Pentatomoids as Vectors of Plant Pathogens 621
beans when roasted. Three candidate causal pathogens have been proposed: Eremothecium coryli,
Nematospora gossypii Ashby and Nowell [= Eremothecium gossypii (Ashby and Nowell) Kurtzman] and
the bacterium Pantoea coffeiphila (Wallace 1931, 1932, Gueule et al. 2015). Importantly, transmission
tests have not been conducted and Koch’s postulates have not been satisfied for any of these candidate
agents. Rather, the evidence is more circumstantial. Kirkpatrick (1937) hypothesized that all Antestiopsis
spp. are able to transmit fungal pathogens, that E. coryli and E. gossypii are widespread in coffee agro-
ecosystems, and that infection prevalence of vectors varies spatially and temporally. Based on previous
work on pentatomid transmission of E. coryli and E. gossypii, we hypothesize that they are transmitted
by Antestiopsis spp. in a semi-persistent manner (Mitchell 2004). The potential for insect transmission
and plant pathogenicity of P. coffeiphila are currently unknown, although the newly described species is
associated with PTD (Gueule et al. 2015). Finally, although more speculative, Small (1923) argued that
Antestiopsis spp. also can infect coffee cherries with Phoma spp. (fungi).
PTD incidence tends to be low but can nonetheless severely reduce crop yield and quality (Jackels
et al. 2014). Management of PTD primarily focuses on management of Antestiopsis spp. which can be
effective (Le Pelley 1942). Economic threshold estimates vary between one and four individuals per cof-
fee plant (Meulen and Schoeman 1990, Cilas et al. 1998); such low thresholds are consistent with other
pentatomid-borne diseases (Greene et al. 2001; see Section 13.5.3, Cotton).
13.5.3 Cotton
Nowell (1918) reported a “stainer bug”, Dysdercus suturellus (Herrich-Schaeffer) that deposited fungi
into cotton bolls in the West Indies. This early work involved collecting field insects and then exposing
them to cotton. Damage to seed and lint quality was labeled as a type of stigmatomycosis that involved
Eremothecium (formerly Nematospora). The infection occurred strictly within the bolls and had a
greater effect on young developing fruit. Symptoms included yellowing of the lint, which decreased the
value of the affected bolls. It was found that control of the sucking insect consequently also decreased
the disease incidence.
Marasas (1971) reported that the yeast Eremothecium ashbyi Guillermond [as Crebrothecium ashbyi
(Guilliermond) Routien] caused an inner boll rot of cotton in South Africa as well as other parts of the
continent. Additionally, three yeast-like species of Spermophthoraceae: Ashbya gossypii (Ashby and
Nowell) Guilliermond (=Eremothecium gossypii), Eremothecium coryli and E. ashbyi were reported to
cause cotton staining in association with sucking insects. The taxonomy of this group is controversial,
yet they all apparently stain cotton similarly. In this study, open, stained bolls were tested for the pres-
ence of fungal structures such as hyphae and spores. It was presumed that a sucking insect had transmit-
ted the fungi as insects were not collected.
More recently, Medrano et al. (2009a) demonstrated the ability of Nezara viridula to transmit
Eremothecium coryli into cotton bolls. The yeast was isolated from field-grown diseased bolls collected
in Florida and Georgia (USA). Interestingly, bolls collected from North and South Carolina did not yield
the fungus. Insects reared in the laboratory were tested for fungal growth and none was detected. Stink
bugs were then provided a food source that had been dipped in a yeast suspension. Finally, the insects
were housed with greenhouse grown bolls. Disease did indeed occur in bolls fed upon by insects that
harbored the fungus. Conversely, bolls fed upon by insects that did not possess the pathogen were neither
stained nor diseased. Further, the fungus was recovered from both the contaminated insects and diseased
bolls; thus, Koch’s postulates were fulfilled. The infection symptomology observed was comparable to
previous descriptions with yellow, matted lint. In contrast, bacterial inner boll infections caused lint and
seed necrosis with a dark brown to black coloration.
13.5.4 Legumes
The association between Eremothecium coryli and bug feeding has been recognized for nearly a century
(Nowell 1918). Although the earliest observations were of cotton stainers, Ashby and Nowell (1926)
reported that in the West Indies, the abundant and polyphagous Nezara viridula transferred the fun-
gus from cultivated legumes to cotton. Daugherty (1967) reported that on soybean and other legumes,