Comparative Biology of the Goldenrod Leaf Beetles, Trirhabda virgata LeConte and T. borealis Blake (Coleoptera: Chrysomelidae)

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Coleopterists Bulletin



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Life histories are presented for Trirhabda virgata and T. borealis, two closely related leaf beetles that co-occur on goldenrod (Solidago spp.) in central New York. Eggs and larvae of the two species were indistinguishable, although T. virgata larvae were significantly larger. Life cycles were similar except for a slight difference in phenology; all stages of T. borealis appeared 1 to 2 weeks earlier in the season than those of T. virgata. Females of T. virgata possess more ovarioles/ovary and laid more eggs/cluster than T. borealis females. Invertebrate natural enemies of Trirhabda included 18 species in 10 families; most common were the host-specific tachinid, Aplomyiopsis xylota (Curran), the generalist coccinellid, Hippodamia glacialis (F.), and the nabid, Nabicula subcoleoptrata (Kirby). Trirhabda distribution and abundance in central New York were determined by surveying 23 old field sites. Mean beetle density was 7.6 ± 1.4 individuals/sweep. Trirhabda virgata, present in all sites, was the dominant species, typically accounting for 90% of the beetles collected per field. Densities of the two species varied independently among sites. Spatial autocorrelation analysis did not detect any geographic pattern associated with either species' abundance. Possible explanations for the relative rarity of T. borealis are proposed.

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