Using elemental profiling to determine intrinsic markers to track the dispersal of Prostephanus truncatus, a pest of stored grain with alternative natural hosts

Abstract

"Detecting sources of insects attacking grain stores can help to develop more effective pest management models. This study considers combinations of chemical elements as intrinsic markers for tracing resource-use by Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) a pest of stored maize which occurs in natural environments where alternative hosts may support reservoirs of infestation. P. truncatus were lab-reared on maize or field-caught in pheromone-baited flight-traps. Beetles and hosts were screened for multiple elements using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). For elements above detection limits we tested relationships between determinations for different host plants, and for beetles according to environment where captured. An alternative host Spondias purpurea (Linnaeus) (Anacardaceae) contained more Al, B, Ca, Cu, Fe, Mg, Si and Sr, and less P and Zn than maize. Trends for P were consistent between maize and beetles infesting maize, but reversed for Ca and Mg. Elemental profiles of beetles were associated with environment, with significantly lower Al, Ca, Cu, Cr, Fe, P, S, Si, Sr, Ti and Zn determinations in maize-reared beetles than those captured in agricultural or natural environments. Additionally, Al, Ba, K, P, Sr and Ti determinations of field beetles captured in agricultural vs natural environments were significantly different. This suggests Al, Sr and Ti as candidate markers for environment, plus other possibilities likely since elemental concentrations (except B, Ba, Ni, and P) were significantly different in comparisons of all field beetles vs maize-reared beetles. We present a robust practical solution which successfully identified combinations of elemental markers for remotely tracing resource-use and dispersal by P. truncatus. We discuss the application of chemical characterisation for identifying intrinsic markers of pests, particularly species with alternative hosts. We discuss how to manage the low replication and unbalanced sample sizes inherent in insect elemental screening, particularly when rarer elements are potential markers. "