Approximately 6,500 American roaches, P. americana, were trapped in sewer manholes, tagged with P32, and then released at selected sites. To capture the specimens, a quart jar fitted with a plastic screen cone and baited with over ripe bananas was placed on its side in each of 9 manholes. A total of 18 traps was operated for 12 days to collect the desired number of specimens. Prior to marking, the roaches were maintained in 18-inch square screen cages on a diet of banana and powdered milk.This is from "The Occurrence and Movement of Periplaneta Americana (L.) Within an Urban Sewerage System," by H.F. Schoof and R.E. Siverly, published in the March, 1954 issue of The American Journal of Tropical Medicine and Hygiene.
To tag the roaches, a radioactive casein solution containing 10 microcuries of P32 per milliliter was sprayed upon the specimens under confinement. The spray mixture contained equal parts of a 10 per cent casein solution and a P32 solution, the former being included to assure adhesion of the spray to the integument of the roach. The initial step in the treatment of the roaches was to place 1,000 to 1,500 specimens in a 10 or 20 gallon garbage container which was covered by a transparent plastic lid. The latter was equipped with an exhaust filter and a center hole for nozzle insertion. The spray was then introduced by means of a nasal syringe attached to a small air compressor. A total of 40 to 50 milliliters of spray solution sufficed for each can application, the operation requiring approximately five minutes.
Following the application of the spray, the container was allowed to remain undisturbed for fifteen minutes. At the end of that time, the plastic lid was replaced by the standard garbage can cover. When treatment of all roaches was completed, the contained specimens were transported to the liberation sites which consisted of four manholes one block apart and serving the same trunk line. Release of the specimens occurred at dusk, the container being lowered into the manhole and the lid removed. The opened container remained in the manhole for a 24-hour period.
For recovery of the tagged specimens, 34 traps were located in sewer manholes within a one-mile radius of the four release sites, the majority of the stations being within the 0.5 mile radius (Fig. 1). On the basis of the direction of sewage flow, stations were selected at manholes below and above the release points and at manholes located on secondary lines. In addition to the manhole sites, 10 traps were placed on premises in the blocks immediately adjacent to four liberation sites. Collection of specimens was effected at each station for 8 1/2 weeks following the release of the tagged roaches, a total of 12 samples being procured from each manhole. Radioactive roaches were detected by examining all samples with a laboratory or field count rate meter equipped with a thin-walled Geiger tube.
What was the logic behind tagging cockroaches with radiophosphorus and releasing them into a municipal sewer? As the authors explained,
These instances coupled with the prevalence and movement of cockroaches in and around food-handling establishments, residences and waste disposal sites have focused further attention upon the importance of these insects as possible vectors of enteric infections. Concurrent with this interest is the renewed effort by communities to control roaches within city sewerage systems (Gary, 1950). The heavy roach infestations within such systems combined with the availability of human wastes are factors which conceivably could constitute a potential hazard to the health of a community.Mercifully, it turns out that the radioactive cockroaches didn't go much of anywhere:
Since it has been demonstrated that roaches resident within the sewerage systems can become contaminated with pathogenic organisms, the next step in the mode of spread of the pathogens would involve the degree of dispersion of the infected roaches and the contact between the insects and the human population. To obtain information on the dispersion of roaches within and from a sewerage system, a study was conducted at Phoenix, Arizona, in October 1952. Previous surveys of 22 selected manholes in that city for a seven-week period had shown a weekly average of 92 to 143 specimens per manhole with all roaches being P. americana.
The collection data are summarized in Table 1. As is apparent, only one tagged specimen was recovered from sites other than the release point. Despite the absence of marked specimens, all manhole stations yielded P. americana, the average number per collection being 39 specimens. Only one specimen was trapped in the 10 yard stations but this roach was radioactive. Three of the four release sites were trapped to provide a total of 929 roaches in 17 collections or an average of 54 specimens per sample. Of this number, 97.5 per cent were radioactive, thus demonstrating that the method of tagging had been effective. Further substantiation of this aspect was shown by the recovery of tagged roaches throughout the 8 week period. Specimens captured 39 days after release displayed counts of 1,000 to 6,000 per minute.The authors concluded from these findings that:
The conclusion derived from the experimental evidence is that P. americana does not disperse throughout the urban sewerage system of Phoenix, Arizona. . . .The results reported tend to raise a question as to the relative importance of roaches as a means of disseminating disease pathogens within the sewerage system and from such locations to human habitations. Further evidence discrediting the concept is the finding that the roach populations in sewer manholes are composed of one species, P. americana, whereas the predominant species taken in homes have been Supella supellectilium and Blattella germanica.Isn't that reassuring?