Graduate Thesis Or Dissertation
 

A revision of the black grass bug genus Irbisia Reuter (Heteroptera:Miridae)

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  • The black grass bug genus Irbisia Reuter was revised. Over 18,000 specimens were examined and information concerning the biology, host plant and distributional relationships of the species was compiled. In addition to external characters, the male claspers and vesica, and the female dorsal libiate plate of the bursa copulatrix and sclerotized rings were used to distinguish the species. Sixty-nine characters selected from male and female genitalia, and external morphology were cladistically analyzed. Thirty-two characters are intracorrelated, defining four species groups. Twenty-three species are recognized in the genus. Two keys to the species are presented. One new species, Irbisia knighti is described. The following synonymies are proposed: I. brachycera (Uhler) = I. gorgoniensis Bliven, I. paeta Van Duzee, I. tejonica Bliven, I. vestifera Bliven; I. californica Van Duzee = I. eurekae Bliven, I. paenulata Bliven; I. elongata Knight = I. retrusa Bliven; I. setosa Van Duzee = I. ustricula Bliven; I. solani (Heidemann) = I. lacertosa Bliven. Irbisia species diversity is greatest in the Coastal, Peninsular, Sierra and Transverse Ranges of California and decreases northward, northeastward and eastward. Major centers of endemism are located in California and the Rocky Mountains northwest of the Wyoming Basin; a minor center is located in the Siskiyou Mountains of southwestern Oregon. Faunal similarity analysis suggests that the present Irbisia fauna is derived from two source areas - one Californian, and one in the Rocky Mountains. The present distribution of I. sericans (StS1) may be derived from Beringian refugia. The distribution of the Irbisia species appears to be delineated by climatic conditions; late winter and early spring precipitation is required for growth of their cool season grass hosts. Over twenty native and introduced species of grasses are utilized by larval and adult stages of Irbisia in Oregon. Larval feeding was observed on four species of nongrass monocots, and species of Lupinus and Lathyrus (Fabaceae). There appears to be no grass host specificity among the Irbisia species. However, all the grass species utilized are in the subfamily Pooideae; genera from the Avenae, Poeae and Triticeae predominate. The Irbisia species are the earliest mirid to consume the grass resource, completing their life cycle before grass seed is mature. Many Irbisia species, upon maturity, leave grasses and congregate on conspicuous nearby shrubs and trees. Their dispersal is correlated with the blossoming of these plants; adult feeding on pollen, nectar or honeydew is suspected.
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