Abstract
A tortoise beetle, Cassida nebulosa feeds on chenopodiaceous weeds, Chenopodium album and C. album var. centrorubrum as its main hosts. The beetle is known as a pest of another chenopodiaceous plant, the sugar beet. However, as a chenopodiaceous vegetable, spinach is rarely harmed by C. nebulosa. Newly emerged adults that had no feeding experience developed a positive feeding response to spinach as well as to C. album var. centrorubrum within 24 h. On the other hand, adults reared on C. album var. centrorubrum did not accept spinach, and their feeding response to spinach was still weak even after rearing on spinach for 4 d. When C. nebulosa were reared on leaves of C. album var. centrorubrum treated with the methanol extracts of spinach, they accepted spinach as well as C. album var. centrorubrum. In contrast, when C. nebulosa were reared on leaves of spinach treated with the methanol extracts of C. album var. centrorubrum, consumption of spinach by the adults was less than that by the adults reared on leaves treated with solvent only. These results indicate that C. nebulosa has the potential to harm spinach due to the habituation to feeding deterrents in spinach. However, the harm to spinach by C. nebulosa could be suppressed because feeding experience on C. album var. centrorubrum can prevent C. nebulosa from habituating to spinach.
