Strategic Integration of Insect-Plant Interaction Study, Natural Enemy Investigation, and Establishment of Callus-Induced Crapemyrtle Regeneration for Managing Crapemyrtle Bark Scale (Hemiptera: Eriococcidae)

Abstract

Crapemyrtle (Lagerstroemia sp.) is the best-selling flowering tree and provides excellent pollen sources for pollinators in the U.S., especially when other resources are naturally scarce. However, the market’s most commercially available crapemyrtle cultivars are easily infested by a recently invasive insect, crapemyrtle bark scale (CMBS; Acanthococcus lagerstroemiae). Heavy infestations of CMBS reduce crapemyrtle flowering/vigor and even cause branch dieback, jeopardizing the production and esthetic value of crapemyrtle anticipated by the Green Industry. Besides its fast spread across 17 U.S. states, the CMBS infestations were observed on other economically important crops and native plant species, potentially posing a devastating threat to the Green Industry and ecosystem. From the perspectives of host-plant resistance and biological control studies, this research strategically integrated insect-plant interaction studies, natural enemy investigation, and establishment of a leaf-derived Queen’s crapemyrtle (Lagerstroemia speciosa) regeneration system for managing CMBS. The insect-plant interaction studies involved host confirmation and evaluation via greenhouse assays and insect feeding behavior study using electrical penetration graph (EPG), artificial diet, and micro-CT techniques. The 25-week greenhouse assays confirmed six crapemyrtle species, nine beautyberry species (Callicarpa spp.), Ficus tikoua, and Lythrum californicum were the host plants. Importantly, Queen’s crapemyrtle was relatively resistant among the crapemyrtle species, as indicated by its lowest number of newly developed CMBS. The feeding behavior study evaluated plant susceptibility/resistance by monitoring insect stylet-tip penetration in different plant tissues. Five main typical feeding waveforms were characterized. It was found that CMBS had difficulty accessing the phloem tissue of a resistant plant compared to a susceptible plant, providing direct evidence for revealing unknown hosts rapidly. The stable callus-induced regeneration system was established by optimizing the combinations of plant growth regulators for callus initiation/differentiation and shoot proliferation/rooting, which forwarded a pivotal step to molecular breeding to improve plant resistance against CMBS. This research first validated green lacewing (Chrysoperla rufilabris) as a natural predator upon CMBS and suggested 2nd and 3rd instar green lacewing as a biological control agent to control CMBS. These results improved our understanding of the CMBS-plant interactions and allowed us to develop more integrated pest management tactics to control CMBS spread efficiently.