Jack L. Butler

Efficacy of Flea Beetle Control of Leafy Spurge in Montana and South Dakota

Abstract Black (Aphthona lacertosa and Aphthona czwalinae) and brown (Aphthona nigriscutis) flea beetles are among the more successful biological control agents used in the control and management of leafy spurge on a relatively large scale in the Northern Great Plains. The objectives of this study were to document leafy spurge population dynamics in response to control by black and brown flea beetles, determine the role of selected site characteristics on establishment and persistence of the beetles, and evaluate the general response of the resident vegetation to control of leafy spurge. In late June 1998, about 3 000 insects of each species were released into permanently marked plots in northwestern South Dakota and southeastern Montana. Beetle abundance, density and foliar cover of leafy spurge, and foliar cover of the resident vegetation were evaluated each year from 1998 through 2004. Black beetles increased rapidly and peaked at 65% of their measurable potential abundance within 2 years (P < 0.05) following release and dominated all release plots throughout the study. Although population growth characteristics of black flea beetles were highly variable, the successful patterns in reducing the dominance of leafy spurge were fairly consistent. By 2004, foliar cover of leafy spurge on both release and nonrelease plots was significantly reduced compared to prerelease values. Foliar cover of grass and grasslike plants increased concomitantly with the reduction in leafy spurge dominance while cover of forbs on release and nonrelease plots remained consistently below noninfested values.

Potential Impact of Two Aphthona spp. on a Native, Nontarget Euphorbia Species

Abstract Flea beetles (Aphthona spp.) are biological control agents introduced from Eurasia to reduce the cover and density of leafy spurge (Euphorbia esula L.). The potential for the introduced beetles to use alternate hosts for feeding and development in North America is slight; however, it is possible. Species at highest risk are native species closely related, ecologically and taxonomically, to leafy spurge. A native spurge, Euphorbia brachycera Engelm. is consubgeneric and sympatric with leafy spurge throughout the northern Great Plains of the United States, and was not included in prerelease host-specificity testing for Aphthona nigriscutis or Aphthona lacertosa. The objective of this study was to evaluate the actual and potential ecological overlap among leafy spurge, flea beetles, and E. brachycera. Wide-ranging and intensive field surveys indicate that E. brachycera is found well within the range of leafy spurge and flea beetles. E. brachycera occurs infrequently, in low densities, in areas with a high percentage of bare ground, and with a root system dissimilar to leafy spurge. Flea beetles released directly into populations of E. brachycera failed to persist beyond a single field season and plants showed no evidence of feeding by beetles. Our results suggest that the potential for flea beetles to host-shift is low due to differences in growth habit and root morphology between E. brachycera and leafy spurge.

Secondary invasion re-redefined: The distinction between invader-facilitated and invader-contingent invasions as subclasses of secondary invasion

Linked Article: https://doi.org/10.1002/ece3.3964

Greater bud outgrowth of Bromus inermis than Pascopyrum smithii under multiple environmental conditions

Tiller recruitment of perennial grasses in mixed-grass prairie primarily occurs from belowground buds. Environmental conditions, such as temperature, soil moisture and grazing can affect bud outgrowth of both invasive and native perennial grasses. Differential bud outgrowth responses of native and invasive species to climate change and grazing could alter competitive interactions that have implications for future land management. The aims of this work were to (i) compare how spring temperature altered bud outgrowth of native Pascopyrum smithii (Rydb.) A. Love (western wheatgrass) and introduced Bromus inermis Leyss.(smooth brome), (ii) compare how watering frequency altered bud outgrowth of these two species and (iii) evaluate how clipping interacts with spring temperature or watering frequency to affect P. smithii bud outgrowth.