Application of nitrogen, phosphorus, potassium + carbon fertilizer improves the growth of Tecoma stans and the performance of its root-feeding biological control agent, Heikertingerella sp.

Abstract

ABSTRACT The invasive tree Tecoma stans (L.) Juss. ex Kunth var stans (Bignoniaceae) has been targeted for biological control in South Africa since 2003. Plant nutrients contained in fertilizers typically improve host-plant quality, thereby enhancing the fitness of insect herbivores deployed as weed biocontrol agents. We investigated the effect of increasing nutrient levels (fertilizer treatments) on the growth of potted T. stans plants and on the subsequent performance of the root-feeding beetle Heikertingerella sp. (Chrysomelidae). Enhanced performance of Heikertingerella sp. in culture will improve mass-rearing initiatives for releases in South Africa. Ten newly emerged mating pairs of Heikertingerella sp. were exposed under glasshouse conditions to caged plants that were treated with four regimes of nitrogen: phosphorus: potassium 2:3:2 (14%) + carbon (8%) fertilizer, namely zero (control), low (5.6 g/m2), medium (9.4 g/m2) and high (13.2 g/m2). Increasing nutrient levels significantly increased leaf production and above – and below-ground biomass accumulation in T. stans plants. Similarly, the performance of Heikertingerella sp. was improved substantially, with significantly and progressively higher levels of P1 adult feeding and F1 progeny production, and significantly and progressively reduced F1 developmental times, under increasing nutrient levels. While F1 adult size was significantly increased by fertilizer application relative to the controls, there were no significant differences between the three nutrient levels. Although the high fertilizer application rates were the most suitable for the culturing and mass-rearing of Heikertingerella sp. adults, medium fertilizer applications may prove more economical to improve host-plant quality and boost beetle numbers for release.