Pentatomoids as Vectors of Plant Pathogens 619
East Asia (Rider et al. 2002). Both nymphs and adults can transmit the phytoplasma from paulownia
to periwinkle in Japan; presence in the plant has been confirmed by electron microscopy and in both
periwinkle and bugs by molecular analyses of 16S rDNA (Okuda et al. 1998). In China, stink bugs were
shown to transmit the pathogen from diseased plants to healthy empress tree seedlings. A 10-day acqui-
sition period was followed by a 30-day incubation period and 5–7 days feeding on healthy plants with
1–3 insects per seedling. Electron microscopy of bug salivary glands and leaf veins and petioles of the
seedlings revealed the presence of the phytoplasma, and disease symptoms developed in 33 of 107 inocu-
lated plants (Shao et al. 1982; cited in Hiruki 1999).
Although both empress tree and Halyomorpha halys now co-occur in the United States, there is no
evidence that paulownia witches’-broom disease is found currently in the United States (Rice et al. 2014)
or elsewhere outside of East Asia (Hiruki 1999). Damage from H. halys in the United States occurs
primarily on reproductive structures of fruit trees, vegetables, and row crops (Hoebeke and Carter 2003,
Rice et al. 2014). Nymphs also feed on leaves and stems, but the resultant stippling damage (see photo-
graphs in Hoebeke and Carter 2003) suggests cell rupture feeding rather than ingestion from vascular
tissues. However, stylet insertion through bark of common landscape trees recently has been observed,
resulting in sugary wound exudates (Martinson et al. 2013, Rice et al. 2014), and interpreted as ingestion
from the phloem (Martinson et al. 2013). Thus, this species may have the potential to transmit pathogens
other than paulownia witches’-broom into vascular tissue.
13.4 Bacterial Pathogens
13.4.1 General Overview of Bacterial Pathogens
Bacteria are single-celled, ubiquitous microorganisms that colonize diverse environments including
stink bug tissues (Kaiser and Vakili 1978, Ragsdale et al. 1979, Mitchell 2004, Hirose et al. 2006,
Medrano et al. 2009b). The majority is harmless, yet a subset consists of plant pathogens. Plant patho-
genic bacteria include fastidious (i.e., difficult to culture outside of the host) and non-fastidious (i.e.,
grow readily in bacterial culture media) species (Agrios 2005). Both types include infective bacterial
strains that cause opportunistic plant infections. The basic penetrative feeding mechanism used by stink
bugs wounds plant hosts and provides a physical conduit for acquisition and transmission of a bacterial
pathogen. Interestingly, the number of studies focused on this vector potential is limited, and any result-
ing plant infection is grouped with the damage associated with insect feeding (Williams 2014). In this
section, we focus on stink bugs known to be vectors of bacterial pathogens.
13.4.2 Cotton
In the late 1990s, a non-traditional cotton boll rot noticeably began to decrease cotton yields in South
Carolina (Hollis 2001). Symptoms of this malady are manifested exclusively inside developing green
bolls with the outside appearing normal. Thus, early diagnosis of infected fields is based on cross-
sectioning of green bolls. Medrano and Bell (2007) reported that an infective bacterium identified as
Pantoea agglomerans that was isolated from a diseased field boll was a causative agent of the disease.
Infections only occurred if the boll wall was pierced mechanically using a needle allowing an entry way
for the pathogen. In other work, Medrano et al. (2007) found that Nezara viridula was a capable vector
of the same P. agglomerans strain used in earlier studies. Stink bugs reared in the laboratory acquired
the cotton pathogen after they were provided a bacterial contaminated food source. The pathogen was
transmitted into bolls upon feeding by these insects resulting in diseased seed and lint with symp-
toms identical to initial reports and a symptomless boll exterior. Feeding by insects not exposed to the
opportunist caused negligible internal damage to the bolls. Interestingly, temporal studies subsequently
showed that bolls became immune to infections following three weeks of development (Medrano et al.
2009b). Also, bolls at two weeks into development could tolerate insect feeding provided that there was
no pathogen present. Collectively, these studies dissected the dynamics between N. viridula and a vector-
borne infection.