Any genetically modified (GM) crop has to be subjected to a rigorous environmental risk assessments prior to commercialization. The evaluation of the potential ecological effect of such plants, in particular insect-resistant GM (IRGM) plants, on non-target arthropods is an important part of the assessments. Most IRGM crops that are currently planted in the world express Cry1 or Cry2 insecticidal proteins targeting lepidopteran pests. Since the non-target lepidopteran insects such as butterflies and silkworms are close relatives to the target pests, their larvae may be also sensitive to such Cry proteins. Therefore, the potential effects of such IRGM crops on several non-target lepidoptera have been studied over last two decades. The larvae of silkworms and butterflies are indeed sensitive to Cry1 or Cry2 insecticidal proteins. These non-target arthropods are expected to be exposed to relatively low of quantities of the Cry proteins under natural conditions in China, so the planting of IRGM crops will not significantly affect the population densities of butterflies in the fields, and will not negatively affect the silk industry.