NATURAL SELECTION 



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tive radiation is seen on the grandest scale 

 among insects, and among the insects the 

 beetles (Coleoptera) are the best example. 

 The two most obvious general characters 

 distinguishing the beetles— the largest order 

 of organisms in number of famihes, genera, 

 and species— are complete metamorphosis 

 and the thickened tough elytra. The mode 

 of metamorphosis is associated with a high 

 degree and variety of caenogenetic adapta- 

 tions, while the adaptive significance of the 

 elytra includes relative protection from 

 predatory attack and from environmental 

 physical extremes. Some of the specialized 

 adjustments resulting from radiate evolu- 

 tion in the beetles are listed here. 



Specialized Adaptations of Beetles 



Hypermetamorphosis with several larval tvpes 



{Epicauta viarginata) 

 Neoteny (Phengodes plumosa) 

 Sexual dimorphism (Liicantis elephas) 

 Male clasping organs ( Dytisciis fasciventris ) 

 Luminescent organs (Photinus scintillans) 

 Family integration ( Popilius disjunctus = Pas- 



sahis cornutus) 

 Stridulation (Popilius disjunctus) 

 Rapid flight ( Cicindela repanda ) 

 Swimming (Dytiscus marginalis) 

 Surface swimming (Dineutes americanus) 

 Water skating by secretion lowering surface 



tension at rear (Stenus croceatus) 

 Rapid running {Cicindela dorsalis) 

 Jumping (Haltica chalybea) 

 Fossorial legs (Clivina dentipes) 

 Flattened shape under submerged stones ( Pse- 



phenus herricki larva) 

 Flattened shape under bark (Hololepta fos- 



sularis; Denroides bicolor larva) 

 Divided eye with upward and downward vision 



(Gyrinus ventralis) 

 Eyeless cave beetle (Pseudanophthalmus 



eremita ) 

 Aquatic air storage under elytra (Dytiscus 



fasciventris ) 

 Diurnal activity (Cicindela lepida) 

 Nocturnal activity (Tetracha virginica) 

 Defensive ejection ( Brachinus fumans ) 

 Defense by thoracic snapping (Alaus oculatus) 

 Hole-plugging phragmotic head (Cicindela 



larva) 

 Death feigning (Boletotherus cornutus) 

 Case bearing (Chlamys plicata larva) 

 Concealing coloration (Goes tigrina; Fig. 244) 

 Warning coloration (Thonalmus suavis) 

 Mimicry (Calocosmus venustus) 

 Caterpillar eating (Calosoma scrutator) 

 Snail eating (Cychrus andrewsii) 

 Aphid eating (Coccinella 9-notata) 

 Scale-insect eating (Smilia misella) 



External parasitism (Platypsylla castoris; Am- 

 blyopinus schmidti) 



Termitophilous symphile with glandular ap- 

 pendages (Spirachtha mirabilis; Fig. 259). 



Myrmecophilous synechthran escaping by 

 agility (Tachyura incurva) 



Myrmecophilous synechthran with defensive 

 ejection ( Megastilicus formicarius ) 



Fig. 244. Cerambycid beetle {Goes ligiina), 

 illustrating concealing (cryptic) coloration on 

 the bark of a white oak, Falls Church, Virginia. 

 (Courtesy of Bureau of Entomology and 

 Plant Quarantine, U. S. Department of Agri- 

 culture. ) 



Myrmecophilous synoekete (Batrisodes glo- 



bosus ) 

 Myrmecophilous symphile with trichomes 



(Adranes lecontei) 

 Carrion eating (Nicrophorus americanus) 

 Dung rolling (Ateuchus sacer) 

 Eating dried insects (Antlirenus museorwn) 

 Hair and feather eating (Antlirenus scrophu- 



lariae ) 

 Leaf eating (Leptinotarsa decemlineata) 

 Leaf mining (Chalepus dorsalis larva) 

 Pith boring (Languria mozardi) 

 Boring in decayed wood (Alaus oculatus larva) 

 Boring in solid wood (Physocnemtim brevi- 



lineum ) 

 Seed boring (Bruchus pisorum) 

 Seed and flour eating (Tribnlitim confusum) 

 Acorn boring (Balaninus nasictis) 

 Pollen and nectar eating ( Chauliognathus penn- 



sylvanicus ) 

 Sap eating (Ips quadriguttatus) 

 Fungus eating (Megalodacne heros) 

 Living and eating in pores of fungi (Cylin- 



drosella dampji) 

 Fungus cultivation (Ips calligraphus) 



Several of these adaptations may be 

 present in the same insect, and some of the 

 adaptations may be characteristic of higher 



