Effect of host-plant age on the performance of the root-feeding flea beetle Heikertingerella sp., a biological control agent for Tecoma stans in South Africa

Age influences host-plant quality, which is a key determinant of the fitness of herbivorous insects and hence biological control agents of invasive plants. We assessed the effect of host-plant age on the performance of the root-feeding flea beetle Heikertingerella sp. (Coleoptera: Chrysomelidae: Galerucinae), which was recently approved for release against the invasive tree Tecoma stans (L.) Juss ex Kunth var. stans (Bignoniaceae) in South Africa. Using similar-sized plants that were aged from one to three years, our aim was to determine an optimal host-plant age to facilitate mass-rearing of the beetle for impending releases. While significantly more F-1 progeny were produced with increasing plant age, presumably due to larger root masses in progressively older plants, plant age did not influence the size of the F-1 adults. There was no significant effect of plant age on the survival and percentage of leaves damaged by the P-1 adults. Tecoma stans plants of all ages produced significantly fewer leaves when exposed to feeding by Heikertingerella sp. adults and their larval progeny, relative to the unexposed control plants. Irrespective of plant age, adults displayed higher feeding intensity on the younger leaves at the top sections of the plants than on the older leaves on the middle and bottom sections. Although plants of all three ages were suitable for adult feeding and survival in quarantine cultures, progressively older plants are best suited for F-1 progeny production and therefore for the mass-rearing of Heikertingerella sp. for releases.