30 OHIO BIOLOGICAL SURVEY 



It is a very general thing among the aphidophagous species for pupa 

 to be formed early in the summer and again in autumn. But definite 

 statements can be made only for particular species. vSome of the species, 

 perhaps many of them, have at least two generations a year. The pupae 

 of J/, polita were found in Florida in late May, in New Jersey in early 

 September and at Raleigh, N. C, in late vSeptember. Microdon tristis 

 pupates in April or May according to Wheeler. Eristalis spp. pupated 

 in large numbers at Columbus in early autumn. 



The duration in the pupal stage varied in the aphidophagous 

 species I studied from 48 hours to 20 da3's. A much more frequent 

 length of this stage was from four to ten days. The pupal stage of 

 Mesogramma polita lasted eight to ten daj's (Ashmead). 



The puparium is usually fastened by an adhesive secretion from the 

 anal glands of the larva to some exposed object: a part of the host-plant 

 in the aphidophagous t3'pe, a stone or other object well above the water in 

 Eristalis. In the case of Syrpluis americanus pupae kept indoors were found 

 buried under a half-inch or more of soil. This subterranean habit has 

 also been noted in the pupae of Eristalis and Helophihis spp. The larvae 

 of Microdon, "when they reach maturity and are ready to pupate emigrate 



to the surface remain stationar}", attached to the walls of the 



galleries b}^ their creeping soles, and are then found near or at the 

 entrances" of the nests. The pupae of Mesogramma polita were found in 

 Florida and Missouri attached to the upper surface of a corn leaf near 

 its base and between the base of the leaf and the stem. At Raleigh, 

 N. C, puparia were found fastened on the tassels of corn; in size, shape 

 and coloration they strikingly resembled the flowers themselves. 



The hard, more or less impervious pupal envelope with the long and 

 formidable-looking spines which are sometimes present, must be an 

 excellent protection for the developing nymph during this stage. Usually, 

 also, a more or less protected position is chosen by the larva in which to 

 accomplish pupation: either a sheltered nook among the leaves, flowers 

 or bark, or in some cases in the ground. 



Within the puparium, the coarctate pupa (Plate IV, Fig. 54 ) iscovered 

 with a delicate transparent membrane (Fig. 54 «) with pockets encasing 

 the developing legs, wings, etc. The changes visible externally are grad- 

 ually produced and give little indication of the radical internal histol5^sis 

 and histogenesis. 



The appendages, such as legs, mouth-parts, and wing-pads differen- 

 tiate very early, while the whole abdomen and the dorsal part of the body 

 is still a mass of fatt>' granules, with the position of the dorsal blood-vessel 



