Role of induced resistance in interactions of Epilachna vigintioctopunctata with host and non-host plant species

The process of host/non-host determination was dissected in interactions of Epilachna vigintioctopunctata, a specialist herbivore of solanaceous plants, with various plant species. On host plants (tomato and egg plant) the ladybird beetle started feeding within 5 min. On red pepper, another solanaceous plant, it also started feeding within 5 min, but did not continue the feeding as vigorously as on tomato or eggplant. This result suggests that the ladybird beetle recognizes red pepper as a host plant but does not overcome its constitutive resistance. On Chinese cabbage, the ladybird beetle did not start feeding as quickly as on the host plants, but once started, it continued feeding as vigorously as on the host plants. This result suggests that the ladybird beetle does not recognize Chinese cabbage as a host plant but overcomes its constitutive resistance. Subsequently, the effect of induced resistance in a host (tomato) and non-hosts (Chinese cabbage and Arabidopsis) was evaluated. The treatment with methyl jasmonate (MeJA) showed no effects in tomato but decreased the damaged area in Chinese cabbage and Arabidopsis. A feeding test with Arabidopsis mutants supported the idea that induced resistance via the jasmonic acid (JA) pathway is effective against the ladybird beetle on the cruciferous plants. We suggest that a specialist herbivore has to overcome not only constitutive resistance but also induced resistance to utilize the non-host plant as a host, and that induced resistance is one of the factors that determine host specificity of the specialist.