January 18 - Diachasma alloeum

Cataloguing biodiversity is an important task – but so is understanding what causes it. Recently, scientists working on the parasitoid wasp, Diachasma alloeum, showed that speciation in the hosts has resulted in the formation of incipient species of the wasp. The hosts in this case are parasites themselves – apple maggots in the genus Rhagoletis. The D. alloeum parasitoid wasps use volatile compounds that the fruits emit to locate them and then they probe the fruit to find the maggot fly larvae within. The female wasp lays her eggs into the maggots, which eventually crawl out of the fruits when they fall to the ground. When the maggot pupates, the wasp larva consumes the maggot, pupates and then overwinters to wait for the next season’s fruits. Recently, the maggot flies have switched from hawthorns as their fruits of choice to domesticated apple trees. Genetic tests of the wasps that use maggot flies in apples vs. those that parasitize the hawthorn maggot flies (as well as in other recently diverged host races) shows that the wasps are following the speciation events of the flies and even show behavioral preferences for the volatiles of the new fruits. This process has been termed a speciation cascade.

Read more about this here.

Parasite nomination and photo by Andrew Forbes.