The biological control program for diffuse knapweed, Centaurea diffusa Lamarck, a Eurasian plant that has invaded large areas of grasslands in western North America, has gone on for over 35 years. This program involved the release of 12 biological control agents of which four are numerous and widely distributed; two species of Tephritid flies, Urophora affinis and Urophora quadrifasciata, the r...

Janzen-Connell effects are negative effects on the survival of a plant's progeny at high conspecific densities or close to its conspecifics. Although the role of Janzen-Connell effects on the maintenance of plant diversity was frequently studied, only few studies targeted Janzen-Connell effects via postdispersal seed predation in temperate grassland systems. We examined effects of conspecific d...

PREMISE OF THE STUDY Biotic resistance is often studied in the context of how interactions between native biota and invading species influence the success of those invaders. Seldom, however, is the strength of "resistance" compared biogeographically, where the ability of a species to impede invader establishment is contrasted between an invader's native and introduced recipient community. MET...

Larvae of two closely related species Cassida palaestina Reiche, 1858 and Cassida rubiginosa Müller, 1776 are described in detail including SEM microstructures. First instars are extremely similar with no clear diagnostic characters, larvae of Cassida palaestina are slightly more contrastingly coloured than larvae of C. rubiginosa, the latter having darker scoli, basal part of supra-anal proces...

Biological control of exotic invasive plants using exotic insects is practiced under the assumption that biological control agents are safe if they do not directly attack non-target species. We tested this assumption by evaluating the potential for two host-specific biological control agents (Urophora spp.), widely established in North America for spotted knapweed (Centaurea maculosa) control, ...

The influence of temperature, shoot age, and medium on gall induction by Subanguina picridis on Russian knapweed (Acroptilon repens) was examined in vitro. The optimal temperature for gall formation was 20 C. Gall induction was delayed as the temperature decreased, and decreased as shoot age increased. Bud primordia (0-day-old shoots and 5-day-old shoots) with an average length of 4.2 mm and 7....