Dynamics of local expansion by an introduced species: Pterostichus melanarius Ill. (Coleoptera, Carabidae) in Alberta, Canada

A recently established population of Pterostichus melanarius Ill., a wing-dimorphic, introduced carabid beetle species, was studied over a 7-year period in Alberta, Canada. We monitored local colonization, and tested classical hypotheses about spatial and temporal changes in proportion of flight-wing morphs in the Carabidae. Between 1991 and 1997, a sizable population in a road verge (0.17 individuals/trap/day in 1991) expanded only slowly into an adjacent aspen-poplar forest: the catch of 0.005 ind./trap/day in the forest in 1997 was not significantly higher than that of 0.001 ind./trap/day in 1991. However, a significantly higher proportion of P. melanarius were macropterous, long-winged (LW) in the forest (80%) than in the road verge and at the forest edge (54%). This supports the hypothesis that newly established populations are characterized by a high proportion of LW individuals, and further indicates that dispersal from the road verge into the forest has taken place primarily through flight. The overall proportion of flightless, brachypterous individuals (SW) captured at the study site increased from 39% in 1991 and 1992 to 57% in 1997, supporting the hypothesis that the proportion of SW individuals will increase with time since establishment of a population. Captures of P. melanarius in the forest were patchy and concentrated in particular areas throughout the study. However, these bridgehead’ populations did not grow or expand obviously, suggesting that populations adapt to forest conditions or reach some threshold size before effective expansion.     

A simple method for the inactivation of St. Louis encephalitis virus preparations for immunofluorescent microscopy.

A study was made of different treatments for the inactivation of St. Louis encephalitis virus in smears prepared for immunofluorescence microscopy. Treatment of infected cells with 0.3% betapropiolactone at 56 degrees C for 40 min resulted in an inactivated virus suitable for immunofluorescence studies.     

Influence of gut parasites on growth performance in the water strider Gerris buenoi (Hemiptera: Gerridae)

Water striders harbor a diverse assemblage of symbionts in their digestive tract We used a field experiment, in which water striders were reared in enclosures in their natural pond habitat, to assess the effects of gut symbionts on growth Trypanosomatid flagellates had significant adverse effects on both development time and adult size, and therefore are clearly parasitic Yet because of their low prevalences (2% or less), trypanosomatids cannot be a major factor in the dynamics of our study population Gregannes occurred in 36% of the water striders, often in high numbers, and filling the entire midgut of some bugs Nevertheless, infected and uninfected gerrids did not differ in their growth, and gregarine loads were uncorrelated with development time and adult size attained We also did not find effects of gregarines in a second experiment with different rearing conditions, including a treatment with food stress We used a quantitative genetic approach to test if resistance against gregarines has a heritable component There was no evidence for any genetic variation, suggesting that variability in gregarine loads is the result of environmental heterogeneity Comparison with published reports from water striders shows that there is a great variability in the diversity and prevalence of symbionts among different populations and species, of gerrids