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By means of an integrative taxonomic approach using morphology and DNA barcodes, multiple cryptic species within Lasioglossum (Dialictus) petrellum (Cockerell) (Hymenoptera: Halictidae) were discovered. Analysis of DNA barcode sequence data from across the supposed range of L. petrellum revealed distinct genetic differences that correlate with patterns of morphological variation and geographical distribution. The most morphologically distinct pair of species had the smallest DNA-barcode gap. The taxonomic limits of L. petrellum are revised and four new species are described and illustrated: L. (D.) tuolumnensesp. nov., L. (D.) griswoldisp. nov., L. (D.) droegeisp. nov., and L. (D.) viridipetrellumsp. nov. A key to species of the “L. petrellum” group is provided.
The first record of a European blackberry leaf gall midge, Dasineura plicatrix (Loew), is confirmed from North America. Specimens were reared from damaged leaves of blackberry, Rubus laciniatus Willd. (thornless variety ‘Chester’), and red raspberry, R. idaeus L. (variety ‘Cascade Delight’) (Rosaceae), in southwestern British Columbia. Photographs of the damage and illustrations of the male terminalia and female ovipositor are presented to assist future determinations.
Fecundity and biomass of nine species of aphids (Hemiptera: Aphididae) feeding on six species of plants were compared to assess whether the two measures are equally effective for quantifying aphid performance. Performance was quantified by measuring both fecundity (the number of offspring born over a defined interval) and biomass (the dry mass of offspring produced) using three variables expected to affect performance: host-plant genotype, aphid genotype, and aphid density. The efficacy of the performance parameters was assessed by comparing their ability to discriminate among treatments for the three variables. Biomass usually provided a more effective measure of performance than fecundity, but for one aphid species, fecundity was more effective than biomass. Biomass of offspring is the preferred measure of performance, but biomass and fecundity should both be recorded whenever practical.
Larvae of the gall-inducing moth Gnorimoschema gallaesolidaginis (Riley) (Lepidoptera: Gelechiidae) attack ramets of Solidago altissima L. and S. gigantea Aiton (Asteraceae), initiating stem galls early in ramet growth. We examined the relationship between ramet size (as an indicator of plant vigour) and galling rate over 3 years at a field site in Toronto, Ontario, Canada. We marked Solidago ramets along line transects, measured their stem diameter, and recorded their fate (galled or ungalled) during the season. For S. altissima, galls were numerous enough for analysis in 2 years, and the frequency of galling increased monotonically with ramet stem diameter in both years. For S. gigantea, galls were numerous enough for analysis in all 3 years, but attack rate - stem diameter relationships were complex. In 2004 the galling frequency peaked at intermediate stem diameter, but in 2005 the galling frequency increased monotonically with stem diameter (and in 2006 the nonsignificant trend was similar). Overall, our data are most consistent with the plant-vigour hypothesis, but the 2004 data for S. gigantea lend some support to the suggestion that herbivore attack might sometimes be most intense on intermediate-sized modules.
Grasshoppers (Orthoptera: Acrididae) are hosts to many internal parasites, including nematodes. However, the effects of nematode parasitism on grasshopper fecundity and how these effects vary with population density are unclear. I report on the fecundity of Melanoplus dawsoni (Scudder) infected and uninfected with mermithid nematodes in northern Wisconsin from 2002 to 2005. Each year grasshoppers were stocked over a range of five densities into field enclosures. Fecundity, body size, and nematode prevalence were measured for female grasshoppers. Nematode prevalence was moderately high, ranging from 15% in 2003 to 37% in 2004. Fecundity was measured by examining grasshopper reproductive tracts. On average, past reproductive activity (number of eggs laid) and current reproductive activity (number of eggs forming) of parasitized grasshoppers were reduced by 40% and 48%, respectively. Interestingly, the reduction in fecundity was less for parasitized females in the low-density treatments (25%–50% of field density) than for those in the moderate- and high-density treatments, suggesting that grasshoppers can compensate somewhat for negative effects of parasites on fecundity when per-capita resources are high. No difference in hind-femur length between parasitized and unparasitized females was observed, indicating that nematode infection did not affect grasshopper body size.
A simple and inexpensive non-destructive trap to catch insects as they ascend tree boles is described. The trap was tested in a capture—mark—recapture experiment on the Warren root collar weevil, Hylobius warreni Wood. A high percentage (77%) of marked H. warreni were recaptured at least once during a 12-day period and 54% were recaptured more than once, with one weevil recaptured eight times.