The 68C Glue Puff of Drosophila

Drosophila melanogaster begins its life as a fertilized egg, which undergoes embryogenesis within an egg shell for about a day and then hatches from the egg as a first instar larva. The wormlike larva eats yeast for a day, then sheds its first instar skin and crawls out as a second instar larva. One day later another molt occurs, resulting in a third instar larva. The third instar stage lasts approximately 40 hours at 25 °C toward the end of this stage the larva crawls out of its medium and onto a dry surface. After a few hours of wandering, it stops, contracts, and secretes a protein glue from its salivary glands that hardens and attaches the larva to its substrate (Fraenkel and Brookes 1953). The affixed larva then tans its third larval instar cuticle into a puparial case, and some hours later pupates within this case. Complete metamorphosis follows pupation, and after several days the pupal case is opened and a new adult emerges.