Facultative bacterial endosymbionts can play an important role in the evolutionary trajectory of their hosts. Aphids (Hemiptera: Aphididae) are infected with a wide variety of facultative endosymbionts that can confer ecologically relevant traits, which in turn may drive microevolutionary processes in a dynamic selective environment. However, relatively little is known about how symbiont diversity is structured in most aphid species. Here, we investigate facultative symbiont species richness and prevalence among world-wide populations of the cowpea aphid, Aphis craccivora Koch. We surveyed 44 populations of A. craccivora, and detected 11 strains of facultative symbiotic bacteria, representing six genera. There were two significant associations between facultative symbiont and aphid food plant: the symbiont Arsenophonus was found at high prevalence in A. craccivora populations collected from Robinia sp. (locust), whereas the symbiont Hamiltonella was almost exclusively found in A. craccivora populations from Medicago sativa (alfalfa). Aphids collected from these two food plants also had divergent mitochondrial haplotypes, potentially indicating the formation of specialized aphid lineages associated with food plant (host-associated differentiation). The role of facultative symbionts in this process remains to be determined. Overall, observed facultative symbiont prevalence in A. craccivora was lower than that of some other well-studied aphids (e.g., Aphis fabae and Acyrthosiphon pisum), possibly as a consequence of A. craccivora's almost purely parthenogenetic life history. Finally, most (70 %) of the surveyed populations were polymorphic for facultative symbiont infection, indicating that even when symbiont prevalence is relatively low, symbiont-associated phenotypic variation may allow population-level evolutionary responses to local selection.

Aphids commonly harbor bacterial facultative symbionts that have a variety of effects upon their aphid hosts, including defense against hymenopteran parasitoids and fungal pathogens. The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is infected with the symbiont Arsenophonus sp., which has an unknown role in its aphid host. Our research goals were to document the infection frequency and diversity of the symbiont in field-collected soybean aphids, and to determine whether Arsenophonus is defending soybean aphid against natural enemies. We performed diagnostic PCR and sequenced four Arsenophonus genes in soybean aphids from their native and introduced range to estimate infection frequency and genetic diversity, and found that Arsenophonus infection is highly prevalent and genetically uniform. To evaluate the defensive role of Arsenophonus, we cured two aphid genotypes of their natural Arsenophonus infection through ampicillin microinjection, resulting in infected and uninfected isolines within the same genetic background. These isolines were subjected to parasitoid assays using a recently introduced biological control agent, Binodoxys communis [Braconidae], a naturally recruited parasitoid, Aphelinus certus [Aphelinidae], and a commercially available biological control agent, Aphidius colemani [Braconidae]. We also assayed the effect of the common aphid fungal pathogen, Pandora neoaphidis (Remaudiere & Hennebert) Humber (Entomophthorales: Entomophthoraceae), on the same aphid isolines. We did not find differences in successful parasitism for any of the parasitoid species, nor did we find differences in P. neoaphidis infection between our treatments. Our conclusion is that Arsenophonus does not defend its soybean aphid host against these major parasitoid and fungal natural enemies.

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), invokes substantial chemical treatment and economic cost in North America. Resistant soybean genotypes hold promise as a low-impact control methodology, but soybean aphid "biotypes" capable of development on resistant soy cast doubt on the durability of soy resistance. We hypothesized that variation in soybean aphid ability to colonize resistant soy is partially attributable to a bacterial symbiont of soybean aphid, Arsenophonus. We used microinjection to manipulate Arsenophonus infection in both virulent and avirulent aphid biotypes, resulting in five pairs of infected versus uninfected isolines. These isolines were subjected to various population growth rate assays on resistant Rag versus susceptible soybean. We found that aphid virulence on Rag soybean was not dependent on Arsenophonus: virulent aphid biotypes performed well on Rag soybean, and avirulent aphid biotypes performed poorly on Rag soybean, regardless of whether Arsenophonus was present or not. However, we did find that Arsenophonus-infected clones on average performed significantly better than their paired uninfected isolines. This pattern was not consistently evident on every date for every clone, either in the population assays nor when we compared lifetime fecundity of individual aphids in a separate experiment. Nevertheless, this overall benefit for infected aphids may be sufficient to explain the high frequency of Arsenophonus infection in soybean aphids.

To explore the taxonomic status, phylogenetic patterns, and character evolution of various groups within Papaveraceae s. l. (Pteridophylloideae, Papaveroideae, Hypecoideae, and Fumarioideae), two data sets were created and analyzed using Bayesian inference, maximum likelihood, and parsimony methods: 1) a Ranunculales data set for 82 genera representing all of the major families within the order using three chloroplast DNA regions (atpB, rbcL, and matK) and nuclear 26S ribosomal DNA, and 2) a Papaveraceae s. l. data set for an expanded sampling of the family (27 genera, 40 species) consisting of chloroplast sequences only. Branch support values on the resulting trees derived from the combined data for both the Ranunculales and Papaveraceae s. l. data sets were comparable among the various ranunculalean families and supported subfamilial recognition of Pteridophylloideae, Papaveroideae, Hypecoideae, and Fumarioideae. Within Papaveraceae s. l., most analyses of both data sets resolved the position of Pteridophyllum as sister to all remaining subfamilies and Hypecoum as sister to Fumarioideae; branch support for these relationships varied from excellent to weak. Within Papaveroideae and Fumarioideae, most taxonomic groups previously proposed were recovered, including a well-supported clade of South African species. Optimization of sixteen key morphological characters on the Bayesian inference tree indicated that some characters (e.g. presence of laticifers and nectaries, floral symmetry, spurred petals, and type of androecium) are highly congruent with the molecular phylogeny. Intrafamilial phylogenetic relationships and character evolution of the various taxa within Papaveraceae s. l. are further discussed.

The sugarcane aphid (SCA), Melanaphis Sacchari (Zehntner) (Hemiptera: Aphididae), has been considered an invasive pest of sugarcane in the continental United States since 1977. Then, in 2013, SCA abruptly became a serious pest of U.S. sorghum and is now a sorghum pest in 22 states across the continental United States. Changes in insect-associated microbial community composition are known to influence host-plant range in aphids. In this study, we assessed whether changes in microbiota composition may explain the SCA outbreak in U.S. sorghum. We characterized the SCA bacterial microbiota on sugarcane and grain sorghum in four U.S. states, using a metabarcoding approach. In addition, we used taxon-specific polymerase chain reaction (PCR) primers to screen for bacteria commonly reported in aphid species. As anticipated, all SCA harbored the primary aphid endosymbiont Buchnera aphidicola, an obligate mutualistic bacterial symbiont. Interestingly, none of the secondary symbionts, facultative bacteria typically associated with aphids (e.g., Arsenophonus, Hamiltonella, Regiella) were present in either the metabarcoding data or PCR screens (with the exception of Rickettsiella and Serratia, which were detected by metabarcoding at low abundances <1%). However, our metabarcoding detected bacteria not previously identified in aphids (Arcobacter, Bifidobacterium, Citrobacter). Lastly, we found microbial host-associated differentiation in aphids that seems to correspond to genetically distinct aphid lineages that prefer to feed on grain sorghum (MLL-F) versus sugarcane (MLL-D).