664 Invasive Stink Bugs and Related Species (Pentatomoidea)
especially the Buchnera genome (Nikoh et al. 2011). But the genome differences of Ishikawaella are
notable: more genes for the synthesis of amino acids, vitamins, and cofactors; the retention of many genes
specific to translation and replication; and genes specific to energy production. Finally, Ishikawaella is
stably transmitted by the female plataspid in symbiont capsules (Hosokawa et al. 2005, 2006), which
may function to nourish and protect the bacteria. The subsequent introduction of M. cribraria into the
southeastern United States and the Western Hemisphere and the accompanying Megacopta-Ishikawaella
symbiosis provided a natural laboratory to test the ability of the symbiosis to facilitate dispersal evolution
through range expansion.
14.3.3 Invasion of Megacopta cribraria
14.3.3.1 Overview
Megacopta cribraria (Eger et al. 2010, Jenkins et al. 2010, Jenkins and Eaton 2011) debuted on kudzu
vine in northeast Georgia, in the United States, in October 2009 (Suiter et al. 2010). Previous research
strongly suggested that the obligate symbiosis would likely disperse from kudzu into soybean fields
(Fukatsu and Hosokawa 2002; Hosokawa et al. 2005, 2006, 2007b), which, in fact, occurred within a year
of its discovery (Seiter et al. 2013). Interestingly, only one female line, designated GA1, was confirmed
from sequence data from initial Georgia collections (Jenkins et al. 2010). By October 2010, M. cribraria
had expanded in Georgia from nine counties in 2009 to 80 counties. A single female line, GA1, was con-
firmed from consensus mitochondrial genome sequences (15,647 bp) from individuals collected in five
counties and mitochondrial fragment sequences (2,336 bp) collected from all 80 counties (83 sequences)
(Jenkins and Eaton 2011). The Ishikawaella endosymbiont also was confirmed in all M. cribraria
(Jenkins and Eaton 2011). Using ecological niche modeling, it had been predicted that M. cribraria had
the potential to expand its range across the southeastern United States and, subsesquently, invade south-
western Europe, southeastern South America, southern Africa, and the eastern coast of Australia (Zhu
et al. 2012). By 2013, the end of the study, the GA1 haplotype and the Ishikawaella endosymbiont had
been confirmed genetically in over 300 collections from across eight southeastern states in the United
States as well as from collections in Honduras, Central America (Tracie Jenkins, unpublished data). As
of March 2015, this bug has been confirmed in 12 states in the United States (http://wiki.bugwood
.org /Kudzu_bug) as well as Central America. Because Ishikawaella co-evolves with its host (Hosokawa
et al. 2006) as well as determines the pest status of the insect (Hosokawa et al. 2007b), has the genetic
fitness landscape of the genome changed since initial invasion? If so can these changes provide insights
into protein evolution relating to the pest status of the host?
14.3.3.2 Ishikawaella Genome in the Western Hemisphere
If evolution is imagined as movement of a population by natural selection across an adaptive or fitness
landscape (Wright 1932), and if the genome is the landscape on which the force of natural selection acts,
then the evolutionary trajectories along that landscape can be explored.
Brown et al. (2014) used population genomics to evaluate the evolutionary trajectory of the Ishikawaella
genome. Twenty-four Ishikawaella genomes were sequenced from three plant species across 23 sites
from 2009, during the first days of insect discovery, to 2011, at the conclusion of the study. The focus
of the research, which was greatly facilitate by the reference sequence from Nikoh et al. (2011), was to
compare the genomics of the pest-conferring symbiont in Asia to the genomics of the United States sym-
biont to determine the direction and extent of the genetic changes in the genome over the 2-year period
of the study. Insect size and color are phenotypic differences in Asia indicative of pest status (i.e., the
smaller and lighter insect was the nonpest or aposymbiotic insect) (Hosokawa et al. 2006, 2007b). This
is significant for United States populations because color and size variation, often associated with host
plant, had been observed and could be indicative of genetic variations (Brown et al. 2014).
Brown et al. (2014) did not observe genotypic changes among symbionts sampled during the study
regardless of insect phenotype or whether the host fed on kudzu or soybean. Comparative analyses
between the Ishikawaella genome of Megacopta cribraria from the United States with the complete