Differential life-history responses in Neolema abbreviata, a biological control agent for Tradescantia fluminensis under water and nitrogen gradients

Due to their sessile nature, plants inexorably endure both transient and chronic environmental stressors with subsequent impact on their interactions with other trophic groups. Water and nitrogen variability are key abiotic factors mediating the interaction between plants and insect herbivores. For insects used in classical biological control of plants, such factors may determine extent of herbivory, population dynamics and ultimately field establishment and persistence. We conducted a full factorial experiment to determine the impact of water and fertiliser variability on the performance of Neolema abbreviata (Lacordaire) (Coleoptera: Chrysomelidae) and its host plant Tradescantia fluminensis Vell (Commelinaceae). Water and fertiliser variability strongly influenced T. fluminensis biomass accumulation and foliar nitrogen content. These changes in host plant quality resulted in preferential oviposition selection by the beetles with optimally irrigated plants that received moderate fertilizer being most favoured. Larval performance, in terms of weight gain and time to pupation, was highest in this treatment providing support for the preference-performance hypothesis. There were similarities in feeding performance and subsequent performance among plant treatments between larvae and adults suggesting uniform nutritional quality requirements between the life-stages. Overall, our study reveals differential effects of paired abiotic stressors and performance among herbivorous insects with both juvenile and adult feeding life-stages. The study, therefore, calls for multi-trait and factor evaluation to understand the impact of plant quality on insect life history traits. Our findings also have direct implications on mass-rearing protocols of N. abbreviata and its potential field performance.