Pentatomoids as Vectors of Plant Pathogens 625
spined citrus bug, Biprorulus bibax Breddin, which was present in large numbers when the disease first
appeared (Shivas et al. 2005).
Halyomorpha halys has been found to transmit Eremothecium coryli in the laboratory to several veg-
etables and fruits. The yeast was recovered consistently from internal tissues damaged by the feeding of
H. halys in the field. In laboratory trials, H. halys was able to infect tomato, green pepper, green beans,
apples, pears, and nectarines (Brust and Rane 2011). Given the highly polyphagous habits of this stink
bug, the potential for dissemination of E. coryli in the United States will be increased greatly as this
invasive stink bug continues to spread.
Aflatoxins are produced by the fungus Aspergillus flavus Link and related species. In cornfields, the
spatial patterns of stink bug-damaged kernels and aflatoxin levels are related; both variables were found
to be aggregated with a strong field-edge effect, and aflatoxin levels were positively correlated with stink
bug damage. The predominant ear-feeding stink bug was Euschistus servus (Ni et al. 2011). In a further
study, results were confirmed; indices of association between these factors were significant at several
sampling locations (Ni et al. 2014b). In contrast, feeding by E. servus had no effect on the incidence of
common smut [Ustilago maydis DC (Corda)] infection in maize (Ni et al. 2014a). In field cage studies,
smut infection percentages did not differ significantly between plants that were exposed to bugs shaken
with smut spores, bugs without smut spores, or no bugs. Interestingly, post-harvest analyses of cornmeal
for aflatoxin in this cage study (Ni et al. 2014a) indicated no significant relationship between bug pres-
ence and the level of aflatoxin, unlike the two previous field studies (Ni et al. 2011, 2014b).
Kernel-spot lesions on pecan, caused by feeding of Nezara viridula and other stink bugs, harbor a wide
variety of fungi including some toxic Penicillium spp. (Payne and Wells 1984). Whether N. viridula is
involved in transmission is unknown, but Penicillium spp. are known to be part of the internal microflora
of N. viridula collected from soybean (Ragsdale et al. 1979).
Moniliasis disease of cacao, or frosty pod rot, caused by Moniliophthora roreri H.C. Evans, is a seri-
ous threat to cocoa production from Mexico to South America (Phillips-Mora et al. 2006). Losses may
reach 80–90% within a few years of establishment of the fungus. The cacao bug, Antiteuchus tripterus
(F.) was implicated as a vector at one time (Eberhard 1974; cited in Agrios 1980) but distribution and
transmission currently are attributed to wind and human activity (Krauss 2014).
13.6 Trypanosomatids
13.6.1 General Overview of Trypanosomatids
Most entomologists are familiar with the insect-vectored trypanosomatids causing human illness —
Chagas’ disease, leishmaniasis, and African sleeping sickness— but a closely related group associated
with plants and insects is less well known. These plant-associated trypanosomatids are mostly non-
pathogenic, but a few cause serious disease of coconut, oil palms, and coffee. Monoxenous trypanosoma-
tids (i.e., species that have only a single host) live within the midgut and hindgut of insects, particularly
Hemiptera and Diptera (Maslov et al. 2013); these occasionally may be found in fruits (Conchon et al.
1989), but the life cycle is not considered truly digenetic. Dixenous species, in contrast, inhabit both
plants and insects during part of their life cycles. Many of these were placed originally in the monoxenous
genera Leptomonas or Herpetomonas, but eventually were classified together in the genus Phytomonas
on the basis of morphology and the plant host (Hollar and Maslov 1997). Despite earlier uncertainty
about this somewhat arbitrary placement, recent molecular phylogenetic studies have confirmed that,
indeed, Phytomonas is monophyletic (Hollar and Maslov 1997, Maslov et al. 2013). Three groupings
within Phytomonas based on the plant structure inhabited (i.e., latex, fruit, or phloem) (Vickerman 1994)
also are supported by molecular analyses (Hollar and Maslov 1997, Jaskowska et al. 2015). A review of
Phytomonas research is provided by Jaskowska et al. (2015); the hemipteran vectors are reviewed thor-
oughly by Camargo and Wallace (1994) and more briefly by Mitchell (2004). An extensive bibliography
is provided by Solarte et al. (1995).
Latex-inhabiting forms generally are considered to be commensals rather than parasites of euphorbs,
milkweeds, and other plants with laticifers. Bugs in several heteropteran families have been implicated