Biology and native host range of the defoliating beetle Ageniosa cf. badenii (Chrysomelidae), a potential biological control agent for Cape ivy (Delairea odorata) in invaded countries

Delairea odorataLemaire, Cape ivy (Asteraceae: Senecioneae), is native to South Africa but invasive in several countries. The plant is a target for biological control in the USA (California and Hawaii) and Australia, where its aggressive smothering tendencies threaten native ecosystems. The beetleAgeniosacf.badenii(Vogel) (Chrysomelidae) was investigated in South Africa as a potential agent forD. odoratain invaded countries. Adults are wingless and nocturnal. Females deposit clusters of 1-10 eggs on the leaf undersides. Neonate larvae are highly mobile and feed on the leaves during the four instars, before pupating in the soil. Mean (+/- SE) developmental time from egg hatch to adult emergence was 30.8 +/- 0.4 days onD. odorata. During larval no-choice tests with 34 asteraceous plant species, survival to adulthood was confined to 10 species in the tribe Senecioneae. Neonate larvae completed development (with sustained fitness >= 65% in relation to the highest ranked host) on three native (Senecio tamoidesDC.,D. odorataandS. skirrhodonDC.) and one exotic (Gynura procumbens(Lour.) Merr.) species. The beetle's narrow host range was confirmed by larval paired-choice and adult multi-choice tests and field observations.Ageniosacf.badeniimay be a suitable agent for Hawaii, where the tribe Senecioneae is not represented in the native flora. However, since Senecioneae are well represented in the native flora of Australia and California, more intensive testing is needed to determine if the beetle is a candidate for introduction into these areas.