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In pupating the head is withdrawn from the chitinous larval covering, and the 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 larvae 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 the central portion, and hence in order to be withdrawn successfully the base must 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 maKormed. 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 

 antennae 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 Dinnnock and Kjiab (1904). They also gave the 

 life history of a bombardier beetle {BracJiinus jantJiinipennis) 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 secured an abundance of material from pupal chambers 

 found about a reservoir in Holyoke, Mass. They said (1904, p. 35) : ^^The larva of 

 Bracliinus, 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 gldber, which I killed and opened for it." Wickman also found a hymenop- 

 terous parasite {Cyrtogaster dineutis Ashmead) upon a Dineutes larva, an ichneu- 

 monid parasite {Gausocentrus gyrini Ashmead) upon two pupae of a species of 

 Gyrinus, and a dipterous parasite (PJiora sp.) upon a pupa of Tropisternus gldber. 



Attention has already been called to the fact that the mud-burrowing larvae 

 are better protected against these parasites than are those which construct a pupal 

 chamber. We see from the above, however, that even the mud burro wers get 

 caught sometimes. 



THE BLACK HORSEFLY. 



Both the larvae and the pupae of the black horsefly {Talanus striatus) are 

 common in the mud around the shores of the ponds and are frequently dug up when 

 searching for beetle pupae. 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 larvae 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 pupae. 



