Cassida rubiginosa Muller 1776

Cassida rubiginosa Müller, 1776 Identification. Live adults of C. rubiginosa are vivid green on dorsal surface, often with yellowish elytral margins, and are black underneath. This green pigment is ephemeral, and dried specimens preserved in collections quickly turn brownish. Its medium size (6-8 mm), confused elytral punctures, and the vivid light green color make adults recognizable immediately, even by non-experts (Fig. 1). The first instar larva was described and illustrated by Świçtojańska (2004). Egg bursters are absent (Cox 1994a). The mature larva was described by Paterson (1931, sub Cassida viridis) and illustrated by Peterson (1951). It can be identified using the key to species of the British cassidine larvae (Van Emden 1962). Descriptions and illustrations of the pupa of C. rubiginosa, are found in Paterson (1931) (sub C. viridis) and Palij & Klepikova (1957). A key, including C. rubiginosa, is provided by Palij & Klepikova (1957). History and distribution. Cassida rubiginosa was first discovered in North America in 1902 in Lévis, near Québec City, where beetles were observed to be defoliating burdock (Arctium minus (Hill.) Bernh., Asteraceae) (Fyles 1902, 1903; Roy 1902). Schaeffer (1903, 1904a, 1904b) contributed to clarify its identity. It was subsequently reported by Brown (1940) on burdock, in Montréal, at Knowlton and Brome in the Eastern Townships of Québec, and in Shediac, New Brunswick. The species is now widely established both across Canada from Alberta east to New Brunswick, and in the United States from Maine south to Virginia and west through Ohio to Wisconsin and South Dakota (Riley et al. 2003). In the Old World, it is found throughout continental Europe (not yet recorded in the Netherlands) from Fennoscandia south through the Baltic republics to Greece and Spain, in Great Britain, and across Siberia to the northern Far East of Russia (Audisio 2005b). Biology. Cassida rubiginosa has been well studied in Europe by Kleine (1917a) and Kosior (1975). In Eastern Canada, C. rubiginosa is found in habitats where Canada thistle and burdocks grow, such as agriculture lands, pastures, abandoned fields, sparsely wooded meadows, neglected orchards, clear cut areas, or similar open and/or disturbed habitats. The species is univoltine in Ontario and Québec (LeSage, personal observations), in Virginia (Ward & Pienkowski 1978a), and very likely so in the Maritime Provinces. Hibernation is in the adult stage. In Poland, Kosior (1975) observed a migration of adults from thistles to forest floor litter in the fall. In Virginia, Spring & Kok (1999) found that leaf litter was the preferred hibernaculum of field caged adults, and inability to access preferred hibernating locations combined with fluctuating winter temperatures may result in the survival of less that one in four beetles. Adults leave their winter shelters in early spring. The earliest specimens in the Canadian National Collection (CNC) were collected on April 2 in southern Ontario and on May 15 in the Ottawa area. The earliest adults collected in the Maritime Provinces are from May 31 (Kentville, Nova Scotia). Females began to oviposit between mid-March and April in Virginia (Ward & Pienkowski 1978a). In Europe, Kosior (1975) stated that oviposition started 3-7 days after mating according to temperature, day length, rain, and wind. Eggs are usually laid on the underside of the leaves, more rarely on the upper surface, and sporadically on the stem. Ward & Pienkowski (1978a) referring to the midrib, observed that 74% of the oöthecae were deposited on the abaxial surface, and 18% on the adaxial surface. The number of eggs in oöthecae is variable but is usually three, although oöthecae with only one egg are not rare (Kosior 1975). In Virginia, Ward & Pienkowski (1978a) found an average of 4.6 eggs per oötheca, and Spring & Kok (1997) found an average of 61.1 oöthecae laid per individual female over a 15-week period. In Maryland, Tipping (1993) observed that many oöthecae were laid on leaves closest to the soil. In laboratory rearing, the fecundity averaged 815 eggs per female; eggs hatched in two weeks at 18°C, in four days above 32°C (Ward & Pienkowski 1978a). The egg-laying period lasted 12 weeks (Kosior 1975). The eggs are usually laid on the lower surface of the leaves. Each egg is enclosed in secretion which turns from whitish to brown in about ten minutes, and finally, the oötheca is closed with a layer of excreta (Engel 1935; Bibolini 1973). Excremental coverings are thought to conceal eggs or act as physical or chemical barriers to repel natural enemies (Muir & Sharp 1904; Damman & Cappucino 1991; Olmstead 1996). Egg deposition, coverings, and oviposition were reviewed by Hilker (1994), Olmstead (1994), and Selman (1994). Damman & Cappucino (1991), who studied this form of double defense (egg clumping and excrement cover) in the hispine Microrhopala vittata (Fabricius), found that the fecal covering significantly reduced egg mortality. Since