# Occurrence and Genetic Variation of Monolepta hieroglyphica (Motschulsky, 1858) (Coleoptera: Chrysomelidae), a Newly Emerging Pest, Among Hosts in Northeast China

## TL;DR

This study examines the occurrence and genetic diversity of the leaf beetle Monolepta hieroglyphica in Northeast China to inform pest control strategies.

## Contribution

The study provides new insights into the beetle's host preferences and genetic variation using mitochondrial DNA markers.

## Key findings

- Maize and soybean fields had higher infestation rates of M. hieroglyphica compared to other crops.
- Genetic analysis revealed high gene flow and significant within-population variation but no clear host-based genetic patterns.
- The beetle's host transfer trajectory suggests movement from soybean and weeds to cabbage and late-cultivated maize.

## Abstract

Northeastern China is recognized as a crucial grain-producing region, but food security is severely affected by diverse pests. Due to changes in climate, cultivation patterns, and crop distribution, the leaf beetle Monolepta hieroglyphica (Motschulsky, 1858) (Coleoptera: Chrysomelidae) has emerged as a destructive pest. However, its occurrence across different hosts remains poorly understood. This study analyzed the pest’s occurrence patterns and genetic diversity through systematic observation and mitochondrial DNA markers. These findings are essential for developing effective pest control strategies in the region.

The northeast region of China plays a crucial role in crop production. The leaf beetle Monolepta hieroglyphica (Motschulsky, 1858) (Coleoptera: Chrysomelidae) has emerged as a potential threat to food security in the region. With a wide distribution spanning Asia and Russia, this beetle affects various crops. However, limited information is available regarding its occurrence patterns and genetic diversity among major crops in the region. Based on systematic observations across various hosts, coupled with genetic variation analysis using mitochondrial DNA markers, the main results were as follows. Leaf beetle occurrence varied among hosts, peaking from late July to mid-August, with maize and soybean fields exhibiting higher infestation rates compared with other crops. Notably, late-cultivated maize fields harbored the highest beetle numbers due to the species’ preference for young leaves. The host transfer trajectory may have originated in soybean and weeds, with subsequent alternation between host plants and other crops, before the final migration to cabbage and late-cultivated maize fields. Genetic analysis revealed nine COI haplotypes, four COII haplotypes, eleven Cytb haplotypes, and twenty-one combined haplotypes. No clear relationship existed between genetic diversity and occurrence, and no distinct host-based genetic patterns emerged from neighbor-joining tree and haplotype network analyses. High gene flow rates were observed, likely contributing to decreased genetic variation. An analysis of molecular variance results indicated major genetic variation within populations, although genetic distance and haplotype distribution indicated divergence among host populations. These results provide foundational data for developing effective M. hieroglyphica pest management strategies.