Mortality and Parasitism of Cassida rubiginosa 1 , a Thistle-feeding Shield Beetle Accidentally Introduced into North America 2

Stage-specific mortality, fecundity, and population changes in Cassida rubiginosa (Coleoptera: Chrysomelidae) on wild thistle

“…In this study, while generalist predators such as predatory bugs, carabids, and paper wasps were observed attacking C. rubiginosa larvae in the field, it was rarely possible to accurately identify the causes of death in these stages. In North America, 6 species of parasitoids have been identified from the larvae and pupae of C. rubiginosa (Ang and Kok 1995;Olmstead 1996;Tipping 1993;Ward and Pienkowski 1978b). Parasitoid fauna and its influence on C. rubiginosa larval mortality have not been elucidated in this study, so further investigation is required.…”

“…Eulophidae) have been reported to be parasitoids of C. rubiginosa eggs in Europe (Besuchet 1960;Girault 1914), whereas no egg parasitoids were observed in North America (Ang and Kok 1995;Tipping 1993;Ward and Pienkowski 1978b). In Europe, egg mortality could be attributed to physical factors such as temperature, wind, and rain (Kosior 1975).…”

“…However, in this study, mortality factors that affect the larval and pupal stages are largely unknown. In Europe and North America, predation by spiders (Araneae), predatory bugs (Hemiptera: Reduviidae, Pentatomidae, and Nabidae), chrysopids (Neuroptera: Chrysopidae), and coccinellid and carabid beetles (Coleoptera: Coccinellidae and Carabidae) was observed (Bacher et al 1999;Kosior 1975;Olmstead and Denno 1993;Ward and Pienkowski 1978b). In Switzerland, Schenk & Bacher (2002) estimated that the paper wasp Polistes dominulus Christ (Vespidae) was responsible for 99.4% of the predation on C. rubiginosa larvae.…”

“…Cassida rubiginosa is capable of severely damaging thistle leaves. However, previous studies have shown that the populations rarely reached sufficient density for effective thistle control in Europe and North America (Ang and Kok 1995;Bacher and Schwab 2000;Ward and Pienkowski 1978b). Understanding the demographic traits of the species, such as mortality and fecundity, is therefore critical for the augmentation of naturally occurring C. rubiginosa populations to higher densities (Bacher and Schwab 2000).…”

“…Abiotic factors such as extreme temperature, rainfall, and severe wind have been reported to be associated with declines in fecundity (Kosior 1975) and increases in the mortality of eggs, early larvae, and overwintering adults (Kosior 1975;Spring and Kok 1999). Biotic factors such as parasitism (Ang and Kok 1995;Ward and Pienkowski 1978b) and predation (Bacher et al 1999;Kosior 1975;Schenk and Bacher 2002;Ward and Pienkowski 1978b) are known to affect larval survival in the field. These multiple factors are likely to influence stage-specific mortalities and fecundity in the beetle, with different effects on the population dynamics of C. rubiginosa.…”