Innervation of the southern green stink bug [Nezara viridula (L.) (Hemiptera: Pentatomidae)] stylet bundle

Authors: Esquivel, Jesus; Droleskey, Robert - Bob; Harvey, Roger

Submitted to: Arthropod Structure and Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2021
Publication Date: 1/24/2022
Citation: Esquivel, J.F., Droleskey, R.E., Harvey, R.B. 2022. Innervation of the southern green stink bug [Nezara viridula (L.) (Hemiptera: Pentatomidae)] stylet bundle. Arthropod Structure and Development. 66. Article 101135. https://doi.org/10.1016/j.asd.2021.101135.
DOI: https://doi.org/10.1016/j.asd.2021.101135

Interpretive Summary: The southern green stink bug is a major pest of crops produced for food or fiber, including cotton. The insect uses needle-like mouth parts known as stylets to transmit plant pathogens and to feed on various plant structures. The mouth part is composed of an outer pair of stylets which encompasses an inner pair of stylets to form the feeding apparatus. Although the external characteristics of the stylets are known, the internal components, such as nerve bundles, have not been reported. We used a transmission electron microscope to obtain high resolution images of the internal components of the stylets. The images revealed two types of nerve bundles within the outer stylets, and suggested the presence of nerve bundles within the inner stylets, which were generally believed to be devoid of nerves. The suggested presence of nerves within the inner stylets improves our understanding of the stink bug needle-like feeding apparatus and, more importantly, provides additional insight on its relationship with the insect’s internal anatomy, feeding behavior, and pathogen transmission.

Technical Abstract: The southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae), continues to threaten high-value cash crops, including cotton (Gossypium hirsutum L.; Malvales: Malvaceae). Earlier reports confirmed ingestion and transmission of disease-causing pathogens of cotton, including elucidation of the dimensions for the food and salivary canals of the stylet bundle. During this earlier work, observations on the innervation of the stink bug stylet bundle were noted. Our objective is to provide the first imagery and descriptions of the different types of innervations (i.e., dendritic bundles) within the southern green stink bug stylet bundle. Each mandibular and maxillary stylet possesses a dendritic canal. Two types of dendritic bundles innervate each mandibular stylet. However, type and numbers of bundles within the mandibular stylets differs depending on location along the stylet. Within the head, six dendritic bundles (3 thick-walled and 3 thin-walled) are present in each mandibular stylet but only 3 thin-walled dendritic bundles are present at the most distal fourth labial segment. Transmission electron microscopy suggests innervation of the maxillary stylets, and this is supported by stained tissue within the dendritic canal of the maxillary stylets. These new observations regarding types and spatial differences in numbers of dendritic bundles within the mandibular stylets improve the current knowledge base regarding internal stylet morphology and feeding mechanics. Also, the suggested innervation of the maxillary stylets may warrant re-consideration of the commonly accepted belief that southern green stink bugs, and potentially other phytophagous stink bugs, do not possess nerves within the maxillary stylets.