. Tests were performed using GraphPad Prism 8.3.1 software.

To examine which factors determine larval survival on host plants under field conditions, the variables were combined into generalized linear models (GLMs). Host plant species (A. curassavica or C. procera) and treatment (bagged or non-bagged) were considered as fixed variables, and larval survival as a response variable (with binomial distribution). We tested models considering the effect of each fixed variable, as well as the additive effect of both variables and their interaction. In order to determine which model best explains the results, we performed model selection using the Akaike Information Criterion (AIC) and the “bbmle” package. Tests were performed in the R environment using R Studio software.

We have included a README.txt file with a caption for the abbreviations in the tables. In the field experiment table, missing values (NAs) ​​are attributed to observations missed by cattle grazing in the study area. In the laboratory experiment table, missing forewing length values ​​are assigned to larvae that did not survive during the larval stage. The developmental time for these larvae was computed but was not used to calculate the mean developmental time.