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Title: Morphological and genetic analysis of four color morphs of bean leaf beetle, Cerotoma trifurcata (Coleoptera: Chrysomelidae)

Author
item TIROESELE, BAMPHITLHI - Botswana College Of Agriculture
item Skoda, Steven
item HUNT, THOMAS - University Of Nebraska
item LEE, DONALD - University Of Nebraska
item MOLINA-OCHOA, JAIME - Universidad De Colima
item FOSTER, JOHN - University Of Nebraska

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2018
Publication Date: 3/30/2018
Citation: Tiroesele, B., Skoda, S.R., Hunt, T.E., Lee, D.J., Molina-Ochoa, J., Foster, J.E. 2018. Morphological and genetic analysis of four color morphs of bean leaf beetle, Cerotoma trifurcata (Coleoptera: Chrysomelidae). Journal of Insect Science. 18:2.

Interpretive Summary: Bean leaf beetle is a common pest in the Midwest United States causing both direct and indirect damage on soybeans and other crops. Adult bean leaf beetles exhibit a wide range of color variation; often these are called color forms. It is unknown if bean leaf beetle color forms mate freely or if they are evolving to be different: if they are evolving it could mean that control measures will need to be different for each color form. To begin to determine if the color forms are becoming different we measured and compared several characteristics of adults (for example, dry weight, head width, leg length, etc.) of four color forms of the bean leaf beetle. We also used genetic analysis to compare the color forms. There were no significant differences either in measured characteristics or genetics of the bean leaf beetle color forms. We concluded that the color forms interbreed as one species. This indicates that, when necessary, control tactics should be equally effective regardless of which color form(s) of bean leaf beetle is present.

Technical Abstract: Bean leaf beetle (BLB) exhibits a relatively large amount of morphological variation in terms of color but little is known about the underlying genetic structure and gene flow. Genetic variation among four color phenotypes of the BLB was analyzed using amplified fragment length polymorphisms (AFLP) and morphometrics. The 175 loci observed with AFLP showed 80% or greater polymorphism. Genetic variation was greatest within color forms (88.5%) and gene flow was relatively high (Nm = 3.82). The pattern of genetic variation was similar to that observed for the majority of the morphological traits examined. This similarity suggests that the four different color morphs are not genetically or reproductively distinct from each other. Morphologically, only the red with no spots BLB showed differences in weight and body-length. All other morphological parameters were similar for the characters investigated. Canonical analysis, based on average morphometric characters, revealed that canonical variable 1 and 2 accounted for 98% of the total variation and distinctly grouped and separated two of the BLB color forms. Although it can be concluded that this is a single, interbreeding BLB population, there is variation in color and other morphological characters.