Biogeographical Studies

In many instances amber insects provide evidence of a more extensive distribution in the past for various insect genera and families as well as indicating a warmer climatic regime in many parts of the world. Perhaps the most spectacular examples of this phenomenon are insects discovered in amber sites located far from their descendants' current habitat. Examples from

FIGURE 5 Paleoendoparasitism in amber is exemplified by a mermithid nematode (Nematoda: Mermithidae) emerging from the body of a planthopper (Homoptera: Fulgoroidea) in Baltic amber. Such records set minimum dates for the establishment of host—parasite associations.

Dominican amber include Mastotermes termites (Isoptera: Mastotermitidae) and Leptomyrmex ants (Hymenoptera: Formicidae) that obviously were part of the insect fauna some millions of years ago in the Caribbean but occur nowhere in the New World today. Both genera are represented today by a single relict species in the North and East Australian Region.

A North American example is the presence of the tropical arboreal ants of the genus Technomyrmex in Hat Creek amber in British Columbia, Canada, living 50 mya, hundreds of kilometers north of their present-day range. These tropical ants in Eocene Hat Creek amber provide evidence that the climate in that region of the world shifted from tropical to temperate. Other examples of past distributions involve the palm bug shown in Fig. 2, which has no present-day descendants in the Dominican Republic, with only a single living Cuban species in the subfamily. Similarly, there are no members of the genus Theope in the Dominican Republic or the Greater Antilles today, all living representatives being restricted to Mexico, and Central and South America. Further evidence of climatic shifts over time are clear with many of the Baltic amber insects, many of whose descendants occur in the Old World tropics today. The primitive honey bee shown in Fig. 1 evolved under subtropical conditions that characterized most of northern Europe in the Eocene. Thus, it is not surprising that most of the species and varieties of the genus Apis live only under tropical conditions today.

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