Dimensions of the Clear Areas in the Skin of Chicks that Resulted from the Feeding by Larvae of Two Strains of Trombicula splendens at Different Periods1

Abstract

The width, length and area (width×length) were determined for the cylindrical clear area that is formed by larvae of the Florida strain and the Louisiana strain of Trombicula splendens Ewing (chiggers), in the skin of chicks. The clear areas and the chiggers were measured from whole mounts of small pieces of skin, each having a chigger and its clear area. The piece of skin was preserved in 70% ethyl alcohol, cleared in lactic acid and mounted in Hoyer’s mounting media. The skin with the clear areas and chiggers (if attached) were removed at 6-hour intervals after the chicks were infested. The skin was removed at the following periods: 6, 12, 18, 24, 30, 36, 42, 48, 54, 60, 66, 72, 78, 84, 90 and 96 hours. The clear areas were measured at each of the above periods and the chiggers were measured at each of the 6-hour periods from the 6-hour to the 72-hour period. The width, length and width×length of the clear areas produced by the Florida strain were greater than that produced by the Florida strain at most of the periods. The length and width × length produced by the Florida strain was greatest at the 60-hour period and the width was greatest at the 54-hour period. The width, length and width×length produced by the Louisiana strain were greatest at the 72-hour period. The dimensions of the clear areas of each strain increased more rapidly during the first 6-periods than at later periods. The greatest width, length and width × length of the Louisiana strain were at the 60-hour period. The greatest width and (Width×length) of the Louisiana strain occurred at the 66-hour period, and the greatest length at the 72-hour period, The methods employed in this study can be used for comparing the effects of different species or strains of chiggers on different hosts and for evaluating the effect of chemical and other factors on the chigger-host relationship