246 
BULLETIN OF THE BUREAU OF FISHERIES. 
IMPERFECT PUPATION. 
In pupating the head is withdrawn from the chitinous larval covering, and the 
latter is left entire. In all the larvse studied the base of the head is narrower than 
the central portion, and hence in order to be withdrawn successfully the base must 
be opened. This is usually done by a division along the dorsal mid line. If for any 
reason the chitin covering fails to divide, it may become impossible to withdraw 
the contents of the larval head, and the pupa will be malformed. Figure 94 (p. 307) 
represents such an occurrence in Dineutes americanus. One of the pupal chambers 
brought into the laboratory did not hatch with the others. On being opened a 
distorted adult beetle was found inside, with a portion of its head, including the 
antennse and mouth parts, still inside the old larval covering. The rest of the 
beetle was perfect, but, of course, it would have died very soon, since it could not 
even get out of the pupal chamber, and if it had done so it could not have eaten 
anything. 
PARASITES. 
A hymenopterous parasite (Spilocryptus incertus Cresson) was found within a 
cocoon of Dineutes americanus by Dimmock and Knab (1904). They also gave the 
life history of a bombardier beetle ( Brachinus janthinipennis ) whose larva is para- 
sitic upon the pupa of Dineutes americanus. Wickham (1894) was the first to find 
this beetle parasite inside of the pupal chamber of Dineutes, but he could not secure 
sufficient material to make a detailed study of the parasite. Dimmock and Knab 
were more fortunate and seemed an abundance of material from pupal chambers 
found about a reservoir in Holyoke, Mass. They said (1904, p. 35) : “The larva of 
Brachinus , until about ready for pupation, keeps its mouth parts most of the time 
imbedded in the pupa of Dineutes, and pupation takes place in the mud cell made 
by its host.” Wickham (1893, p. 332) also mentioned that the parasite larva, 
“perhaps on account of the partial decomposition of the Dineutes pupa, on which 
it was originally feeding, consented to complete its growth on the pupa of Tropi- 
sternus glaber, which I killed and opened for it.” Wickman also found a hymenop- 
terous parasite ( Cyrtogaster dineutis Ash mead) upon a Dineutes larva, an ichneu- 
monid parasite ( Gausocentrus gyrini Ashmead) upon two pupse of a species of 
Gyrinus, and a dipterous parasite ( Phora sp.) upon a pupa of Tropisternus glaber. 
Attention has already been called to the fact that the mud-burrowing larvse 
are better protected against these parasites than are those which construct a pupal 
chamber. We see from the above, however, that even the mud burrowers get 
caught sometimes. 
THE BLACK HORSEFLY. 
Both the larvse and the pupse of the black horsefly ( Tabanus striatus) are 
common in the mud around the shores of the ponds and are frequently dug up when 
searching for beetle pupse. In a single instance a larva was obtained from the shore 
of pond 5D, August 10, 1920, that had nearly consumed a pupa of Tropisternus 
lateralis. These larvse have been recorded as attacking and eating the grubs of 
Phyllophaga and Cyclocephala. In all probability when they are as common as 
around these fishponds they consume many of the beetle pupse. 