the parasites generally attacked the bottom egg, and while the predators rarely penetrated the fecal covering, egg masses were virtually protected against all natural enemies likely to pose a threat. Such a protection can be expected in Cassida rubiginosa which also lays small oöthecae of a few eggs (Kosior 1975; Ward & Pienkowski 1978a). There are five larval instars in C. rubiginosa, each one easy to recognize by its exuviae attached to the caudal fork together with excrement. In addition to the shield and fork, the larvae possess lateral spines, or scoli, that are used as sensory organs, and when they are stimulated the shield is moved to cover the body (Olmstead 1996). This distinctive structure, made of dried exuviae and accumulated fecal wastes, attracted the attention of early naturalists (ex. Réaumur 1737)."Stercoraceous parasol" (Walsh & Riley 1869), "faeces pack" (Rabaud 1915b), and "frass mask" (Engel 1935), were used to described this structure but the term "fecal shield" popularized by Eisner et al. (1967) is now in use. The smallest exuviae (first instar) is attached at the extremity of the fork, the largest at base, each sliding on the branches of the new fork after each molt (Rabaud 1915b). As the larvae feed again, the newly produced faeces accumulate behind the previous ones. Consequently, the fecal shield grows and moves forward at each molt with the result that before pupation, this pack contains the whole series of exuviae and all the faeces produced by the larvae during their life (Rabaud 1915b). The shield is also highly maneuverable and can be moved to cover areas of the body that are stimulated (Olmstead 1994). The anus is extrudable. Consequently, it can be projected and curved over the back and, through the aid of the fork and of some of the lateral spines, it forms the protective fecal shield (Walsh & Riley 1869). The role of the shield has been the subject of several hypotheses. According to Frisch (1720), cited by Engel (1935), the fecal shield protects the body from rain and pests, while for Huber (1846) and others, it is a protective shelter from insolation, but this assumption was recently rejected (Bacher & Luder 2005). Larvae covered with their fecal shield are similar to droppings which may confuse large predators like birds, but not insect predators. For Eisner et al. (1967), ants are undoubtedly among its chief natural enemies. They were always seen foraging in large numbers in the dense herbage that included the beetle's host plants. Confronted with the inanimate shield rather than with the body of the larvae, they were quick to lose interest in such potential prey. Larvae deprived of their shield were bitten and killed, or carried away live into ant nests. On the other hand, these authors noted that the shield did not protect larvae from all predators. For instance, tests with a lycosid spider invariably resulted in the larvae being killed, an observation already made by Engel (1935) with the larvae of Cassida viridis Linnaeus. Engel (1935) also stated that the violent movements of the larvae when disturbed actually constitute a protection insofar as they chase away enemies. According to Franz (1941), the shield can protect against parasites although its effectiveness is not absolute. Eisner et al. (1967) argued that the fecal shield of C. rubiginosa larvae was effective in deterring ants in laboratory tests. Vencl et al. (1999) found that shields were necessary for the survival of the larvae of Plagiometriona clavata (Fabricius) and that the chemicals derived from their nightshade host plant (Solanum dulcamara L.) formed a deterrent barrier against the ant (Formica subsericea Say) attacks. They concluded that the incorporation of deterrent metabolites in shield defenses represented responses to selection from invertebrate predators. The role of these allelochemicals from host plants and other antipredator devices was reviewed by Blum (1994). Olmstead & Denno (1992) estimated that the cost of bearing fecal shields was minimal. Being made of recycled waste products, fecal shields provide an inexpensive mode of protection from certain natural enemies. Tipping (1993) noticed that smaller larvae were very susceptible to generalist predators, especially coccinellids. However, Olmstead & Denno (1993) observed that predators with short mandibles, such as coccinellids, were effectively deterred by the larval shields of cassidines whereas nabids and pentatomids with long piercing mouthparts easily circumvented the shield defense. Consequently, a particular kind of defense does not provide complete protection against generalist predators in natural habitats. Müller (2002) found that feeding by the lacewing larvae Chrysoperla carnea (Stephens, 1836) was not influenced by fecal shields, and concluded that the effectiveness of shields of tansy-feeding cassidine larvae (C. denticollis and C. stigmatica) varied with predators and might be based more on mechanical than on c

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