Molecular and Morphological Identifications Reveal Species Composition of Lygus (Hemiptera: Miridae) Bugs in Potatoes Fields in the Lower Columbia Basin of the United States.

Lygus bugs are highly polyphagous insect pests. In recent years, Lygus bugs have become more conspicuous on potato, Solanum tuberosum L., fields in the Pacific Northwest, particularly in the Lower Columbia Basin. There are concerns that direct feeding damage or potential pathogen transmission can reduce yield. Lygus species on potatoes in the region are collectively identified as 'Lygus bugs'. Overlapping physical traits and the fact that the same species exhibit morphological variations across a geographic range makes it difficult to identify Lygus to species level. Thus, in this study we used DNA barcodes in combination with morphological characters to identify Lygus species on potatoes. Three species were identified in the Lower Columbia Basin: Lygus hesperus (Knight) and Lygus elisus L. were the most common, whereas Lygus keltoni L. was the least common. Interspecific genetic distances among Lygus species were relatively low, ranging from 0.013 to 0.004. Neighbor-joining (NJ) tree clustered L. hesperus and L. elisus into two major clades, with L. keltoni forming a subclade within L. hesperus clade. Statistical parsimony analysis corroborated findings from phylogenetic analysis with L. keltoni and L. hesperus sharing one haplotype. Our study demonstrates the utility of integrating morphology and molecular markers in identifying morphologically similar species such as Lygus bugs. The study also serves as a fundamental step in contributing to developing suitable management strategies against Lygus bugs on potato.

Host-associated differentiation in a highly polyphagous, sexually reproducing insect herbivore.

Insect herbivores may undergo genetic divergence on their host plants through host-associated differentiation (HAD). Much of what we know about HAD involves insect species with narrow host ranges (i.e., specialists) that spend part or all their life cycle inside their hosts, and/or reproduce asexually (e.g., parthenogenetic insects), all of which are thought to facilitate HAD. However, sexually reproducing polyphagous insects can also exhibit HAD. Few sexually reproducing insects have been tested for HAD, and when they have insects from only a handful of potential host-plant populations have been tested, making it difficult to predict how common HAD is when one considers the entire species' host range. This question is particularly relevant when considering insect pests, as host-associated populations may differ in traits relevant to their control. Here, we tested for HAD in a cotton (Gossypium hirsutum) pest, the cotton fleahopper (CFH) (Pseudatomoscelis seriatus), a sexually reproducing, highly polyphagous hemipteran insect. A previous study detected one incidence of HAD among three of its host plants. We used Amplified fragment length polymorphism (AFLP) markers to assess HAD in CFH collected from an expanded array of 13 host-plant species belonging to seven families. Overall, four genetically distinct populations were found. One genetically distinct genotype was exclusively associated with one of the host-plant species while the other three were observed across more than one host-plant species. The relatively low degree of HAD in CFH compared to the pea aphid, another hemipteran insect, stresses the likely importance of sexual recombination as a factor increasing the likelihood of HAD.

Spatial and temporal variation in fungal endophyte communities isolated from cultivated cotton (Gossypium hirsutum).

Studies of fungi in upland cotton (Gossypium hirsutum) cultivated in the United States have largely focused on monitoring and controlling plant pathogens. Given increasing interest in asymptomatic fungal endophytes as potential biological control agents, surveys are needed to better characterize their diversity, distribution patterns and possible applications in integrated pest management. We sampled multiple varieties of cotton in Texas, USA and tested for temporal and spatial variation in fungal endophyte diversity and community composition, as well as for differences associated with organic and conventional farming practices. Fungal isolates were identified by morphological and DNA identification methods. We found members of the genera Alternaria, Colletotrichum and Phomopsis, previously isolated as endophytes from other plant species. Other recovered species such as Drechslerella dactyloides (formerly Arthrobotrys dactyloides) and Exserohilum rostratum have not, to our knowledge, been previously reported as endophytes in cotton. We also isolated many latent pathogens, but some species such as Alternaria tennuissima, Epicoccum nigrum, Acremonium alternatum, Cladosporium cladosporioides, Chaetomium globosum and Paecilomyces sp., are known to be antagonists against plant pathogens, insects and nematode pests. We found no differences in endophyte species richness or diversity among different cotton varieties, but did detect differences over time and in different plant tissues. No consistent patterns of community similarity associated with variety, region, farming practice, time of the season or tissue type were observed regardless of the ecological community similarity measurements used. Results indicated that local fungal endophyte communities may be affected by both time of the year and plant tissue, but the specific community composition varies across sites. In addition to providing insights into fungal endophyte community structure, our survey provides candidates for further evaluation as potential management tools against a variety of pests and diseases when present as endophytes in cotton and other plants.