Gross Morphology of Diseased Tissues in Nezara viridula (Hemiptera: Pentatomidae) and Molecular Characterization of an Associated Microsporidian

Abstract

Nezara viridula (L.) (Hemiptera: Pentatomidae), commonly known in the U.S. as the southern green stink bug (SGSB), is a cosmopolitan, highly polyphagous feeder that causes severe damage to a wide range of agronomically important crops such as fruit, vegetable, grain, tobacco, and cotton, throughout much of the United States, and is a global pest of considerable ecological, agricultural, and economical interest. During dissection of female Nz. viridula, conspicuous black and brown spots or lesions were observed on various internal organs. To determine the cause of these spots or lesions, tissues of fat body, spermatheca, ovaries, and ovulated eggs were collected from healthy and infected individuals. The gross morphology of the spots was characterized, and the microorganisms associated with the infection were identified by amplicon sequencing of the V4 region of the small subunit rRNA gene. The presence of a microsporidian pathogen Nosema maddoxi, Becnel, Solter, Hajek, Huang, Sanscrainte, & Estep (Microsporidia: Nosematidae) which has been observed on other species of stink bug, was evidenced for the first time. The characterization of the gross morphology of this associated microsporidian may enable more rapid determination of microsporidia infection in stink bug colonies and field populations.

Keywords: fat body; infected tissue; insect pathogen; insect rearing; stink bug.

Fig. 1.

A comparison of the reproductive system of spotted and unspotted adults of Nezara viridula. Images (a and b) show both unspotted, and spotted female reproductive systems, respectively. Images (c and d) show unspotted and spotted male reproductive systems, respectively. Images (e and f) are of fat bodies from unspotted and spotted individuals, respectively. Note: all individuals (male and female) showing spotted tissues were from the infected colony (none were unspotted); examples of unspotted tissues were harvested from noninfected individuals.

Fig. 2.

Infected tissues. Infected Nezara viridula fat body from the infected colony displaying numerous black spots throughout the tissue field (a, b). Infected Nezara viridula spermathecal gland from the infected colony displaying numerous black spots throughout the tissue field c). Note smaller spots extending outwards from the main black spotted area—see arrows. The same black spotted spermathecal gland shown in the previous image showing what appear to be tethers/connections between the larger black spots and the smaller (satellite) spots (d).

Fig. 3.

Presence of Nosema sp. in spotted and unspotted tissues based on amplicon sequencing of the V4 region of the small subunit rRNA genes and presented using a centered log ratio analysis (Gloor et al. 2017). The two charts reflect the same data.