Evaluation of δ15N analysis to trace the origin of Diaphorina citri (Hemiptera: Liviidae) to citrus orchard fertilization management

Abstract

We investigated the variability of nitrogen stable isotope ratios 15N/14N (expressed as δ15N) on citrus orchards with different fertilization management practices (organic versus conventional) and its correlation with the δ15N values of the key citrus pest Diaphorina citri Kuwayama (Hemiptera: Liviidae) feeding on such plant material. Tracing the origin of this pest in open field is crucial since the insect is a vector of the incurable and devastating citrus disease known as Huanglongbing. We hypothesized that the origin (natal tree) of the pest may be deduced by correlating the δ15N values obtained from the young citrus leaves and from adults of D. citri raised on them. First, laboratory experiments were performed to understand the acquisition and incorportation of the δ15N values by D. citri. Second, we confirmed the positive correlation between the δ15N values of the young citrus leaves and D. citri. Finally, field sampling was carried out in 21 citrus orchards from Southern California to study the variability on the δ15N values on organic and conventional commercial citrus orchards. Laboratory results suggest that the analyses of the δ15N values can be regarded as a useful method to trace the origin of the pest. However, the high variability in nitrogen resource used in both fertilization management practices (especially in organic orchards) by growers makes the application of this technique unfeasible to pinpoint the origin of D. citri in the citrus agroecosystem.