U. S. I). A., H. K. Hul. fifi, Part II. Issued April •a. ]907. 



SOME INSECTS INJURIOUS TO TRUCK CROPS. 



THE WATER-CRESS SOWBUG. 



{Mancasellus brachijurns liaryer. ) 



By F. H. Chittenden, 

 Entomologist in Charge of Breeding Experiments. 



During the past three years this isopod has attractjed very consid- 

 erable attention because of its occurrence in troublesome numbers in 

 water cress {Nasturtium o-fflcinale) grown for market in portions of 

 Virginia, West Virginia, and Pennsylvania. The species is purely 

 aquatic, thus differing from our common doorj^ard sowbugs, which, 

 although most abundant in moist locations, are strictly terrestrial. It 

 belongs to an entirely different family, the Asellidae, which contains 

 three genera, mostly fresh-water forms, inhabitants of streams, wells, 

 pools, and lakes. 



DESCRIPTIVE. 



This species is so distinct from the more common sowbugs (Onis- 

 cida?) that a brief description will suffice. Its general appearance 

 is shown, dorsal view, in figure 3. The body is much depressed, and 

 the legs are long and strong. Seen from the side, it is decidedly 

 slirimplike. The peculiar structure of the antennai may be noticed 

 in the illustration. They terminate in long flagella, composed of 

 many joints. When mature this sowbug attains a length of 13 or 14 

 millimeters, or a little upward of half an inch, and is a little more 

 than twice as long as wide, and gray in color. This creature is not an 

 insect, but a crustacean, and therefore classed with crayfish and crabs. 

 A detailed description is given by Miss Richardson," who briefly men- 

 tions McKees Spring, Gaylord, and Lexington, Va., as localities 

 where this sowbug was " reported injurious to water cress." 



By recent correspondence we have obtained necessary information 

 in regard to the habits and manner of operation of this sowbug, and 

 we have also been successful in ascertaining what promises to be a 

 very perfect remedy for the pest in its occurrence in streams and in 

 spring water. It appears to affect cress only below the surface of the 

 water, attacking the roots and lower leaves, and cutting off the stems 



a Monograph of the Isopods of North America. By Harriet Richardson. Bui. 

 54, U. S. National Museum. Washington. liHt"). pp. 411-412, figs. 4(;(>-4Gl. 



11 



