Luthrodes pandava Larvae Can Distinguish Cycas Leaf Quality in Cafeteria Experiments

Cycads are being endangered by several anthropogenic threats, and invasions of non-native herbivores are among those threats. Various country invasions by the cycad blue butterfly Luthrodes pandava have threatened the local horticulture cycad trade and native cycad populations. Little is known about behaviors of the larval stage of this specialist herbivore, the life phase that causes damage to cycad leaf tissue. The objective here was to determine larval ability to discriminate among Cycas species that are known to exhibit contrasting susceptibility to L. pandava herbivory. Dual-choice cafeteria protocols were used whereby a single larvae was provisioned with one leaflet of minimally damaged species (low quality) and one leaflet of heavily damaged species (high quality). Consumption after an 8 h feeding cycle was measured as loss in leaflet area. Wild L. pandava populations derived from in situ Philippine and Thailand Cycas habitats preferentially fed on high quality leaflets. In contrast, invasive L. pandava populations from urban locations in Guam, Philippines, and Thailand exhibited no preferences in leaflet feeding choice. The findings indicated that larvae of this Lycaenidae specialist herbivore exhibit complex selection behaviors that depend on origin of the butterfly and feeding history. Discrimination capabilities of the in situ populations that evolved with a single native Cycas species demonstrated beneficial behaviors that appear to be lost over time by invasive populations that feed on numerous novel Cycas hosts within the invasive range.