ing aphids on plants such as roses. 



But the trophobiosis between Acro- 

 pyga and their mealybugs is a particular- 

 ly strong relationship. Acropyga's unusu- 

 al dependence is demonstrated by the 

 queens behavior on her nuptial flight. 

 A queen carries only one item in her 

 trousseau: a live mealybug clamped in 

 her mandibles. Somehow — how, exact- 

 ly, remains a mystery — that single 

 mealybug will proliferate into an entire 

 herd, ample food for the queen's new 

 colony. Perhaps mealybugs reproduce 

 from unfertilized eggs, as some insects 

 do. Perhaps the Acropyga queen makes 

 sure she carries a pregnant mealybug. Or 

 perhaps multiple queens combine forces 

 to found a nest together, thus supplying 

 more than one mealybug for the herd. 



Some evidence suggests that ants and 

 mealybugs have co-evolved; in other 

 words, evolutionary changes in one 

 might have come about because of evo- 

 lutionary changes in the other, and vice 

 versa. Each time a new Acropyga spe- 

 cies evolved, a new species of mealy- 

 bug may have evolved as well. Much 

 more research is needed, however, be- 

 fore investigators will know for sure. 



Just as observations of modern species 

 illustrate how A. glaesaria probably 

 lived, amber fossils also provide im- 

 portant details about the evolution of 

 modern Acropyga behavior. The an- 

 cient formation of Dominican amber 

 implies that trophophoresy is an an- 

 cient behavior. Look at it this way: 

 People began raising cattle for milk 

 about 6,000 years ago, but at least 15 

 million years before then, A. glaesaria 

 were already transporting their mealy- 

 bug livestock to their new nests! 



The distribution and variations 

 among living species of Acropyga lead me 

 to think that, in fact, the genus origi- 

 nated even earlier than the Miocene pe- 

 riod, perhaps as early as the Cretaceous 

 period, between 144 and 65 million 

 years ago. My research on the forms and 

 structures of ants indicates that the old- 

 est Acropyga lineages live in Africa. It I 

 am right, the genus Acropyga is probably 

 much older than A. glaesaria. Acropyga 

 species are poor dispersers, so it would 



Ant queen (A. epedana) (large, golden 

 insect), even while mating, keeps a grip on 

 the white mealybug she is carrying in her 

 mandibles on her nuptial journey. The male 

 (small, dark ant) will soon die, and the queen 

 will found a new colony. Having already shed 

 her wings, she won't be burdened by them 

 as she digs an underground nest. The mealy- 

 bug will proliferate into a herd that will 

 sustain the queen's progeny. 



be hard to explain their present distri- 

 bution in tropical areas worldwide if the 

 origin of the genus did not stretch back 

 to a time when the continents were clos- 

 er together. It is possible that little 

 Acropyga queens may have been toting 

 mealybugs to their new nests when 

 dinosaurs still roamed the Earth. 



The intimate and ancient relation- 

 ship between Acropyga ants and mealy- 

 bugs offers biologists a chance to study 

 the evolution of a complex kind of 

 symbiosis. Not only can this example 

 inform questions about how symbi- 

 otic relationships evolve between or- 

 ganisms in general, but it may also have 

 some practical implications for human 

 agriculture. Acropyga have been herd- 

 ing mealybugs for so long that their 

 successes may help investigators ad- 

 dress how people, too, can sustain agri- 

 culture for the long term. One thing 

 remains certain: as more field studies 

 of Acropyga are conducted, more spec- 

 imens are pondered under the micro- 

 scope, and perhaps more fossils are 

 found, there will undoubtedly be plen- 

 ty of surprises driving further study of 

 this fascinating group of ants. 



John S. LaPolla has been fascinated by ants 

 since childhood, when he often convinced his 

 mother to collect ant nests with him. He is a 

 postdoctoral fellow at the National Museum oj 

 Natural History in Washington, D.C., and 

 will be taking a position as assistant professor 

 of biological sciences at Towson University in 

 Maryland in the fall. 



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22 



NATURAL HISTORY May 2006 



