110 



which build their nests in nearby trees or sheds close to their foraging 

 ground. The prickly branches of the osage orange trees, which often 

 grow along the roadsides, are favorite locations for them. 



It is difficult to estimate the amount of good done by the wasps, 

 but there can be no doubt that it is ver}'^ considerable, probably exceed- 

 ing that done by any other of the predaceous enemies. They are at 

 work from daylight until dark, constantly in search of larvae, and the 

 vast numbers foraging in the cotton fields must necessarily destroy 

 the boUworm almost exclusively. The most abundant and undoubt- 

 edly the most beneficial form is Polistes annularis. 



On one occasion a nest of P. annularis at Pittsburg, Tex., was 

 watched by Mr. Bishopp to ascertain the number of bollworms brought 

 in by the wasps. The nest was of medium size, consisting of about 

 twenty-five or thirty cells, with pupae, 200 to 250 larvae, and 30 adults 

 present at one time on the nest. During a period of half an hour eight 

 bollworms and one Geometrid caterpillar were brought in by the 

 wasps and fed to their larvae and to other adults. 



From these facts it is apparent that the present custom of wantonly 

 destroying the nests of these wasps where the}^ occur in or about cot- 

 ton fields is a bad practice and should be disparaged strongly, so that 

 the wasps ma}^ have full sway in their beneficial work. 



The wasps also frequent corn fields, and we have often watched 

 them searching for bollworms w^here we have passed along the rows 

 stripping the shucks from the ears and removing the larvae. Several 

 times they were seen to pounce upon larvae left intentionally upon the 

 ears. In cotton fields, where the larvae are most exposed, the wasps 

 are continually in search for them, feeding by turns on the honey 

 secreted by the nectaries on the squares. 



Forming another group of predaceous enemies are a few large species 

 of robber flies (Asilidae) which frequent the fields. These flies do not 

 destrov the larvae, but confine their attacks solely to the moths. The 

 only species actually seen with a bollworm moth was the large brown 

 Deromyia angustipennis Loew, but judging from their observed habits 

 the numerous Erax and Mallophora (PL XVIII, figs. 3 and 4) must 

 undoubtedly catch the moths also. On one occasion a specimen of 

 Deromyia was brought into the laboratory and tested as to its feeding 

 habits. A bollworm moth was introduced into the jar with the fly, 

 and although the latter was much hampered by lack of freedom, 

 scarcely two seconds elapsed before it had secured the fluttering moth 

 firmh^ betw^een its legs and was inserting its sword-like proboscis into 

 the moth's body. The following is a list of the more common robber 

 flies which were observed in the cotton fields: 



Erax lateralis Macq. Deromyia umhrinus Loew. 



Erax bastardii Macq. J)izonias hicinctus Loew. 



Mallophora orcina Wied. iScleropogon latipennis Loew. 

 Deromyia angustipennis Loew. 



