Invasive Stink Bugs and Related Species (Pentatomoidea)

612 Invasive Stink Bugs and Related Species (Pentatomoidea)

13.1 Introduction

13.1.1 Modes of Transmission of Pathogens by Hemiptera

Vector-borne pathogens can be categorized functionally according to the degree of symbiosis that they
acquire with their vectors. Three modes of transmission have been broadly described: non-persistent,
semi-persistent, and persistent. Although Nault (1997) originally compiled these modes specifically for
viruses transmitted by sternorrhynchan and auchenorrhynchan vectors, they can usefully be applied to
all taxa of microbial pathogens and hemipteran vectors.
The differences in persistence among different transmission forms are directly related to which vector
tissue(s) are colonized by the pathogen (Nault 1997). Pathogens transmitted in a non-persistent manner tend
to colonize the stylets of hemipteran vectors and generally require only brief periods to be acquired by vec-
tors and to inoculate subsequent hosts (on the order of minutes); infections also are lost quickly by vectors
thereby requiring the vectors to move quickly from infected to healthy hosts (Uzest et al. 2010, Blanc et al.
2014). Semi-persistent pathogens colonize the foregut of their vectors; as a consequence, acquisition and
inoculation access periods are longer and vectors remain infective for longer periods of time (Nault 1997).
Finally, persistent pathogens colonize vector tissues more systemically, colonizing the digestive system and
haemocoel. Importantly, salivary glands eventually are colonized from which inoculation of hosts occurs
(Nault 1997). In addition, a subset of persistent pathogens also multiply in the tissues of vectors; these
“persistent-propagative” pathogens often are transovarially transmitted as well. While transmission modes
can be useful for understanding vector-pathogen relationships, they also relate to patterns of induced phe-
notypic changes in host plants (Mauck et al. 2012), are a conserved trait within virus taxa (Nault 1997), and
define the epidemiology of associated diseases (Madden et al. 2000; see Section 13.7).

13.1.2 Heteropteran Feeding Mechanisms

The ability to transmit pathogens depends on feeding behaviors, which, to a great extent, are determined
by the structure of the mouthparts. All Hemiptera are characterized by mouthparts composed of four
piercing structures, two outer mandibular stylets and two inner maxillary stylets, enclosed (when not
in use) by the 4-segmented labium, which usually functions only as a protective sheath. The labrum is
reduced, and there are no maxillary or labial palps. A food canal and a salivary canal are formed by the
interlocking maxillary stylets, and liquid food is sucked into the precibarium and then through the cibar-
ium into the esophagus (Figure 13.1; also Section 13.1.3.2, Formation of the Stylet Bundle). However,

Md Md

Mx Pr Mx

Sd

FIGURE 13.1 Convergence of the maxillary and mandibular stylets with the precibarium and salivary duct within the
head of Nezara viridula. Md, mandibular stylet; Mx, maxillary stylet; Pr, precibarium; Sd, Salivary duct. (Courtesy of
Robert E. Droleskey, USDA, College Station, Texas.)