Defensive Adaptations and Natural Enemies of a Case-Bearing Beetle, Exema canadensis (Coleoptera: Chrysomelidae)
The larval habit of constructing and carrying a portable case has evolved many times in the Holometabola. It is a widespread trait of the Trichoptera and Lepidoptera (e.g. the Coleophoridae and Psychidae). Among the Coleoptera, casebearing is found in four related subfamilies of the Chrysomelidae, the so-called camptosomates: Clytrinae, Cryptocephalinae, Chlamisinae, and Lamprosomatinae (B6ving and Craighead 1931). The larval case of many insects is thought to function primarily in defense by providing armor or camouflage (Otto and Svensson 1980). Here we describe the uses of the case and other defenses in a chlamisine beetle, Exerna canadensis Pierce, and speculate briefly on the evolution and consequences of the case-bearing habit.
The genus Exema Lacordaire contains nine species in North America (Karren 1966). All of the species appear to be univoltine and to feed on a fairly restricted range of herbaceous or shrubby genera in the Asteraceae (Jenks 1940; Karren 1966, 1972). In central New York E. canadensis is commonly found on goldenrods (Sol# dago spp.) and asters (Aster spp.). Its life cycle was summarized by Messina and Root (1980). Le Sage (1982) recently described the immature stages.
Root, R.B. & F.J. Messina. 1983. Defensive adaptations and natural enemies of a case-bearing beetle, Exema canadensis (Coleoptera: Chrysomelidae). Psyche 90: 67-80.