Invasive Stink Bugs and Related Species (Pentatomoidea)

662 Invasive Stink Bugs and Related Species (Pentatomoidea)

Megacopta cribraria (Eger et al. 2010) and its obligate gut endosymbiont, Ishikawaella (Jenkins et al.
2010), made its Western Hemisphere debut in Northeast Georgia in the United States. It was discov-
ered feeding and developing on kudzu, Pueraria montana Loureiro (Merrill) variety lobata ( Willdenow)
(Suiter et al. 2010). In less than a year, M. cribraria, commonly identified as the kudzu bug in the United
States, was found feeding and developing on soybean, Glycine max (L.) Merrill (Suiter et al. 2010, Zhang
et al. 2012, Del Pozo-Valdivia and Reisig 2013). Although kudzu is an invasive plant in the United States
(Zhang et al. 2012), soybean, worth about $40 billion to the United States economy, is not (Jenkins and
Eaton 2011). The Western Hemisphere has, therefore, become a natural laboratory experiment for testing
two hypotheses: (1) A mutually obligate extracellular symbiosis indigenous to the Eastern Hemisphere
will adapt rapidly and expand its range into novel environments in the Western Hemisphere, or (2) The
symbiont genome will rapidly evolve as the symbiosis expands its range across the Western Hemisphere.

14.3.2 Genetic Baseline

14.3.2.1 Vertical Transmission in Symbiont Capsules

Fukatsu and Hosokawa (2002) were the first to genetically characterize the vertically transmitted extracel-
lular gammaproteobacterium, Candidatus Ishikawaella capsulata (Ishikawaella) and its obligate relation-
ship with its indigenous plataspid host, Megacopta punctatissima (Hemiptera: Heteroptera: Plataspidae).
Studies showed that, like bacteriocyte symbioses, Ishikawaella has a drastically reduced, AT-rich genome
(Hosokawa et al. 2006, Nikoh et al. 2011), is vertically transmitted, has a long history of co-evolution with
its host, and provides its host with the essential nutrients lacking in phloem for insect growth and develop-
ment (Fukatsu and Hosokawa 2002; Hosokawa et al. 2005, 2006, 2007a,b, 2008; Nikoh et al. 2011).
Adults of Megacopta punctatissima were shown to harbor the bacterium in the crypts of the midgut
posterior region (Fukatsu and Hosokawa 2002, Hosokawa et al. 2006). The capsules, likely produced in
the enlarged end section of the crypt-bearing midgut part (Fukatsu and Hosokawa 2002), were shown
to be vertically transmitted and deposited underneath and proximal to the eggs (Figure 14.4) (Fukatsu
and Hosokawa 2002). Newly hatched nymphs were observed to probe these capsules (Figure 14.4),
ingest the symbiont, aggregate, and then become quiescent 1–2 days before dispersing to feed on phloem

A

0.5 mm 0.5 mm

0.5 mm 0.5 mm

B

C D

FIGURE 14.4 (See color insert.) Capsule symbiosis in plataspid insects. (A-B) Egg cluster of Brachyplatus subaeneus:
A. Dorsolateral view; B, Posterolateral view. Arrows indicate symbiont capsules. (C) Symbiont capsules removed from egg
mass. (D) First instars of Megacopta cribraria. Note: nymphs feeding on capsule contents.