Climate suitability analyses based on ecological niche modeling provide a powerful tool for biological control practitioners to assess the likelihood of establishment of different candidate agents prior to their introduction in the field. These same analyses could also be performed to understand why some agents establish more easily than others. The release of three strains of Aphalara itadori (Shinji) (Hemiptera: Pysllidae), each from a different source locality in Japan, for the biological control of invasive knotweed species, Reynoutria spp. Houtt. (Caryophyllales: Polygonaceae), provides an important opportunity to compare the utility of climate suitability analyses for identifying potential climate-based limitations for successful biological control introductions. Here we predict climate suitability envelopes for three target species of knotweed in Europe and two target species of knotweed in North America and compare these suitability estimates for each of these species to the source localities of each A. itadori strain. We find that source locality of one strain, the Kyushu strain, has little-to-no suitability compared to other locations in Japan based on knotweed records from Europe, supporting an earlier study based on North American Japanese knotweed records. The source locality of a second strain, the Murakami strain, was predicted to have medium-to-high suitability based on records of knotweeds from North America. In contrast, European records of R.  bohemica Chrtek & Chrtková and R. sachalinensis (F. Schmidt) Nakai predicted no suitability for this locality compared to other locations in Japan, while European records for R. japonica Houtt. predicted low suitability. The source locality of the final strain, the Hokkaido strain, was predicted as having medium-to-high suitability based on knotweed records of all examined species from both North America and Europe.