COMMUNITY ORGANIZATION: STRA.TIFICATION 



491 



Diptera; at least four families in Lepi- 

 doptera; and many Tenthredinidae in 

 Hymenoptera. 



All four orders have larvae that converge 

 in form and general behavior (Fig. 164). 

 They are conspicuously flattened and have 

 reduced legs. Some mine leaves of a single 



Fig. 164. Convergence in form of three 

 types of leaf -mining larvae: (1) Hylemyia 

 (Diptera); (2) Metallus rubi (Hymenoptera); 



(3) external feeding sawfly (Hymenoptera); 



(4) external feeding caterpillar; and (5) leaf- 

 mining caterpillar ( Lepidoptera ) , illustrating 

 reduction of the thoracic legs and abdominal 

 prolegs and horizontal position of head in con- 

 trast to 4. (After Frost; in part original.) 



plant species. Others tunnel leaves of 

 species of plants in the same genus, and still 

 others feed upon groups of related plant 

 genera within a family. Some feed upon 

 many plants of unrelated genera. Obviously, 

 the majority of leaf miner larvae are strati- 

 fied in the forest. 



Leaf miners can be found for each epi- 

 patomic layer. Thus in Agromyzidae, 

 Agromyza borealis mines the leaves of the 

 jewelweed (Impatiens) of the herbaceous 



stratum, Agromyza melampyga in various 

 hlacs, Agromyza aristata in elm. A volume 

 has been written on the leaf miners alone 

 (Frost, 1923; Needham, Frost, and Tothill, 

 1928). Then there are the leaf-rolHng 

 insects (seventeen families of Lepidop- 

 tera); gaU-forming insects, mites, and 

 nematodes. Felt (1917, 1940) Hsted 1440 

 North American species of gall makers: 162 

 Eriophyidae (mites), twelve Coleoptera, 

 seventeen Lepidoptera, sixty Homoptera, 

 701 Diptera, and 488 Hymenoptera. 



Gall insects attack mainly epipatomic 

 strata; they attack all parts of plants (buds, 

 leaves, petioles, flowers, twigs, branches, 

 trunk bark, even roots in the subterranean 

 stratum); over half of the plant famihes 

 are attacked. Wasps of the family Cynipi- 

 dae attack species of Quercus almost en- 

 tirely (Kinsey, 1929). Felt found 500,000 

 cynipid wasps attacking a single oak tree. 



Then there are the boring insects. These 

 have a convergent larval form, usually cy- 

 lindrical (in some groups where the larvae 

 bore close to the exterior, the form is flat- 

 tened), legless, reduced antennae, head 

 capsule telescoped into the thorax, strong 

 wood-cutting mandibles. Borers are con- 

 veniently separated into two groups (Frost, 

 1942) : those species with larvae feeding 

 on living tissue, and those feeding on de- 

 caying or dead tissue. The latter group 

 overlaps with the floor stratum, including 

 many species boring in prostrate logs and 

 dead standing trees. The former group in- 

 cludes species that bore in buds, exca- 

 vate the cambium, or fruit, or stem, and 

 even the roots in the subterranean stratum. 



Wood-borers are well developed in Cole- 

 optera. Here are numerous species of 

 Buprestidae, Cerambycidae, Elateridae, 

 Brentidae, Curculionidae, and the bark 

 beetles or Scolytidae, to mention a few of 

 the many famihes with wood-boring larvae 

 or adults. 



Nor must we omit mention of the myr- 

 iads of insects which suck the leaf sap or 

 are bark feeders (Aphidoidea, Coccidoi- 

 dea), or those which eat the leaves by cut- 

 ting out portions (many Scarabaeidae, such 

 as adult Serica, Phyllophaga) . 



Forest communities, with their well- 

 developed epipatomic vegetational strata, 

 have numerous herbivores that are species- 

 specific, in a part of their hfe cycle at least, 

 and are stratal indices. Lengthy tables 



