Morphometry of Lygus bugs: Implications in pest management
Texas Agricultural Experiment Station, 1102 East FM 1294, Lubbock, TX 79403
Correspondence: m-parajulee@tamu.edu
The genus Lygus (Hemiptera: Miridae) consists of 43 described species worldwide. Since there is no published information on the molecular phylogenetic and biological species determination for Lygus, the most common way of species determination is based on a phenotypic species concept using taxonomic keys. Other species concepts are difficult and not practicable in field level species identification; therefore phenotypic species identification is the common practice and will remain popular in the future. Taxonomic keys that have been developed use very few phenotypic characters of Lygus and some characters are largely qualitative and very difficult to quantify. Thus, special taxonomic skills in related taxa are necessary for better identification at the species level. Moreover, taxonomic keys cannot be used to identify cryptic species or hybridization between species. Due to difficulty in species identification and occurrence of multiple species of Lygus in most ecosystems, many scientists had combined all species and reported them as a “Lygus complex.” Because there exists a considerable variation among species in terms of their population dynamics, damage potential, host preference, and insecticide resistance, lack of proper species identification limits the ability to develop more effective Lygus pest management strategies. A comprehensive morphometric phylogenetic study at the Lygus species level is a reasonable solution for this problem until we can develop molecular phylogenetic techniques for this genus. Morphometric studies were conducted on Lygus species collected from alfalfa fields in the Texas High Plains region. Morphometric measurements of various body parts located on the dorsal side of adult Lygus were taken using digital image analysis while the computations were performed using MATLAB functions. Various geometric parameters including surface area, length, shape, roundness, and convexity of six body parts were measured and analyzed using PCA, one-way ANOVA and stepwise discriminate analysis. The detail protocol of morphometry using digital image analysis and comparison between traditional morphometry and landmark based morphometry will be discussed. Clavus convex hull perimeter, dorsal body length, clavus area, dorsal body perimeter, and clavus length were the most informative characters among the 36 measured variables showing higher loading values for the major principal components. These characters were similar in both male and female specimens. Morphometric comparison between Lygus hesperus and Lygus lineolaris was done by using digital image analysis of 12 morphometric characters. The Lygus hesperus specimens had significantly larger pronotum, longer rostrum and longer second antennal segment as compared with that of Lygus lineolaris.