Habituation by a tortoise beetle to the deterrents of spinach

Feeding responses of Cassida nebulosa to spinach vary depending on prior dietary experience. Adults reared on spinach, eat much spinach whereas those reared on Chenopodium album var. centrorubrum rarely eat it. However, there are a few reports that address the mechanisms of this phenomenon, which is termed 'induction of preference'. It has been presumed that this phenomenon arises in response to a reduction of sensitivity to the feeding deterrents contained in spinach as a result of early experience feeding on it. Therefore, we attempted to verify the effects of the feeding deterrent that was isolated from spinach. The feeding-deterrent response was reduced in adults reared on spinach compared with adults reared on C. album var. centrorubrum. Additionally, consumption of spinach by adults reared on deterrent-treated leaves of C. album var. centrorubrum was significantly higher than that by adults reared on control leaves of C. album var. centrorubrum. These results indicate that C. nebulosa acquires the ability to tolerate spinach because sensitivity to the feeding deterrent contained in spinach is reduced by early experience with the deterrent.