364 EXPERIMENT STATION RECORD. 



Papers on cereal and forage insects — The sorghum midge, W. H. Dean 

 (U. 8. Dept. Agr., Bur. Ent. Bui. 80, pt. J/, pp. 30-58, pis. 2, figs. i2).— The 

 sorghum midge {Contarinia [Diplosis] sorghicola) is said to be the most de- 

 structive of the insect and other pests which injure sorghum seed. The first 

 report of injury by this pest, made by D. W. Coquillett in 1895, was based 

 upon sweet sorghum material received from Dillburg, and Montgomery, Ala. 

 ►Since 1898 when the species was described by Coquillett as new to science, 

 several accounts of its injury have been published. Investigations were com- 

 menced by the author on July 25, 1908, at Baton Rouge, La., and continued 

 during 1909 at San Antonio, Tex. He reports that in addition to the many 

 varieties of sweet sorghum, this pest infests broom corn, kafir corn, Johnson 

 grass, and milo maize and that specimens have been reared from the conunon 

 foxtail grass (Sctaria glauca) and Sicgliiigia scslcrioidcs. 



Technical descriptions of the several stages of the midge are followed by 

 a discussion of its life history and habits. The place of deposition of the egg 

 varies, being dependent upon the stage of seed development. Upon hatching, 

 the larvfe immediately make their way to the ovary and are invariably found 

 lying directly against it. A faint discolorntion of the ovary takes place at the 

 point of contact with the larva shortly after the latter has taken its normal 

 position. The pupa is formed in exactly the same position as has been occupied 

 by the larva during its growth and develoiiment. There are no well-detined 

 broods or generations, the midge being found from early spring until late fall 

 in any stage from egg to adult. At Haton Ilouge, with an average daily mean 

 temperature of 79° F. and an average daily mean humidity of 74.3, the life 

 cycle from oviposition to emergence of adults was found to be 2.32 days, while at 

 San Antonio with an average daily meiin temiterature of 84.7° and a humidity 

 of 07.5, 14 days were required for I heir development. ''In the latitude of San 

 Antonio, Tex., generally speaking, the egg stage will cover from 2 to 4 days, 

 the larval stage from 9 to 11 days, and the pupal stage from 3 to 5 days, depend- 

 ing upon the temperature and humidity. . . . Females were found upon dis- 

 section to contain from a dozen to ujnvard of a hundred eggs." At San Antonio 

 in 1909 the first midges were observed on May 14, at which time they were 

 actively ovipositing in Johnson grass. " At this date the neighboring sorghum 

 had not headed, and it was not until June 19 that the first brood emerged from 

 the sorghum, which puts the date of this first infestation at approximately 

 June 5." The cocooned larva is reported to be the true hibernating form but 

 normal pupje will stand considerable cold and later upon being exposed to 

 sufficiently high temperature will emerge. 



In certain localities the midge is highly parasitized by Aprnstocetus diplosidis 

 and Tetrastich us sp., but these species do not become sufficiently numerous to 

 check the midge materially until late in the summer when the second and third 

 crops of sorghum are heading. These crops are found to mature upward of 90 

 per cent of sound seed, while the earlier crops are a total failure. During the 

 latter part of the summer these iiarasites often outnumber the emerging midges 

 5 to 0. The Argentine ant (Iridouiyrmcr humilis) is the most important of 

 the predaceous enemies. A dolichopodid fly (Psilopodinus flaviccijs) was ob- 

 served to prey upon the adults and a humming bird is also thought to do so. 



The destruction of Johnson grass is said to be one of the most vital factors in 

 midge control. If this grass is allowed to remain over winter in and about 

 sorghum fields, it carries the midge until spring, and being the first to head and 

 bloom, gives the midge a good start, so that by the time the sorghum is headed 

 there is a large brood of midges from the grass ready to infest it. Sorghum 

 stalks if allowed to stand in the harvested fields will continue to send out until 

 late in the winter branching heads which furnish breeding possibilities and 



